The spectra of the daytime sky of Venus were recorded on the Venera-11 and Venera-12 descent vehicles at various altitudes above the planet's surface, within the interval of 4500 to 12,000 Angstroms. The angular distribution of the brightness of the scattered radiation was recorded and the ratio of water and carbon dioxide were studied, with respect to the cloud cover boundaries

Ekonomov, A. P.

Golovin, Y. M.

Moroz, V. I.

Moshkin, B. Y.

Parfentev, N. A.

Sanko, N. F.

English

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NASA TM-75640
SPECTROPHOTOMETRIC EXPERIMENT ON THE "VENERA-11" AND "VENERA-12"
DESCENT VEHICLESt SOME RESULTS OF THE ANALYSIS OF THE SPECTRUM OF
THE DAYTIME SKY OF VENUS
V. I. Mor •oz, B. Ye. Moshkin, A. P. Ekonomev, N. F. San'ko,
N. A. Parfent'ev, and Yu. M. Golovin
(NASA-TM-75640) SPRCTROPflrTCMETh:C
	 N79-25962
EXPERIMFNT ON T;:E VFRFRA-11 AND VFNEPA-12
DESCENT VEHICLES: SOME RESULTS OF THE
ANALY:;IS OF THE. SPECTRUM OF THE DAYTIME SKY
	 Unclas
OF VENUS (National Aeronautics and Space
	 G3/91 22269
Translation of "Spektrofotometricheskiy eksperiment na
spuskayemykh apparatakh "'lenera-11" i "Venera-12": Nekotoryye
rezultatu analiza spektra dnevnogo neba Venery, Academy of
Sciences USSR, Institute of Space Research, Moscow, Report, 1979,
PP 1-15
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ti JUN1`^^9	
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NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON, D.C. 20546	 JUNE 1979
SPECTROPHOTOMETRIC EXPERIMENT ON THE "VENERA-11" AND "VENERA-12"
DESCENT VEHICLESr SOME RESULTS OF THE ANALYSIS OF THE SPECTRUM OF
THE DAYTIME SKY OF VENUS
V. I. Moroz, B. Ye. Moshkin, A. P. Ekonomov, N. F. San'ko,
N. A. Parfent'ev, and Yu. M. Golovin
Synopsis
Recorded on the descent vehicles "Venera-11" and "VPnera-
12", in the course of re-entry in the atmosphere (from an
altitude of 65 km to the surface), were the spectra of the
daytime sky of Venus at an interval of from 4500 to 12,000
and the angular distribution of the brightness of the scattered
radiation (in four filters). Visible on the spectra were
zones of absorption of CO;,, H 2O, and slight absorption in the
blue-green portion of the spectrum, which probably belongs to
gaseous sulfur. The abundance of [H ? 0]: [C0; ]:-2 . 10 -9 is in the
area of the lower scale of altitudes. If the identification
with sulfur is correct, then its abundance is about 10
-Q
 in
this same area. About 6% of the total solar flow reaches the
surface of the planet. The lower boundary of the clouds is
located at an altitude of about 47-48 km, and the clouds have
a Stratus structure.
Solar radiation penetrates into the deep layers of the	 /*
atmosphere of Venus, in spite of its great optical thickness.
It is scattered repeatedly in the cloud cover and the atmos-
phere below the clouds, and direct solar radiation is impossi-
ble to detect in the depth of the atmosphere; however-, the
scattered radiation may be quite intense in some sections of
the spectrum. An appreciable portion of the flow reaches the
surface, and, as a result, because of the great nontransparency
*Numbers in the margin indicate pagination in the foreign text.
1
K
_i
iof the atmosphere for thermal radiation, a strong hothouse
effect occurs, which explains the high temperature of the
t`	 surface.
The task of the described experiment is the measurement
of the spectral and angular distribution of the energy of the
scattered radiation, as a function of the altitude, using
an instrument mounted on the descent vehicle. Interpretation
of the results of the experiment makes it possible to solve
problems of three typest 1) determination of the radiation
influx of energy as a function of the altitude, which is
necessary for understanding of the thermal balance and the
dynamics of the atmosphere; 2) determination of the structure
of the cloud cover; 3) ascertaining of the chemical nature
of the different absorbing agents present in the atmosphere
of Venus in the gas and aerosol phase.
The first experiment for, measuring the radiation flow
in the deep layers of the atmosphere of Venus was carried
out on "Venera-8" in 197.' (Avduevskiy et al., 1973). The 112
flow from above was measured in a zone about 2500 A wide,
centered at a wavelength of 6500 A. Two different experi-
ments on the investigation of the field of scattered radi-
ation in the atmosphere were carried out in two different
groups on the "Venera-9" and ''Venera-10". In one of them
(Avduevskiy et al., 1976, Ekonomov et al., 1978), flows
from above and below were measured with five wide (on the
order of a thousand Angstroms) filters, encompassing an
