dudley kvo- "y Savalpost. .: school MONTEREY, »^. - •-. j3940 /V?6 - (^ NAVAL POSTGRADUATE SCHOOL Monterey, California THESIS APPLICATION OF THE GLOBAL POSITIONING SYSTEM TO NEARSHORE HYDROGRAPHIC SURVEYS by Virginia E. Newell Donald D. Winter September, 1981 Thesis Advisors: R. W. Garwood J.J. Von Schwind Approved for public release, distribution unlimited T202317 SKCU^tTv CLA»$l'lCATlOH OF TWIS P ^G€ rW>i««« D—m gntmfd) REPORT DOOJMEHTATIOH PAGE 2. GOVT ACCeSSION MO. 4. TlTuC fm%d Sutllilt) Application of the Global Positioning System to Nearshore Hydrographic Surveys 7. AUTmOAi'O READ iNSTRurrrnss BEFORE COMPLETING FORM J WeCl»lCNT'S CATALOG NuMSf « S TY»E OF REPOW » PERIOD COVERED Master's Thesis September, 1981 «. PCRroRMiMO ORG REPORT SUMMER t. CONTRACT OR GRAmT NuMSERr*; Virginia Elisabeth Newell Donald Dane Winter ». RCW^ORMIHO ORGANIZATION NAME ANO AOORE»« riaval Postgraduate School Monterey, California 93940 CONTROLLING O^'ICE NAME AND AOORESS !aval Postgraduate School, Monterey, CA 93940 li MONlTOKINC AGENCY NAME * AOORCSVf/ i« Global Positioning System, hydrography, translocation, ARTEMIS, theodolite 20. ABSTRACT (Caittlnua •» fvmta »>*• tl nacmaamr •«* l^mmtltr *r •!•€* •«»*•»; Translocation of the Global Positioning System has proved to be a highly accurate method of position determination for onshore and airborne navigation but it had not been previously evaluated for nearshore hydrographic surveys. The technique of translocation for hydrographic operations involves the simultaneous reception of signals from the GPS satellites by two independent receivers; one receiver onboard the survey vessel and one located at the DO , J AN "71 "l<73 COITION O* > MOV •• IS OBSOLETE S/N 0 102-0 14- ««0 1 • tCuHlTY CLASSIFICATION O' 'Mil PAGE »>«•" 0«'« «»<•'•<«) t0C>«^«c*yto«i o> tmi* *>«»<•■%«■ ri»«« «■«•»»< known stationary position. A position correction is obtained at the station ary receiver, which is then applied to the shipboard receiver online or during postprocessing. An accuracy determination of translocated GPS was conducted at the Naval Postgraduate School, Monterey, CA, May, 1981. Two methods of positioning were used for comparison with GPS: 1) a least squares solution of three lines of position observed from three Hi Id T-2 theodolites, and 2) a position determined from ARTEMIS, a range-azimuth short range microwave positioning system. Translocated GPS accuracies of 10 meters were determined. It is anticipated that greater accuracies will be obtained by using a more sophisticated receiver and more advanced processing methods. DD Fornj 1473 S/ N 0102-014-6601 2 iicu"i»* CLAMi^tCATiow o' ▼•••• •*otr^— o« Approved for public release, distribution unlimited Application of the Global Positioning System to Nearshore Hydrographic Surveys by Virginia Elisabeth Newell Donald Dane Winter Lieutenant, NOAA Lieutenant Commander, lOAA B.A., University of Maine, 1971 B.S., University of Michigan, M.S., Virginia Polytechnic Institute 1973 and State University, 1975 Submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIEr^CE IM OCEANOGRAPHY (HYDROGRAPHY) from the NAVAL POSTGRADUATE SCHOOL September, 1981 7: ABSTRACT "°"t»", cal^"^?J="Ool Translocation of the Global Positioning System has proved to be a highly accurate method of position determination for onshore and airborne navi- gation, but it had not been previously evaluated for nearshore hydro- graphic surveys. The technique of translocation for hydrographic opera- tions involves the simultaneous reception of signals from the GPS satellites by two independent receivers; one receiver onboard the survey vessel and one located at a known stationary position. A position correction is obtained at the stationary receiver, which is then applied to the shipboard receiver online or during postprocessing. An accuracy determination of translocated GPS was conducted at the Naval Postgraduate School, Monterey, CA, May, 1981. Two methods of positioning were used for comparison with GPS: 1) a least squares solution of three lines of position observed from three Wild T-2 theodolites, and 2) a position determined from ARTEMIS, a range-azimuth short range microwave position- ing system. Translocated GPS accuracies of 10 meters were determined. It is anticipated that greater accuracies will be obtained by using a more sophisticated receiver and more advanced processing methods. TABL2 3F CONTENTS I. INTEODaCTION 16 II. EQaiPaSNT DESCBIPTION AND OPEEATIONAL CAPABILITIES .. 22 A. AHTEMIS POSITIONING SYSTEM 23 B. THEODOLITE NETWORK 26 C. THANSIT POSITIONING SYSTEM 3° III. GPS SYSTEM DESCRIPTION AND OPERATIONAL CAPABILITIES 38 A. SYSTEM DESCRIPTION 38 B. MANPACK RECEIVER 58 C. DIFFERENTIAL GPS 57 17. TEST PROCEDORE 70 A. POSITIONING NETWORK 70 B. POSITIONING EQUIPMENT 72 1. Theodolites ^^ 2. GPS and ARTEMIS 77 C. LOG OF EVENTS 83 1. Stability Test 84 2. Static Test 84 3. Shipboard Test 84 7. DATA PROCESSING METHODS 88 A. BASIC SURVEY COMPUTATIONS 88 B. THEODOLITE AND ARTEMIS SHIP POSITION „. DETERMINATION 9^ C. DIFFERENTIAL GPS SHIP POSITION DETERMINATION ...95 D. STATISTICAL DATA ANALYSIS 99 VI. ERROR ANALYSIS ^^3 A. ARTEMIS POSITIONING SYSTEM 103 1, Microwave System Errors ^^3 2. ARTEMIS System Errors 110 B. CONTROL NETWORK ''''2 C. THEODOLITE NETWORK "'"'^ D. TRANSIT POSITIONING SYSTEM 120 E. GPS ERROR SOURCES ^21 711. RESULTS 135 A. STATIONARY GPS EVALUATION ^^^ B. EVALUATION OF NONDIFFER SNTIAL GPS 158 C. DIFFERENTIAL GPS EVALUATION WITH STATIC CORRECTIONS 174 D. EVALUATION OF DIFFERENTIAL GPS WITHOUT STATIC ,«, CORRECTIONS 1°' VIII. CONCLUSIONS 221 APPENDIX A 224 LIST OF REFERENCES 228 BIBLIOGRAPHY 232 INITIAL DISTRIBUTION LIST 236 LIST OF TABLES I, Ionospheric Group Delay as a Function .-, of Frequency ^^ 56 68 II. MANPACK Interface Wiring Code III. Range Error Budget IV. Satellite Observation Tines 1'^ 7. Statistical Definitions ^01 VI. Theodolite Instrument Errors 1^6 VII. TRANSIT system Errors 122 7III. Ephemeris Update Tiaes 127 LIST OF FIGaRES 2.1. TRANSIT Satellite 32 2.2. TRANSIT Satellite Orbital Network 33 2.3. AN/PRR 14 Geoceiver Antenna 36 3.1. The Nonuniform 18 Satellite Constellation 45 3.2. Hallcer 18/3/0 Constellation Outages 46 3.3. NAVSTAR Satellite ^8 3.4. Pseudo-Range Description 57 3.5. Global Positioning System MVOE Receiver 59 3.6. avos Receiver Face 60 3.7. Cutaway of MVUE Receiver 61 3.8. MVUE CDO Keyboard/Display Layout 63 3.9. Circuit Diagram of Receiver Interface 65 4.1. Test Area with Traverse Sketch 73 4.2. Antenna Tower on Coast Guard Pier 78 4.3. E/7 ACANIA Equipment Layout 81 4.4. Equipment Installation on the R/V ACANIA 82 4.5. Survey Area and Location of Sets by Day 86 5.1. Error Ellipse 93 5.2. Differential GPS Processing 58 6.1. ARTEMIS Range Holes 106 6.2. ART2MIS System Error 109 6.3. Representative Theodolite Intersections for ,,-, Error Ellipse Computations I'y 7.1. Stability Test Results 9,10 May 136 7.2. Stability Test Results 9,10 May 137 7.3. Stability Test Results 9,10 .lay 138 7.4. Total User Range Error 9 Hay 139 7.5. Total aser Range Error 10 May 140 7.6. Static Test Results 11 May 142 7.7. Static Test Results 11 May 143 7.8. Static Test Results 11 May 144 7.9. Satellite Elevation Angles 145 7.10. Satellite Azimuth Angles 146 7.11. Total User Range Error 11 May 147 7.12. Geoceiver vs. Gps Position Computation 148 7. 13. Distance Between Geoceiver and Stationary GPS Position 12 May 150 7.14. Distance Between Geoceiver and Stationary GPS ^^. Position 13 May ibl 7.15. Distance Between Geoceiver and Stationary GPS ,^„ Position 15 May 152 7.16. Total User Range Error 13 May 153 7.17. Total aser Range Error 15 May 154 7.18. Azimuth Between Geoceiver and Stationary GPS Position 12 May 155 7.19. Azimuth Between Geoceiver and Stationary GPS Position 13 May 155 7.20. Azimuth Between Geoceiver and Stationary GPS Position 15 May 157 7.21. Distance Between T-2 5hip Position and ^ _^ Uncorrected GPS Position (4 Satellites) Set 1 .. 159 7.22. Distance Between T-2 Ship Position and Uncorrected GPS Position (U Satellites) Set 2 .. 160 7.23. Distance Between T-2 Ship Position and Uncorrected GPS Position (U Satellites) Set 3 ..161 7.2U. Distance Between T-2 Ship Position and ^.„ Uncorrected GPS Position (U Satellites) Set 4 ..152 7.25. Distance Between T-2 Ship Position and Uncorrected GPS Position (4 Satellites) Set 5 .. 163 7.26. Distance Between T-2 Ship Position and ..^ Uncorrected GPS Position (4 Satellites) Set 6 ,. 154 7.27. Distance Between T-2 Ship Position and ^._ Uncorrected GPS Position (4 Satellites) Set 7 .. 165 7.28. Distance Between T-2 Ship Position and Uncorrected GPS Position (4 Satellites) Set 8 .. 156 7.29. Distance Between T-2 Ship Position and Uncorrected GPS Position (4 Satellites) Sets 9 and 10 167 7.30. Distance Between T-2 Ship Position and Uncorrected GPS Position (4 Satellites) Set 11.. 168 7.31. Distance Between T-2 Ship Position and Uncorrected GPS Position (4 Satellites) ,^„ Sets 12 and 13 169 7.32. Total User Range Error 12 May 170 7.33. 7.35. Distance Between T-2 Ship Position and Uncorrected GPS Position (5 Satellites) 12 May.. 1/1 7.34. Distance Between T-2 Ship Position and ._. Uncorrected GPS Position (5 Satellites) 13 May.. '72 Distance Between T-2 Ship Position and Uncorrected GPS Position (5 Satellites) 15 May.. 173 10 7.36. Distance Between T-2 Ship Position and Differential GPS Position With Static Correction ,__ Set 1 175 7.37. 7.39. Distance Between T-2 Ship Position and Differential GPS Position With Static Correction Set 2 176 7.38. Distance Between T-2 Ship Position and Differential GPS Position With Static Correction, ^^ Set 3 177 Distance Between T-2 Ship Position and Differential GPS Position Without Static Correction Set 1 1 78 7.40. Distance Between T-2 Ship Position and Differential GPS Position Without Static ,_^ Correction Set 2 1/9 7.41. Distance Between T-2 Ship Position and Differential GPS Position Withour Static Correction Set 3 180 7.42. Azimuth Between T-2 Ship Position and Differential GPS Position Without Static .._ Correction Set 1 I ^-^ 7.43. Azimuth Between T-2 Ship Position and Differential GPS Position Without Static Correction Set 2 183 7.44. Azimuth Between T-2 Ship Position and Differential GPS Position Without Static Correction Set 3 185 7.45. Distance Between T-2 Ship Position and Differential GPS Position Without static .^^ Correction Set 4 186 7.46. Azimuth Between T-2 Ship Position and Differential GPS Position Without Static Correction Set 4 187 7.47. Distance Between T-2 Ship Position and Differential GPS Position Without static .-. Correction Set 5 189 7.48. Azimuth Between T-2 Ship Position and Differential GPS Position Without Static ,^^ Correction Set 5 1 90 n 7.U9. Distance Between T-2 Ship Position and Differential GPS Position Without Static Correction Set 6 191 7.50. Azimuth Between T-2 Ship Position and Differential GPS Position Without static Correction Set 6 192 7.51. Distance Between T-2 Ship Position and Differential GPS Position Without Static Correction Set 8 193 7.52. Azimuth Between T-2 Ship Position and Differential GPS Position Without static Correction Set 8 194 7.53. Distance Between T-2 Ship Position and Differential GPS Position Without Static Correction Sets 9 5 10 196 7.54. Azimuth Between T-2 5hip Position and Differential GPS Position Without Static ,^^ Correction Sets 9 & 10 197 7.55. Distance Between T-2 Ship Position and Differential GPS Position Without Static Correction Set 11 198 7.56. Azimuth Between T-2 Ship Position and Differential GPS Position Without Static Correction Set 11 199 7.57. Distance Between T-2 Ship Position and Differential GPS Position Without Static Correction Sets 12 5 13 201 7.58. Azimuth Between T-2 Ship Position and Differential GPS Position Without Static ^^„ Correction Sets 12 5 13 202 7.59. Distance Between T-2 Ship Position and Differential GPS Position Without Static Correction (5 Satellites) 12 May 203 7.60. Distance Between T-2 Ship Position and Differential GPS Position Without Static Correction (5 Satellites) 15 May 204 7.61. Latitude Comparison Sets ^, 2 206 7.62. Longitude Comparison Sets 1, 2 207 12 7.63. Latitude Comparison Set 3 208 7.64. Longitude Comparison Set 3 209 7.65. Latitude Comparison Sets 4, 5 210 7.66. Longitude Comparison Sets U, 5 211 7.67. Latitude Comparison Sets 6, 7 212 7.68. Longitude Comparison Sets 6, 7 213 7. 69. Latitude Comparison Sets 3, 9 214 7.70. Longitude Comparison Sets 8, 9 215 7.71. Latitude Comparison Sets 10, 11 216 7.72. Longitude Comparison Sets 10, 11 217 7.73. Latitude Comparison Sets 12, 13 218 7.74. Longitude Comparison Sets 12, 13 219 BPS C/A CDO CMAS DMA GMT GPS HTC LMT MCS MIS M70E NAVSAT NAVSTAR OTES P PVC SAMSO ORE OSAP WGS 1972 I.X^ OF ABBREVIATTONS Bits Per Second Coarse Acquisition Code Control Data Unit Circular Map Accuracy Standard Defense Mapping Agency Greenwich Mean Time Global Positioning System Hydrographic/Topographic Center at DMA Local Mean Time GPS Master Control Station MVOE Instrumentation System MANPACK Vehicular User Equipment Navy Navigational Satellite System Global Positioning System NCAA Office of Ocean Technology and Engineering Support Precision Code Polyvinyl Chloride Pipe Space and Missile Systems Organization User Range Error United States Air Force World Geodetic System of 1972 U ACKriQl.'LEDGEriENTS We would like to thank all the •'IPS students and other individuals who contributed their time and expertise during the long nights at the T-2 locations--without their support this thesis would not have been possible, Thanks go to: Marjorie Amazeen, Bill Anderson, Gene Brown, Bob and flac Clark, Ron Dickerman, Barry Donovan, Pat Eaton, Mike Ellett, Jerry and B.J. Mills, Dave Minkel, Roger Parsons and Annette Parsons, Alan Shaffer, Keith Toepfer, Gerry Wheaton, and Jon Winter. Special thanks also to Ted Calhoon for his cooperation and to the Captain of the ACAMIA, IJoody Reynolds; and the crew members who contributed their ideas for the equipment installation onboard the ship. 1/e would like to thank Mr. Knute Berstis and Mr. Gary 'Ihitsell from OTES for their time and efforts in making the thesis possible, and Cdr. A. Durkee, of the Joint Programs Office, for his interest and support in providing the GPS receivers. 15 I. INTROPgCTION Shipboard operations for the purpose of oceanographic research, commercial transport, tactical operations, or hydrographic surveying require accurate and dependable positioning systems. The operation of most electronic positioning systems is hampered by atmospheric effects on the propagated signal and design limitations which restrict operating ranges, positional accuracy and dependability. A universal positioning system that provides accurate information to the user regardless of atmospheric conditions and that is free of range limitations is desirable. with the advent of satellite positioning techniques, such a system is now available. The Navy Navigation Satellite System (NAVSAT) , or TRANSIT, has been operational since 1964 and has proved dependable and sufficiently accurate for certain users. Although developed for military uses, the application of TRANSIT in the civilian community has continued to expand at an exponential rate. The system, however, is limited by the time interval between fixes, which is 90 minutes on the average, and the requirement for precise Icnowledge of the ship's velocity. Although the system does not provide 16 One method of improving system accuracy is by using two receivers simultaneously in a technique termed translocation, or differential mode. The method is based on the assumption that signal propagation errors to two proximate receivers are nearly the same. One receiver is placed over a known position, and the variation of the observed position with time is determined relative to the absolute position. This variation is applied to the observed positions determined by a simultaneously operating receiver located at another location — on a survey vessel, for example. The assumption underlying this technique is that the distance between the two units is not sufficient to introduce a significant additional propagation error. The resulting position of the translocated receiver should be more accurate than the position obtained using a single receiver. For hydrographic operations, the translocated Global Positioning System (GPS) provides an alternative to presently used positioning systems. The satellites orbit at 20,000 1cm, which theoretically would allow receiver separation of as much as 500 Icm without causing significant additional system error. With this flexibility, one 17 sufficient positional accuracy for hydrographic surveying, it has been used for geodetic application by the Defense Mapping Agency (DMA) using fixed shore-based receivers to establish positioning networks in inaccessible areas worldwide. [ Ref . 1] The Global Positioning System, or NAVSTAR, is a more sophisticated system designed to replace TRANSIT in the mid-1980s. Six satellites are currently in orbit with twelve more to be launched before the operational date of 1987. The 18-satellite orbit configuration will provide a multi-user, passive system with 2t*-hour availability, global coverage, and possible fix intervals of less than one second. The operational network consists of three elements — the satellites, the ground-based control segment, operated by the Space and Missile Systems Organization (SAMSO) , and the user's receiver. Prototype receivers have been tested under optimum conditions by SAMSO at the Yuma Proving Ground, Arizona, on both mobile and stationary platforms. Results show excellent system stability and accuracy when compared to currently used positioning systems. C^ef. 2] 18 shorebased receiver could be placed at a central location and a survey of several hundred kilometers of coastline or offshore area could be completed with only one additional receiver on the survey vessel. [Ref, 3] The value of this flexibility would be realized in the significant decrease in survey planning, cost, and time compared to that spent presently in conducting hydrographic operations. The accuracy of the system would be sufficient for all survey scales. The National Ocean Survey (NOS) defines the required accuracy of a positioning system to be no more than one-third of the survey accuracy, which is 1.5 millimeters at the scale of the survey. [Sef. 4] Non-translocated GPS has been shown to be of sufficient accuracy for 1:80,000 scale surveys and smaller. [Bef. 5] The object of our research is to determine whether GPS at the present operational level is adequate for 1:10,000 scale surveys. To do this, a position determined by two GPS receivers in the translocated mode is compared to the same position determined by two other methods. If translocated GPS can be shown to achieve specified inshore survey accuracies, the system would provide sufficient accuracies at all smaller scale surveys. 