A HYDROGRAPHIC AND ACOUSTIC SURVEY OF THE PERSIAN GULF - PART I Jay Lee Wri ght DUDLEY KNOX LIBRMW NAVAL POSTGRADUATE SCHOOL MONTSRSY, CALIFORNIA BB949 NAVAL POSTGRAD Oil Monterey, California TH A HYDROGRAPHIC AND ACOUS TIC SURVEY OF THE PERSIAN GULF - PART I by. Jay Lee Wright ! September 1974 Th ssis Advisor: R. H. Bourke | Approved for public release; distribution unlimited. T166572 Unclassified SECURITY CLASSIFICATION OF THIS PAGE (rYhan Data P.ntnred) REPORT DOCUMENTATION PAGE I, REPORT NUMBER 2. GOVT ACCESSION NO «. TITLE (and Submit,) A Hydrographic and Acoustic Survey of the Persian Gulf - Part I 7. AUTHORfa; Jay Lee Wright PEAD INSTRUCTIONS BEFORE COMPLETING FORM 3. RECIPIENT'S CATALOG NUMBER 5. TYPE OF REPORT 4 PERIOD COVERED Master's Thesis; September 1974 6. PERFORMING ORG. REPORT NUMBER 8. CONTRACT OR GRANT NUMBERfaJ 9. PERFORMING ORGANIZATION NAME AND ADDRESS Naval Postgraduate School Monterey, California 93 940 10. PROGRAM ELEMENT. PROJECT, TASK AREA 4 WORK UNIT NUMBERS II. CONTROLLING OFFICE NAME AND ADDRESS Naval Postgraduate School Monterey, California 93 940 12. REPORT DATE September 1974 13. NUMBER OF PAGES 89 l«. MONITORING AGENCY NAME A ADDRESSf// dl /latent from ControlUnt Oltlce) 15. SECURITY CLASS, (at thle report) Unclassified I5a. DECL ASSI Fl C ATION/' DOWN GR ADIN G SCHEDULE 16. DISTRIBUTION STATEMENT (at thle Report) Approved for public release; distribution unlimited. 17. DISTRIBUTION STATEMENT (ol the lb. trees entered In Block 20, II dlllerent from Report) 18. SUPPLEMENTARY NOTES 19. KEY WORDS (Continue on reveree eide It neceeemry and Identity by block number) 20. ABSTRACT (Continue on reveree eide It neceeemry and Identity by block number) A survey of literature and historical data is utilized to investigate the seasonal variations in the hydrographic and acoustic properties of the Persian Gulf. The Gulf has a year round salinity of about 40 o/oo. The surface temp- o _ o . erature varies from 30 C in summer to 20 C in winter. An area of significant importance in the Gulf is near the Strait of Hormuz where the Persian Gulf water encounters the warmer less saline water of the DD ,™r71 1473 (Page 1) EDITION OF I NOV 65 IS OBSOLETE S/N 0102-014- 6601 I Unclassified SECURITY CLASSIFICATION OF THIS PAGE (Wnen Data Kntarad) Unclassified CtiCUHITY CLASSIFICATION OF ThI'j PUGtWTur Data Enttrt 20. (continued) Arabian Sea. Utilizing the FACT acoustic transmission loss model detection ranges for diesel and nuclear submarines are investigated. Generally, ranges appear to be greater in winter due to increased vertical mixing, creat- ing strong positive sound speed gradients. DD Form 1473 . 1 Jan 73 S/N 0102-014-6601 (BACK) Unclassified SECURITY CLASSIFICATION OF THIS PAOECWhmr. Dml* Enfrtd) A Hydrographic and Acoustic Survey. of the Persian Gulf - Part I by Jay Lee Wright Lieutenant, United States Navy B.S., United States Naval Academy, 1968 Submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN OCEANOGRAPHY from the NAVAL POSTGRADUATE SCHOOL September 1974 It* S394Q ABSTRACT A survey of literature and historical data is utilized to investigate the seasonal variations in the hydrographic and acoustic properties of the Persian Gulf. The Gulf has a year round salinity of about 40 o/oo. The surface temperature varies from 30 C in summer to 20 C in winter. An area of significant importance in the Gulf is near the Strait of Hormuz where the Persian Gulf water encounters the warmer less saline water of the Arabian Sea. Utilizing the FACT acoustic transmission loss model, detection ranges for dies el and nuclear submarines are investigated. Generally, ranges appear to be greater in winter due to increased vertical mixing, creating strong positive sound speed gradients. TABLE OF CONTENTS NOTE: Portions of this thesis are contained in Part II. I. INTRODUCTION 11 II. LITERATURE SURVEY 12 A. AREA DESCRIPTION 12 1. Political 12 2. Geography 13 3. Climatology Part II 4. Hydrology 15 B. RELEVANT OCEANOGRAPHIC CHARACTERISTICS--- 15 1. Physiography Part II 2. Bottom Sediments Part II 3. Currents Part II 4. Sea and Swell Part II 5. Temperature, Salinity, Density and Circulation 15 6. Sound Speed Part II 7. Biologies Part II III. HYDROGRAPHIC INVESTIGATION 18 A. SOURCE OF DATA 18 B. PREPARATION OF DATA 18 C. APPLICATION OF DATA 19 D. ANALYSIS OF "WINTER CONDITIONS - 24 E. ANALYSIS OF SUMMER CONDITIONS ■ 30 F. SUMMARY OF HYDROGRAPHIC INVESTIGATION 31 IV. SOUND PROPAGATION INVESTIGATION 36 A. PROPAGATION LOSS ANALYSIS 36 B. SUMMARY OF SOUND PROPAGATION 41 v 1. Passive Case 45 2. Active Case 46 V. CONCLUSIONS 47 APPENDIX A NODC Tape Data Transfer Program 49 APPENDIX B Propagation Loss Profiles 50 APPENDIX C Figure of Merit Computations 70 APPENDIX D Sound Speed Profiles 72 LIST OF REFERENCES 86 INITIAL DISTRIBUTION LIST FOR PART I 87 LIST OF TABLES Table Page No. 1 FACT model input parameters 37 2 Figures of Merit for summer and winter for the passive and active cases 42 3 Passive detection ranges (nm) for summer and winter 43 4 Active detection ranges (nm) for summer and winter 44 LIST OF FIGURES Figure Page No. 1 Persian Gulf with bordering countries and important cities 14 2 Diagramatic representation of water circulation in the Persian