SOME RESULTS OF SPECTROPHOTOMETRIC MEASUREMENTS OF THE EARTH FROM THE SOYUZ-7 SPACECRAFT

MSA

TECHNICAL TRANSLATION

MSA TT F-13,892

SOME RESULTS OF SPECTROPHOTOMETRIC MEASUREMENTS OF THE EARTH
FROM THE "SOYUZ-7" SPACECRAFT

K. Ya. Kondrat'yev, A. A. Buznikov, B. B. Vinogradov,
V. I. Volkov, V. V. Gorgatko, 0. I. Smoktly and V. M. Orlov

Translation of: "Nekotoryye rezul'taty
spektrofotometrirova niya zemli s kos micheskogo
korablya 'Soyuz-7' ".{Akademii 5lauklpokladyl SSSR
Vol. 195 (5), 1970, pp I08U-IO8V

^72-U36 8

Unci as
1173 7

IffCTHopHOTOHETlt^ ^°"^ RESULTS op

CSCi.

MTIOML AEROMUTICS MD SPACE ADMINISTRATIOK
WASHINGTOW, D.C. 205^+6 NOVEMBER I97I

Reproduced by

NATIONAL TECHNICAL
INFORMATION SERVICE

Springfield, Va. ,22151

SOME RESULTS OF SPECTROPHOTOMETRIC MEASUREMENTS OF THE EAR'iH
FROM THE "SOYUZ-7" SPACECRAFT

K. Ya Kondrat'yev , A. A. Buznikov, B. V. Vinogradov, V. I. Volkov,
V. V. Gorbatko, 0. I. Smoktiy, and V. M. Orlov*

ABSTRACT. It is found that spectrophotometric measurements
from "Soyuz 7" made it possible to compare data on reflectivity,
radiation temperature, and other reflective and radiative
characteristics of the Earth's surface.

The first experiments on spectrophotometric measurements of the twilight /1084
halo of the Earth from space were made in January, 1969, during the flight o f tpre
"Soyu2-5" spacecraft. The basic results of this experiment were discussed irK
the papers [1-4]. With the combined flight of the spacecrafts "Soyuz-6,7,8",
the program of complex optical experiments was broadened to include the solu-
tion of the following basic problems:

1. Spectrophotometric measurements of the sun and the twilight halo of
the Earth's atmosphere under various observation conditions, solar radiation,
and the position of the observer in space in order to study the brightness
and colors of the halo, and to determine the vertical. distribution of various
atmospheric components .

2. Spectrophotometric measurements of various natural formations with the
goal of determining the feasibility of identifying them from spectral reflec-
ting characteristics, measured from space.

**

*
Associate member of the Academy of Sciences.

Numbers in the margin indicate pagination in the original foreign text.

3. Synchronous execution of a complex program of earthbound and airborne
optical investigations of the atmosphere and of various types of underlying
surfaces in the region under the satellite for obtaining data which would
characterize the spectral transmission function of the atmosphere, spectra,
and spectral contrasts of natural formations as a function of the basic optical
parameters .

]> .^- Spectrophotometric measurements of the twilight atmosphere and the
underlying surfaces were made from the "Soyuz-7" spacecraft by means of ^
modified manual RSS-2 spectrograph(v^[5] . The input telescope objective simul-
taneously focused the image of the distant object at the input slit of the
spectrograph (spectrograph channel) and directly on the photographic film
(photographic channel). The focal distance was f — 135 ram; the relative
opening was D/f = 1:4. For this model of the spectrograph, the linear dis-
persion was 166 A/mm, the spectral width of the slit was 50 A, and the spectral
range for measurements was 430 to 690 my. The limiting angular resolution of
the spectrographic channel was 2 minutes of arc; that of the photographic
channel was 4 minutes. The spectra were reduced using the method described in
[4].

This experiment [1] did not evaluate the effect of the spectral transmis-
sion of the solar radiation through the spacecraft illuminator. Evaluation of
this quantity ahead of the spectrograph objective was carried out by installing
a light-scattering filter with known optical characteristics. Then the appa-
ratus was pointed at the Sun.

Photographic film in the spectrograph was exposed to a standard source
and the Sun using the light-scattering filter. The darkening densities of
the photographic films from the two sources were compared. The comparison
made it possible to find the spectral illumination of a unit area, which gave
the solar illumination transmitted through the spacecraft illuminator.