19 Part of the difficulty in ietermining this level of accuracy concerns the reference system used. Most geodetic positions published by the I?ational Geodetic Survey (!IGS) are based on the North American Reference Datum of 1927 (IIAD-27) and the Clarice 1866 Ellipsoid, the best approximation to the shape of the earth for the continental Onited states. The satellite systems, however, use a reference system which is not based on a portion of the earth's surface. A mass-centered ellipsoid referenced to the earth's center of mass has been computed using observed gravity and astronomical data. The best fit to this global ellipsoid is the World Geodetic System of 1972 (MGS-72) , which is utilized by both '' TRANSIT and GPS. Transformation equations exist which convert NAD-27 coordinates to WGS-72 coordinates, but uncertainty in the gravity model produces errors as large as 10 meters due to the transformation process alone, [Sef. 6] To establish all positions on the same reference ellipsoid for this research, a TRANSIT receiver was acquired from DMA and a first order Doppler station was established at the central location of the test area. A third order geodetic survey was conducted from the TRANSIT station to 20 establish two additional stations on the WGS-72 ellipsoid. Two single channel Manpack GPS receivers were obtained from SAMSO. Stability testing and a receiver comparison test were conducted prior to shipboard testing to determine a guanxitative measure of receiver performance. 0ns of the receivers was then placed over the TRANSIT station mark and the other aboard a survey vessel which maneuvered along predetermined track lines. Data were recorded via an interface to an HP-9825 computer and printer at each site. Simultaneously, two additional independent measurements were made of ship position — one using a range-azimuth short range microwave positioning system (ARTEMIS) and the other a position determined by a least squares solution of three lines of position observed from three 1-second theodolites set on the three pre-established WGS-72 locations. The comparison of the ARTEMIS and theodolite-derived ship positions with the translocated GPS ship position provided the test results. 21 II. EOaiPMENT DESCRIPTION AND OPERATIONAL CAPABILITIES Two positioning systems were chosen for comparison with the Global Positioning System: a theodolite network and a microwave positioning system. The theodolite network consisted of three shore-based units so as to provide three lines of position. The microwave positioning system provided, a range and an azimuth from a known location on shore. Both systems are accurate at short ranges and represent two contrasting methods of positioning--visual and electronic. The theodolite method of positioning at short range has been and continues to be used for hydrographic operations as an alternative to electronic systems when geometry and system accuracy limitations impose the need for a more flexible positioning system. The requirement for experienced theodolite observers as well as the communication and logistics difficulties involved limit the use of this method to special cases. This chapter describes the ARTEMIS short-range electronic positioning system, the operation of the theodolite network as used during the comparison test, and the TRANSIT satellite system. 22 i, ARTEMIS POSITIONING SYSTEM The ARTEMIS position fixing system is a short-range licrowave system (to 30 km), bailt by Christiaan luygenslaboratorium B. V., in the Netherlands, It has been ised operationally (primarily in Europe) since 1972, when :he system was introduced at the International Hydrographic :onference in Monaco. At the present time, fifty systems ire in use. The system is unique in design, is highly iccurate at short ranges, and is particularly useful for small harbor surveys, river surveys and relative positioning ises. For this study, the ARTEMIS system, along with technical assistance, was obtained from the American iistributor, MARINA7 Corporation of Houston, TEXAS. ARTEMIS is a range-azimuth positioning system which employs a unique tracking method. A stationary or fixed unit is placed over a known position on shore. Osing a telescope that is mounted on the antenna, the antenna is sighted onto another known point and the known azimuth between the two locations is entered into the system via a digital display on the fixed unit. The unit is then locked into place for operation. A mobile unit is placed on the vessel whose position is desired. 23 The mobile and fixed antennas resemble radar antennas which, while operating, track each other so that the two antennas are always parallel to each other and perpendicular to the line of position between them. A microwave link is established between the two antennas during periods of measurement and information is relayed between the mobile and fixed units. (A voice link is also available during operation.) The fixed unit provides the direction and the azimuth of the mobile unit with respect to the point sighted on by the telescope. At the same time, the mobile unit transmits a coded interruption of the signal to the fixed unit, which replies with the same interruption. The time difference between the transmission and reception at the mobile unit determines the distance between the two antennas. Distance accuracy is determined by the number of measurements averaged over time and is available in two modes — a dynamic mode which averages 1000 measurements or a static mode which measures 10,000 measurements per displayed distance. The azimuth and distance information is displayed by the mobile unit so that personnel are not required at the stationary unit once operation has begun. The system can be 24 operated in long or short-range nodes, which determine the amount of power output for the system. The microwave freguencies used are 9.2 and 9.3 GHz. Problems arising with signal interference, observed with all microwave positioning systems, therefore can occur with ARTEMIS. The regions of range holes, or multipath interference, can be computed for up to 10 !cm range by prior knowledge of the antenna elevations above sea level and the operating distance from the shore- based antenna. [ Sef . 7] Sach antenna is designed with a 22° vertical beam width and a 2° horizontal beam width. A power source of 22 volts DC per unit is required, with- an average current load of 2.5 amps. The accuracy of the system depends on both the distance and the angle measured. The angle measurement has a 2 a probability of measuring within 2' of arc (0.033°) . The distance measurement has a 2 cr probability that the mean distance value will vary within + 1.5 meters. One of the advantages of ARTEMIS over other electronic systems is that the two lines of position defining the fix always intersect at 90*^ . A unique advantage is that the coverage around the fixed unit can be circular, with a 25 aaximum range cf operation to 30 km, dependent on antenna heights. The short range applications of the ARTEMIS fill a need not provided by many currently used positioning systems. For this study, the ARTSMIS was used in conjunction with the positions derived from the theodolite network to determine the best estimate of the ship's position. The accuracy of the ARTEMIS was more than adequate for the ranges encountered during the test, and the ease of use and operational versatility of the system made its use very advantageous. B. THEODOLITE NETWORK A network of three Wild r-2 theodolites was used as the control positioning system. The theodolite is widely used for surveying as a means of measuring angles between two observational locations — either in a horizontal plane for traverse or triangulation surveys, or a vertical plane for astronomical observations. The use of three theodolites as a short-range positioning system was an accepted method of positioning prior to development of electronic distance measuring systems. There remain disadvantages when using electronic 26 positioning systems for hydrogra phic operations at short ranges (1-2 km) . Most short-range electronic systems are designed for measurement of position at line-of-sight ranges. This region includes a large portion of inshore hydrographic surveys. Inshore positioning involves more thorough planning to obtain the required accuracy for the scale of the survey. For example, in a harbor or cove it may be difficult to place two range-range electronic units so that the area to be surveyed is not within the region of positioning system uncertainty, or 30° (radially) on each side of the baseline between the two units. To reposition the electronic units as often as is required to obtain optimum geometry is time-consuming and requires manpower and extensive planning, and can result in operational delays. Interference of the signal due to reflection from a calm sea surface, or multipathing, is also a problem at short ranges for microwave systems. Theodolites can be set at any intervisible location with preplanned geometry and can be used for the entire region to be surveyed. This method requires less expensive equipment (three theodolites) , more manpower (a recorder and an observer at each site) , communication between the three 27 locations (via portable radio, for example) and, reasonable w€ather conditions. The basis of this procedure is that three angles observed from knovn locations to a predeterained point on the vessel constitute three lines of position. After removing all possible systenatic errors and through a least squares solution of the three lines of position, the position of the vessel is determined. A major disadvantage is that observational errors are not determined in real time because the data cannot be processed imnediately. The basic procedure for the method requires predetermined sites which are known relative to each other. This may be achieved by using published geographic positions or by conducting a local plane survey to establish new positions using preestablished stations nearby. Either way, all three locations must be based on the same datum and preferably permanently positioned by a disk or a station mark. Each theodolite was aligned using a plumb bob or optical plummet over one of the known station marks or disks. 3y a predetermined scheme, each site was marked so as to be clearly visible to the other sites (lights were used for 28 this study) . The telescope of each theodolite was sighted onto one of the other sites and the horizontal circle set to read an arbitrary value close to O''. The crosshairs in the telescope were set to intersect the aark. When the theodolite was exactly sighted, the horizontal circle was read and recorded. (At this time the lights were turned off.) The operation began when all three sites completed this step, called the "initialling procedure", or "initial pointing". The instrument was sighted on a point on the survey vessel that was visible to all operators. The ship was trac)ced by the operators by using the micrometer wheels on the instrument until a "mark" was called over the radio by the recorder at the control theodolite location. At that instant, the operator stopped tracking and the horizontal circle was read and recorded. This observation constituted a fix. After a series of fixes wers recorded, or when the survey vessel reached a predetermined location, a set of fixes was completed. The lights were then reactivated at each site, each observer intersected the original mark, the horizontal circle was again read and the "final pointing" was recorded. If necessary, the instrument was relevelled. The process was then repeated by starting with the initialling procedure. 29 It was assumed that the theodolites were in good operating condition. Collimation error had previously been determined. The observers were kept at the same locations throughout the test to minimize the error due to individual observer variations. Since only one portion of the horizontal circle was used, and no reverse readings observed, a systematic error was introduced. This was assumed to be minimized during computation of the vessel position. The observations were corrected for collimation error and for pointing error by evenly distributing the difference between the initial and final pointing values. The resulting angles were processed using an intersection computation with a least squares fit applied to optimize the result. The computations for this study were processed using an HP-9815 computer and software prepared by Cdr Ludvig Pfeifer, NOAA. The resulting position was used as the best estimate of the position of the ship. C. THANSIT POSITIONING SYSTEM The TRANSIT, or Navy Navigation Satellite System, is the most widely utilized satellite positioning system at the present time. The network of satellites and ground tracking 30 stations has been in operation since 1964 and is becoming widely used by both the military and civilian communities. It is expected to continue operation until at Isast 1995, when the Global Positioning System is expected to replace it. The system consists of a series of TRANSIT satellites (fig- 2.1.) in fixed polar orbits of 1095 km elevation, forming a network within which the earth rotates (fig. 2. 2.). The orbits are spaced so that satellite passes occur, for a given ground location, at intervals of between 35 and 100 minutes. Each satellite travels an observable distance of between 4400 and 7000 km per pass, providing a sufficient time interval and baseline over which the user can record data. The idea of positioning an observer on the earth's surface by using the satellite as a reference system originated from observation of Sputnik 1, launched by the Soviet Onion in 1957. By recording the change in frequency of the satellite signal as the satellite passed overhead, a Doppler shift could be measured. The Doppler shift gives a spatial relationship as a function of time between the observer and the satellite. If the position of the 31 Fig. 2.1. TRANSIT SataKite 32 "ig. 2.2. Transit Satellite Orbital Network 33 satellite is known at the tiae of observation, the observer's position can be determined. In the TRANSIT system, the satellite positions are precisely determined by tracking stations located at Prospect Harbor, Maine; Rossnount, Minnesota; and Wahiawa, Hawaii. The tracking information (in the form of the Doppler frequency shift as a function of time) is relayed to the computing center at the Naval Astronautics Group Headquarters, Pt. Mugu, California. Here the actual satellite orbits are computed. This information is used to predict orbit information. Parameters of this predicted orbit are relayed to two injection stations at Rosemount and Pt. Mugu. During the next satellite pass, the information is relayed to the satellite as part of the navigation message, with new updates occurring every 12 hours. The satellites therefore contain predicted orbit information which is received by the user via a satellite receiver. Several receivers are available with complexity and positional accuracy dependent upon the needs of the user, A computer is normally required to determine the user's mobile or fixed position in real time from a single satellite pass. 34 For many users having a dual channel receiver and known velocity, this method of positioning provides sufficient accuracy with typical error of 27 to 37 meters root sum square. Optimum accuracy is obtained, however, if the receiver position is fixed, and several consecutive passes of the same satellite are recorded. During each pass, lasting from 10 to 16 minutes as the satellite travels from one horizon to the other, many Doppler counts (observations of shift in frequency as a function of time) are recorded. After a predetermined number of passes are stored, the data can be forwarded to the Defense Mapping Agency in Brookmont, Maryland. There the precise ephemeris data from the ground tracking system is applied to the data from the recorded passes to provide the optimum solution. The resulting position has a typical error of 6.3 meters root mean square for a series of passes, with a 3-dimensional result of 1.5 meters per axis repeatability after 25 precise ephemeris passes. This method is used to determine positions in r smote areas by DMA geodetic survey groups using the Magnavox AN/PSR-14 Geoceiver (fig. 2. 3.). [Hef. 8] The TRANSIT system uses the World Geodetic System of 1972 (WGS-72) reference ellipsoid which is based on the 35 ^^ h X "7 ^ i AN/PRR-14 GEOCEIVER ANTENNA Fig . 2.3 . 35 Universal Space Rectangular Coordinate System — an earth, mass-centered coordinate system. The WGS-72 ellipsoid describes the best fit of the entire earth to a mathematical model. The satellite orbits are computed using this geopotential model, the accuracy of which is based on gravitational and astronomical data. For the present study, a Magnavox AN/PRR-14 Geoceiver was acquired from the Department of Satellite Geophysics, Satellite Tracking Branch, DMA. The receiver was placed over a fixed point and t*0 passes of one satellite were observed. The procedures described previously for an optimum solution of point positioning were followed. The resulting latitude, longitude, and height relative to the WGS-72 ellipsoid are coordinates of a first order TRANSIT position as defined by DMA standards. This position was used as the basis for horizontal control for the study (see test procedures) . 37 III. GPS SYST5I1 DESCRIPTION AND OPERATIONAL CAPABILITIES A. SYSTEM DESCRIPTION NA7STAE, or the Global Positioning System, was designed for maximum operational capability — high accuracy, twenty-four hour access, passive user, and world-wide coverage. A brief description of the GPS, and the satellites (NAVSTARs), will serve as a background for the more in-depth discussion immediately following. GPS navigation is based on the measurement of four ranges, or pseudo-ranges, from each of four satellites with known, or predicted, positions. Each range determination is computed using the propagation velocity of the signal multiplied by the satellite-to-user travel time. Satellite transmission time is included as part of the navigation signal message. Prom the four known ranges, the user position and user clock error are computed on a three-axis, orthogonal coordinate system. This computation is then used to transform the user position onto the WGS-72 ellipsoid. The remainder of this chapter will provide the background for GPS development and the three :najor system segments of the GPS: the space system segment, the control 38 segaent, and the user system segment. Included in the user system segment will be a discussion of the Jlanpack receiver as developed by Texas Instruments Corporation used for this study. Hith the successful operation of the TRANSIT system in the early 1960»s, the Department of Defense (DOD) began to consider the specifications of, and the technology required for, the development and implementation of a second generation system. On 17 April, 1973, the Deputy Secretary of Defense stated that a Defense Navigation Satellite System was to be developed. [Ref. 9] Osing the new synthetic oscillator technology, and the Department of Defense surface and nearsurface navigation objectives and requirements, a DOD interdepartmental task force developed the GPS as the second generation satellite navigation system. With the United States Air Force (USAF) as the managing agency, the GPS became a joint service program, with representatives from the DMA, Army, Navy, Marines, Coast Guard, and the North Atlantic Treaty Organization- [Ref. 10] The Joint Programs Office was established within the Air Force Space and Missile Systems Organization to design, develop, and iipiement the GPS program. 