Gulf 17 3 Distribution of all known hydrographic data by- month for each 1 square 20 4 Confidence level based on the number of observations for the months of February and July 21 5 February transect and data points for 1 squares 22 6 July transect and data points for 1° squares 23 7 Vertical cross section of winter temperature (°C) along the transect 25 8 Vertical cross section of winter salinity (o/oo) along the transect 27 9 Nested winter TrS profiles along the transect 28 10 Vertical cross section of summer temperature (°C) along the transect 29 H Vertical cross section of summer salinity (o/oo) along the transect 32 12 Nested summer T-S profile along the transect 33 13 Modification of Sugden's 1963 diagramatic representation of water circulation in the Persian Gulf 35 14 Winter areas of acoustic similarity 39 15 Summer areas of acoustic similarity 40 ACKNOWLEDGMENTS Many people have been helpful in the research and composition of this paper and I thank them all. In particular I wish to thank Assistant Professor R. H. Bourke and Lieutenant Commander D. C. Honhart, USN, for without their guidance this project could not have been completed. Finally, I wish to thank the person who has provided constant encourage- ment throughout this undertaking, my wife, Penny. 10 I. INTRODUCTION It has been proposed that in 1975 the Naval Underwater System Center with the assistance of the Naval Postgraduate School, conduct a hydrographic and acoustic survey of the Persian Gulf. The purpose of this cruise will be to prepare a report for the Shah of Iran on sound propagation conditions within the Gulf applicable to specific sound sur- veillance systems. This thesis is submitted as a pre-cruise report to aid NUSC in planning the expedition. The objectives of the thesis are: 1) to provide a survey of the literature, consolidating relevant material into a single reference; 2.) to report on the hydrographic structure of the Gulf, using historical data; and 3) to report on sound propagation conditions in the Gulf, based on the hydrographic structure. Hopefully, realization of these objectives will enable NUSC to determine areas in the Gulf where study should be concentrated. 11 II. LITERATURE SURVEY A. AREA DESCRIPTION 1. Political Only in recent years has the importance of the Persian Gulf region come to the attention of the general public, this resulting mainly from the highly journalized oil export practices of the Gulf countries. The United States Government in recognizing the strategic importance of the Gulf region as a source of petroleum has been vitally interested in maintaining a friendly relationship with the one politically neutral country bordering the Gulf, Iran. Iran has become immensely wealthy through its oil industry, and under the strong leadership of Shah Mohammed Reza Pehlavi, it is emerging rapidly as the key to stability in this area of the world. Because Iran maintains friendly relations with both the United States and the Soviet Union, it enjoys the technical assistance and material support of both nations. In particular the United States is providing current weapons platforms, such as the F-14 and P-3 aircraft, and the Spruance class destroyer. Furthermore, the proposed NUSC cruise will be undertaken at the request of the Shah, who has recognized that in order for Iran to assert itself as the "peace keeper" of the Persian Gulf, it must have a thorough understanding of the ocean environment to make optimum use of new weapons platforms. 12 2. Geographical The Persian Gulf is a shallow basin 500 miles (311 km) long by 200 miles (124 km) wide which separates the Arabian Plateau from Iran. Its deepest channel, seldom deeper than 50 fathoms (91 m) lies close to the Iranian shore. Along the coastal areas of the Gulf there is scant vegetation, a result of a meager annual rainfall of only 3 to 1 1 inches (7. 6 to 28. 0 cm) most of which falls during the winter months. o o o o Temperatures averaging 90 F (33 C) and exceeding 120 F (48 C) in some locations are common during the summer months. During the o o winter season temperatures are cooler averaging 70 F (21 C), with o o nighttime lows of 40 F (5 C) in the western part of the Gulf. Viewed from Iran, the Persian Gulf appears as a remote region, kept inaccessible by the vast arc of the Zargos Mountains (Figure 1). Only in the northern part of the Gulf, where Iran's oil-rich Khuzestan plain merges with the Shatt-al-Arab River to form a delta is the Gulf easily accessible. The 120 mile-long (75 km) Shatt-al-Arab River is formed by the confluence of the Tigris, Euphrates and Karun Rivers. It provides a waterway to the main port of Iraq at Basra. The Karun River, which joins the Shatt-al-Arab downstream from Basra provides access to the major Iranian ports of Khoiramshahr and Abadan. On the coast, northeast of the mouth of the Shatt-al-Arab, lie the Iranian sea ports, Mashur and Shapur. To the south lies the brief, open coast of Iraq. 13 SAUDI ARABIA Figure 1. Persian Gulf with bordering countries and important cities (modified from Emery, 1956) 14 The western side of the Gulf is 1300 miles in length from the Shatt-al-Arab to Oman on the Musandam Peninsula. The coast line is ill defined in this region and navigation is hazardous due to the presence of numerous shoals, reefs, and islands. 