During the group flight of the "Soyuz-6,7,8" satellites, spectrophotometric
measurements of the twilight halo were taken on the 87*^ revolution of "Soyuz-
7". at 21A7 hrs Moscow time as the sun set. The geographic coordinates of the /1085
spacecraft were 23.18" north latitude and 23.39° east longitude (in the region
of northeast Africa) . The altitude of the orbit at the moment of the experi-
ment was approximately 218 km.

The results of the experiment were compared with similar data taken during
the flight of "Soyuz-5". The comparison showed that the qualitative behavior
of the monochromatic curves of the halo brightness was the same for both
experiments. However, the absolute values of the brightness in the first
experiment [1] were 2 to 3 times smaller (A = 650 my). The monochromatic
', brightness curves of both the previous experiment and the current experiment
'; showed an absence of noticeable depressions^ caused by aerosol layers, locali_zed . . ^^
j at various levels in the atmosphere.

-^ This communication also presents data on the spectra of various natural
^urfaces,/ which were obtained on October 13, 1969 from "Soyuz-7" on the tra-
jectory from the Arabian peninsula to the Aral Sea. Spectrophotometric measure-
ments of various parts of the Earth's surface were made in a short period of
time from 1319 hrs to 1329 hrs, Moscow time, for a solar height of 35-50°.

During the flight of "Soyuz-7" spectra were obtained on the following
identified types of natural surfaces: 1) thick clouds, 2) thin clouds,
3) rocky wilderness, and 4) cloud shadows (Figure la). Continuous and dense
cumulus and stratocumulus clouds are characterized by a maximum brightness in
the range of 0.20 to 0.24 watt/m -mysteradian in a wavelength range of 440
to 580 my (Curve 1, Figure la). The brightness significantly decreases to
0.14 to 0.14 watt/m^ 'mysteradian in the orange-red part of the spectrum
for X = 580 to 690 my. Thin clouds of the high-altitude stratus and strato-
cumulus types at various levels give an integral image for a cloud layer and
for shaded surface. This type of surface has little effect on the spectral
distribution of the brightness, but its absolute brightness is lowered to

2,11

1.0

4

■0.1

2,i

J/}) — 'm HI ko mm ; "^0 Ifo no m oiOK^
}, — _. r f. —

Figure 1. Curves of Spectral Brightness B (watt/m •
mysteradian) for ten natural surfaces obtained on
October 13, 1969 during the flight of the "Soyuz-7"
spacecraft, a - from the spacecraft: 1 - dense
clouds; 2, 3 - thin clouds; 4 - surface of the desert
in the northern part of the Arabian peninsula; 5 - O
surface of the desert on the Ust Urt plateau at the
eastern bank of the Caspian Sea; b - from an air-
craft: 1 - thick clouds, 2 - thin clouds, 3 - sand,
4 - salt marsh, 5 - rocky wilderness, crossed by
dirt roads, 6,7- rocky wilderness.

0.12 to 0.14 watt/m -mu'steradian in the interval \ - 440 to 480 my, and to

9

0.07 to 0.1 watt/m -mysteradian in the interval X = 580 to 690 my (Curves
2 and 3, Figure la).

The rocky wilderness of the Ust-Urt plateau is composed of limestone
and is covered with a rough gray loamy stoney soil. In places there is takyr
soil and thin dusty-sandy deposits. The plant covering is sparse, and has little
effect on the spectrum of the landscape. Underlying surfaces of this type
yield spectral brightness curves with very weak spectral intensity changes
in the range 0.05 to 0.07 watt/m 'mysteradian (Curves 4 and 5 in Figure la).

Finally, it is interesting to analyze the darkest, spectrophotometrically
analyzed surfaces — regions of ilight shadows from clouds. Since the

shadows were discontinuous, their brightness was much lower than was the rocky

2
wilderness (0.04 to 0.05 watt/m •mysteradian) . The differences were signif-
icantly less in the blue-green region of the spectrum than in the red-orange
region.

The spectral contrasts were calculated from data given above on
spectral brightness in all possible combinations of natural surfaces (Figure
2a).