39 GPS was conceived and designed to provide continuous, real-time, world-wide navigation coverage for subsurface, surface and nearsurface operational vessels, vehicles, and aircraft. Accuracy of better than 10 meters was desired under all conditions, with navigational capabilities to update and interface with other forms of existing and projected navigational systems. Another requirement of the GPS satellites was nearly trouble-free and simple user operation, even in low signal-to-noise environments. An encoded signal structure was required for the satellite system for security reasons. In addition, the signal transmitted by the NA7STAR satellites had to include other operational information in conjunction with the navigational message. To provide for navigational requirements in event of hostilities, the GPS was designed to permit the use of redundant satellites. To achieve these objectives and requirements, the GPS program was organized according to three developmental tasics: concept validation, full-scale engineering development and systems tests, and production and operation. Starting in 1974, the concept validation task was initiated with the merger of the TIMATION series satellite program and 40 the OSAF system 21B (a highly accurate three-diiensional navigation system) program. Tests with the Navigation Technology Satellite, NTS-1, utilizing two rubidium clocks 1 3 (accuracy 5-10 parts per 10 ) and an orbit 7500 nautical miles (nm) above the surface and three ground based receivers (called inverted range) provided concept verification. [Ref, 11] Additional tests were conducted with an improved NTS-2 satellite positioned at an altitude of 10,980 nm and containing two cesium clocJcs (accuracies on the order of 1 part per 10^^). [Ref. 12] Orbital height of 10,980 nm permitted the evaluation of the effect of the planned GPS constellation altitude on navigational accuracies using the improved cesium frequency standards. In 1980, NTS-3 was launched and the Advanced Developmental Model (ADM) hydrogen maser frequency standard evaluated for use on the GPS (providing an expected frequency accuracy of 1 part per 10^^). [Bef. 13] The results obtained from the NTS-3 satellite have not yet been released. Since 1978, additional satellites have been orbited to provide the six-satellite constellation required to fully evaluate the first development task — concept validation. Phase I. 41 During Phase 1, user requirements were consolidated to allow the development and construction of four basic types of test receivers: continuous traclcing receivers, sequential traclcing receivers, lew cost receivers, and the Manpaclc receivers. [ Ref . 11] These receiver types were then constructed for Phase I testing by various contractors and their performances evaluated aboard helicopters, aircraft, ships, vehicles and personnel at the Joint Programs Office's testing facilities. Phase I, concept validation, was completed in late 1979 and Phase II testing was begun in early 1980 with full scale engineering, developmental, and systems tests. Phase II tasks, finishing the operational and control segments of the testing, are scheduled for completion in mid-1983. The operational control station will be relocated at a central continental anited States site during this phase. Additionally, all satellite monitor receivers at the remote monitoring stations will be updated to operational status. Oser equipment and receiver selection will be made in two increments. Four contractors will be asked to compete for the second increment of the receiver selection process by providing upgraded and refined user receivers for 42 extensive testing and evaluation. Two of the four contractors will then be selected to continue the coipetition and will provide additional receiver design, refinement and modification, leading to prototype production and extensive field testing. When Phase II is completed in mid-1983. Phase III, production, will commence with the selection of one of the two contractors to produce the user receivers. Manufacture of these receivers will commence shortly after selection, and commercial availability of receivers is expected in 1985. [Ref. 15] The GPS should be fully operational with world-wide coverage using a constellation containing a total of eighteen satellites in 1988. [Ref. 16, 173 The GPS is considered to be composed of three inter-related system segments: the space system segment, the control segment, and the user system segment. Of these, the space system segment may be considered the most important since the other two require the space segment to be operational at all times. Operationally, the space system segment consists of 13 satellites placed in orbits at altitudes of 10,398 nm and having orbital periods of about 12 hours. [Ref. 18] 43 The original plan for the satellite constellation consisted of 24 satellites in three planes of 3 satellites each. These three planes were to be placed 4S° of longitude apart and at an inclination of 63 ° to the equator. [Ref. 19] As a result of 1980 budget cutbacks the space system segment has been reduced to a total of 18 satellites, £R9f. 20] Several different types of 18 satellite constellations have been proposed, but all have drawbacks. One which appears the most promising is the 'Nonuniform 18* constellation containing 6 planes, each of which contains 3 satellites spaced 120° apart (fig. 3.1.). The areas of user outages (fig. 3. 2.) are a disadvantage of this configuration. The user outages are indicated by the darker areas shown on Figure 3.2. These outage areas will appear to rotate about the globe at the indicated latitudes, and positioning with the GPS will be intermittent, or of decreased accuracy for users at these latitudes. The final constellation configurchtion is to be selected early in 1982. [Ref. 2l] Sach NAVSTAR satellite has the following characteristics: weight of 9 82 pounds, length of 17.5 feet from tip to tip of the 5 square solar panels, three atomic 44 # Proposed Satellite O jeleted Satellite Fia. 3.1. The nonuniform 18 Satellite Constellation 45 ^ (averaged earth magnetic field strength along the path) GO = group delay between points G and D Term Healected; B f3 Range Error at f - 1 .5 GHz ^ 1 inch - 3 inches 49 the following algorithm, the error is decreased but not totally eliminated. [Ref, 25] T ■ - T = A T GDL] GDL2 = A Where: GDL ^ GDL." ^2 "L. where A = ionospheric constant and "^ qq|_ , '^ qql are the respective ionospheric group delays at frequencies Li and L2. Both frequencies are also modulated to transmit the GPS time codes and the navigation message. GPS time is transmitted using two pseudo-random noise chip codes — the Coarse Acquisition (C/A) and the Precision (P) codes. Modulation on the L1 frequency carries both the C/A and P codes in phase quadrature, while the L2 frequency carries only the P code. These codes identify each acquired satellite by matching the unique pseudo-random noise code pattern generated by each satellite with similar user generated codes. 50 Both codes are required to measure the navigation signal propagation time. The phase shift is measured and used to match the user generated signal with the incoming satellite signal, [Bef. 26] The C/A code has a repetition period of one millisecond and has a short code stream, transmitting 1.023 million bits per second (bps) . This code is easily acquired and matched with the user generated pseudo-random noise code but only provides a coarse time signal for computing the pseudo-range. However, the P code has a long code stream, repeating only every seven days, and it is transmitted at the higher rate of 10.23 million bps. With this higher data transmission rate and long repetition period, a more accurate time signal is available for pseudo-range determination. However, the long period and high data rate makes the P code difficult to match with the user-generated pseudo- random noise code pattern unless the receiver has a highly accurate time standard, and the approximate receiver location is known. In lieu of this, the usual method of acquiring the P code is by matching the C/A code of the desired NA7STAR, then using the Handover Word (HOW) , to locate the correct P code sequence within the 7-day pseudo-random noise code. GPS time is transmitted 51 with the HOW every six seconds and provides very accurate GPS time to the user. Both of these codes provide the proper time reference for computation of the pseudo-range. The C/A code provides a lass accurate time reference than the P code. The selection of the code depends only on the navigational accuracy desired. The navigation message is also modulated on frequencies LI and L2 but at a much slower rate (only 50 bps) than either the C/A or P code. On both frequencies, the navigation message is identical and consists of 5 subsets of 6 seconds duration each. Each navigation message begins with the telemetry message (TLM) and the HOW message, which are used to transfer from the C/A to ? codes. The remainder of the entire navigation message allocated to each subsection is transmitted after the TLH and HOW messages. Information in the navigation message includes approximate satellite ephemerides, status of other NA7STAR satellites, parameters for cloclc corrections, atmospheric signal delay corrections, satellite performance status, momentum dump status since last upload, time since last upload, almanac and identification codes for all satellites, and provisions for inclusion of any special or important messages from the 52 control system segment to the user. [Hef. 27, 28J Navigation is thus achievable by combining the information transmitted by the space system segment in the form of the C/A and P codes and the navigation message. Accuracy and proper function of GPS are governed by the second segment — the control segment. The control segment monitors and uploads the individual NAVSTAR satellites, checlcs operational characteristics, determines the ephemeris and almanac data and corrections reguired, computes the time delay and clock corrections for each satellite atomic standard, determines the atmospheric delay corrections for pseudo-range computations and includes special messages in the body of the navigational message. These functions are under the command and operational control of the Master Control Station, currently located at Vandenberg AFB, California. Four unmanned remote monitor stations, located in Hawaii, Guam, Elmendorf AFB, Alaska, and Vandenberg AFB, collect the pseudo-ranges to each satellite, the change in pseudo-range of each satellite signal, local meteorological data, and the remote monitor station atomic standard parameters. 2ach set of data is transmitted, on request, to the Master Control Station, where all the data is combined 53 and the satellite upload corrections and parameters are computed. These corrections and parameters are then relayed to the Opload Station, Vandenberg AFB, for transmittal to the respective NAVSTAR satellites. The uploads occur when the satellites are first visible to the Upload Station and when the User Range Error exceeds U meters, as computed by the Master Control Station. [Ref. 29, 30, 3lJ The last segment, the user system segment, combines the information provided to the space system segment (by the control segment) with the information received from the space system segment to obtain the pseudo-ranges from four NAVSTAR satellites. These ranges are computed using the following algorithms: where R^- = true slant range to satellite i, c = speed of light in a vacuum, tt^ = time of received GPS signal by user receiver (assumed to be simultaneous from all satellites) , t^ = time of transmission at satellite i, and i Aty^ = atmospheric propagation delay time from satellite i 54 (fig.3.U.)« Assuming a user cloclc error, the true range can be expressed in terms of a pseudo-range: R^ = R. + cAt „ ♦ c(At,-At^ ) P. 1 A. ^^ R ^ S. 1 1 1 where Rp. = pseudo-range including clock error, ^""^r ~ "tini© delay in the user receiver of the received signal, and Ate = time delay in satellite transmission from satellite i. To determine the slant ranges: R=Ni{xc--x) > (yc -y) ^ ♦(Zc -2) ^ 0. :i. b. R. =^|(Xc -X)^ ^{Yc -y)^ >(Zc -Z)^ +cAt, ^c(At^-At ) The following quantities are known: x , y , z obtained from navigation ephemeris data; A t« computed using the i ionospheric delay correction obtained from observing frequencies LI and L2 (tropospheric delay neglected) ; A ts. obtained from the navigation message as the satellite clock error. Thus, there are four unknowns: x, y, z (user position coordinates) and ^ t p^ ( user clock error or bias). To solve this set of equations, four satellites must be observed simultaneously. [Ref. 32] 55 should only three satellites be observable, the altitude may be assumed and the solutions can be computed for the other two location variables and the user clock error. Solutions of this type (altitude hold) significantly degrade position accuracy. The above description is over-simplified since the relativistic effects of NAVSTAR satellite velocity, as observed by the user, are neglected in terms of the satellite time delay correction and the atmospheric propagation delay correction. The actual user velocity, in terms of velocity in the x, y, and z directions, is calculated using the Doppler shifts of the two frequencies LI and L2 and the estimated satellite position taken from the ephemeris data. With the relativisric effects as an integral part of the data set, solution of the navigation position problem becomes more complex. Phase I receiver manufacturers have included them in the solution of the problem by several different methods. Methods of solution depend on the usage of the receiver (whether static, high or low dynamic) and the expected cost/benefit ratio for the receiver (in terms of the total cost, weight and size). Current state-of-the-art design technology and navigational 56 u o Q.-a o = 5- TS Fig. 3.4. Pseudo-Range Description 57 algorithms, developed since Phase I, will be included in the Phase II receivers and will significantly improve accuracy of future receivers. B. MANPACK REC2IV2R The Phase I receiver used for this research was the Texas Instruments GPS Manpack, also known as the Manpack Vehicular User Equipment (MVUE) . MVUE is a singla channel low dynamic receiver, usable for receiver velocities from 0 to 25 meters per second. [Ref. 33] System configuration is illustrated by figure 3.5. Composing the system are the aanpack control data unit (CDU) , antenna and vehicle mount, and vehicle power converter. The Manpack is the receiver unit (fig- 3.6.) with provisions to connect an external data output, through the MVUE Instrumentation System (MIS) interface, figure 3.7. Facilities for an internal preamplified antenna mount, or an external preamplified antenna, and an attachment for either an external power source or the integral battery pack are also shown (figure 3.7). Together, the MVOE and the SBP/9900 microprocessor data processing unit have storage capacity for 47,360 sixteen bit words. This storage capacity allows interrogation of NA7STAR satellites sequentially, with the 58 s. •^ 0) o (U 0£ UJ =3 > s. s: E X (U ul ■M 0 VJ C^ B o> Ul £= H •r» J C hu o •r- K -M w •r- A 1 a. ai u 60 Fig. 3.7. Cutaway of MVUE Receiver 61 receiver computing a position fix every 24 seconds. The relativistic velocity effects on the received signals are determined by matching the incoming frequencies with the expected frequencies. The user velocity relative to the satellite is determined from the observed frequency shifts. The nominal frequency shift for each satellite transmission is computed using the simultaneously transmitted ephemeris data. Total weight of this receiver unit is 33.5 pounds, and it has a volume of 17,958 cubic centimeters. The second element of the avOE, the CDU (fig. 3.8.), is the input/output device for the non-automated Manpack user. Inputs are entered by keying the pressure pads set in six rows of four pads per row. To obtain a navigational position, the approximate user latitude, longitude, and Greenwich Mean Time (GMT) are keyed. After the warmup period of 3 to 5 minutes, the satellite signals are received, and the CDU will display the actual position. Additional input may include NA7STAR satellite selection, user altitude, and other position datums. Output options include position, GMT time, and system error messages. Other inputs and outputs are listed in the MVUE manual. £Hef. 3U] 62 r I 1 r- I (1) I (2) i (3) h --4----^- - -1 h I (11) I (12) I (13) T--T--T (4) j (5) 14) I (15) (6) (7) 1_ . I I (16) I (17) 1 f (8) , (9) I (10)1 ; I I I ---4- +--H I i.- . J L . _J._ ON (18) 1 (19) 1 (20) I _- i. . . J . . -L_ 1 - J AUTO STBY ENT B^ i RAO Li-, m fwT SEL HI i ! ! CLR I f^^=^ GRD B in C D k. ^ k. h) E Tl 1 IjL MAN HI \, 7 • • • 1 » TIM / > (9) 6 H (10) ^ / h ij jni W k T ^\ ' RNG L. ^ ;=7i M N jnz rz 1±L 0 \P 8 Tl V r~ Ll.ft). ; ' W, Q |R ' I f — ^'-^ •) /j ALT U V 0 ( 2 1 , (rn W X Lb=i TT i..^n.i Y^ FIX Fig. 3.3. iMVUE CDU Keyboard/Display Layout 63 Automated users may elect output either to a radio interface or through the MIS interface. For this research, a special interface unit, designed and constructed at the Office of Testing and Evaluation of Systems, NOAA, was used to link the MIS interface board within the receiver with a Hewlett Packard 9825T computer. With this interface, user latitude, longitude and GPS time were logged onto magnetic tape for future processing. Figure 3.9. and Table II are the engineering documents used in construction of the MVOS interface unit. Other MVUE elements are the antenna and the antenna external preamplifier vehicle mount. Located within the antenna are two antenna subassemblies associated with frequencies LI and L2. Both of the subassemblies are connected to the external preamplifier with two lengths of coaxial cable, enclosed in a flexible conduit. The entire unit, antenna and preamplifier, is connected to the Manpack receiver with a power cable and a coaxial antenna cable. Cable length is determined by the location of the external antenna but is limited by the minimum strength required by the Manpack receiver. The combined antenna and preamplifier unit is 36 inches long, and it weighs 1.9 pounds. 