4. Hydrology Although the Persian Gulf acts as the drainage center for most of Arabia, all of Iraq, parts of Syria, Turkey and Iran, little fresh water flows into the Gulf except at the northern end via the Shatt-al- Arab River [Sugden, 1963]. This inflow amounts to about 45 cubic kilo- meters per year, most of which occurs during the flooding season (January-March). Flow rates during the flood season are affected by the yearly variation of rainfall. For example, in 1929 the maximum 3 flood discharge rate of the Euphrates River was 4, 700 m /sec, while 3 in 1930 the rate was only 650 m /sec. Occasionally there is an additional fresh water input along the coast of Iran as a result of flood discharge during the winter [Sugden, 1963]. B. RELEVANT OCEANOGRAPHIC CHARACTERISTICS 5. Temperature, Salinity, Density and Circulation During the summer Emery [1956] found a general increase in o o sea surface temperatures from 75 F (24 C) in the Arabian Sea to more o o than 92 F (33 C) in the Persian Gulf. Temperatures of the winter are o o far different from those of summer, with values of only 60 F (16 C) at 15 o ° the head of the Gulf, increasing to about 75 F (24 C) in the Arabian Sea. Thus the water at the head of the Gulf undergoes an annual change of at least 30°F (17°C) [Emery, 1956]. The summer surface salinity increases from about 36. 5 o/oo in the Gulf of Oman to over 42 o/oo in the Persian Gulf. Winter salinities in the Gulf of Oman differ little from their summer time value. The Persian Gulf, on the other hand, is diluted in winter by the increased flow of the Shatt-al-Arab River and therefore has a salinity of 40 o/oo or less [Emery, 1956]. The Gulf is similar to a land-locked sea in which evaporation exceeds precipitation [Sverdrup, Johnson and Fleming, 1942], The water loss due to evaporation is made up by the inflow of water from the open ocean through the Strait of Hormuz. This water moves on the surface toward the Gulf's coastal margins gradually increasing in density. Eventually the water sinks to lower levels where it flows out of the Gulf below the incoming water. Figure 2 is a schematic of this density driven circulation [Sugden, 1963]. Summer in the Gulf is sub- stantially hotter than the winter, but the differences between summer and winter surface salinities are not great; hence, evaporation evidently continues at a high rate throughout the year [Sugden, 1963]. The control of density by salinity is, of course, modified by temperature changes which vary in effect according to the seasons. However, salinity, as opposed to temperature, is a much more important determinant of density than in the open ocean [Sugden, 1963], 16 fnrt "E«S>*-( OJL' *»E STRAiTS 0^ 3ULF OP OMAN "fc> 4 ^'W, 3 '^"^mmmnrrmm^^^ "•cwontai. but \o VEDT.C4. CONS"!iCT.ON Figure 2. Diagramatic representation of water circulation in the Persian Gulf (Sugden, 1963) 17 III. HYDROGRAPHIC INVESTIGATION A. SOURCE OF DATA The National Oceanographic Data Center, NODC, provided all known temperature and salinity observations for the Persian Gulf, which consisted of bathythermograph and hydrographic observations. Only hydrographic data were used in this thesis. Specifically, only values of temperature, salinity and sound speed, as calculated by Wilson's equations, were utilized. The data were converted to printed output and punched cards through the use of an existing FORTRAN program utilizing the Naval Postgraduate School IBM 360 Computer (Appendix A). B. PREPARATION OF DATA In order to make optimum use of the data the Gulf was divided o o into 1 (one degree) squares, with 60 E as the eastern boundary, thus including the Strait of Hormuz and the Gulf of Oman in this study. Fur- ther, since a seasonal description of the oceanographic character of the Gulf was desired, two months from each of the primary seasons, winter and summer, were chosen for investigation. The months of January and February were chosen as characteristic of winter conditions while July and August were chosen for summer. After sorting the data, as described above, it became obvious that there is a paucity of data from 18 the Persian Gulf area. Figure 3 shows a plot of the monthly distribution for each one degree square. The number of observations in the squares vary from 100 to 0. The data were concentrated to some degree within the months of February and July; therefore, the other months were eliminated from further consideration. Figure 4 entitled, "Confidence Level" assigns an arbitrary value of good, fair or poor according to how many observations are in each square for February or July. The next step in the data preparation was to perform a statistical analysis of the data for February and July. The monthly mean temp- erature, salinity, and sound speed were determined at standard depths for each 1 square. As the data were sparse for most 1 squares, the mean was the only meaningful statistic obtained. The resulting values of mean temperature, salinity and speed sound were used to investigate the hydrography of the Gulf. C. APPLICATION OF DATA o Rather than describe the hydrographic character of each 1 square within the Persian Gulf, the analysis has been concentrated on a transect located in the center and deeper portions of the Gulf which are considered more representative of areas in which ASW operations might be conducted. Figures 5 and 6 show the transect and the location of the associated data points for February and July. It is important to note that the positions of the data points in these figures are arbitrary because the values they represent are based on data taken throughout each 1 square. Vertical 19 rt n T3 0 o K p.