l e n ~ u s 16, 253-280 (1972)
Mariner 6 and 7 Ultraviolet Spectrometer Experiment:
Photometry and Topography of Mars
C H A R L E S W. H O R D
Department of A stro-Geophysics and Laboratory for Atmospheric and ,~pace Physics,
University of Colorado, Boulder, Colorado 80302
Received September 27, 1971
From data obtained by the ultraviolet spectrometers aboard the Mariner 6 and 7
Mars missions the reflectivity of the illuminated disk of Mars was found to have
two distinct spectral types, associated with polar and nonpolar regions. In this
work the characteristic spectrum of nonpolar regions on Mars is discussed. An
interpretation of the variation of the intensity at 3050=3~due to surface pressure
variations is given. A comparison of the ultraviolet observations with pressures
inferred by the infrared spectrometer is used to test this interpretation and to
determine physical parameters of Mars which lead to the observed reflectance.
Earth based pressures obtained by broadening of the 1/~ band of CO2 and radar
topography are compared with the ultraviolet results.
INTRODUCTION
p h o t o m e t r i c model a t w a v e l e n g t h s shorter
I n 1969 the Mariner 6 a n d 7 s p a c e c r a f t t h a n 3500 A. Initial analysis has shown t h a t
s w e p t p a s t Mars on the a f t e r n o o n side of w a v e l e n g t h s longer t h a n 3500 A h a v e dift h e p l a n e t o b t a i n i n g spectroscopic a n d ferent p h o t o m e t r i c properties which will
not be discussed here.
i m a g i n g d a t a of high spatial resolution.
T h e u l t r a v i o l e t s p e c t r o m e t e r s a b o a r d the
DATA
Mariner s p a c e c r a f t o b t a i n e d i n f o r m a t i o n
a b o u t the m a k e - u p of the Mars a t m o s p h e r e
T h e long w a v e l e n g t h channel of the
b a s e d u p o n emission s p e c t r a f r o m the
Mariner ultraviolet s p e c t r o m e t e r s o b t a i n e d
u p p e r m o s t p a r t of the a t m o s p h e r e (Barth
one s p e c t r u m e v e r y three seconds in t h e
et al., 1969, 1971). I n addition, o v e r 400
1900-4300A r a n g e at 2 0 A resolution
s p e c t r a were o b t a i n e d of the illuminated
(Pearce et al., 1971). An i n s t r u m e n t field of
disk of Mars. Of these disk spectra, a b o u t view of 0?23 × 2?3 g a v e spatial resolution
40 were o b t a i n e d while viewing the
which varied f r o m a b o u t 30 × 3 0 0 k m n e a r
s o u t h e r n polar cap. Initial analysis of the
the bright limb to 14 × 1 4 0 k m a t t h e
polar cap s p e c t r a shows a distinctive
closest a p p r o a c h of the spacecraft. T h e
a b s o r p t i o n f e a t u r e at 2550 A which is m o s t long axis of t h e p r o j e c t e d field of view
s i m p l y explained b y the presence of was oriented p e r p e n d i c u l a r to the solar
1 × l 0 3cm_atm of ozone which gives t h e direction.
o b s e r v e d a b s o r p t i o n optical depth, r
I n analyzing the s p e c t r o m e t e r d a t a it
(2550A) = 0.3, ( B a r t h a n d H o r d , 1971). was f o u n d t h a t only small changes in
N o n e of the n o n p o l a r s p e c t r a shows this spectral shape occur s h o r t w a r d of 3500A.
a b s o r p t i o n feature, which is p r e s e n t in a l l This m e a n s t h a t the general p h o t o m e t r i c
40 polar spectra. T h e p h o t o m e t r i c proper- p r o p e r t i e s in this w a v e l e n g t h region are
ties f o u n d f r o m the u l t r a v i o l e t polar d a t a r e l a t i v e l y w a v e l e n g t h i n d e p e n d e n t . I n
h a v e been discussed b y P a n g a n d H o r d
order to describe the p h o t o m e t r i c function,
(1971).
the i n t e n s i t y or reflectance m e a s u r e m e n t s
I n this w o r k the p h o t o m e t r i c p r o p e r t i e s
in a 100A w a v e l e n g t h b a n d centered at
of t h e n o n p o l a r or desert regions of Mars
3050A are analyzed. T h e p h o t o m e t r i c
are discussed. Specifically considered is t h e p r o p e r t i e s deduced are r e p r e s e n t a t i v e of
253
© 1972by AcademicPress,Inc.