64 u , O) S- CO 0 S- 0 OJ OJ 0 ■t-j ■4- -»-) f gj OJ M- H- q; ja ro UJ 0 a. a; 0 Ln cn • (/I >- M •* CO ^r 0 «^ CVJ "a- -l-> H- (U 00 uo C\J CNJ CSJ 1— r— 0 0 ^^ -M CTl •< 0 0 0 0 0 0 Q. l««— » r— ' ^o UD 1 1 1 1 1 CQ ^M m CTs ID r— r^ CT^ UJ < #* •a- n-) m 00 CVl r— C^ -J -t-J «r ^ tn Ln ID ID LD LD ■=) n3 =tfc =«= 0 0 0 0 0 0 < OO O) > > ■> -C • ca: «::^ 1/1 oo -M _i C oo cC 0 «% UJ 1— itJ 2: 0 c r— H- 2 3 p 0 >- 2; CO Cf- 0 0 M^ CO >— c C <3: 03 0 r> --— ^ Q. • r— q; (— t/1 ■(-> LU 2: ro 00 0 O) U CQ ^— ' * — . E 0 0 Q ^ •r— -M ' — UJ 0 -i-> U H- 1— 1 O) CT> 0) •1— 1— 1 CC E x: .c -J UJ 0 •> 4-) CL _J Q- O) LO ra UJ 0 E S- (— >- " m CTl LD r— r~- 0-1 0 CT1 r-^ r~^ r-v r-». r*- r^ Ct- Oi _J • t— »> 0 0 0 0 0 0 01 • )— c , U3 1 1 1 1 1 1 >i > CQ ,_ m a^ Lr> r— r«- cn s_ 0) 1— 1 < OJ #t 1 — 0 0 0 ID >=r rT3 x: _1 -(-> «^ r>~ r^ r~. r^ <^ UD > -t-j fO =«te 0 0 0 0 0 0 UJ 5c 'j~> 00 i_ _i > => OJ 0 CO «a: LTl OO ^ cu- CC ■^ 1— 1— a. 0 1— 2: UJ •a: cn 0 CVJ 00 LD -t-J 0 ■«-> > s- , >s >> >, >, >, f— T3 T TJ T3 Tl 'O 0 74 1 . Theodolites This section describes the placement and operation of the equipment during the test. One theodolite was set on a tripod at each of the three stations, and each was occupied by an observer and a recorder. Communication between stations was maintained via portable radios. Because tests could be conducted only between 10 PM and 2 AM local mean time (LMT) due to GPS availability times, it was necessary to plan a systems of lights for the stations. The three theodolite sites were made visible by placing battery powered lights directly over the station marks. In addition, battery operated light packs for the theodolites were used. All shorebased lights and light pacJcs for the test were provided by the Pacific Marine Center, NOAA. The ship system was designed with an omnidirectional pair of lights anchored around the support pipe for the GPS antenna. Also, the equipment shelter on the boat deck of the ship was lighted by spotlights so that the GPS antenna was easily seen by the shorebased theodolite operators. During the test, each theodolita observer initialled on one of the other stations and recorded the reading on a log sheet. The theodolita operators then intersected the 75 lights on the ship GPS antenna using the theodolite telescope and tracked the ship until a 'aark« was called over the radio from the personnel aboard the ship. The angle measured at this time was recorded on the log sheet as a fix. The time interval between fixes was approximately one minute. 2ach series of approximately twenty fixes constituted a set. At the end of each set, a final reading was made of the angle to the reference station. The fixes were numbered consecutively throughout the test, and the Greenwich Mean Time (GMT) of each fix was recorded on the ship log sheets. The length of the sets depended on the ship position and heading. To correct the observed theodolite angles, the mean of the final pointing and the initial pointing was determined for each set and for each station. This value was assumed to be a constant throughout the set and was removed from each angle. A collimation error for each theodolite was also removed from each theodolite observation. The same observers and theodolites were used nightly at all stations except MOSSEL, where two different individuals observed over the test week. This continuity of personnel and equipment was designed to reduce operator and instrument error to a minimum. 76 2. GPS and ARTS MIS To colocate the different pieces of equipment at the GEOCEIVER STA 31370, a wooden tower was built as shown in figure 4.2. This tower was set over the station for the period of the test. An NPS equipment vehicle was parked as close as possible to the tower. Electrical power was obtained from the Monterey Coast Guard facility. Prior to the ship test, both GPS antennas were placed on the tower and centered over the station mark. ?or the first two nights, 9 and 10 Hay, equipment problems allowed the use of only one system each night and data were acquired only to determine the stability of each system. During the next night, 11 May, position outputs for the two simultaneously operating GPS receivers were recorded. This static test gave a determination of any difference between the two receivers under almost identical conditions. For the ship test, the GPS antenna was centered over the mark and was anchored at the top of the tower; the geoceiver antenna was centered over the mark and anchored at the middle level; and the theodolite on the tripod was set over the mark at ground level. This arrangement provided colocation of all three systems. It was assumed that no 77 I— 0 -j: CO o s t— V4D 1 a; t— C9 UJ LU C2 o O -o C3 -t-> 00 o o O) CM 78 error was introduced by the presence of the wooden structure. The shorebased ARTEMIS antenna unit was offset from the theodolite to eliminate interference in the signal due to the tower. An offset position was computed relative to the station mark and was used in postprocessing of the ARTEMIS data. Except for the antennas for the GPS, the ARTEMIS, and the geoceiver systems, all other equipment was installed in the equipment vehicle, where an operator was stationed throughout the test to monitor the data quality. The GPS Manpack is a manually operated system. As mentioned previously, it was decided that manual operation of GPS was detrimental to the goal of the test, and that an interface that would provide an automated printout of positions from the Manpack as well as a printout of GPS time would be desirable. Knute Berstis and Gary Hhitsell of the Office of Testing and Evaluation of Systems (OTES) , NOAA, assembled two interfaces that provided data storage on cassette tapes as well as the desired printout. Each system operated in conjunction with a HP-9825 computer and a HP-78a5 printer/plotter. Software was provided by OTES, NOAA. This arrangement permitted storage of the satellite 79 messages for further processing and provided an automated printout of the ARTEMIS data. A GPS ManpacJc had been sent to OTES for testing during the construction of the interface. Technical expertise and operation of the interface during the test were provided by OTES. The data from the GPS receiver were printed at an interval of 24 seconds, and consecutive data were continually recorded on tape and printed during the test periods. In addition, a manual record of the GPS position from the CDO was logged as the • marks* were called via the radios. The ship positioning systems were installed as shown in figures 4.3. and 4,4. An equipment shelter was secured to the boat deck of the R/V ACANIA. A length of six-inch diameter polyvinyl chloride (PVC) pipe was attached to the aft wall of the building on the centerline of the ship. The GPS antenna and the system of lights previously mentioned were set on top of the pipe. The ARTEMIS mobile antenna unit was set on a platform located on the centerline of the ship and at the top of the building high enough to not interfere with the signal from the ship radar beam. For the period of the 80 -t-> 3 O >^ E a. 3 o CO 81 i 9.205 m 7.935 m 6.6 m 3.6 m IT 31 Fig. 4.4. Equipment Installation on the R/V ACANIA Mean Higher High Water Level 82 test, the weather conditions allowed ship operations without use of the radar, thus there was no possibility of damage to the ABTEMIS unit. All other equipment — the ARTEMIS receiver unit, the GPS receiver, control data unit, power filter, and interface, the HP-9825, the HP-7845 plotter/ printer, and the real time clock — was placed inside the building. An operator monitored the equipment during the ship tests and another individual radioed the 'mark*, or fix, to the theodolite operators on shore. The equipment used at the shore location was installed in a vehicle and consisted of the same components as on the ship. Operation of equipment during the ship tests was monitored by an individual located in the vehicle. C. LOG OF EVENTS The test was divided into two portions — 1) a shorebased test which consisted of two nights of stability testing, and one night of receiver comparison tests, and 2) the ship test consisting of three nights of shipboard operation. The R/V ACANIA from the Naval Postgraduate School was the platform used for the shipboard tests. 83 1. stability Xs^ Operations began on 9 May, 1981, GMT. One of the GPS systems was placed over the station mark, and continuous data was recorded during the satellite availability periods. In this manner, system 1 was tested on 9 May, and system 2 was tested on 10 May. A position was defined as a quality observation if four or more satellites were used by the receiver to obtain the output. 2. Static Test Both GPS antennas were centered over GEOCEIVER STA 31370, and data from simultaneous operation of both receivers were recorded at the equipment vehicle. One antenna was placed on top of the wooden structure and the other immediately below it on the middle level. The vertical displacement was assumed to cause negligible error in the horizontal positions. Data were acquired on 1 1 May from both receivers with a quality observation defined as a position determined from four or more satellites. 3. shipbgflgg -gst ?or the entire period of shipboard testing, the wind speeds were less than 5 knots and the seas were calm with 1- 2 feet or less of swell. Visibility was excellent throughout 84 the test week. The ship track for each set is shown in figure 4.5. A log of subsequent operations follows: 12 May The GPS Manpack receiver was installed on the R/V ACAHIA and SPS and theodolite operations were conducted. The ship was allowed to drift during sets 1-3 (fix 1-69) with 23 fixes per set, in a east-northeasterly direction. 13 May The ship cruised at U knots on track lines from south to north for sets 4 and 6, and lines from north to south for sets 5 and 7. During fixes 139 through 157 the radio at the Coast Guard pier was disabled, and no data were acquired by either the theodolite observer or the operator in the equipment vehicle. 14 May The shipboard GPS system was inoperable. The trouble was traced to a faulty antenna cable, requiring replacement. No data were acquired, 15 May The ARTEMIS, the GPS and the theodolite network were all used for this test period. Data from sets 9 through 13 were acquired (fixes 165-262) . 16 May The control data unit on the shore based GPS system failed before the start of ship operation and could not be repaired without factory maintenance. 85 Q CO (V o (T3 u o -a c > >^ >, >^ 03 (T3 IT3 2~ in IT) CSJ n ^— lO ^^ ^^ «« , M •> oo m r~- ' — 1 •^ CO 1/1 CO l/» 4-> ■•-> -kJ cu <) of the major axes of the error ellipse are included as part of the output of the Geodetic Package and can be used as input if desired. The circular standard error (CSE) is also included in the output with the error ellipse parameters. The value of CES is the radius of a circle whose area is equal to the area of the error ellipse. That is: CSF = max min EXAMPLE: Error Ellipse Az-Max Max Min CSE 144. g"" 0.235 m 0.211 m 0.223 m Fig. 5.1 93 For this study, 262 vessel positions, or fixes, were observed and recorded. On examination daring processing, 51 fixes were found to contain errors and data omissions which rendered the vessel positioning computation invalid or indeterminate. The remaining 211 fixes comprised the data set which was then broken down into smaller sets for analysis and comparison. These sets were numbered 1 through 13 and categorized according to vessel trade. All sets were then processed using several different methods to determine the most accurate approach. B. TBEODOLITE AND ARTEMIS SHIP POSITION DETERMINATION Before processing the GPS Manpack data, the ARTEMIS data were processed to ensure the vessel positions, as obtained by theodolite, were correlated with the correct automated and hand recorded GPS data. ARTEMIS data consisted of an angle, MOSSEL-ARTEMIS OFFSET- vessel, and distance from the ARTEMIS OFFSET to the vessel. The angular measurement was first converted to an azimuth from south using the azimuth of ARTEMIS OFFSET to MUSSEL as the correction and adding the measured angle. Vessel position based on ARTEMIS was then computed using the direct geodetic program (also used for the basic survey) . Comparisons of the resulting geographic 94 positions and the theodolite derived geographic positions, were lade for corresponding fix numbers using the inverse geodetic computation on the WGS-72 allipsoid. The inverse computation utilizes two geographic positions as inputs for calculating the forward and back azimuths and the distance between the positions. [Hef, 46] For comparison, if the two positions differed by more than 20 meters, the ARTEMIS positions on either side of the suspect ARTEMIS fix were then used to compute the inverse computation to the theodolite ship position. In seven fixes, the fix position values were changed in the May 15 GPS data to give more accurate results. C. DIFFERENTIAL GPS SHIP POSITION DETERMINATION Hith the check and adjustment of the GPS data and the theodolite determined vessel position complete, the first GPS data processing was the comparison of the uncorrected, non-differential ship GPS Manpack receiver data to the theodolite computed ship position. Using the inverse geodetic computation, the forward azimuth and the distance between the theodolite computed ship position and the ncn-dif ferential GPS ship position were completed. These results were then used in the analysis of the differential 95 processing to examine the stability of the shipboard Hanpack receiver compared to the GPS Manpacic receiver located over GE0CEI7ER STA 31370. There were two methods of analysis of the differential GPS. The first of these was the determination of a static correction to be applied to all the GPS data. This static correction in the differential GPS computations was to account for a suspected bias between the two similar, but not identical, Manpack receivers. A mean static correction was computed for the most stable reception period during the static tests on 11 May. With the two receivers colocated over the GEOCEIVER STA 31370, a mean correction of -0.954 seconds of latitude and -0.3 07 seconds of longitude was found between GPS Hanpack System 1 and System 2 during times 07:16:00 GMT and 07:25:12 GMT. This static correction was then added to the latitude and longitude of GPS Manpack system 1 (located over GEOCEIVER STA 31370) data. The second method of analysis or processing in the differential mode used the latitude and longitude obtained directly from the GPS Manpack receivers. la either processing method, the computation of the differential corrector to the shipboard GPS Manpack receiver data was the 96 same. An explanation of the computations and processing of the differential correction for both methods follows. Computation of the differential corrector for each GPS fix position was accomplished by using the geographic position obtained with the stationary Hanpack receiver, located over GEOCEIVER STA 31370, and the geographic position of GEOCEIVER STA 31370. These two positions were then used ia the inverse geodetic computation to obtain a differential correction vector (forward azimuth, and distance) from the stationary GPS receiver to GEOCEIVER STA 31370, In figure 5.2, the differential correction vector is labelled "A". Using the direct geodetic computation, the differential correction vector was applied to the corresponding shipboard GPS Hanpack receiver position, and the differential GPS position was obtained. These resulting positions were computed on a one-to-one basis using the fix numbers as identifiers. Vector "3", the differential corrector vector which is identical to the vector "A" in figure 5,2, is applied to the shipboard GPS Manpack receiver and results in the differential GPS ship position. Comparison of the differential GPS ship position with the theodolite-computed ship position was accomplished using 97 T-2 COMPUTED SHIP POSITION ^ DIFFERENTIAL GPS SHIP ^ POSITION DIFFERENTIAL CORRECTOR VECTOR APPLIED, 1 GPS SHIP POSITION GEOCEIVER STA 31370 POSITION DIFFERENTIAL CORRECTOR VECTOR COMPUTED, t STATIONARY GPS POSITION Fig. 5.2. DIFFERENTIAL GPS PROCESSING 98 the inverse geodetic computation for both methods of differential GPS processing. The resulting forward azimuth and distances for both processing methods were used in the statistical analysis. D. STATISTICAL DATA ANALYSIS Statistical analysis was done on data separated into sets according to the method of data processing. The static data and stability data were graphed as functions of latitude and longitude versus time, Oser range error, furnished by the Space Division, GPS/OL-AQ, Vandenburg, AFB, was plotted as a function of time for each day of the test (see Results). Other graphed relationships are the geographic positions of the stationary GPS Manpack receiver data versus the GEOCEIVER STA 31370 and the theodolite semi-aajor radius as a function of fix number (see Results) . Other statistical data analyses were represented by histograms. Plotted on these histograms are the relative frequency on the left margin, variable bar increments scaled on the bottom, number of variable observations in each bar increment on the top, and the total sample size on the top margin. Within the histogram the frequency bars are denoted by asterisks, the mean by a capital M, the quartiles by 99 periods and the empirical density function by the capital F curve. The empirical density function was computed using: 1 N X-Z F(Z) = Z W — J N(B(N)) i=1 B (N) [B€£. 47] where: F(z) = the empirical density function, z = the frequency of observation, x = individual observation, N = the total number of observations, H = weight function, B = bandwidth, ff = 1 - z B(N) = range of all observations / W The statistical values listed below the histogram are defined in Table 7. Computed histograms show the distances between: 1) the theodolite-computed ship position and the differential GPS ship position, both with and without the static correction, by set; 2) the theodolite-computed ship position and the differential GPS ship position, without static correction, for five satellite observation periods on each of the three ship test days; 3) the theodolite-computed ship position and the non-differential GPS ship position for the five satellite-observation periods on each of the three 100 TABLE V. STATISTICAL DEFINITIONS The definitions of the basic statistics computed by the program are listed below: . MEAN: Average of the sample MEDIAN: Mid-Value of the sample, if there are an odd number of sample points, or the average of the two middle values for an even number of points TRIMEAN: 0.25 * (Q^ + 2Q2 + Q3), where Q^. are the quartiles MIDMEAN: The average of all sample values lying between the upper and lower quartiles MIDRANGE: Average of the maximum and minimum GEOMETRIC MEAN: GM =^>ix,'X^-. . . x„ 1 „2 n HARMONIC MEAN: HM = n 7^4] ^/^i VARIANCE: Unbiased estimators for variance and standard deviation are used - the square of the standard deviation STANDARD DEVIATION: S =j^x^ - n^ V ' — 1 = — ' n - 1 COEFFICIENT OF VARIATION: Standard deviation / |Mean| when the mean is less than 10. ** -30, the coeffic- ient of variation is set to zero. MEAN DEVIATION: The average of the sum of the absolute differences between the sample values and the median RANGE: Maximum - minimum MIDSPREAD: Q^ - Q^ , also called the interquartile distance M3: Third central moment. Unbiased estimator is used M4: Fourth central moment. Unbiased estimator is used COEFFICIENT OF SKEWNESS: MS / (Standard Deviation) ** 3 COEFFICIENT OF KURTOSIS: (M4 / (Standard Deviation) ** 4) - 3 BETAl : Biased estimate of third central moment; can be used in testing for normality BETA2: Biased estimate of fourth central moment MAXIMUM: Largest sample value MINIMUM: Smallest sample value QUANTILES: The al pha-quanti 1 e, x(alpha), is the solution to the equation: Probability (x .le. x(alpha) ) = alpha 101 ship test days; and 4) the GE0CEI7ER STl 31370 position and the uncorrected stationary GPS position for the three days of ship tests. In addition, the azimuths between the theodolite-computed static corrections, for each subset, were graphed as a series of histograms. To illustrate the difference between the GE0CEI7ER STA 31370 position and the stationary GPS position, the azimuths between the two positions are graphed on histograms for each of the three test days. 102 71. ERROR ANALYSIS The error sources contributed by each positioning system are described. Estimates of the effect of each on the final results are determined where possible. A. ARTEMIS POSITIONING SYSTEM The sources of error in the ARTEMIS ship position can be divided into two categories — those sources of error inherent in all microwave positioning systems and those unique to the ARTEMIS system. All are investigated and the contribution of each to the total error is determined. 