° M C 2 ° rt n T3 m £ ^ tn (? ^ u > d <" £i . 5 -t-> « c! i-l O ■* h O Ci id Rj 0) U O 0 10 en C O "C y -S ■p ni C en 0) 3 Q u ° -a ^ c co £ m in a n J-< 0 oj m ,n o aaninvi 20 & rj b rt l u 01 V n) & X, U o 4-> M a <1> tr> o k A ^z. T> <+H Tl in a» O o rJ-l W n u ^3 in ii H r-( C ^ 0) 0 o > a . o (3h n V -t u w Eo ° >> Ri :" vh ? II w O >-> ro aanxuvT 21 o _ m O •—< CO -u J) PL, CO ■H «J „, 4-J CD R) C •o 3 M CD rtj jh 4J CO U ni h <-> 0 ,_( to 2 £ ,c a *> o 2 . <" TO r— 1 T3 T3 T3 0) C & ci en o Q V to 3 CO to 1) *1 !h ** a !» 0 "ri cr . i? w a> 1-3 > 0 h f— 1 3 VO rg O a 3 2 o -l-i rH «i-I **-l aanniVT 23 o plots of mean temperature, salinity and sound speed for each of the 1 squares along the transect were then constructed. In order to establish the continuity of this technique verticle cross sections of temperature and salinity and a nested temperature-salinity plots were constructed. D. ANALYSIS OF WINTER CONDITIONS During winter the Gulf is affected by the influx of water from the Shatt- al-Arab River at the northwestern end of the Gulf (Figure 7). The cooling effect of the river is seen as far south as point 8, where the 20 C water o underlies the 21 C water. This finding agrees with Sugden [1963], as he states that the river discharge can influence the temperature of the Gulf water at least as far south as 28 N, 50 E or near point 4. The temperature generally decreases with depth until point 9- o Between points 9 and 12 the temperature increases from about 22 C at the surface to 23 C at depth. The reason for this increase with depth is unclear. Emery [1956] found that in this area, between points 9 and 12, there is mixing between the warmer Arabian Sea water entering the Gulf, and the cooler Persian Gulf water, exiting the Gulf. However, the strong halocline which exists during winter in this area would prevent mixing below about 30 meters (Figure 13). As points 10 and 11 are based on only two observations taken by the same vessel during February o of 1961, the 23 C temperature could be an anomalous condition or erro- o neous data. Since there are no other sources of water as warm as 23 C in the Gulf, the data are probably in error. 24 U V c •r-t .2 a w a; tn +> O bD a o id u h o > a> . P. u (m) Huaa 25 The temperature between points 13 and 18 decreases from 22 C at the surface to 13 C at 500 meters. A warm nose of 22 C water can be seen at point 13, where the Persian Gulf water spills over the sill into the Gulf of Oman. Figure 8 shows that the surface salinity decreases from 41 o/oo at the head of the Persian Gulf to 37 o/oo in the Gulf of Oman. This is contrary to Emery [1956]; however, it is in agreement with Schott's data of 1918. Both of these reports were based on single cruises indicating possible year-to-year variability. Salinity generally increases with depth at all locations until point 8. At points 8 and 9 the water column is nearly isohaline at 39 0/00. This is indicative of a well mixed area, as is expected, since this is the region in which Arabian Sea water and Persian Gulf water encounter each other and mix. The salinity increases with depth between points 10 and 13 from 37 0/00 at the surface to 39 0/00 at depth. This confirms the inflow of the lower salinity, Arabian Sea water at the surface and the outflow of the more saline, Persian Gulf water at the bottom. Further, at point 13 the Persian Gulf water can be followed over the sill in the Straits of Hormuz and down the slope into the Gulf of Oman. There it reaches an equilibrium depth between 200 and 300 meters, thus confirming what Emery [1956] found. The winter picture is further clarified by examining the nested T-S diagram shown in Figure 9. At data points 1 through 7 the water column is approximately homogeneous with temperatures between 15 C and 20 C, 26 0) VH o o .1-1 u o CO rn n 01 t_. X u w—l 00 o t-4 -t-> n) u o o oo "— ""* >* u 4-> u •H & U • i-t 1—1 £ 01 HIJ3Q 27 a n fe :%. rx O 3 ft H MS 53 M •J < CO ft 3 ft- /t 7 o^S (o0) annivHidwax ' o en 0) .