The spectral contrasts of the cloud density and the partially shadowed
surface of the rocky wilderness reached maximum values of k = 0.77 for X = 630
my. This contrast was somewhat lower in the blue-green region, where k = 0.62.
The spectral contrasts of the dense cloudlines and of the rocky wilderness
also gave high absolute values of k between 0.6 - 0.7. The changes in the
contrasts were the same over the entire curve or decreased in the short-wave-
length part of the spectrum (Curves 1 and 2 in Figure la) . The spectral
contrasts for the thin clouds and the rocky wilderness had an analogous
brightness pattern. However, the absolute values of the contrast decreased /1087
to about 0.4 (Curves 3 and 5, Figure 2a). Moderate contrast values arose
from thick and thin clouds (Curve 4 in Figure 2a). The shape of the curve was
monotonic, with variations of k in the range of 0.40 to 0.45. The spectral
contrast of the illuminated and shadowed rocky wilderness was also rather
small (k ^ 0.3). Here the contrast was significantly decreased in the short-
wavelength region of the spectrum, and increased in the long-wavelength region
(Curve 6, Figure 2a). The contrasts between distant parts of the rocky wild-
erness were the least, k = 0.05 to 0.15 (Curve 7, Figure 2a). The contrast
was higher in the green-blue region of the spectrum for X = 520 my, as well
as in the red region for X = 660 my.

These results were compared with simultaneous measurements of the
brightness and the contrasts, which were made with analogous equipment (RSS-2)
in an airplane flying over the Ust-Urt plateau at the "meeting point" of the

^'^X^.^^^f^s^

0,tl

3 V

0.5

0,6

"0,1

0.2

0.1

-0.1

A

7 0!,'^^.,

"o , « ; ..«' I''..--

filr^JOO 600 *fji '700

Figure 2. Spectral contrast (K) curves for natural
surfaces. These curves were obtained from spec-
trophotometric data from the flight of the manned
spacecraft "Soyuz-7" on October 13, 1969. a -
from the spacecraft: 1 - dense clouds over the
Arabian desert, 2 - thick clouds over the Ust-Urt
desert, 3 - thin clouds over Ust-Urt, 4 - thick
clouds and thin clouds , 5 - thin clouds over the
Arabian desert, 6 - illuminated Arabian desert,
7 - illuminated desert, partially shadowed (Ust-

. Urt) . b - from an aircraft: 1,2 - thick clouds
over a rocky wilderness, 3 - thick clouds over
loamy rocky wilderness, crossed by roads, 4 -
thick clouds over a loamy-stoney wilderness,

.5,6 - loamy-rocky wilderness, crossed by roads
— rocky wilderness, crossed by roads, 7 - loamy-
stoney wilderness loamy-stoney wilderness, .

crossed by roads, 8 - loamy-stoney wilderness —
rocky wilderness, 9 - two sections of the rocky
wilderness on the Ust-Urt plateau.

spacecraft and the scientific-research, airplane. Spectrophotometric measure-
ments were made from the satellite at an altitude of 220 km, and from the
airplane at about 2.7 km. Comparison of the satellite results (Figures la
and 2a) and the airplane results (Figures. lb and 2b) for the measured spec-
tral brightness and contrasts of the same types of underlying surfaces show
that the effect of the haze on the optical characteristics was small as '
compared with the measurements made at 2.7 km. The haze effect is more

important in the short-wavelength region of the spectrum, as should be
expected. In the long-wavelength region, the solar radiation scattered by
the atmosphere above 2.7 km only slightly affects the absolute brightness
values of natural surfaces.

In conclusion, it should be noted that the shape of the spectral
brightness curves of natural surfaces makes it possible to differentiate
several types of natural formations from their spectra, which are measured
from spacecraft. It should also be emphasized that the atmosphere distorts
the shape of the spectral brightness curves and lowers the spectral contrasts.
However, the optical density of the Earth's atmosphere is not very large, in
the absence of clouds. Thus it is possible to compare data on reflectivity,
radiation temperature, and a combination of other reflective and radiative
characteristics of underlying surfaces. These comparisons give a rather
precise differentiation of natural formations based on their spectra.

REFERENCES

1. Kondrat'yev, K. Ya. , B. V. Volyhov, et al. Doklady Akademii Nauk

(DAN), Vol. 190, No. 2, 1970.

2. Kondrat'yev, K. Ya. , A. P. Gal'tsev, et al. DAN, Vol. 191, No. 4,

1970.

3. Kondrat'yev, K. Ya. , A. P. Gal'tsev, et al. DAN, Vol. 191, No. 5,

1970.

4. Kondrat'yev, K. Ya. , B. V. Volypov, et al. Izvestiya Akademii Nauk,

SSSR; Seriya, Fizika Atmosfery i Okeana, Vol. 6, No. 4, 1970.

5. Gal'tsev, A. P., V. V. Mikhaylov, et al. Problemy Fiziki Atmosfery,

No. 7, 1969.

Translated for Goddard Space Flight Center under contract No. NASw 2035, by
SCITRAN, P. 0. Box 5456, Santa Barbara, California 93108.