1 , Microwave System Errors Sources of system error include range holes, inaccuracies in calibration, non-ideal geometry of the lines of position describing the fix, and interference with reflections of the signal from nearby objects. Range holes are a cause of unreliability in microwave positioning systems. The problem exists when the sea surface is calm enough to reflect part of the transmitted signal. The reflected signal will arrive at the receiving antenna at a later time than the signal which travels directly, causing a phase difference between the two signals. A zone or region of destructive interference of 103 the directly transmitted signal and the reflected signal will occur within which the vessel will receive an attenuated signal. When the phase difference of the two paths is exactly 180 °, no signal will be received provided the reflected signal is as strong as the direct-path signal. Prediction of the range holes, therefore, is useful in survey planning so as to avoid this problem. The range hole is a function of shore unit and ship unit antenna heights, the wavelength of the system, and the distance from the shorebased unit. If the operating area is known, antenna heights can be determined and equipment can be installed so that no range holes exist in the survey area. If fixed antenna heights are known, the region of uncertainty can be determined from the equation: [Bef. 48] The following equation is used for this computation: Dp = 2(h1) (h2)/nX, where X is the wavelength (constant for ARTEMIS at .032 m) , hi and h2 are antenna heights, and D^ is the distance from the shore based unit to the nth range hole. For this study, the antenna height of the fixed unit above mean sea level at the GE0CSI7ER STA 31370 was 3.8 meters. The mobile antenna was installed on top of the equipment shelter on the boat 104 deck of the R/V &CANIA at a height of 7.9 meters above the the waterline. Two range holes within the survey area were determined to be located at ranges of 1376 meters for n = 1 and 938 meters at n = 2 (fig. 6.1). These two ranges were computed for the case of mean lower low tide. The change in width of the range hole due to a tidal fluctuation of 1.5 meters during the test is shown in figure 6,1. (During the night of 15 May the sea surface was sufficiently disturbed by a two-foot swell and a surface wind of 2-4 knots such that surface reflection was minimal and no loss of signal was observed at the computed ranges) . Calibration of the ARTEMIS system was accomplished in two stages. As part of the study, the ARTEMIS was obtained for a one week test of the system from 13 to 17 April. During this time it was calibrated for azimuth and range over the baseline between the GE0CEI7EH STA 31370 and MOSSEL. The azimuth readings required no adjustment but the range was reduced by two meters. The equipment was returned to Marinav Corporation to fulfill prior commitments and then was returned to Monterey for the ship test on 15 May. Before the evening operation, the ARTEMIS was used to measure the same baseline as previously. A plus two meter 105 c on < ^ S\ y w TS \ S^^ ^ <. - c 1 ^*^^ \— c r o •1— »— ^ r«* U- -J LlJ m LU ^_^ o r— C/1 VI (/) c ro 1— « oo LU z: ■4-1 -a 3 «J _) en t^ c '-»— 0) •F— OTTJ r— ^ 3 03 fO r— -3 c^ U • r- S ■t-l • fiM *— ' CVJ VO CO )^ CNJ r— CM '— VO 00 r-* oo ca CT> =1 ^ ^ 106 bias was observed at this time, but no immediate compensation was made. This error was assumed constant throughout the test and was included in the calculation of the ship-determined ARTEMIS position during postprocessing. One of the advantages of the ARTEMIS system, unlike other microwave positioning systems, is that the geometry is always ideal for the lines of position that determine the fix. The range-azimuth technique of determining the vessel position defines an uncertainty ellipse having axes that are always mutually perpendicular. This allows prediction of errors as a function of range only, independent of the angle. The manufacturer's specified error in range measurement of the ARTEMIS is ± 1.5 meters for all line of sight ranges. One axis of the uncartainty ellipse is therefore constant. The other axis, that describes the error introduced by the system azimuth uncertainty, is 60 cm per 1000 m range. (This is determined from an angular error of 0.033° or 2' of arc). Both system error values represent an accuracy of twice the standard deviation value, or a 95'5 probability of the true value occurring within the margin allowed by these parameters. 107 The positional uncertainty can be expressed in terms of the radius of a circle of equivalent probability within which the true fix is expected to occur. The method of computation of this radius is described in Appendix A. The technique allows the conversion of uncertainty ellipses to radii of circles of equivalent probability. Values from this computation for the radii of circles of 90% probability at different ranges used in the survey area for 15 May are displayed in figure 6.2 along with the circlss of 90% probability, the magnitude of the radii at the ranges used for the study do not exceed 5.4 meters. One goal of this study was to measure the difference in positional accuracy between ARTEMIS and GPS. A maximum error of 1.0 meters, an order of magnitude smaller that the tested system accuracy, is desirable. At the present time, however, there are few systems that can provide the order of accuracy system for the position of a moving vessel, so the 5.4 meter error observed at 4000 meters had to suffice. Error caused by reflection of the signal from nearby objects is difficult to measure. To minimize this problem, the offset position for the ARTEMIS unit was planned so as to be clear of possible interference from the wooden 108 o i- ■t-i 1/1 en CM 109 structure and the ej uipment vehicle. No signal interference was observed despite the ship's motion. This source of data unreliability was therefore not considered to be significant. 2. ARTEMIS System Errors Errors unique to the ARTEMIS system include a pointing error source and the lack of resolution of the azimuth measurement in the dynamic mode of operation. The operation of the ARTEMIS system requires a manual alignment of the fixed antenna so that it is perpendicular to a known object. This is necessary to establish an original reference direction upon which all angular measurements are based. It is possible that a pointing error could be produced by the operator if the crosshairs of the telescope used to align the antenna are not exactly sighted. This would introduce a systematic error into all subsequent angle measurements. To minimize this source of error, the alignment of the antenna was checked before and after the period of operation. The original azimuth displayed on the antenna unit display agreed exactly with the final azimuth value. Any contribution to ship position error was considered minimal. TTO The AHTEHIS was operated using the dynamic mode option (see Squipment Descript ion--ARTEMIS) . The resolution of the system in this mode is 1 meter for displayed range and 0.1° for azimuth values. This resolution limit introduces an uncertainty of _0.5 meters m range and 0.05 in angle measurements. The computed uncertainty ellipse as expressed by radii of circles of equivalent probability, is shown in figure 6.2. The system error and all other errors mentioned above are assumed to occur within the scope of this resolution uncertainty. Another source of system error has been proposed in a study conducted in June, 1980, by NOAA. [Ref. 49] The test compared the ARTEMIS system with two ranges measured by two Del Norte Trisponders (a short range microwave range/range positioning system) and two lines of direction measured by two shore-based theodolites. The results described an underway bias of -0.05° of unknown origin in the angle measurements. This discrepancy has aot been resolved. The preliminary test conducted in Monterey in April, 1981 compared the ARTEMIS system with three lines of direction determined by three theodolites. The purpose of the test was to resolve the underway bias problem. Results are enclosed in a separate report. [Ref. 50] in B. CONTROL NETWORK The entire survey was oriented relative to the TRANSIT position on the Coast Guard Pier (GE0C2I72R STA 31370). Therefore, errors inherent in the position of this station mark affected all results. Assuming that the geographic coordinates published by DSA/HTC represented the best estimate available of the GEOCEIVER STA 31370, the remaining significant sources of error affecting all results were survey errors. The control network for the study was determined from the traverse and it was assumed that all positions used in the study were oriented relative to each other on the HGS-72 ellipsoid. A change in the ellipsoidal surface within the area encompassed by the traverse was assumed to be insignificant. Survey errors stem from the methods used for obtaining the initial azimuth for orientation of the survey, the type of traverse chosen, and the geometry of the traversed triangle. To obtain a starting azimuth for the traverse, two sets of observations on Polaris were recorded at the GEOCEIVER STA 31370. A striding level attachment to the theodolite was not used. The instrument level bubble was observed 112 repeatedly during the observations to ensure constant instrument alignment with the vertical. Failure to keep the instrument level could have introduced a + 30" uncertainty into the starting azimuth of the survey. [Ref. 51] To consider the significance of such an error, all stations were recomputed using a deviation of + 15" from the computed azimuth. The resulting shift in the positions of MUSSEL and aSE MON are listed: USE MON 0.133 m distance at 230° 36*47 . 16" azimuth MUSSEL 0.132 m distance at 230° 33* 4.08" azimuth The change is considered insignificant relative to the other errors described above. The survey was a closed loop traverse using 3E0CEIVSR STA 31370 as the origin and closing position. The weakness in this method involves the measured distances. A method of checking the observed angles in the triangle exists via the angular closure if a significant deviation in one of the angles can be detected. The distance measurement, however, can produce an undetected bias in the survey if the distance measuring instrument contains a systematic error. This error would shift all the surveyed positions. Correct 113 measurement of distance by the MRA V Tellurometer, therefore, was important. The equipment was calibrated over a known baseline and the errors were within the centimeter range. This error was therefore negligible. The geometry of the triangle was not optimum. Ideally, the triangle would have been equilateral to minimize the source of observing error. The choice of traversed points was based on the location of preexisting station marks and the desired geometry of the theodolite fixes to the ship. The closures computed for the traverse met third order specifications for accuracy, and the survey was not adjusted to remove the closure error. [Ref. 52, 53J The survey errors were considered to be within the uncertainty of the TRANSIT station location and were therefore not considered significant for the study. C. THEODOLITE NETWORK The errors generated by the theodolite network are divided into equipment errors, operator related errors and system errors, of which the latter is the most significant. The equipment used for the theodolite network were three 1-second theodolites which have a measurement resolution of 10.5". All theodolites were in good condition. 114 Instrumental errors of a theodolite are listed in Table VI. [Ref. 54] The lajor source of equipment error was introduced by not changing face, the process of observing angles a second time Mith the telescope reversed. Due to the nature of the test coupled with 1-minute fix intervals, it was not possible to observe all the fixes in both the direct and reversed modes. As an example of the magnitude of this error, the horizontal collimation errors were determined for each theodolite prior to the study. The results are listed below: Theodolite Collimation 5rroip » iauo5 - 1.0" # 14482 * 2.7" » 14452 - 0.7" All the measured angles were adjusted for this error as described in the processing section. The largest influence on the remaining instrumental errors was the non-vert icality of the main axis. If the non-verticality were large (for example, one division off-level in the lower spirit level bubble) , the angle measured could be in error by 7". [Ref. 55] To minimize this error, each theodolite was 115 TABLE VI. Theodolite Instrument Errors ERROR ELIMINATED BY Eccentricity, misplaced indices Graduation of circles Micrometer run and vernier error Non-verticality of main axis Bad setting of the upper spirit level Vertical ity of cross wires Horizontal collimation Vertical collimation and index setting error Reading both sides of circle and changing face Changing zeros Selection of suitable zero setting Error is not cancelled by any observing procedure Correct setting or applica- tion of correction Changing face and using same part of wire Changing face Changing face 116 relevelled if necessary between sets of observations. The magnitude of this and the collimation errors were considered to be insignificant relative to the system errors discussed later in this section. The operator-related errors are a function of the individual performance of the observers. The experience and personal comfort of the observer, for example, are two major factors which can influence the observed angles. An observer's performance and resultant impact on the guality of the results depend on the judgment and reaction time of the observer and are influenced by variables such as fatigue and age. The subjective nature of the problem makes an estimate of the error difficult, therefore, for this study the error was considered random. The major source of error in the theodolite positioning system dealt with the timing of the fix. A delay existed between the time the • mark* was called over the radio and the actual time the angle was observed. The timing problem was most critical when the ship was close to one of the three observer locations because the rate of change of the bearing of the ship was greatest at this time. Hence a small delay generated a large amount of error in the angle 117 recorded. To indicate the effect this error source may have had on the position of the ship, two fixes were chosen arbitrarily — one at close range to each of MUSSEL and GEOCEIVEH STA 31370. A one ninute value was added to the angle which was most affected by the timing error and the fixes were recomputed. The same process was repeated for the three fixes with the one minute value subtracted from the critical angle in each fix. The results follow: Number Original Fix *• 1 Minute - 1 Minute 210 36 °37« 20.62282" 36° 37» 20.6 1468" 36°37» 20. 63081 " 121°53«iH. 9718U" 121° 53» 4 1 .96933" 1 21 °53' U 1 . 97U26" 259 36°36»45. 88048" 36° 36« 45.87574" 36 °36 • 45. 89082" 121°52«54. 05062" 121 ° 52» 54. 04635" 121°52« 54. 05459" No significant error was generated from this source. Another source of system error was associated with the geometry of the fix. Ideally, the three theodolite angles would describe two equilateral triangles to the ship; however, within the operating area, the geometry varied. As an indication of the size of this error, representative fixes were chosen and the circular map accuracy standards (CMAS) of each of the combinations was determined. Figure 6.3 illustrates the approximate error caused by variations lis t/) c o 4-1 3 9. O a in Q. UJ o s- o CO c o u I/) i- a ^ / 0 yfh ^^-'^ T3 y\K - J? 0 X )^ /""•^ 0) ^ c ^ ^ >^ ^■^^ /T Q£ •f— W LU 0 w > r^ fO n ■*-> _i UJ ,— c LU C_) CO 0) on UJ (U ^ 0 ^ 2: X (4- 0 <4- a. PO ^ 0) U3 a; 3 -a f^ • — .