—i O I H a) 4-> ■ i-l £ V 4-1 CO V a-- jj h J3 28 and salinities near 40o/oo to 41o/oo. The water column is also stable at these points as density increases with depth. The characteristic at points 8 and 9 is the instability of the water column at the surface changing to neutral stability at 50 meters. This further substantiates the idea that Arabian Sea water and Persian Gulf water mix in this region, however, only in the first 30 meters. Points 12 through 18 show the nose of the warmer, less saline Arabian Sea as it pushes into the Persian Gulf between the surface and about 200 m. E. ANALYSIS OF SUMMER CONDITIONS During summer the flow of the Shatt-al-Arab River is less than in the winter and the Gulf is relatively unaffected by the influx of water. The temperature is stratified throughout the Gulf, always decreasing with depth. There are several abnormally hot areas present, one of 32 C located at point 4 and a 30-32 C area located between points 13 and 16 (See Figure 10). These areas are similar to those found by Emery [1956]. The mean temperature for point 4 is based on 15 obser- vations. However, the reason this point is relatively hot is unclear. The possibility that a majority of the observations were made in the o nearshore portion of the 1 square was investigated and found to be invalid. Also a search of any reports of local heating phenomenon was conducted with no success. The hot area in the vicinity of points 13 through 16 is in the region where Persian Gulf water and Arabian Sea water meet. During the summer months there appears to be little vertical mixing, and hence 29 en o n u n X 0> 4-> H -u Cj c R) o 1 n a 3 hA CO 4-1 o • M c u O n (L> m en -u> cl CO u rrt 0) a> u fl CO -w i—i n 0 > 0} .fl C n 4-> o . — I GjO c O a rt i— 1 o 10 M •rH rf s CJ Vi u T> ' — ' CO 0) nS u ^ o i-H 0) 2 re! u >H ID n a CM 1 •H . — i Hidaa 30 strong stratification occurs. A thin quiescent surface layer is formed which is heated considerably by insolation. The salinity in summer is well stratified throughout the Gulf. A low salinity region of less than 39o/oo is associated with the intrusion of the Shatt-al-Arab River at the extreme northwest end of the Gulf as depicted in Figure 11. As in winter, in the vicinity of the Strait of Hormuz, points 12 through 15, the 37-38 o/oo salinity nose of Persian Gulf water is observed to descend to about 300mdepth as it passes over the entrance sill of the Gulf. The nested T-S diagram in Figure 12 reveals the cooling effect at the surface of the Shatt-al-Arab River at point 1. Looking at points 2 through 11 the Gulf is seen to be well stratified. Points 12 through 14 show the intrusion of less saline Arabian Sea water between the surface and 30m in the Gulf. Points 15 and 16 show that the Arabian Sea water in the northern part of the Gulf of Oman is contained in a layer from the surface to approximately 200m. F. SUMMARY OF HYDROGRAPHIC INVESTIGATION In summary, the water temperature throughout the Gulf is almost o 10 C warmer during summer than in winter. The salinity behaves differently, as it remains fairly constant throughout the year. The only exception occurs during the winter months when the discharge of fresh water from the Shatt-al-Arab River reduces the salinity in the northern portion of the Gulf. 31 u tn £ a C o a —J a s «J CD »i O o jd ^ o h-l M fl o o • H CO O a> in 4-> O C !h CD rt () r£ 0) 4--" a «— 1 OXJ a c ■H o o rH h nt T) n en o i— I o cd r— 1 u ^ ni ^ CD ^-> >■ M •a O rf 3 CNJ § OJJ i— i i " ftf r- vh en ^H o Hiaaa 32 O o O O H x w_i o- 55 CO ►J o PH: _ <"> — 2 -4« + \ J_ (0o) 3HJlIVH3aW3I CO CD 2 CM i — i 33 During both seasons there exists a region in the vicinity of the Straits of Hormuz, where the Persian Gulf water and Arabian Sea water meet causing an area of horizontal stratification. It is in this region where the most irregular temperature and salinity structures occur. The basic circulation of the Persian Gulf appears to remain the same year round; that is, there is an outflow of the Persian Gulf water at the bottom, through the Straits of Hormuz and an inflow of Arabian Sea water at the surface. In Figure 7 the basic circulation was shown as described by Sugden [1963]. The analysis of the mean values of temp- erature and salinity would suggest a slightly different circulation pattern. Figure 13 shows this alternative. As stated by Emery [1956], in the Strait of Hormuz there is an area of convergence where Persian Gulf water and Arabian Sea water come together. It appears from this analysis, based on mean temperature and salinity profiles, that Arabian Sea water does not penetrate into the Gulf very far beyond this point. Without question the winds play a very important role in the circula- tion of the Gulf. Their actual influence has not been investigated; how- ever, as surface winds are generally northwesterly throughout the year, the concept of a southerly surface flow in the Gulf is most logical. 34 Persian Gulf Strait of Gulf of Hormuz Oman Figure 13. Modification of Sugden's 1963 diagramatic representation of water circulation in the Persian Gulf 35 IV. SOUND PROPAGATION INVESTIGATION A. PROPAGATION LOSS ANALYSIS The Fast Asymptotic Coherent Transmission model (FACT), a low frequency ray-acoustic model, was utilized to analyze acoustic propaga- tion conditions in the Persian Gulf. This particular FORTRAN library program has been adapted to provide both graphical and numerical out- put of propagation loss versus range, as a function of a variety of input parameters shown in Table 1. Note that the bottom loss index, scale 1-5, is based on bottom composition, roughness, and slope. Basically, the Persian Gulf has a flat mud-sand bottom for which an intermediate loss index of 3 is assigned. In the Gulf of Oman a slope is present: however, the bottom is almost entirely sand, so the value of 3 is assumed to be valid. Although salinity is high in the Persian Gulf (40o/oo), it does not appear explicitly in the expression for absorption, but it is recognized that high values of salinity would increase the effect of the MgSO relaxation process. Preliminary computations indicated that absorption coefficients would increase approximately 0. 