~54
CHARLES W. HORD
the wavelength region from 2 6 0 0 ~ to
a b o u t 3500A. Second order changes in
spectral shape, which do occur, are felt to
be due to v a r y i n g atmospheric opacity at
the shorter wavelengths and the increase
in ground albedo contribution at longer
wavelengths. Using the intensity sum over
a 100A wavelength interval gives relative
measurements to an accuracy b e t t e r t h a n
1%. Absolute intensities are limited by
our knowledge of the solar flux and the
i n s t r u m e n t calibration (Pearce et al., 197] ).
PHOTOMETRIC MEASUREMENTS
Reflectance properties of Mars at 3050 A
measured b y Mariner 6 and 7 are shown in
Figs. l, 2, and 3. Reflectance is defined as
- ~B/F,
(1)
where B is the measured intensity, or
surface brightness, and F is the solar flux
at Mars. These figures show d a t a t a k e n at
phase angles ranging from 46 ° to 91 ° as the
i n s t r u m e n t field of view swept from the
bright limb across the afternoon side of the
planet t o w a r d the terminator. Also plotted
are the cosine of the emission angle,/~, and
cosine of the incidence angle, tL0, which
have their usual radiative transfer meaning
(Chandrasekhar, 1960) with emission angle
defined as the angle between observed
e m i t t e d radiation and the local normal,
and the incidence angle defined as the
angle between the Sun and local normal.
The base maps used here show the ultraviolet observation swath across Mars in
the combined c o n t e x t of Mariner television
pictures (e.g., Leighton et al., 1969) and a
classical map of Mars. Mariner 6 data,
shown in Fig. 1, are ibr regions extending
from n o r t h of' J u v e n t a e Fons to Aurorae
Sinus and t~om Chryse to the west edge of
Meridiani Sinus. Mariner 6 data, shown in
Fig. 2, are for a region south of Margaritifer
Sinus extending from P y r r h a e Regio to
Deucalionis Regio. I n the Mariner 7 case,
shown in Fig. 3, ultraviolet observations
e x t e n d from south of N e c t a r across the
Argyre 1 region t o w a r d the polar cap, and
from the P a n d o r a e F r e t u m region across
Noachis and Hellespontus into Hellas. A
t a b u l a r listing of d a t a shown in Figs. 1, 2,
and 3 is included in Table I along with
latitude and longitude values.
In order to compare these measurements
with E a r t h - b a s e d measurements it is useful
to find p a r a m e t e r s k and R 0 t h a t provide a
best fit of the Minnaert fnnction
R-
R0/~0~'/~~ ~
(2)
to the 3050 :~ reflectance (Minnaert, 1941).
A recent discussion of the properties of this
function and its application to Mariner 6
and 7 television data is given b y Young
and Collins ( 1971 ).
I t is i m p o r t a n t to note t h a t the ultraviolet location being observed on Mars is
changing t h r o u g h o u t the measurements.
E v e n t h o u g h Mars shows relatively small
contrast in the ultraviolet, the albedo may
be varying. [n order to make a more nearly
valid application of Minnaert's law to these
data, regions can be selected which have
a nearly uniform albedo at visible wavelengths. Using the Mercator p h o t o m a p of"
Mars prepared by Cutts et al. (1971) from
Mariner 6 and 7 television d a t a and the
1969 Mars map prepared b y Lowell
O b s e r v a t o r y (Inge el al., 1971 ), four regions
having nearly uniform albedo were selected
fbr analysis.
Consider first Mariner 6 d a t a obtained at
a phase angle of 91 °. In the Aurorae Sinus,
Margaritifer Sinus region extending from a
latitude and longitude o f - 1 2 7 7 , 42?7 to
-15?9, 1878 the Minnaert parameters were
k - 0.71 ± 0.(t2 and R 0 - 0.037. F o r the
Deucalionis Regio region south of Meridiani
Sinus in the latitude and longitude range
from
1778, 357?7 to -1775, 34971 the
Minnaert parameters were k 0.69 ± 0.06
and R 0 = 0.031. The Mariner 7 d a t a
obtained at a phase angle of 91C' covered
two regions of nearly uniform visual albedo.
One of these regions extending from
Deuealionis Regio across P a n d o r a e F r e t u m
t o w a r d Hellespontus covering the latitude
and longitude range from - I 9?8, 353?8 to
37?9, 33170 gives k = 0.31 ± 0.01 and
R 0 = 0.022. This region appears uniibrm
on the Lowell map; however, the Mercator
p h o t o m a p based upon Mariner television
pictures indicates a slight decrease ill
albedo approaching Hellespontus. This
decrease in albedo could account for the
MARINER
6 AND
7 ULTRAVIOLET
SPECTROMETER
EXPERIMENT
255
ao
io
0
I0
W
ZO
I--
I,.J
30
40
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/
/
/
1
.2
if
0
80
,,
I
a
60
I
!