-0 zn 3 > *^" J^ u_ xcC 119 in the geometry. Within the area outlined in the figure the geometry creates a CMAS of not more than 10. U meters. This is therefore the source of the largest probable error in the theodolite method of positioning. Nevertheless, this method in combination with the ARTEMIS system provided the best estimate of the ship location. D. TRANSIT POSITIONING STSTEH The method used to determine the TRANSIT position (GE0CEI7EE STA 31370) is the most accurate satellite positioning technique presently available. Error sources are reduced both during data collection and during postprocessing of the recorded values. DMA places requirements on the collection of data that will minimize error. For this study, only satellite passes whose maximum altitude ranged between 10° and 30 ^ were recorded. Meteorological data (temperature, pressure, and humidity) were collected for each pass, and a determination of the receiver clock drift was computed after each pass. The amount of clock drift as a function of time gave a real-time indication of receiver performance. Equipment checks were conducted routinely, and the results were included with the data package submitted to DMA. 120 An error budget of the TRANSIT system for point positioning is listed in Table VII. [Ref. 56] The precise ephemeris method of postprocessing accounts for all of these errors: 1) for each pass the tropospheric correction is computed from the meteorological data; 2) the ionospheric correction is determined by observing the shift in frequency between the two transmitted frequencies; 3) the receiver clock error is known; 4) the satellite orbits are observed by the tracking stations so that precise satellite positions are known; 5) errors due to uncertainties in the geopotential model and surface drag forces are accounted for during computation; and 6) the receiver altitude relative to the ellipsoidal surface is computed approximately from the given MSL elevation. The accuracy of the computed TEANSIT position is stated as 1.5 meters per axis within a 90% confidence interval. This is assumed to provide the best estimate possible of the GEOCSIVER STA 31370 relative to the MGS-72 coordinate system. E. GPS ERROR SOURCES Global Positioning System error sources are separated into two main categories, the space vehicle systam errors 121 TABLE VI I. TRANSIT System Errors SOURCE ERROR (m) Uncorrected propagation effects (ionospheric and tropospheric effects) 1-5 Instrumentation and measurement noise (local and satellite oscillator phase jitter, navigator's clock error) 3-6 Uncertainties in the geopotential model used in generating the orbit 10-20 Incorrectly modelled surface forces (drag and radiation pressure acting on the satellites during the extrapolation interval) 10-25 Uncertainties in navigator's altitude (results in a bias in longitude) 10 Ephemeris rounding error 5 122" and the GPS user receiver errors. There are seven possible sources of error in the space vehicle systein--errors associated with satellite equipment, satellite clock, ephemeris, atmospheric delays, signal multipath effect, satellite update, and satellite propulsion firing. Table III lists these error sources and the approximate user equivalent range error for each. [Bef. 57] The satellite equipment error, also termed the group delay, is caused by differences and uncertainties in processing and transmission of the message through the individual satellite's circuitry. Each satellite has the group delay calibrated prior to launch and this known group delay is included in the satellite time corrector within the navigation message. However, unknown delays in signal processing and circuitry not accounted for by the corrector contributes an estimated one meter to the error budget. Satellite clock error is caused by variations in each satellite clock. Satellite clock time may depart by up to 976 microseconds from the correct GPS time. Corrections for the predicted clock variations are included in the navigation message. Residual clock variations contribute to the error budget and are included in ephemeris errors since 123 the clock errors are small and have the same affect as ephemeris errors. Ephemeris errors are the result of satellite clock variations, drift by the monitor station clocks, monitor station signal processing delays, lack of precise monitor station geodetic positions, solar wind and pressure parameter variations, and earth gravity model error. These sources all contribute to the ephemeris error budget. The ephemeris error budget is monitored over long time periods and translated by the Master Control Station into an Oser-Eguivalent Range Error (ORE). When the ORE exceeds the prescribed value of 4 meters the satellite ephemeris data is uploaded to reduce the ORE. [Bef. 58] Most of the ORE is included into the user clock corrector obtained in the GPS position computation. However, not all of the ephemeris error is removed during the position computation, and the residual error has been estimated to be approximately 1.5 meters. See Table III. Atmospheric delays in signal propagation are the result of two effects, ionospheric delay and tropospheric delay. Of these, the ionospheric delay, which depends on the freguency of the transmitted signal, is greater. With the 124 two frequencies, LI and L2, transmitted by each satellite to the user receiver, the ionospheric propagation delay can be modelled. Osing this model, the majority of the propagation delay is accounted for, but a residual delay results in an error. The other part of the atmospheric delay error depends on the tropospheric propagation delay. Propagation delay in the troposphere is a function of signal path length through the layer, the receiver air temperature, and air pressure and humidity. Since the tropospheric delay is not a function of frequency and is highly localized, the tropospheric delay corrector has not been incorporated into the atmospheric correction computation and is therefore an additional source of error. These two error sources combine to yield an atmospheric delay error estimated to have a magnitude of between 2.U to 5.2 meters. Ionospheric scintillation of the GPS signal, in addition to the ionospheric propagation delay, cause errors in positioning. Scintillation has the effect of random interference with the propagated signal as the signal is transmitted through the upper ionosphere. [Hef. 59] Interference caused by scintillation combines with the GPS user receiver processing noise to cause a random ranging 125 error and, if the interference is severe, interruption of the pseudo-random number binary code causes loss of signal. Errors and signal losses caused by scintillation cannot be predicted or estimated. Signal nultipath errors result from the reception of a satellite's signal transmitted via different propagation paths. Received signals thus may have been distorted or reduced in strength to a sufficient degree so as to affect the range determination from the satellite. Error due to multipathing is highly localized and cannot be modelled. Estimates of the error magnitude are between 1.2 and 2.7 meters. The last two space vehicle system error sources are attributable to the Master Control Station (MCS) satellite accuracy and maintenance functions. Usually the MCS uploads each satellite at a given time each day and the ephemeris data is changed(Table 7III) . Should the user not be aware of occurrence of upload and if the receiver therefore does not obtain the new ephemeris data, ranging to the satellite in question will contain a possibly very large error. In addition, if the HCS, through the Remote Stations, determines that the four skewed reaction wheels cannot 126 en un o o o o c o o o o in •a- \r> o LD un IT) in o O O o o Ln o o ID O r- r- O o o o O «d- o on ^3- en «^ 00 O U3 r— U3 CO O vo en Ln r>. O O r- o .— O O p— o o O O o CO oo OD «r <— IX> o o ^— o o Ln ir> Ln o o o o to o «a- in «3- o o o o ui Q Q. VO CO 1 — Ln o o o o o o Ln r— o o o o c o ^ Ln Ln o o o o o Ln en ) TS CM ro ir» 127 maintain satellite antenna alignment with earth, the hydrazine propulsion system is activated and the satellite is rotated. Once the propulsion system has used, the satellite orbit cannot stabilize immediately, and the ephemeris data will be inaccurate. A period of up to several hours may be required for orbit stabilization and for the new ephemeris data to be computed and uploaded. During that period, the ranging computations to the satellite will have large errors. The magnitude of these two error sources cannot be estimated but is assumed to be several orders of magnitude larger than the previously stated errors. The second error category is that related to the GPS user receivers. These sources of error associated with the user GPS receiver, the Manpack, are receiver signal noise, receiver vessel velocity, signal resolution, method of signal processing, ephemeris update capability, and, for the differential GPS computations, system accuracy comparison. Received signal noise errors result from interference introduced into the receiver GPS signals through processing and internal receiver circuitry. Additionally, quality of signal resolution is dependent upon receiver type and can be 128 a source of error. The combined errors from these two sources are estimated to be 1.5 meters. [Ref. 60] Estimates of these error sources for the avUE have not been made but are estimated to be of the same magnitude. Velocity of the receiver vessel results in GPS errors of varying magnitude. The higher the velocity, the larger the error. This error is due to the time lag required to obtain and process each NAVSTAR satellite range with the MVOE single channel receiver, to compute the average vessel velocity and to use the average velocity for positional computations. The Manpack requires a six second time interval to obtain and process the pseudo-range from each satellite used. Thus the fix position is an extrapolation of the four satellite ranges to obtain a convergent fix position. At one knot, the vessel travels 0.51 meters in one second. During the full twenty-four seconds required to obtain four satellite ranges, the vessel would have travelled 12. 2U meters. With the vessel travelling at four knots, the distance travelled during the total time interval required for a GPS fix position would be 48.96 meters. Processing the pseudo-ranges from four satellites requires the solution including the average vessel velocity during 129 the 2U-second ranging period. Use of this average neglects the relative velocity of the recaiver antenna which is mounted on the mast. During this test, the GPS antenna was mounted 9.06 meters above the waterline of the R/V ACANIA. Assuming five degrees of pitch and roll and a vessel roll period of 15 seconds, relative average antenna velocity was ,0.16 meters per second. The antenna velocity error translates into a random error of 0.16 meters. The other velocity errors have not been estimated but are assumed to be less than one meter for the low vessel velocities used in the test. One error source mentioned previously requires further clarification: error due to the relative position at the time of the fix. The ManpacJc requires up to twenty-four seconds to obtain and process the satellite ranges. The position of the fix and the associated time of fix are then recorded. However, the time of the fix may not have been the same time the computational results were printed. Thus the output position may not have bsen correlated with the correct theodolite computed ship position since the theodolite lines of position were observed when the GPS position was printed. Errors from this bias source may 130 range from 12.24 meters at one knot of vessel velocity to 43.96 meters at four knots. This error varied with the processing time required to obtain a convergent position. An estimate of this error magnitude was not made because of its wide variability. The type of receiver and the method of signal processing also contributed to the error. Multichannel receivers designed for Phase I testing have a lower magnitude error for satellite signal reception and processing than do the single channel receivers, such as the Manpack. In the multichannel receivers, four or mors satellite pseudo-range data are taken simultaneously. The single channel receiver sequentially receives each satellite and computes the pseudo-range data. Simultaneous data reception reduces the user velocity error and therefore has less position aliasing than that found in the single channel receivers. The method of signal processing may induce positional errors through the use of non-optimal weighting functions in the position computation. Should the ephemeris or ranging data change significantly, as happens during uploading, signal processing using Kalman filters as used in the aanpack do not change the computed position rapidly enough 131 to reflect the large changes in ranges and result in a slow change drift of the GPS position. Estimated time requirements for user receivers to stabilize after an upload are up to two hours. [Ref. 61] The capability of the user GPS receiver to receive ephemeris data immediately after upload reduces the ephemeris errors caused by using an outdated ephemeris. The ephemeris data is repeated every thirty seconds and its length requires sections of two message subframes. ( Bef • 62, 630. The use of current ephemeris data in the computations reduces the error for the ephemeris to the value shown in table III. The Manpack has the capability to accept new ephemeris data immediately, but during the test large errors were introduced into the computation on satellite ephemeris upload because this selected optional function either did not operate properly or was neglected by the operators. ?or the differential GPS user, an additional error source is introduced into the error budget: the assumption that both GPS receivers will observe, obtain the pseudo- ranges , and compute the position solution in exactly the same manner. If this were true then both receivers 132 should be able to compute the identical position if placed at the same position at the sane time. With the Manpacks, the assumption that the units were identical and the position solutions were identical was not made because prior testing established that the receivers differed in position computations by as much as 3.08 meters. [Ref. 64] For the static testing on 11 May, one error source not previously discussed was the vertical separation of the two Manpaclc antennas, colocated over the GEOCEIVER ST A 31370 control station, and the possible interference of the uppermost antenna. System 1, with the GPS signals received by the lower System 2 antenna. Separation of the two antennas was 2.1 meters. Calculations using the speed of propagation in a vacuum and the two GPS frequencies produce wave lengths of 0.19 meters and 0.24 meters. Since separation of the antennas was much greater than either wavelength theoretically there should have been no positional errors due to antenna interaction or interference. Differing elevations of the antennas above the ellipsoidal surface also may have induced errors in the position computation. Estimated errors for the elevation differences are less than 0.1 meters. Total errors for the 133 antenna vertical elevation separation and antenna interference or interaction have not been estiaated. Thus, the error budget for the Global Positioning System suggests a combined error of up to 57.35 meters. tJsing the differential technique, the bias errors can be reduced in magnitude or eliminated. These bias errors include ionospheric propagation delays, tropospheric propagation delays, variations from predicted ephemerides, and satellite clock perturbations. Teasley, Hoover, and Johnson (1980), evaluated the error budget for a more advanced GPS receiver and found the predicted filtered solution error was reduced from approximately 11 meters to approximately 3 meters with differential GPS processing. [Ref. 65] Error budgets for the aanpaclc and the differential correction vector processing method used in this test did not attain the four meter accuracy but were not expected to because the receivers used were less accurate, and of different types. 134 VII. RESULTS Results of the GPS tests have been separated into four sections: stationary GPS evaluation, evaluation of non- differential GPS, differential GPS evaluation with static correction, and evaluation of diffsrential GPS without static correction. Tables IV and VIII list the optimum satellite observation periods and the NAVSTAR upload times for each day of the testing period, A. STATIONARY GPS EVALUATION Stationary GPS receiver evaluation was separated into the stability tests, the static tests and the tests of the stationary GPS receiver used during differential testing. Figures 7.1, 7.2, and 7.3 illustrate the results for the stability test conducted on 9 and 10 May. The receiver was less stable than expected and depended to a great extent on the HAVSTAR uploading times and the UHE of NAVSTAR 1 (fig. 7.4 and 7.5) . Correlation between times for the NAVSTAR upload and changes in the stability can be observed at 0620 on 9 May (fig. 7.1), 0655 on 9 May (fig. 7.2), 0815 on 10 May (fig. 7.3), and 0845 on 10 May (fig. 7.3). The relationship between stability and ORE is illustrated by comparison of the ORE for NAVSTAR 1 at 0640 on 9 Hay (fig. 135 36 37 15 _ STABILITY TEST RESULTS 9/10 MAY 1981 XXX 00 _ 45 36 36 30 121 53 45 X XX X XX X (10 MAY NAVSTAR 1) (10 MAY X XXK >Q— O- NAVSTAR 3,5,6) (9 MAY NAVSTAR 5,6) X ** X 30 o 121 53 15 - «^ - irx X X n X jr « — X 9 MAY - SYSTEM 1 0 10 MAY - SYSTEM 2 ( ) SATELLITE UPDATES 1 1 1 ! ! 0545 0600 0615 0630 GREENWICH MEAN TIME 06^15 0700 Fig. 7.1. 136 36 37 15 STABILITY TEST RESULTS 9/10 MAY 1981 00- UJ 45 36 36 30 121 53 45 a 3 C3 o 30 (9 MAY rmVSTAR 1) 121 53 15 * 9 MAY - SYSTEM 1 a 10 MAY - SYSTEM 2 ( ) SATELLITE UPDATES I L 0645 0700 0715 0730 GREENWICH MEAN TIME Fig. 7.2. 07^5 0800 137 36 37 15 - STABILITY TEST RESULTS 9/10 MAY 1981 00 X 9 MAY - SYSTEM 1 a 10 MAY - SYSTEM 2 ( ) SATELLITE UPDATES 45 (9 MAY NAVSTAR 5 10 MAY NAVSTAR 6) (10 MAY NAVSTAR 1) Jr X X a o 30 — ;< * K X 121 53 15 - 0800 0815 0830 0845 GREENWICH MEAN TIME 0900 0930 Fig. 7.3, oi o ac a: t3 CO z en =3 O o> """^ »— -— ^ «c ^r a a. ro =j ^.^ <— ^ ir> m kO UJ a: cc ai cc a: — => > > => H- < cj: «-c < «: cc z z z z ■zz UO U3 LU CC o T I I- O CM o (Sy3i3W) o I o 139 to o (J3 00 OJ Q£ CC s. Lu ie: en =» o <: o CO / / "V. - V. ^ „— «v ■ r / ^o / / uo / ■ — ' Ul / f .*— » »— ■ / ro < "^ / « o A f-^ a. ~— 3 ^-^ ,_ »»• tr) rn vD UJ ^ 1 — ro c a: ex < 1 < _j *«_«•' ►— 1— t— t— t— -J O) OO t/n oo t/^ UJ =» => =» •> > h— <: «< 40 30 20 TO SATELLITE ELEVATION ANGLES VISIBLE GPS SATELLITES MONTEREY, CALIFORNIA MAY 1 , 1981 NAVSTAR 1 (SV 4) NAVSTAR 3 (SV 6) NAVSTAR NAVSTAR ^ 5 (SV 8) (SV 5) NAVSTAR 6 (SV 9) 4 6 3 10 GREENWICH MEAN TIME (HOURS) Fig. 7.9. 12 16 145 LU 200 160 120 80 LU 40 o LU o LU -J 0 CJ3 Z a^ rs) < -80 120 -160 -200 SATELLITE AZIMUTH ANGLES VISIBLE GPS SATELLITES MONTEREY, CALIFORNIA MAY 1, 1981 NAVSTAR 1 (SV 4) MAVSTAR MAVSTAR MAVSTAR MAVSTAR 3 4 5 6 (SV 5) (SV 8) (SV 5) (SV 9) 4 6 8 10 12 GREENWICH MEAN TIME (HOURS) Fig. 7.10. 14 16 U6 o a: O) CJ3 00 2 ^ < »— o o> 00 a: — T;r LO CO VO ai Q£ q: q: q; 1/1 lyi 00 <-0 'jO •a: d <: «a: <: < o a. 1 I I I I I O (Sa3i3W] o I U7 GEOCEIVER VS. QiP% POSITIOM COMPUTATIOri GEOCEIVER POSITION VS. GPS SHORE-BASED POSITION FROM DATA COLLECTED 9, 10, 11 MAY STATIC AND STABILITY TESTING GEOCEIVER ^M>^^ GPS n 36 37 10 00 50 40 30 Fig. 7.12, 20 10 121 54 10 00 50 40 30 20 10 I 36 36 00 TTi 53 00 U8 stationary GPS receiver position ani the geoceiver position reinforce this conclusion. In figures 7.13, 7.1U, and 7.15, the mean distances between the two positions are 127, 173 and 1U3 meters, respectively. The higher means for the data shown in figures 7.1U and 7.15 are due to the ORE (fig. 7.16 and 7,17) for those dates and the NA7STAR upload frequency. If the data from 13 May is deleted because of the high ORE for that date (fig. 7.16), and the median distance used for 15 Hay is taken to be a representative value (130 meters on fig. 7. 15) , The difference is approximately 129 meters Between the two positions. The azimuth was also nearly constant with the observed median values of 181° , 207° and 178 " from south as shown in figures 7.18, 7.19, and 7.20 respectively. Neglecting the data on 13 May because of QRE values (fig. 7.16), the remaining two values are nearly o identical and have a mean of 179.5 from south. Thus the data indicates a nearly constant offset between the position obtained with the geoceiver and the position obtained with GPS. This difference is about 130 meters and has an almost north-south orientation. 149 Figure 7.13, 0| 4 Ol UJ i^ uj t^ uj vu u ® ir> tr* >f '^ ^- '*^ ^^ rg csi CM rg <*> *r LL* » • * U.» • • « • u.* • • • a) u. ♦— »• F> Q> ^ OX • • • • aX ►-000000 2* ♦ I ♦ ♦ ♦ LU LU UJ tU UJ UJ UJ yasM— o — i^ UJ ZO-^X — O ujac>— ►• >-— Xxx>/i>£a)ai O oca. 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OC(^a" a cdO — 4-- — * 1^ O ^/^ (^ ^• ^» - r f^ «B f^ trv u^u^ o <\J •« o* en • ••«•.. ^ O -^ — eg rg o* UJ- O Z I & Ui . vJ • — I :xt-<< I- o ujoe»->- I /1>£>OA ►-0 fn-^«^.«<>ir4 oooooo >- ♦♦!