05% from the standard ex- pression when considering a body of water with an average salinity of 40 o/oo. Therefore, this additional absorption factor was ignored. After running the FACT program for the six frequencies at each point along the transect, it became obvious that an unwieldy number of 36 TABLE 1 FACT model input parameters PARAMETER VALUE HOW DETERMINED 1. 3. 4. Layer Depth (ft) Bottom Loss index Sea State Varied Frequencies (Hz) Source/ Receiver Depth Combinations (ft) February 2 July 3 300, 500, 1000, 3500 5000, 8000 60/60 300/300 60/300 Determined from temperature profile Based on scale of 1 to 5 (1 low, 5 high) Based on scale of 2, 3, 4. Winds light in winter; shamal winds present in summer Arbitrary. These frequencies cover most passive and active detection systems Arbitrary These combinations provide for source/re- ceiver in layer, below layer, and mixed 37 graphical representations would be required to describe the results. Thus, methods of reducing the amount of data without loss of continuity were investigated. Utilizing the nested T-S plots and FACT generated propagation loss curves, it was found that large areas of the Gulf along the transect were acoustically similar. Hence the transects were portioned into areas according to their hydrographic and acoustic similarities. These acoustic areas are shown in Figures 14 and 15 with the 10 fathom (18m) bottom contour defining the approximate limits for a submerged submarine. A further reduction of data was made in that the 500Hz and 5000Hz propagation loss curves could be eliminated from the investigation, because they closely matched those of 300Hz and 3500Hz, respectively. The resulting propagation loss curves for summer and winter conditions are shown in Appendix B. In order to use the propagation loss profiles to determine the seasonal and geographic variability of detection ranges, it was neces- sary to generate Figures of Merit (FOM) for passive and active detection systems. It was assumed that passive detection would be made by an air dropped sonobuoy and active detection would be made by a hull mounted sonar. For the passive analysis FOM's were computed for 300Hz and 1000Hz signals, for both a snorkeling diesel and a nuclear submarine. The FOM's for the hull mounted sonars were based on 38 w n H M O o ►J aaninvi 39 w Q i=> H M o o aaninvi 40 transmission frequencies of 3500Hz and 8000Hz. The resulting FOM's are shown in Table 2. The sonar equations and associated calculations are located in Appendix C. Tables 3 and 4 show the passive and active detection ranges for the winter and summer seasons, respectively. B. SUMMARY OF SOUND PROPAGATION Several important points can be gleaned from the propagation loss profiles in general. The most significant point is to question what phys- ical processes or mechanisms permit detection ranges of 30 nm, seen in Tables 3 and 4, to exist in a "hot bath tub" like the Persian Gulf. The propagation loss profiles in Appendix B show that there is little loss of acoustic energy in Areas 11. IV, V, VI, VII in winter. The loss that does occur falls in the range between cylindrical and spherical spreading favoring the former. In these areas the positive sound speed gradients present cause the Gulf to act as a waveguide with minimal surface scattering and bottom loss. The propagation loss in areas I, III, VIII in winter and in areas I, II, III, IV, V in summer is greater because there is no capability for channeling of sound energy. Losses greatly 2 3 exceed spherical spreading (1/r ) often approaching a 1/r loss rate. Again, this is a function of the sound speed profile, which in these areas has a negative gradient (Appendix D). Comparing the two situations it is apparent that the shape of the sound speed profile, and not the high 41 TABLE 2 Figures of Merit for summer and winter for the passive and active cases Passive FOM's (db re 1 u bar) for summer and winter Nuclear Submarine FREQ FOM 300 Hz 82 db 1000 Hz 92 db Snorkeling Diesel Submarine FREQ FOM 300Hz 85 db 1000Hz 95 db Active FOM's (db re 1 u bar) for summer and winter FREQ FOM 3500Hz 195 db 8000Hz 180db 42 u 3 „ r- <* •* oo o 0"» N Z ^ H CO s o o t— i o V r— 1 CO 0) • H Q m co vo ui m o h |-H H m H ft co" ^ CD CO w •H 0) 2 o CO CO CO CO t- O vD U R) u S 2 CO V CO 4J & > •H ft d CO ,_l co P co 1— 1 1— 1 f' S» K„ t^ 1— 1 1— 1 1— 1 I— 1 r^ K* Y* pi o CO 4J •H M < o r-l O u <4H A o a> o ■4-> 1— ) CO CO -4-) I— 1 nJ •H CO nc! cd u ^J ' CO H u -H n m h 1— 1 1— 1 1— 1 1— 1 1— 1 1— 1 O h ^ b> 1 — 1 1 — 1 1 — 1 1 — 1 »— 1 1 — 1 1 — 1 HI— ll— (l— lr>r>r>r>r>P>r->r> •■-I O w a o o o oo N o o in co ?n CD Tf CNJ ■* "tf t> CO -£> -* O "* "* 00 O 0s- ro ro CO Q l— I 1— I r> r* r^* ^rtiniMino^^r-oof- ts-O00OOOr0O00v0r0'* CO mcONHNNHHH CO H CO i— i i— i h-i > CO CO >>>>>>> A d> T3 «« O bo a •m -u> J-* -u T3 • H CD 0) -i-> o a CD 2 ?H o T3 6 £ t— i nj r— < 0 E TRANSFER PMCGRAI' c C >>>>>>>>>>>> XX >XXXXXX>>>XXXXXX>>X>>XXXXXXXXX c