interval from 0.5 to 1.2 microns. Carried out in the second
experiment (Moron et al., 19"6) were measurements of the in-
tensity of the radiation with three narrow (about 50 A) fil-
ters, centered on zones of CO- and H 2O, and a section of
the .ininterrupted spectrum, located in the 8000-9000 A inter-
^al .
2
During preparation of the new experiment on "Venera-11"
and "Venera-12", the efforts and experience of both groups
were joined, and, as a result, a new instrument was created,
which possesses substantially new capabilities (fig. 1).
The instrument consists of two functional units— a spectro-
meter and a scanning photometer. The radiation enters the
spectrometer through a flexible light guide C 1 , which accepts
the radiation from the area of the zenith at an angle of
about 150 . It then passes through a hermetic window 01,
a wedge-shaped interference filter KIF and a lens L 1 , and
is collected at the receiver P 1
 (a germanium photodiode).
The circular wedge-shaped interference filter consists of
two half-rings, one of which analyzes the range from 4500
to 7000 A with resolution of about; 200 X, and the second—
the range from 7000 to 8000 A, with a resolution of about
400 A. The external diameter of the filter is 50 mm. The
disk with the wedge-shaped filter rotates with a cycle
of 10 seconds, and it is set in motion by a motor D through
a reduction gear. Mounted on the same disk as the wedge-
shaped interference filter are It broad glass filters F, made
up in the form of sectors of 90 0
 each and pointing out broad
spectral intervals, centered at 4900, ((FACE MISSING AT THIS
POINT)) ....................... ................0..............
here, within a 10-20110
 range, do not differ (with the ex-
ception of the blue portion of the spectrum) from those
which would be radiation reflected from the Lambertian
screen, illuminated by the sun. Presented in figure 2 are
several characteristic spectra, related to this conditional
standard. The spectra are given schematically, without
showing some weak details, the reality of which requires
additional verification. The high-level surveying is pre-
liminary.
The intensity of the radiation is weakened in proportion
to the descent at all wavelengths, right up to an altitude
3
I"
of 47-48 km, i.e., inside of the cloud cover. Also visible
are weak, but fully-certain depressions, which are gradually
intensified. These are bands of absorption of CO :, and H;,O,
and slight absorption in the blue portion of the spectrum.
After the passage of a level of 47-48 km, the changes
in the spectrum (both according to absolute magnitude and
according to distribution) cease. The spectra at an alti-
tude of 38 and 48 km are practically identical. We explain
this as the effect of crossing of the lower boundary of the
°	 cloud cover. The first 10 km of the atmosphere under its
lower boundary almost never add to the measurable intensity.
On "Venera-9" and "Venera-10", the lower boundary of the
cloud cover was recorded (Avduevskiy et al., 1976; Marov et
al., 1976; Moroz et al., 1976= Ekonomov et al., 1978) at a
close altitude (49-50 nm), but a somewhat we^ker scattering
environment was observed below the boundary.
Below 38 km to the surface, the depth of the CO ;, and H.0
zones increases systematically. In addition, there is a
severe "avalanche" in the blue-green region of the spectrum—
stronger than that which may give a Rayleigh scattering. One
can indicate several molecules, gaseous sulfur, Bra, and NO S ,	 1
which, with a very low abundance (10 -•9 -10 i , with respect to
`	 C07) ma,y be responsible for this absorption.
It was decided to carry out analysis of the spectrum
of passage of the atmosphere under the clouds as the first
step during interpretation of the data obtained in the
spectrophotometric experiment on "Venera-11" and "Venera-12".
The measured dependence of the ratio of the intensities on the wave
length at altitudes of 0 and 47 km (surface of the planet and
lower boundary of the cloud cover) was compared with that-
calculated for the following models homogeneous CO 2
 layer
with an admixture of a small amount of H--0 (variable para-
4
,peter in the model), the pressure in the layer is equal to
the pressure on the :surface (91 atmospheres), and the thick-
ness of the layer is equal to the altitude of the homo-
geneous atmosphere. The passage of such a layer, for a
diffuse source, is equal to
AIr	 ^:Z
r'
where p =0.7 is the average value of the cosine of the angle
of incidence, Ei- = 1 is the cosine of the angle of sight
(optical axis of the spectrophotometer is oriented towards
the zenith).
i s
 the albedo of a single scattering,
— U. U ^ ^ JU ./^ G' M -