♦»* UjO UJUJUJUJUJUi • (Suj o-^ooo*.o -nT */hj — -r^mvOTS -^ -— acuj *N^-ti^oao-^ UJOC lM-«ff■-.^^0 ujO • z >r Z3 -^ — a — Ui Ui ac> < (/'X vj>«*iu Ui uj^- 07uj>a oc o -t^io ui^ ;TQ ui«- u.ZOk'i • ■<» ;» iXncO>Li«l^O rsj^^j r«j '^i Aj '>j *S4 OOOOOOO ♦ « * ^ « * ♦ i/> ^. -ti ••••••• n • -^ IJ'UIO -1 ^ T -1 . uj r «- .-— 1 -» ^ -I <_> - u. — •_! T r ► 73 10 and 52 meters. The large standard deviation for 15 May is apparent in the bimodal empirical frequency curve (fig. 7.35) and is caused by the NAVSTAR upload (fig. 7.17). in this case, the GPS receiver did not obtain the new ephemeris until halfway through the time period of the observations. The data for 13 May (fig. 7.3U) reflects frequent NAVSTAR 1 uploads and the resulting high URE values (fig. 7.16) for that date. C. DIFFERENTIAL GPS EVALaATION WITH STATIC CORRECTION The results of the evaluation of the data of 12 May (sets 1, 2, and 3), computed using the differential GPS positions and the static corrections, are shown in figures 7.36, 7.37, and 7.38. Mean difference between positions for the theodolite ship position and the GPS position are 29.1, 27,4, and 64.8 meters, with standard deviations of 7.7, 7.5, and 22.7 meters. These distances are larger than those determined for the theodolite ship position and the differential GPS position (fig. 7.39, 7.40 and 7.41). This higher mean distance indicates that the static correction, as applied, results in a larger error in the differential GPS position. 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H«l UJO a rt X Hi «» < k--J 0>aIUi UJ lixt nzuj>0 06- (Ow •ton ua. w. UJ— u.ZO>/» 00 <^^ v^KiX.nL X ui o t — ooooooo ■yi'C ujujujujujujuj uj^B O ^~' "^ O U^ '*^ '*^ •— « IJ O OO— •'Of-^'M O :i t ^ -T '^ ^r\r^rsi uj< *t «t :r *t *t ;• y j: I- - — mc TT. UJ lUIUUJQf •* — UJ ^ 180 D. EVALUATION OF DIFFERENTIAL GPS WITHOUT STATIC COHHECTIONS Evaluation of differential GPS without the static corrections were computed by sets for the five satellite constellations for each day of testing. Set 1 (fig. 7.39) shows a mean distance of 10.1 meters between the two positions and a standard deviation of 5.0 meters. The median azimuth between the two was 257° from south (fig. 7.42), which also was the approximate course of the vessel during the test. These values indicate that the error is caused by the bias, or alias, in GPS position due to the Manpack 2U-second fixing interval and positioning algorithm. For this set, the GPS position was obtained after the theodolite position. During set 2 the mean distance difference between the two positions was 11.7 meters, and the standard deviation was 6.8 meters (fig. 7.40); the median azimuth was 71 (fig. 7.43) . These values were slightly greater than those of set 1 due to the increased URE for NAVSTAR 1 during the set (see 0700 on fig. 7.32) Additionally, the azimuth was nearly 180° from that computed in set 1, with the vessel on the same track as set 1. Unlike the error obtained from the 181 Figure 7.42. O I I I O I I O I I I I I o I I t *> Ol I I Ol I I * O I I I ♦ -• I t O I I I « u. ♦♦♦•••♦♦*•« •♦ ♦ a. O I u. • ^ I • Ik ♦ VL O I U. I O. I u. * u. o t u. I u. t u. * u. •— t a. «*•••*••«••«*•«*« tn I a. **•*••«">***«•••*• I U. • #••«•'»••'»•«* •«•« ♦ u. •». 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Mean distance increases for set 3 were due to the upload of NA7STAR 1 (fig. 7.32) and the availability of only a four satellite constellation. Set 2 had a five satellite constellation available. For set 4, figures 7.45 and 7.46 show the distances and azimuths for the set. These histograms fail to illustrate the constantly increasing distances between the two positions. These increasing distances result from the uploads of NAVSTAR's 5 and 6 and the large ORE for MAVSTAR 1 (fig. 7. 16) . Onboard the vessel the new ephemaris data uploaded for NAVSTAR 's 5 and 6 was not obtained until late in the set. Also near the end of the set, NAVSTAR 1 was uploaded with the result that the last several distances were very large, as shown in figure 7,16. In set 5, a very high QRE value for NAVSTAR 1 contributed to the extremely large position difference 184 Figure 7.44 I I oi I I ♦ OI I I -I ot t I ♦ -4 I I OI I I « OI I I O ) I ® p*« P" f^ <*s -^ ir\ — r— 11J4UJ Z02 ' • • • -> xri 3 ZZZZ^ OCXCJOOOOX ■ '«— -* rsitr* f^ ^ ^ Qi: * ►-000000 z* « « » * > UJ LU LU i iJ UIUJ • u o ^ VJ t/l*'! ^ vii za-"«>i •«I X Jt>— <•« ^» D O X I 1^ •••••«•«•-« oooooo ♦ Ik *X«*I**« 0 I Ik r Z luujujuju^aj :lt I • o 2r '^u^O'Crsim u. I r — o — oo~'^-^i^ 01 tk I — ^ ■MN> ■-■i^O'V*^® 1 a. I o«^ m.o'M^^'OO ♦ u. * a.a • • • • ' • OJI •••••••••••.. u. ••-••••••••••••••••••••••••••••••••• a. -«r»\(nCM— ixxixxxxxrxmxxjix »;r3-> r -rr-y IT r mr i>< — >oO lii s> 4 I U. •••••••••«••••••• 0>'««Ui'iJ I U. •••••••••••»•••»• '>4^ 0^ai>0 :^ ♦ Ik * I UJ-' a.Z^ t 'XL, ••••••••••••••••«•••••••«••••••••••••••• • • »- CL'XCmj't ^^ » Ik >— ^3 ZUJ u^>>/luX(XX (^.•••••••••••••••••••••••••••«»«««»*«*««****«»>»»*» UJ I .u.***'* ^u. « u. ♦ lUU. I Ik •••••••••«•»••••• 'TO OOCOOOO I Ik •••••••••••••••••-o>- ♦♦*»*** ^ tk * -^-^ ojuj i^iL,aj;^uj' ijui •^1 It •♦••••••• -t)icAfn-"ir~ I u, ♦♦•♦••••« ^ f-.*— cT'-^Ti -rv% I It ••*•••••• -A ,T.*^'*>^ -.-^.^ *- ^ > ^.Nj'^j r '*j'\i T>m "3 4 ,--.o'-o rw'a u-l 4 , ,,^ r __.^4 185 Fig-ire 7.4F '-C-0'"000 zoz 1X1 -T 3:x«J«J'« «»«x Lt xoo JOOX "- •- — '\H/> P- ^ ^ ox X 91 « I — I Ol i ■ i * vu Of Ui I -i I a. * r Ol •* I Ol Ol I I ♦ Ol I ►•ooo z* LUUJUJUJ 000 I ♦ ♦ UJUIUJ — 0!/> rj ar !/>•« •o ac OC UJ*/> ni (_) Ol zo-o« 0 X i»-<.« Z ■0 UJ— 0^ --'^J':^3ujul — ■3 :r x^^ojo • t-O -V -M -r m 0— a ■» 000000 o-Z ♦ ♦!♦♦♦ —'D UJUJU^UJUitU • 'Z—' >n/^.r t^ IMi/l /-->'- 0 -»• "^IT* 10 »n^u-^^*w^li^ >-Q. Ol- oo xxxxxxxxxxxxXTTXxrTxrxrxxxu.xxxrXTXxxxxrT-i»-xi:xT rxxi Zv^ m— ^— •»r»»Nj • lua. ■^ .no -«r X Q rvj >- J lU IX> ^ ui-t >-J>«»lU >« aj*--> QZUJ>Q (X. h^ -til uja. ./IZ uj— u-ZOw^ « jriu otnt '^liJ-TZt^ -^ u.^ 'V ^>-'_^ u-t — 0 ►-'U »/^>vr>.jXoe X • ^ Xu. .4 '-J'M^J'N**J'><'N ■ u O'^OOOOO .^ "C * * ♦ * * * * -O 'U'JIUI>tJIU'.^UJ — - A --^Orvi --f J •^(-J ^«-rj.^.^ .*-.• — - - 1 • ~- .5 « •— •! v--^->'— -I r -^-- -0 0'*'0-tJ'-)'%l-* — • -^ ^f j.r»^ ".^,a»^/> -3 0 O *" J -—•*-* '*^ -•'^ >- ^ Z t -■' 1 -t ^- 1 X r> t w -_•.■■' 1 r r fc. >U UJ.- J.« — .— -u *f ./» v^i.a>-r>ox 186 Figure 7.46. O <" X' O ® r^ -r ^ ^43 O -oooooo Z ♦ • I I ♦♦ I iJuj UJUJUjLLiUl -lO iOO>rrv* -• 3 -O O -• I 0.0 — O'MO—O oooooo ♦*!♦♦♦ OJUItUUJtUUi CIO — •»<»>-< O JW^O>0»*> >f (T T3 ^O-C* ot I i Q ZUJ>Q -Ouj< — >v<-)jt(XX OOOOOOO «- ^^ -J ."T -« -t .- T X r -1 "'.i-i >- r-—r Tt TT .'•I ■ -— jt^w^ 187 between that determined by the theodolites and that for the differential GPS position (fig. 7.U7). The azimuth remained nearly constant between the two positions with a median o azimuth of 43 (fig* 7.U8). These values for set 5 show that the large ORE for NAVSTAR 1 was the most important contributing error source (fig. 7,16). The large ORE may have been caused by activation of the hydrazine stabilization jets to dampen momentum on NA7STAR 1. For set 6, the mean distance difference between the two positions was 60.0 meters and a median azimuth of 93 (fig. 7.49 and 7.50). These values indicate that the upload of NAVSTAR 1 near the beginning of the set (0715 on fig. 7.16) was received and utilized in the Hanpack position algorithm, but the higher distance between the positions also indicates a large ORE (also shown on fig. 7.16). Data from set 7 were not evaluated because the stationary ManpacJc receiver did not record the GPS position for each fix due to radio failure. The mean distance , between the two positions for set 8 was 121 meters with a I mean azimuth of 63 ° (fig. 7.51 and 7.52). Both the „ distances and azimuths show that the URE for NA7STAR 1 at I 0530 (fig. 7.17) was increasing in magnitude and thus 138 Figure 7.47. X Of ; I I ♦ Ol I I •Ml I ♦ ijnii'i fuiiiniiii/ »^ i/> rg (Nj (^ ^ u% l/^ C ^■ 1^ r» >^ ^ — z— UJ4UJ o— o zoz XXX 3 ZZZZZ ax • • • • .X Z ♦ ♦ I ♦ ♦♦ UJ UJ UJ UJUi UAU XV^^g^-m«^ rrXXXxmxrixxxxxxixxxxxrxJ:ru.rj:rr3-rr^j-xxxxxxxTrm- r- 1/1 ^ oe Z I o o Ol ♦ ►- o i/n/» LU o i/»— h^m4 UJ ac ^ •r -« f«- o o uj«r>-»- * o — rt,»-^3iuuj o z XXXv/lJ^lO* ♦ Ot~ Ol ►-0 a^ — X . v/1»- 'O.y-"*** ■a o— oooooo $ a.^ ♦ ♦ 1 ♦ ♦ ♦ lUllJlULXJtUlU « a.Z ^rafflO'*^'* OJ —a »fMO^o-» >»• i/i>- — ^tMr-OO . 1^ OIMO-«00«> •O r^uo -rm»l-OCT>>r -* 1 o • *.... o t-a. iO(Mrrir44>.# •♦♦••♦♦•♦«♦*•«•♦•♦< ZV» UJO. o oio ui (X> « >--i ozuj>a s B"* UJ"— k^ZO«/1 >— aacaaiv^oXacX ZQ OOOOCJOO JJ kXJUJUJUJUJ*UUi — ao'O'O'or'-'O-a ^. ZZ OJ-K ^ ^zoujui < z<-»zxx — «t< < — '*>^i£3ujui xxTxxxrrrrrrx'rxxxxrrrxxxxxxxxxxxxxrxxrx U. — 3 Lk X oooooo IL ►- ♦♦«♦♦* \X, Z"" UJUJUJUJUiUJ It O — ^C'2l^--<«^ U.*«4>i ^z t/^>/S^^^f tf\ it -- — O u^(^(rg^c''^'^ • 0.0 XXXU.XXXXXXX— o X a -4 v^t/1 ' « ••♦•♦• UI ae> < a. o>Tuj Ol rsio azuj>a oc I -Ko oia. ^— J uj« j.ZO»/» t «t crotouj«/1«_)XacX i-Z Ol ■Zf UJUJ • JU. ooooooo « -M t— — **«♦«*« ^^>4n ojo ujujujuljujujuj • UJ O — -O'CnTnT^ \ (/^ X » O O ITN A) f**** k x^- ^ "^lA^r •*■'*- ^--- ► • 3C3 ITO-^O— r-^^o ► »»• T.7:. -u -J ZZOuiUi < Zt-«ZXX ►-T" — r-^xrx »- Z/> oxrt-Txox 190 Figure 7.49. O I Ol ri III III m 111 111 iiji C(*^-"U^ol'^0 LU4UJ zoz IXX 2> ZZZ2Z xa:<<<'<«ix —3333333 aCXOOOOOX or X ►-000000 Z ♦ ♦ ♦ ♦ ♦ ♦ UjUJLUUjUJUJUi C — — O^»^OP• X<3Dtf^^rr*^0^U^ o z >- UJ ULI VO»M IX 3e UJU1 « UJ ZO-<*>« U X !•-<< — <«^ >»■■)£ 3 luui T*- X7X£aica 03 ax ir:?: u-irrr 3:1:^3:3:1: s:3:rxrjmr-z3:3:Trxi:T-mrmj:3:rrrmTi:3:x 000000 a. ♦♦!♦♦♦ Z UJtUUUUJUIUJ »/ifc« p^f^-r^OW o cc S^. UJ»« u.ZO(/l Z iXqlOuj >i/ivj zoe X 2_l i "-^ '♦«*«♦ ^ 3 ooooooo I *JJ * * * ^ « « « X UJIUUJUJUJUiUJ ■yi uj««**»«« ^ zz ^ ZZOUiUJ 19! Figure 7.50. UJ LU lU LU iU UU (U OiNimrsjOfMO •*- «j o ® "^ O 00 vnoif^f*"— mo* • •••••• ■ UJ o 1 X 01 < 1 . 1 m ■♦•• — aj 1 1 r>j 1 ! . 1 0 ♦ ^ 1 1 0«rOx OX « . • • •£ a>o ►-000 z* ♦♦ VUUJLUUJ ro— -o 000 ( * ♦ a.Luuj -omf" >-f>>a^tf% r xxxxu-xxxxxxxxxxxj-xxxxxxxTrrrxxx^nrrrxT-XTT-^-xxxy UJ < a. oxuj UJ AJO 0ZUJ>0 CL I 'TvXO aj& h*^ 'l>^ u. ZO^ . < **% t/* ^ -i^ "* -^ 0 ^,J^^ir^'Of^f^ r^O 20 Z-^mf*» s0^5 -yO rz u....... —•J 0-< J><7-a«-i •^ *. « S.J ►- zz lil«J^ _l Z^UUJIU ■« Z-«<2XX 4} -X 'tiJLU< -.- — »• Tot XX ^^ ^ 10— ~ooa aj -uujajoc — **Ui^ 1/1 JXXl-XXOX 192 Figure 7.51 . -^ -4 rvi rjr>i rsi o;r-f~^• • •••••• "Z — O— O zoz XXX 3 zrzzz —3333333 zzoor>j U. ♦ 1-0 z u. I OC Ui >^ I • a o « • ••••••••••••••••••••••••. ••••••...•U. ••••••••••••• QC X 3>--»< • •••••*•*• 'v^* ••*••**••*• • ce O uja:^»- u. ♦ O — (^-r^SuAU u. I zo xxT'u^^oa kk I • o It I m — ». Ik *•— *» t-a u. I — — o It. I l/ll IN 1. ■ wji « U. I o>- oooooo Ik ♦ Ol"" ♦■♦ I ♦ ♦ ♦ • ••••• •U.* ••••••••••»•• -k* * 3 UJUJOIUUIUUJ • ***• u„-» 4k •»•** -fr* »***••*••••* * r^ .^Z O'^'Nimf^oQ ik ♦— ^Ni xcj msTo^*^**'^ a. I 'Nj.— (7'--t/>fnr>4rl^fn u. I • a. a. I o Z U. ••*•••••«••«••••••*•••••* -4 UJO. IXI <£> < It ••••*••'»••••«•»'•«•«•*•••« ZO OXUi Ol u. •*•*••*••*•*•••••••«•*••• t- azui>a ft— a./)>i-njXaCX u. • rr.'x. • u.»«#»*#««»*«******«-»»«*'»'***-»«***-»*«**>*ft-**»'*-*«*»** J. ^rMr\irstrj'Mf\4 o.* *••••'»••••••*•••••*»•••**•'»•*»«'•••••••*•••«•**« • • Z— ooooooo U.* •*••*•••••*••*•••••»•<»•»•••••*•••••••'»•••*••••• • -^ -tO *.«««««* Kl^ « -^O LlJUJIUUJUJLUUJ U-. •......•••..•.•■.•....•.••«.....••.. •*.•.*.*•.•• — ' i/iui ira>'Mr^k^'r' r^ 4u.*****«********»«*******<*»*****»»***** •-*■•»'•«•'*••• o*— .rO'*^'^oo '*^ • •«*U.**************«>»««»4.»*«**»**»*«****«»******» • ►-^ Z'MO — -" ^ — -^ **#***U.*****^*****'*'*************'***'**'************* ^'^ ^''^ u....... It -.-—4/* -^ O— •'^— — 4—4— •»* It •••■••»•••■•■•■»••■•■•••••»•••♦»•••••» cj ^ X Tuj'-*'** o « -o ^ %( h- z«i o-*'-JOuat -^ O O O O UJ ujiuLLinc*— ^'iu^ • • • • • Wl oXZ»-ZX'-3X 93 Figure 7.52 •41 I I I i ♦ I I % I I I I Ol I t o< I Ol I I ''I I Ol Ol 2 I ♦ Ol I ■ I ♦ uj O I isl t ;;; i a I ui I -I I &, ♦ r —I < I « * ••'»••* •.*■*♦•♦♦ n III m 111 HI 111 itii • ••••■• rsMNj f«^ ^ ^ •^•^ "• i Ik ♦ 3 ZZZ2Z '"zoinoine^x OX X ►-000000 S ♦ ♦ ♦ I ♦ ♦ UJ UJ LLf UJ UJ tuui XOi^>r— ^lO < CD C* *Nj -^ irf> ^ XXZXXXXZZXXXXXXXXXXXXXXZXXXXXXXXXXXXXXZXU.XXXXXXXXX r^ — UJ (£•••••• s ►—«—*-«-• oe Z 1 c Ui o « ^* I -«»-■<< < O uiac>-l— w — >*» J-^3UJUJ !/> XZXv/t^tad W- 3 O X (*1 « 1. ini^ 000C3O0 ■M * « 1 * « ♦ ZT UJUJUJUJUiUi O •MOf-^f—O — S' o-oo— -ovn >-a <^f-^.oa'0 I 1 rgii\^^^ o<^i>*•0 C a 1/1 o. Ui aO < O <->XUi UJ — .%acOuj«»ZQ txiM- a.o— ouj<^- XZ >/>»v>vJXCCZ •♦••♦•••« ooooooo UJU» • X — — i-O -^ oj ajijjujujujujui 33UJ f^NO-OU* vrmiA **»m* «rfl^ O o T< LU ••••••• -rfcn>i'C*n 'T ^^ A. < UJ ►- Z^ -J ZZOujui • < Z4-4ZXX wM — r— T-irorTX UJ UilJJUJCCi !■ UJ -t i/i oxx>-xroi 194 resulting in a greater positional difference. Another factor was the bias introduced by the Manpack 2U-second reception period. This is evident in the azimuth for the theodolite ship position obtained from the GPS shipboard receiver. The data for sets 9 and 10 were combined for evaluation and the results were a mean distance between positions of o 241 meters and an azimuth of 267 (fig. 7.53 and 7.5U). Values of that magnitude show that the ORE for NAVSTAR 1 was the error source. Data were sampled from 0600 to 0640 (fig. 7.17). Thus the correlation between the high NA7STAR 1 ORE and the high mean distance difference between positions. Again, receiver bias also introduced an error into the evaluation. Analysis of set 11 shows a bimodal distribution in both the two position differences and azimuths (fig. 7.55 and 7.56). The peaks on the distance histogram are approximately 133 and 160 meters; the peaks on the azimuth histogram, approximately 220 ° and 236° . Both peaks are caused by the upload of NA7STAR 3 halfway through the set and the increasing magnitude of the MAVSTAR 1 ORE just after the upload as shown by figure 7.17. The total positional difference for set 11 was approximately 154 meters. 195 Figure 7.53. ».-<«>j*»jiMr>«t ♦ ♦ ♦ UJUJUI OtO-O ooo i Ol I 1 "I 01401 o»-o ZQZ UJ^^tUlU 3 ZZ2Z^ — 0033333 acroooaox ^/)^OX^O«^0>< OZ • • • • cX ^oooooo 2* ♦ I I ♦♦ wij UJ UJ UiUJ UlUi T'(Mr^m»A^O h- ) f~.i-<7'm«N»r» (?• 1 o cD'*^u^rga»(^ rfn i-a. rjaso— 0« IN( ^•vAnO-O^ 7-W1 a>no-f iM^O UJ& o— — r-OO LUO X • >-_J ~r UJ< ■r-j (Q>- O isi ^ Ui ot> < >/>Z UXLU lU OCUI o^ai>Q ££ ojor •I-*Q lO^ »-ai oj-^ u.ZO*/» • ^u. ::Cccr3Ui<2Q -Cuj-t — O i<^> -< •^-*tr o-^'N<» i/» r\l-0-T-O-'-r^ ■M 1i~^i*\r^^^m.\r\ Q • i ■r~r~T^^r^n <-> O u •••••• • ■a> OfNirgrjrgi^iiNioj -M i£ O iM z <- iCX «» aj44 ^ ^20UiUJ • !7- t 2-t/> ijH>-ZTOI 196 Figure 7.54. O O f*^ *Nr0 -O ^^ l/^ (M Csl O a>cD>r>f vr>v>OX «— *— - rg in r* o» < OX • • . • .X - i ■ Ui O I X Ol of I • Zl- >f 03 — t-r u. a> a.c ik >/)>- i/t-oooomte «-oooooo z* ♦ ♦ ♦ ♦ ♦ ujuj lu uJ iLnjj uj x-/'^a a. JCnCOuj4ZO 3.'<>-OUJ< — i/»«/njXacX 3 Ui O I Mrt j .^ -o -* T) cr p* 'n xf. ••••«. 3 CM rg (N rsi .— r*i oj ^ ZZOUjuj •* Z-t«tZXT t X UJ 2C— '^ CC X Jt>-<-< o •J UJOCH-I- o **•*% vr^3uiuj TT. rxxvijiioia • C^— —3 ►-0 -^ — X l.'V*- IN 1 1 1 < < 2 'JXUJ UJ • h- aC(XOLLIx/^oXocX -^ VUCC >-ui UJU. XU. — rsjrgrsI'Mr^'NrsI . za ooooooo ^^V^ UJ I i II ■ 1 tl: III iiiiiH 198 Figure 7.56. rg«M«M«M ♦*♦♦*♦* I1 1 11 1 Hf lAjLU lij W 1.4 ^^ r>4 n t m <*\ Z ujiuuiUNU 3 2ZZZZ — 0303333 OCX ooooox i/>ZOinO«f>Ox •- — — ZO—«M !►— <^ -xi/ij^ajia •o vt XN IN* ►- a oooooo X • ♦ I ♦ ♦ ♦ h* a J UJUi UJLU UJ • Z»-* ri^r-IMIM^^ >» OX />o— CM/Mn f\j H-z r-o^wMN*^ — O ^3>0-*ON C»— •••••• 1/1 «M H-O Z* UJUJ ir- xcr uo o O <-<) OC Ui o UJ O X -. o l/» - < >/) U > 4 Ui Ui a. azuj>a cc I aj« u.ZO«i • >--i .tneooKzc^ ►-Z ♦ ZQC UJU) 'MfNJpgrg'^NjrsjrNJ 1 • UJl^ ooooooo 1 '> xu. *■ ♦•♦***■♦ » BM^^ »*»M UJ UJUJ LULUUiUU 1 'M ujo ■^^TJ (DU^'*^^^ Ol rg^»n-**D-^0 UJ — « r*» -^ f*- -7* CT* ^" * i/lX >r\rfrsjoO^O<^ X^- 4 r^ « >- IX UJ4-4 ^ Z ZOUJUi • -• < z-»-rxox 199 Evaluation of the combined sets 12 and 13 (fig. 7.57 and 7.58) result in a mean distance between the two positions of 172 meters and a mean azimuth of 262° . The mean distance was large because of the large magnitude of the NA7STAR 1 ORE (fig. 7.17). A contributing source of error was the bias introduced by the Manpack receiver. Overall, the data using a five-satellite constellation were as good or better than the data using only four satellites. The results for 12 May using five satellites (fig. 7.59) show a mean distance of 11.4 meters and a median of 10.6 meters. This compares favorably with the results from sets 1 and 2 (fig. 7.39 and 7.40), which had mean distances of 10.1 and 11.7 meters, respectively. The five satellite data from 13 Say showed a very large variance due to the large NA7STAR 1 ORE. Therefore, data were not compared to remaining 13 May data. Data on 15 May for the five satellite constellation had a bimodal distribution because NAVSTAR 1 was uploaded. Once the uploading occurred, the peak distance was 137 meters (fig. 7.50) which compares favorably with 121, 2U1, 154, and 172 meters for sets a, 9 and 10, 11, 12 and 13. Thus with a five-satellite constellation, positioning results were as good or better than the four-satellite constellation. 200 Figure 7.57 i •4 »«iM(M rg rsi rM or^ooooo ♦*♦♦♦+♦ UJ LU LU UJUJ UJ lU C O "" CD -O — * *«^ ^ ^ "^ r\j f*^ r»» 1^ ocooco^sim^ i i^ x»:xrrrrxxara:a:«Txr-u.rT'iyxTs:a:i"rrrr5-rrxy7TT:3-»-y*"ry3ryys:>" -• a. 4 < a z — 3 — r a— a.x az — o OICL UJ19 3 ■Z.-Z.-Z-Z'X. xzoouroox i/iZOinOinox OX .... .X ►-000000 z* • I ♦ ♦ ♦ UJUJUJUJUJUJUI X'"^J^-rgo■0 fMNi*^ f*^ -^ <^ oc • • . • . • Z I III UJ UJ 4:0— 1< XXZ>/)>£ < l/IZ <_l>a ae OJ of < < O ixK^ ^uj -U"» llZO . OIU. XOCCOKZO a> xll a.<>— cuj-««« — ^ — »/»>»*^OXqcX HI in so -o -< ^ I ► — ^ •« o- OOOOOC ♦ ♦'*'*' 'fc < UJUJUJUJUJU UJ • • > • • -J ^^Ol TC -ltUUJ*« iriJQ — ^CJ UJUJUJCt*-"^ 01 201 Figure 7.58. I I O I I I * I I O I I t I ;;; i O I I I O I I I * O I I I O 1 I I * I * O I O I I I I I Ik •«• • ♦♦ ■*■ Ik I U. •*•••'•••••«••'»»•*••• I u. •*••**»*•»•*••»»*••« * ;^a<»««>a««»«>««*>. ••••••••••• «..• I •••••U.** **••««•••••• •••«"»•• ••••*•••'»••*••'»••••«**« « Ik * O I Ik I Ik ) Ik * Ik O I Ik I Ik Ol I I Ik— ^ zo Ik -• oz U. 90 O.C Ik — <^^- one I VI y-o. — o U. ♦ lO ujuj -^ -^ rV) 4 ♦»**♦*♦ UJ lij UJ UU UiUi UJ rsi oj (\( r^ •— ro «»i • •••••• 1*1 m»M»M«\j«n«n UJ■''ZOl/^Ol/^OX *- — — UJ ZI_I-«»M O ujae>-»- — in^^iiaujui xxxJO> • •••«• Q UJ oO « 0>«tuj UJ OZuj>Q at <v>>OX<£Z O I I I — 'Njrgrgrgrvjrsjrsj • - <: /> ^ZX>-XXOX 202 Figure 7.59. U. 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I I I ♦ -I I <7- > r-.o-.-. r^ .%) l/^ — (7^ m rf^ f\4 fN* «*i ^ fn f^ ^ o— o ZQZ It ♦— ^ It Q(j — I .r o C<•^^- •* N*fl£ GC • • • . • • OU UJ • a. <_> i/M/t XX X ■xt-«< iNX zxx fO-^»^i .JM^^ Ui"-. oooooo X»^ ♦♦!*«» ^O uJUJUJUJUJUi ^^ ...»•• — zz a » ^ — Itl UJ oO < • OC '^XIU Ui • a at • UJlt «f<0 UJ& I ot UJ— u.:tov» I • Z» aacauJ«/xjXaeX t -^ K/iUi I —X I 3»- o rsjrjfSirsj'Nirj'-sj • z ooooooo -4 < ♦*♦♦♦♦♦ ■ ^ UJ UJ UJUJ LU UJ UJ «« < >r o-^0*M ►• p^-z^Orst-ru^O -< .O -- '-M#M O O -^ o » • Ui Z-«om *NI fc- LJ«*»««a* ^<»^ M« Q^M *rt »^ w^M ^i^*^ -* .