C TUS PFCCPAf WILL REAO A S-TRACK NOCC C C VfE *NC TRANSFER Tt-E CATA TC A 9-TPACK C C NFS TAFE. EY PROPER CTILIZATICN CF THE C t "CM* ISI>..." CAKU, SPECIFIC CATA CNLY C c ffYCETRArvsrERREO. c ccccccccccccccccccccccocccccccccccccccccccccccccccc CCC 1 C I f- E h£ 1CN IVALI21) CCC£- CAU NF-CAC .NPRlNT.NFLNCH/5,6,7/" ' r.cccccc ccccccccccccccccccccccccccccccxccccccccccc.ee C ^CC TfPE INCLLCGS THREE SETS OF CATA. C C SETS /RE DELINEATED UY THE LAST CIGIT GN C C EACH C/"RC. I.E., A 6 IN CCLLMN HC SIGM- C C * IE? 57AN[*RO DEPTH CATA. EY DECLARING C C ISIX ECCAL T"j 6, ALU STANCARD CCPTH C C ■ CATA fclLL Pr TRANSFERRED CNLY. C CCCCCCC CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCGCCCCCCXC CC03 CM/" ISIX/ •£ V CCC4 ICFK=C CCCCCCC tCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC C CC LCCF LCCKS AT CARD CN NCDC TAPE ANO C C II^ESTlGiTES FCR THE NLM13ER IN CCLLNN C C EC. IF IT IS ECUAL TC ISIX, THE CARC IS C C UEN FFINTtC AND/OR FUNCFEC DEPENDENT C C C N THE h R I 1 t STAT EVENT BEING UTILIZED. C CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC CCC5 CC ICC IJ=1,1CC000 CCCt RE/C (2,lC,EPR=98,ENC = S91(IVALll ) ,I = l,2L) CCC 7 1C FLCf/T i ISM, AJ, All CCCt IF ( IVALIZ 1) .NE.ISIX) GO TC 100 CCCC. WRITE ( 7 , 1C> < I VAL1 I ) ,1 =1,21 ) CC10 WRITE ((,11) ( 1VAL( I ), 1 = 1,21) CC11 11 FCFMT < IX, 19A4.A3, Al) CC 12 ■ ICFH = 1CHKU CC 1 ? GC TC ICC C C 1 4 • 58 hMU K.2CI IJ COt*: 2C F C P ^ AT ( IX , I 5 ,5X, • I S THE NUMBER CF THE RECORD WITH THE ERRC3«) COW 110 If ( IJ.GT .455S6) GO TO 200 CC 1 / ICC CCM INLE - - CCW ^ hMH I6,f£l IJ CClf, C6 FCFf-Al Ilx.'ENC OF FILE HAVING RE AO « , I 7 , • F ! L ES • ) IC2C 2CC CCM INLE CCCCCCC CCC CCCC CCC CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC C 1CHK IS THE TOTAL NUNUER OF CATA CARDS C C TFAMSFERRECTC THE NFS TAPE. C CCCCCCC CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC C021 WH11E W.1C3) ICHK T C C <■ 2 1C2FCFMT(5X,I5) CC2J STCP CC24 ENC ' •• i 49 APPENDIX B Propagation loss profiles for winter and summer. Each profile is for a particular area of acoustic similarity. (Refer to Figs. 19 and 20). 50 (ap) SSOT Nonvovao^j 51 o r» ill i ' \ i / i / \ 1 '•. «\ ( • K r V I N — CI '■'■' ;..-: o \ ' ^ , a - ) / v '. \ ; '■ •o / /' . ■• ' H — • \' ' — c« ! P •' O ' . o Mil 1 — w .• " K - {' ' • ' ' *■> V ^ • . .. B i c • O I \ W,o — 1 — O- y. /"' P* 2 *~~"\ C ■ * *n J-**5 ^ • ' ' ci o (c-^ * o Vi/~" ■ ..." 0 '"'.':■ «o K S— • * • O v> 7 ^ . ■ 1 1 1 «■» 1 • „C« 1 M o 1 1 M M o o 8 S w o o o o r> •- o » o • i | 1 U-l — o cd •o 01 u •U to <0 u P o •H a (J r-i O ■H a) U-t M O M o. (X u <*-! m m o o << rH *J a 03 o •w Q> u u to M 60 3 to O Cu co o M a. • u • 0) 4-1 CN c 1 •H « 5 0) 60 M c 3 •H 60 n •H 3 Pm -o o o CO o ex o o o c« (9P) SSOT NOIIVDVJOStl 52 o 1 i 1 i r> •q . K — a . o 3 ■ / / )i «o / 1 CNl m 1 1 ~ M • /->' O t< / d M /.' "■ c« 1 C--j.^ y •o e — // s' 9 II \ c // ) o \ i J \ / 53 /v • — 3 "•. « f \ • c< j "n t _ r~ o d _ tr^- «r»' K <;3 ••-••. - o •>-i vi - c '. • iii: v> *^£*"^ ' i • • > n i ' . ,c* ^ ^^>L) . I i i . - •*- o o o O Q o o o S •> o n «- t* a o i i i 1 u _ "M - O 01 M *J M M O 0) M-l > 0) 0) rH o •H 0) IM p O P •» O. u U-l W CO o O rH 4J C cfl o -.< 0) x-> y rt M 60 3 to o O. lO o n c* • M • 0) ■w CO G 1 •H « > / * ^ .• e / / _: 0 i < \ ^ ^ '• O - ! / » • _ o- / / 1 f ' rf V-l '. •o A N CI 7, s o f / ' © V ' «r» \ N K H-:.-.:'::- f - o >/' / ■•;'.. . v» — J~- N >- I ' ' «> > 1 * .c« .-••: 1 • 1 *! x x •*- o c> o © o O 3 « M X o o o r» — » o o 1 1 1 1 > ^ o id •o •rl 01 o ■ ') , . •• •' a , 1 1 ■-. y t • > •* i ~v> . y r' .•' ei 1 / .-'. ■ j . . . • i ^-•. o i 1 ;> .- d . r ■•. „ M i i 0 ^ ■ > •" • ■ •A •O , ^ . • s" •*' ' ■•. _ 0 f~ < O ■> ^- ~ 25 . _^- , * - ■ * * «s* <- .» .* . , . s , *r .■' «o ■». C>i CI. — r" * r- . - ■ * , -•' . C--^ .* O t; £ .•• — r . - ■ /* f" ; «o *. 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M M M ! r/y ^- o o o O o o ° o 5 «> o //■' t-1 — r» O o i 1 t 1 4J 4-1 > O nj O a) M u cd n) M U o a) U-( > •rl oj 01 rH o •H eg IM M Q M A ex *J <« (/I (0 o o o r-H 4J a fO o •rt a) /J o 03 1-1 co 3 nj O (X CO o u Ph • u * QJ K 0 r— a 1 3 « 01 . • " «o 1 > .-> ". K 4 /' \ - c* . ■ ( ! ' » s ! / o / ' i » r -1 - • 1 > ■' •o cJ ii ■ * _ c« 'v i ) / ( o I i r i • d - r f .-••• — C* > ,' / ) v. - c ' .> 0~ ^ ^ -> 53 , /"■ a r\ -— s. ■ . . «o 1 z' ci • (. , ™ ••, © 2 ,b> ;;■;::' • «» • " K \\* ■" ;> O r* . •• • *i / .-" ill! *n .- I 1 * * fi* lit*-. .. w n M ^- O O O O r> O O o S n O <->*-*■> o o i i i 1 > o cd 8 0) u •u cd rt u K o 0) U-l > •H 01 0) iH o -H 0) U-i M Q M •k P. W | 1 II «n K / "" a / / / / / / o / ' " 3 / / / / / / •o / / S H « o / ' o 1 / ~ J 1 / ' / _ / / J s /< ' a o / ' ' — / / 53 ! 1 ■ lit ^* I 1 i o 1 1 o / ) ; 1 // J y * / v» -/£?' ,-" K /// ■ ■ /// o - ji ■ /// ,- •- r» m O I.I 1 1 o O CB > o <0 8 -rt a) d» rH O -H ai U-< M Q M * o. W 05 CO ,- ^ O a ctf o •H (1) «-> O CO VJ t>0 0 CO o aui o M CM • p » 0) O B a 1 3 pq m H ■ 75 100 5260 5300 5320 5340 SOUND SPEED (ft/sec) 5360 5380 Figure D- 3 . Sound speed profile, winter, arealli 75 0 . 