is the coefficient of Rayleigh scattering for CO_, (X is the
wave length, in microns); k is the total coefficient of
absorption (CO2, H;X, S;.--S.) , etc., '^ is the optical thick,
ness; /o(4i o p 29 CL, V) is the coefficient of brightness for
the scattered radiation;e -^ is the coefficient of brightness
for the direct radiation weakened by extinction; A is the
albedo of the surface. The optical thickness of the layer
2'o
 for the Rayleigh scattering varies within the range from
roughly 0.8 (X=12,000 k) to 40 (a =4500 A) . The terms which
include AV/(1-AVJ) take into account the re-reflection between
the surface and the gas layer. The corresponding auxiliary
functions V, VJ, and F were calculated according to the asymp-
totic formulas of the theory of scattering, given in the
study of Danielson cw t al. ( 1969) . The magnitudes of
5
(µ,µ 2 ,04 rO were calculated by two methodso first was the	 i
calculation ..ccording to the strict formulas of the theory
of multiple scattering of light, using the auxiliary functions
of Chandrasekar for the Rayleigh indicatrix Y(Y)=3/4 (1_cos'Y),
and the second—calculation according to the asymptotic
formulas of Danielson et al. (1969). assuming a spherical
indicatrix. Both methods give identical results with X>
0.95 and TA. With lesser values of Z and d, we utilized
the f, obtained by the first method, and the second method
was used chiefly for extrapolation into the region of larger
`r, for which there are no tabular data according to the X,Y-
functions (used here were the tables of Sweigart, 1970).
The coefficients of absorption. of CO- were taken
according to the data of Gal'tsev and Osipov (calculations
which lay at the basis of the study of Gal'tsev et al., 1976).
For the coefficients of absorption of H;.O, N!e did not find
Ir	 the data in the literature necessary for the model (A<1.2
microns, measurements under conditions of a tei,,perature of
700-750 0
 K and high pressures). We measured these coefficients
of absorption in the laboratory, using a high-temperature
absorption cuvette 1 m long, with an H 2O content of 3 g•cm-`,
on a line of sight with spectral resolution of from 4 to 8 R.
The pressure in the cuvette was about 12 atmospheres, which,
according; to the conditions of expansion of the lines, satis-
factorily simulate the conditions in the lower atmosphere of
Venus (coefficient of self-expansion of H,
'
0 of about 4 with
respect to CO., and the ling
 widths in our cuvette should be
the same as those in the atmosphere of Venus at an altitude
of 10 km). The rotational structure of the H `0 zones in the
lower levels of the atmosphere of Venus should be severely
obliterated, and is practically absent in the CO- zones.
Comparison of the measurements with the model calculations Z2
6
OW
(carried out with averaging of 50 A) showed that, within the i
limits of the lower scale of altitudes of the atmosphere of
Venus
0; .,Z^,;!v	 Vz iZ /^,
The slight indeterminateness is associated with :;he dis-
regarding of the rotational structure of the H,,O and the
inaccuracies in the utilized values of the coefficients of
continual absorption of CO ;., brought about by the sides of
the far zones, but we are convinced that the given evaluation
does not differ from the true abundance of H.0 by more than
2 times. This result does not coincide with the results of
measurements on "Pioneer-Venus" (Oyama et al., 1979)9
according to which there is 0.5% H,10 at an altitude of
34 km, and 0.135% at an altitude of 24 km. It is safe to
say that, with a 0.1- 0.5% content of H_0, the spectrum of
the atmosphere under the clouds would be of an entirely
different form. According to preliminary evaluations, ob.-
tained on the basis of our spectra, the content of H c0 in
the atmosphere of Venus, at any altitudes, does not exceed
levels on the order of 10-'.
The absorption in the range A<6000 A, using the very
same model, is explained most satisfactorily by the absorp-
tion of gaseous sulfur, although the contribution of other
molecules (Br a,, NO 2 ) cannot be excluded. The weakly-pro-
nounced, but probably actual structure of the measured spec-
trum, which is available in this range, matches that of sulfur.
We carried out laboratory measurements of the absorption of
gaseous sulfur at temperatures of 600-600 0
 K, which show simi-
lar details. If this identification is correct, then the
relative abundance is
J t^s^ J t `sd^ 	 1v -s
t7
K
We would note that, at the indicated temperature:, all of
the enumerated modifications of sulfur , are present. Such
low evaluations for gaseous sulfur in the atmosphere under
the clouds probably create difficulties for the hypotheses,