-#-^ ^ »/1 • -J Z-^vJiijuj --ZX'JX 204 Figures 7.61 to 7.74 show the diffarence by fix between the latitude and longitude plots of the theodolite ship position, the differential GPS position, and the uncorrected GPS position. During most of the testing, the longitude of both methods of GPS positioning was in closer agreement with the theodolite ship position than was the latitude. Shown on figure 7.9 and 7.10 are the satellite elevation and azimuth data for the testing period. This data indicates that the satellite constellation had a larger effect on latitude than longitude because the predominant ranging was computed from one quadrant. The large differences between the GPS position relative to the theodolite ship position were easily identified during the shipboard testing period. Latitude and longitude plots (fig. 7.65, 7.66, 7.69 through 7.74) for sets 4, 5, 9, 10, and 12 show the deviations of the GPS receiver positions from the predicted positions that were obvious to the GPS operators during the shipboard testing. For sets 4 and 5, the stationary GPS receiver positions began to deviate greatly from the geoceiver position, resulting in a large differential correction to the GPS ship position. These large differential corrections caused the differential GPS 205 36 38 00 LATITUDE COMPARISON SETS 1,2 "" T-2 POSITION ° UNCORRECTED GPS POSITION • TRANSLOCATED GPS POSITION SHIP TEST RESULTS 12 MAY 1981 50 40 « SET 1 o^ 30 20 10 SET 2 36 37 00 20 30 FIX NUMBER Figure 7.51 . -10 206 LONGITUDE COMPARISON SETS 1 , 2 121 53 20 SHIP TEST RESULTS 12 MAY 1981 10 53 00 _ o 3 o 50 SET 1 SET 2 40 30 121 52 20 »T-2 POSITION -UNCORRECTED GPS POSITION •TRANSLOCATED 3PS POSITION J I IW 20 30 FIX NUMBER Figure 7.62. iO 50 207 36 37 50- UJ 40 30 20 10 LATITUDE COroARISOr! SET 3 SHIP TEST RESULTS 12 MAY 1981 ^ T-2 POSITION o UNCORRECTED GPS POSITION TRANSLOCATED GPS POSITION SET 3 36 37 00 50 60 70 FIX NUMBER Figure 7.63, 80 ?0 208 121 52 40 30- LOHGITUDE COMPARISON SET SHIP TEST RESULTS 12 MAY 1981 X T-2 POSITION a UNCORRECTED GPS POSITION . TRANSLOCATED GPS POSITION o o o 20- 10- 52 00 121 51 50 50 60 70 FIX NUMBER Figure 7.54. 30 90 209 36 38 40 - 20 - 38 00 - o 40 - 20 - 37 00 40 LATITUDE COMPARISOri SETS i, 5 SHIP TEST RESULTS 13 MAY 1981 SET 5 3 UNCORRECTED GPS POSITION 36 36 20 70 80 TRANSLOCATED GPS POSITION 90 100 FIX ,NUMBER Figure 7.65. 110 120 210 121 53 50 30 10 52 50 o LOnGITUDE COflPARISOn SETS 4, 5 SHIP TEST RESULTS 13 MAY 1981 30 >«x SET 4 ■*■» *« 10 SET 5 51 50 i-a X T-2 POSITION o UNCORRECTED GPS POSITION • TRANSLOCATED GPS POSITION 121 51 30 70 30 90 100 FIX NUMBER Figure 7.66. no 20 211 36 38 20 38 00 40 20 - 37 00 40 36 36 20 no LATITUDE comparison: SETS 6, 7 SHIP TEST RESULTS 13 MAY 1981 ^ T-2 POSITION a UNCORRECTED GPS POSITION • TRANSLOCATED GPS POSITION 120 130 FIX ^lUMBER Figure 7.67 40 SET 7 150 60 212 LOriGITUDE CCnPARISQ'l SETS 6, 7 SHIP TEST RESULTS 13 MAY 1981 121 53 50 30 53 10 V"--.^ SET 6 ^^ ^ o 3 Hi* o z o -J 50 30 — ' T-2 POSITION a UNCORRECTED GPS POSITION SET 7 52 10 — • TRANSLOCATED GPS POSITION 121 51 50 1 1 1 1 1 1 0 120 130 140 150 160 FIX NUMBER Figure 7.63, 213 36 38 20 LATITUDE COMPARISON SETS 8, 9 SHIP TEST RESULTS 15 MAY 1981 18 00 40 SET 8 20 37 00 40 20 ^ T-2 POSITION o UNCORRECTED GPS POSITION • TRANSLOCATED GPS POSITION 36 36 00 60 70 180 190 FIX NUMBER Figure 7.69. 200 210 21.4 21 53 40 20 53 00 o 40 20 52 00 40 121 51 20 160 SET 8 70 LONGITUDE COMPARISOr! SETS 8, 9 SHIP TEST RESULTS 15 MAY 1981 SET 9 TRANSLOCATED GPS POSITION 2 POSITION a UNCORRECTED GPS POSITION 180 190 FIX NUMBER Figure 7.70. 200 210 215 36 38 30 _ LATITUDE COMPARISOfl SETS 10, 11 SHIP TEST RESULTS 15 MAY 1981 10 SET 11 37 50 - 30 10 36 50 - X T-2 POSITION a UNCORRECTED GPS POSITION • TRANSLOCATED 3PS POSITION 36 36 30 200" Tra" 220 230 FIX NUMBER Figure 7.71 , 2^0 250 216 LOriGITUDE COMPARISOr: SETS 10, 11 SHIP TEST RESULTS 15 MAY 1981 121 54 10 - 53 50 _ 30 o o 10 L 52 50 30 121 52 10 200 * T-2 POSITION a UNCORRECTED GPS POSITION . TRANSLOCATED GPS POSITION SET 11 210 220 FIX NUMBER Figure 7.72 230 240 217 LATITUDE COMPARISCN SETS 12, 13 36 38 30 _ SHIP TEST RESULTS 15 MAY 1981 38 10 50 - 30 37 10 50 36 36 30 240 SET 12 T-2 POSITION UNCORRECTED GPS POSITION TRANSLOCATED GPS POSITION SET 13 250 260 FIX NUMBER Figure 7.73 270 280 213 121 53 10 LOriGITUDE COMPARISON SETS 12, 13 SHIP TEST RESULTS 15 MAY 1981 52 50 30 UJ Q SET 13 o SET 11 51 50 21 51 10 12 250 » T-2 POSITION ■ UNCORRECTED GPS POSITION • TRANSLOCATED GPS POSITION 260 FIX NUMBER Figure 7.74, 270 280 219 position shown on figures 7.6 5 and 7,66 to deviate a large amount from the theodolite position and the uncorrected GPS position. 22(7 7III. CONCLDSIONS The objective of the study was to determine whether the application of GPS in a translocated or differential mode provides sufficient position accuracy for near-shore hydrographic surveys. Several assumptions were made prior to the test: (1) two GPS receivers required for the differential mode performed the computations similarly, so that in the worst case a constant bias would be displayed if both receivers were colocated; (2) the process of updating the ephemeris information would not contribute a significant positional error to GPS in the differential mode; (3) reasonable accuracy could be obtained by using the output from the receiver control display unit, that is, sophisticated processing methods were not required; and (U) the Manpack receiver results would not differ when used in stationary or low-dynamic environments (shipboard at U knots) . None of these assumptions proved to be valid. It was originally expected that the two receivers would produce similar positions if both sets were operating at the same time over the same location. One limitation of these receivers, however, is that current ephemeris information is 221 not received unless the receiver has been activated prior to the update. [Re£. 66] For a period of time after the receiver is activated, the portion of the satellite message that contains the updated ephemeris is not acknowledged. Therefore, position degrades rapidly when a NA7STAR is updated and the current ephemeris information is not utilized by the receiver. For this study, unfortunately, the initial times of activation of the two receivers were not recorded. Hence, the effect on position caused by this receiver parameter was not defined. The ORE plots illustrate that the ephemeris updates did contribute significantly to the range error and, consequently, the resulting position error. The position determined by the Manpaclc receivers was not affected as seriously by the clock error in NAVSTAR 1 when a five-satellite constellation was used. The inaccuracy of pseudo- ranges received from this satellite required frequent updates from Vandenburg, especially on 13 May. A receiver that had the option of totally eliminating the erroneous pseudo-range would have given the best results for the study. Since the receivers operated independently, and the ephemeris information was not concurrent, the differential mode was effective for only a few cases. 222 A simple correction was applied to the values output on the control display unit of the Manpack receiver. This did not permit application of tropospheric or refraction error corrections, other than that applied by the receiver during computation of the position, & more sophisticated processing method, resulting in greater accuracy, would require acquisition of the pseudo- ranges and subsequent postprocessing to determine the receiver positions. The best results during the onboard portion of the study were obtained when the ship was allowed to drift at approximately 1 knot on 12 May. In conclusion, use of two Phase I Manpack receivers in the differential mode meets the required accuracy of 10 meters only if the ship speed is less than 1 knot and other parameters such as ephemeris information and the number of satellites used for the position computation introduce a minimum amount of error. Further testing using differential GPS should incorporate more sophisticated processing methods and more advanced receivers to achieve the survey accuracy required for nearshore hydrographic surveys. 223 APPENDIX A^ DESCRIPTION OF ERROR THEORY From applicatioa of error theory in the evaluation of positional information, it is possible to establish a meaningful accuracy statement subject to uniform interpretation. To provide a logical and acceptable basis FOR COMPOTATION AND COMPARISON, POSITIONAL ERRORS ARE assumed to follow a normal distribution. The assumption is valid because positional error components generally follow a normal distribution pattern when sufficient data is available. The statistical treatment of errors utilizes measurable errors obtained in the sources of positioning information. Analysis of the linear components provides a two-dimensional expression of the accuracy of the positioning system in the form of an error ellipse. The use of an error ellipse is complicated by the problem of axes orientation and propagation of elliptical errors. Therefore, the ellipse is commonly replaced by circular form which is easier to use and understand. The linear standard errors are combined and converted to a circular distribution and the final accuracy statement is expressed in terms of circular errors. 224 The circular form assumes the circular probability distribution function. This function expresses the probability that the radial error will be equal to or less than the radius of the probability circle. The dispersion of errors within the distribution is measured in terms of precision indexes, each of which represents the error which is unliJcely to be exceeded for a given probability. The preferred circular precision indexes are the circular standard error {o ) , the circular probable error (CPE or CEP), the circular map accuracy standard (CMAS) , and the circular near-certainty error, or 3.5 sigma (3.5 a ). For each precision index, the given probability is 39.35%, 50%, 90%, and 99.78%, respectively. Each of the precision indexes can be converted to one of the others by using the following table: Circular Error Conversion Factors 39.35% 50% 90% 99.78% 39.35% 1.0000 1.1774 2.1460 3.5000 50% 0.8493 1.0000 1.32 27 2.9726 90% 0.466 0 0.5486 1,00 00 1.6309 99.78% 0.2857 0.3364 0.6131 1 .0000 225 The rapid approximation for deteraining the circular standard error is CSE = 0.5000 (ax ♦ ay) where f^ x and ^y are linear standard errors obtained from the sources of positioning information, and therefore are the axes of the error ellipse. For a truly circular distribution, where '^ c is identical to the circular standard error, a x and a y are equal and the angle of intersection between the two is 90°. In all other cases, a normal circular error distribution is substituted for the elliptical distribution. The substitution is satisfactory for an analysis within specifiedcmin/omax ratios, where a min is the minor or smaller linear standard error of the two. Distortion in the error distribution berween elliptical and circular forms at lower a min/ a max ratios limits the use of the circular concept to ratios greater than 0.2 . The CMAS is the precision index used as the O.S. National Map Accuracy Standard. It is interpreted as limiting the size of error which 90% of the positions will not exceed. CMAS is computed from circular standard error as follows: CMAS = 2. 1U60 a c 226 The two-dimensional error distributions for positions determined by the ARTEMIS system and the theodolite network are described by CMAS. The accuracy of the specific positions is expressed by a statement of probability and error magnitude. The accuracy statement does not mean that the error in position is exactly the value shown in figure 5.1, rather it expresses the probability that the error in position will not be larger than the error given. 227 LIST OF REFERENCES 1. Stansell, T. A. , Jhf^ tt^rn^^tt Mavicration Satellite System , Magnavox, 197a. 2« Denaror R.# et al, "GPS Phase I User Sguipmeat Field Tests", Navigation, v. 25, No. 2, Slimmer 1978. 3. Personal communication, Lt . T. Rulon, NOAA, 2 February, 1981. 4. 5. 10 Munson, R.C. RADM- NOAA, Positj.onipa Systems--geport on the Work of WG aiab. NOS Pubiicatibn, June 1977. Dunn, P. and Rees, J., Hydroaraphic Applications of the Global Positioning System- Master's Thesis. Naval POSTGRADOATE SCH00L7 •950, 6. Ibid. 7. Van der Ree, A., The ARTEMIS Position Fixing System. A Range Bearing System. paper presented Datore the Canadian Hydrographlc Conference, Halifax, N.S., 1980. 8. Op cit. , Stansell, 1978. 9. Dew, a. E., LCOL, aSAF. , "The NA7STAR Global Positioning System", Proceedings of the Second International Geodetic symposium on Satellite Spsitioninq; 7ol. 2> DMA and K53, 1979. Henderson D.W. and Strada- J. A., "NAVSTAR Field Test Results", Navigation, v. 25, No. 2, Summer, 1978. 11. Baston. R.L. and Buisson, J. A., "The Contribution of Navigation Technology Satellites to the Global Positioning System", Proceedings of the Second International Geodetic Symposium on Satellite Doppier Positioning. Vol. 2. PHA and M03. 1979. 12. Bartholomew, C.A., "Satellite Frequency Standards", Navigation. 7. 25, No. 1, Summer, 19/8. 13. Ibid. 14. QLB.-C±t# Dew# 1979. 15. Personal communication, W. Hoover, Texas Instruments Corporation, 3 March 1981. 228 16. Jorgensen, P.S., "Combined Pseado-Range and Dopt5ler Positioning f ~ "'" -- • • Plans 80. Po Ifecord.M^auT Positioning for the Stationary HAVSTAH Oser", lESS Plans 80 1 Position Location and Navigation Symposium 17. Book S.A., et al, "The Nonuniform GPS Constellation", IEEE Plans 8 0 - •• • - ■ • , .. . Symposium Recor IEEE Plans 80, Position Location and Navigation d, 19M7 18. Milliken R.J. and Zoller, C.J., "Principle of Operation of NAVSTAR and System Characteristics", Naviaation. 7. 25, No 1, Summer, 1978. 19. 9p cit. Dew, 1979. 20. Aviation Week and Space Technology. 10 Xarch, 1980, p. 16. 21. Op cit. Book, 1980. 22. GPS Diagram. Rockwell International — Space Division, PuB. 35ll-P-1, 1976. 23. Pasahow, E, , "A Constellation of North Stars. NAVSTAR Global Positioning System", OCEANS , May 1979. 2H , Spilker, Jt^-jt "Signal Structure and Performance Characteristics", Navigation V. 25, No. 1, Summer, 1978. 25. Ibid. 26. 0£ cit. Milliken and Zoller, 1978. 27. 0£ cit. Spilker, 1980. 28. Van Dierendonck, A.J., et al, "The GPS Navigation Message", Navigation. V. 25, No. 1, Summer, 1978. 29. Russell, S.S. and Shaibly, J.H., "Control Segment and User Performance", Navigation. V. 25, No. 1, Summer, 1978. 30. Ob cil# Dew, 1979. 31. Personal communication, CAPT E. Gonzales, OSAF, 5 May 1981. 32. 0£ cit. Van Dierendonck, 1980 229 33. Global Positioning Systam Kanpad^/Yghiculac Psgr Equipment rnvaE) Manual. Texas Instruments Inc. , 1979. 34. Ibid. 35. q£ cit. SpilJcer, 1980. 36. 0£ cit. MilliJcen and Zoller, 1978. 37. 49. Teaslev. S.P.. et al, "Differential GPS Navigation", IEEE Plans 80, Position Locatioa and Navigation Symposium Record. 1980. 38. 2£ cit. Munson , 1977. 39. Ombach, M. J. , CAPT, NOA&, Hvdrographic Manual. Fourth Edition, NOS, 1976. 40. Gossett, F.S., Manual of Geodetic Triangulation. NOS, 1950. 41. Poling, A.C., Tellurometer Manual, NOS, 1961. 42. Mueller, I.I. and Ramsayen, K.H., Tntrodnrt^gr to Surveying- Frederick anger Publishing Company, 19/9. 43. Hodgson- C.7., Manual of Second and Third-Order Triangulation and Traverse, NOS, i 9bv. 44. Pfeife?, L, CDR, NOAA and Gergen, J.G., Direct Geodetic Computation Algorithm, NGS, 1975. 45. Pf eif er , L. CDR- NOAA, Intersection Computation Algorithm. NOS, 1981. 46. Pfeifer, L. , CDR, NOAA and Gergen, J. G. , Inverse Geodetic Computation Algorithm, ngs, 1975. 47. Library Program, NONIMSL, IBM 3033, Naval Postgraduate School, Monterey, California, 1981. 48. q£ cit, 7an der Ree, 1981. Pfeifer, L. , CDR, NOAA, Report of the Pi^ld T^stof the ARTEMIS Ranae-Azitnuth Electronic Positioning System. NOS, 30 June, 1980. 230 50. Newell, V. LT, NOAA and Winter, D. , LCDR, NOAA, ARTEMIS Test Results. NPS, 1981. 51. Personal communication, R. Helby, PMC, NOAA, 5 Aoril, 1981. 54. U.S. Department of Commerce, NOAA- NOS. Clas?j,^ications. Standards of Accuracy, and General ■Specifications of Geodetic Control Survey. February, 53. a.S. Department of Commerce, NOAA, NOS, Specifications to Support Classification, Standards of Accuracy. and General specifications of ^Geodetic Control Surveys. July 1975, Revised June 1980. Admiralty Manual of Hydroaraphic Surveying, Vol. 1, Hyarographer ot the Navy, I9bb. 55. 0£ cit. Admiralty Manual, 1965. 56. Oa cit, Stansell, 1978. 57. Qjs, cii, MilliJcen and Zoller, 1980. 58. OEE plotted data received from SAMSO, May, 1981. 59. Goodman, J. M., "The Environment and Earth-Space Propagation — Challenges for the Future'', Naval Research Reviews . Naval Research Laboratory, Fail/Winter, 60. g£ cit. Millilcen and Zoller, 1980. 61. Ibid. 62. Qb cil, Spilker, 1980. 63. 0£ cit. Van Dierendoncic, 1980. 64. Op cit. Henderson and Strada, 1980. 65. .02. £li# Teasley, et al, 1980. 66. Personal communication, W. Porter, Yuma Proving Ground, Arizona, August 1981. 231 BIBLIOGRAPHY Air Force ACIC Technical Report Number 96, Principles of Error Theory and Cartographic Applications^ By Greenwalt and Shultz, February, 19 62." Air Force systems Command Test and Evaluation Master Plan Number J-190, NA7STAR Global P9SJ-tiQning <^ystg>m fnr Navy Annex, by Headquarters, Space Division, July,' 1980. Army Map Service Technical Report Number 47. Integration Orbits for Satellites, by S. W. Henriksen, 1964. Army Map Service Technical Report Number 61, Pre~orbiter Investigation , by R. W. Harpe and others, 1967. Bossier, J. D. .Interagency Coordination Plan foy Development of the Application ol. the NA7STAR Global ?ositionina System (GPS) fQg 'ieoaetic surveying, paper distributed" to the National Acaaemy or sciences Committse on the Panel for Global Positioning Systems and members of the Interagency Group, Roclcville, Maryland, 31 October, 1979. Bowditch, N., American Practical Navigator, 2 vol.. Defense Mapping Agency^ Hydrographic center, MA Stock Number N7 Pub9VI, 1977. Christiaan Huygenslaboratorium ARTEMIS Manual, pperation and Installation Manual for the ARTEMIS Position Fixing System. MK III-S, 1972. Cnossen, R.. Low Cost GPS Receiver for General Aviation. paper presented at the J2nd Annual Helicopter Association of America Meeting and Industry showcase. Las Vegas, Nevada, 11-13 February, 1980. Dean, ff. N. and Feldman, D. A.- Coast Guard/MARAD Tests of the GPS Navigation Set Type Z Phase I sta^tic JesT|7 paper presented at the Marine Meeting of The Institute of Navigation, Yorktown, Virginia, 1930. Defense Mapping Agency, Availibility of Data as of 15 July, 1979, Doppler Geodetic Point Positioning Accomplished with Portable Tracking Equipment. Satellite Records Desk, T3 July, 1979. Defense Mapping Agency, The Department of Defense Wcrld Geodetic System 1972. by Seppeim, T. 0. and others. May, Dunn, P. D. and Rees, J. ». , Applications of Global Positioning System (GPS) Satertite j i-u ^^°^al posit. *^^ ^""^Phic surveys. thesN4494 Application of the global positioning sv 3 2768 001 89937 0 DUDLEY KNOX LIBRARY • T.-'Mv^"— ;.;^ • _* ." i-.'^y-^ k* *. . _" .■ ■}': '^f •■4 y,i " . 'i-» - .^ / . .•' '. % 1 _'« .■ t '^■\ 1 ' \-.''t ■ - *'*' '-'J^, ■ ■^ V. -' ■ V • -* ■ ,' .> ■ * ' V ■ ' ; '■>. : 1." 1 11 v^^^^H m H ■^TT « ■•^^^^^1 •:. 3 * \ .^^* ;; y • C l''!^H />^--' 1 1 \v^H .. 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