10 '1 ?0 30 /~\ \ *J \ «H \ V-* \ W 50 \ H a. w « 75 100 . — 5280 5300 5320 5340 SOUND SPEED (ft/sec) 5360 53S0 Figure D-4 . Sound speed profile, winter, area iv 76 5280 5300 5320 5340 SOUND SPEED (ft/sec) 5360 5380 Figure D- 5 . Sound speed profile, winter, area v 77 0 10 20 30 W50 1 H 75 100 5: 220 52 40 52 60 5 280 5 300 53: SOUND SPEED (ft/sec) Figure D- 6 . Sound speed profile, winter, area VI 78 o 10 \ • . 70 \ 30 ■ 4J W50 / ■ • H // 0, a, w 200 s Q 400 600 / 75 ■ 100 5 50C 5 00 5200 5300 5 280 53 00 5: 120 5; 40 53 60 53 SOUND SPEED (ft/sec) Figure D- 7 . Sound speed profile, winter, area vn 79 o 10 20 / 10 / / K50 | H \ o1 fe u 200 400 600 > Q / 75 100 4900 2000 3100 5 200 53 s: >60 5: 280 5 300 £ 320 53 40 SOUND SPEED (ft/sec) Figure D- 8 . Sound speed profile, winter, areavu 80 5400 5450 SOUND SPEED (ft/sec) 5500 5300 5350 Figure D- 9 . Sound speed profile, summer, area l 5550 81 0 10 70 ■ III | II 1 ■ ■ HI • 30 +J <4-l K50 H CM W O 75 100 5300 5350 5400 5450 5500 5550 SOUND SPEED (ft/sec) Figure D-10 . Sound speed profile, summer, areall 82 5300 5350 5400 5450 SOUND SPEED (ft/sec) 5500 5550 Figure D— 11. Sound speed profile, summer, area 83 5300 5350 5400 5450 5500 5550 SOUND SPEED (ft/sec) Figure D-12. Sound speed profile, summer, area iv 84 100f_ 5300 5350 5400 5450 5500 SOUND SPEED (ft/sec) 5550 Figure D-13. Sound speed profile, summer, area v 85 LIST OF REFERENCES 1. Crozait, V. J. , 1973. Stability in the Persian Gulf. U. S. Naval Institute Proceedings, vol. 99 (7/845):48-59. 2. Dubach, Harold W. , 1964. A summary of temperature - salinity characteristics of the Persian Gulf. NODC Pub. G-4 Washington, Naval Oceanographic Office. 233 p. 3. Emery, K. O. , 1956. Sediments and water of the Persian Gulf. Bulletin of the American Association of Petroleum Geologists, vol: 40 (10):2354-2383. 4. Honhart, D. C., 1974. Acoustic forecasting notes. U. S. Naval Postgraduate School, Monterey. 163 p. Unpublished. 5. La Violette, Paul E. and Theodore R. Frontenac, 1967. Temperature, salinity, and density of the world's seas: Arabian Sea, Persian Gulf, and Red Sea. U. S. Naval Oceanographic Office IR No. 67-49, Washington. 105 p. 6. National Oceanographic Data Center, 1973. Bathythermograph data tape for marsden squares 102 and 103. Washington. 7. National Oceanographic Data Center, 1973. Hydrographic data tape for marsden squares 102 and 103. Washington. 8. Sugden, W. , 1963. The hydrology of the Persian Gulf and its significance in respect to evaporite deposition. American Journal of Science, vol. 26 1(8):741-755. 9. Urick, Robert J. , 1967. Principles of underwater sound for engineers. McGraw-Hill, New York. 342 p. 10. U. S. Defense Mapping Agency Hydrographic Center, 1973. Persian Gulf, 3rd ed. Chart N. O. 62032. Washington. 11. U. S. Naval Oceanographic Office, I960. Sailing directions for the Persian Gulf, 5th ed. H. O. Pub. No. 62. Washington. 404 p. 12. U. S. Navy Hydrographic Office, I960. Summary of oceanographic conditions in the Indian Ocean. SP-53. Washington. 142 p. 86 INITIAL DISTRIBUTION LIST FOR PART I No. Copies 1. Defense Documentation Center 2 Cameron Station Alexandria, Virginia 22314 2. Library, Code 0212 2 Naval Postgraduate School Monterey, California 93940 3. Professor R. H. Bourke, Code 58Bf 3 Department of Oceanography Naval Postgraduate School Monterey, California 93 940 4. LCDR D. C. Honhart, USN, Code 351 1 Naval Postgraduate School Monterey, California 93940 5. LCDR Glen Eubanks, USN 1 Naval Underwater Systems Center New London Laboratory New London, Connecticut 06320 6. Office of Naval Research 1 Code 480D Arlington, Virginia 22217 7. Oceanographer of the Navy 1 Hoffman Building No. 2 200 Stovall Street Alexandria, Virginia 22332 8. Naval Postgraduate School 1 Code 58 Monterey, California 93940 9. LT J. L . Wright, USN 3 U. S. Naval Facility Box 100 FPO San Francisco, California 96614 10. LCDR L. E. McGovern, USN 1 Naval Postgraduate School, SMC #2347 Monterey, California 93 940 87 11. LT J. G. Bodie, USN Defense Mapping Agency Hydrographic Center Honolulu Office Box 116 FPO San Francisco, 96610 12. Dr. Robert E. Stevenson Scientific Liaison Office, ONR Scripps Institution of Oceanography La Jolla, California 92037 13. Naval Oceanographic Office Library, Code 3330 Washington, D.C. 20373 14. S.I.O. Library University of California, San Diego P. O. Box 2367 La Jolla, California 92037 15. Department of Oceanography Library University of Washington Seattle, Washington 98105 16. Department of Oceanography Library Oregon State University Corvallis, Oregon 97331 17. Commanding Officer Fleet Numerical Weather Central Monterey, California 93940 18. Department of the Navy Commander Oceanographic Systems Pacific Box 1390 FPO San Francisco 96610 19. LCDR John Ciboci, USN Ocean Operations Division Fleet Numerical Weather Central Monterey, California 93 940 20. Commanding Officer Environmental Prediction Research Facility Monterey, California 93940 88 21. Oceanographer of the Navy Hoffman Building No. 2 200 Stovall Street Alexandria, Virginia 22332 ATTN: CDR Applegarth 22. LCDR S. E. Wheeler, USN Patrol Squadron ONE FPO San Francisco 96601 89 IL83J S11225 ' i$8Sl^ lp of the 1 • par1 accuse - ,f -*\iz* pet** a3i Thesis W912 Wriqht c.l A hydrographic and acoustic survey of the Persian Gulf - Part I. 158316 lhesW912 AnH,Hdr°9raPh'C 3nd aC0UStic surveV 0' th 3 2768 001 90657 1 -, DUDLEY KNOX LIBRARY