which explain the "ultraviolet" absorption in the clouds by
	 L
the presence there of condensed sulfur (Young, 1977)• If one
is diverted from the mentioned weak details in the measured
spectrum, then the "blue avalanche" may be explained also by
the presence of bromine molecules with a relative abundance
of a total of 10 - 1` , and of N0,- ( roughly 5-10- /0  ) . In any
case, the indicated abundances of sulfur, bromine, and N0;
may be viewed as the upper limits. In the range from 6000
to roughly 7000 A, the albedo of one-time scattering in the
lower atmosphere of Venus is located in the range from 0.999
to 1.000. In this section, about 10/ of the sunlight reaches
the surface. The portion of the total (integrated according
to the spectrum) sunlight reaching the surface is about 6o.
Given schematically in figure 3 is the dependence of
the intensity at the zenith (for several wavelengths) on the
altitude, also according to the data of the spectrometer.
Points in the cloud cover are added. Evident in addition to
the sharp lower boundary of the clouds are intermediate
boundaries, which evidently reflect their complex vertical
structure: they are subdivided into at least three layers.
The presence of a somewhat vertical structure in the clouds
was noted earlier in the experiments on "Venera
-9" and "Venera-
1C" (Avduevskiy et al., 1976; Marov et al., 1976; Moroz et al.,
1976)• Analysis of the data on the characteristics of the
cloud cover, obtained in the current experiment, will be given
in subsequent reports.
The preliminary results given here demonstrate the
special capabilities of the spectroscopic procedure as applied
to the chemical t ialysis of the lower atmosphere of Venus.
8
q
r
i
Even with resolution of 200-300 A, it proves possible,
according to some components, to obtain sensitivities on the
order of 10 -Q , which are unattainable for on-board mass-
spectrometers and pas chromatographs. An increase in the
resolution by an order considerably expands these capabilities.
The contradiction in the ratio of H ;0 is not limited to
the discrepancies between the American chromatopraph and our
spectrophotometer. Obtained on "Venera-W "Venera-5", and
"Venera-6" (Vinogradov et al., 1970), using chemical pas
analyzers, was up to 2% H.O. These results seem doubtful.,
but the possibility of strong local variations is not pre-
cluded. Further investigat ons are necessary, utilizing some
standard and absolutely reliable procedure] with the utili-
zation of direst chemical analyses, as the available experi-
ence shows, spectrophotometric monitorinj- will be very useful.
Q
I^	 _
I. Avduevskiy, V. S., Marov, M. Ya., Moshkin, B. Ye., Ekonomov,
A. P. , Dok a . AN SSSR , 210, 799 ( 1973) .
2. Avduevskiy, V. S., Golovin, Yu. M., Zavelevic:h, V. S.,
Lilchushin, V. Ya., Marov, M. Ya., Mel'nikov, D. A.,
Merson, Ya. T., Moshkin, B. Ye., Razin, K. A., Cherno-
shchekov, L. 1., Ekonomov, A. P., Kosmich. issled., 14,
735 (19?6) .
3. Bar • sukov, V. L., Zolotukhin, V. G., Kovtunenko, V. M.,
Sagdeev. R. Z., Pis'mo v AZh, 5, 3 (1979).
4. Danielson, R. E., Mooze, D. R., van de Hu] st, H. C.,
J. Atm. Sci., 26, 1078 (1969).
5. Ekonomov, A. l., Golovin, Yu. M., Moshkin, B. Ye., Kosmich.
issled. 16, 6, 901 (1978).
6. G al'tsev, A. P., Osipov, V. M., Shari, V P., Kosmich.
issled., 14, 417 (1976).
7. Moro z, V. 1., Parfent'ev, N. A., San'ko, N. F., Zhegulev,
V. S., Zascva, L. V., Ustinov, Ye. A., Kosmich. issled.
14, f , 743 (1976) .
8. Oyama, V. J., Carle, G. C., Woeller, G., Pollack, J. B.,
Science, 20 4; , at press.
9. Sweigert, A. V., Astrorhys. J., Supp. Ser. 182, 22, 1
(1970) .
10. Vinogradov, A. P., Surkov, Yu. A., Andreychikov, B. M.,
Dokl. AN SSSR, 190, X52 (1970).	 €
11. Young, A. T., Icarus, 32, 1 (1977).
10
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Fig. 2, Normed spectra of scattered solar radiation in the
depth of the atmosphere of Venus at different altitudes above
the surfa;,e. Along the x-axis are the wavelengths, and along
the y-axis—the relative intensity (taken as the standard for
norming are the spectra at altitudes of 63-65 km, see text).
The numbers near the curves ar ,. :ie altitude above the sur-
faces 1--56 km, 2-50 km, 3_4 •1 :.m, 4-38 km, 5-27 km, 6-
14 km, 7-0 km.
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Spectrophotometric experiment on the Verera-11 and Venera-12 descent vehicles:  Some results of the analysis of the spectrum of the daytime sky of Venus

Spectrophotometric experiment on the Verera-11 and Venera-12 descent vehicles: Some results of the analysis of the spectrum of the daytime sky of Venus

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