40
I
20
340
320
500
280
LONGITUDE
F r o . 1. M a r i n e r 6 reflectance m e a s u r e m e n t s a t 3050A. Tile t o p p a r t o f t h e figure s h o w s a p r o j e c t i o n
of t h e u l t r a v i o l e t s p e c t r o m e t e r field o f view on a m a p p r e p a r e d b v tile A r m y T o p o g r a p h i c Service.
This m a p d i s p l a y s an early version of t h e M a r i n e r 6 a n d 7 television p i c t u r e s ill t h e c o n t e x t of a
classical m a p of Mars. R e f l e c t a n c e a n d t h e cosines o f t h e incidence a n d emission angles, F0 a n d / ~ ,
are g i v e n as a f u n c t i o n o f longitude. T h e s e d a t a were o b t a i n e d a t a p h a s e angle o f 62 °.
........
CHARLES ~ . HORD
256
20
I0
0
I0
0
20
I-V--
,~
.J
30
40
5D
6o
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i
!
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t
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.06
LU
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LIJ
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1.0
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.... i
60
I
I
40
!
I
20
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0
340
J
320
i
........ |
300
LONGITUDE
Fzo. 2. M a r i n e r 6 reflectance m e ~ s u r e m e n t s ~t 3050.3~ o b t a i n e d ,~t ~ p h a s e angle of 91 °.
I
!
28O
257
M A R I ~ E R 6 AND 7 ULTRAVIOLET SPECTROMETER E X P E R I M E N T
:2
1
..........
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~o .............
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. . . . . . . . .
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W
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I
1.0
.I
11
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,i,/
~
tt
f
t/I
,)
.2
80
6o
4o
2o
o
340
32o
300
28o
LONGITUDE
F](~'. 3. Ma,riner 7 refleeta~;ce m e a s u r ( m e n t s a t [ 0 5 0 A . P a t a in t h e l e f t - h a n d s w a t h w e r e o b t a i n e d
a t a p h a s e a n g l e o f 46 ° a n d a t 91 ° in t h e t w o s w a t h s on t h e r i g h t .
,
258
CHARLES
W. HORD
TABLE
Mariner6,
Lat.
1.2
0.5
-.2
-.8
-1.4
-1.9
-2.4
-2.9
-3.3
-5.7
-4.1
-4.5
-4.9
-5.3
-5.6
-5.9
-6.3
-8.6
-6.9
-7.2
-7.4
-7.7
-8.0
-8.3
-8.5
12.9
12.6
I2.1
11.7
11.3
10.8
10.4
10.1
9.7
9.3
9.0
8.6
8.3
8.0
7.6
7.3
7.0
6.5
6.2
5.9
5.7
5.1
4.9
4.7
4.4
4.2
4.0
3.8
3,3
3.1
Lon.
65.2
65.8
62.5
61.4
60.3
59.3
58.5
57.4
56.5
55.6
54.8
54.0
53.2
52.5
51.7
51.0
50.3
49.6
49.0
48.3
47.6
47.0
46.4
45.7
45.1
37.4
37.0
36.4
55.8
35.2
34.6
54.0
33.5
52.9
32.4
31.8
31.3
30.8
30.3
29.8
29.5
28.8
27.8
27.5
26.8
26.4
25.5
25.0
24.5
24.1
23.6
23.2
22.7
21.9
21.4
~
0.230
0.257
0.281
0.303
0.324
0.343
0.361
0.378
0.394
0.409
0.424
0.438
0.451
0.464
0.477
0.489
0.501
0.512
0.523
0.534
0.544
0.555
0.564
0.574
0.584
0.382
0.388
0.399
0.411
0.421
0.432
0.442
0.452
0.461
0.470
0.479
0.488
0.496
0.505
0.515
0.520
0.528
0.542
0.549
0.556
0.563
0.576
0.582
0.588
0.594
0.600
0.605
0.611
0.621
0.627
I
Phase Angle=62.5
Uo
0.969
0.975
0.980
0.984
0.988
0.990
0.993
0.994
0.996
0.997
0.998
0.998
0.998
0.998
0.998
0.998
0.997
0.996
0.995
0.994
0.993
0.992
0.990
0.989
0.987
0.891
0.890
0.890
0.889
0.888
0.887
0.886
0.884
0.885
0.881
0.879
0.877
0.875
0.875
0.871
0.868
0.866
0.861
0.858
0.855
0.852
0.846
0.843
0.840
0.837
0.~34
0.850
0.827
0.820
0.816
R
0.0555
0.0557
0.0523
0.0525
0.0524
0.0461
0.0456
0.0451
0.0441
0.0448
0.0444
0.0436
0.0446
0.0437
0.0437
0.0454
0.0455
0.0473
0.0485
0.0481
0.0462
0.0451
0.0442
0.0442
0.0432
0.0483
0.0502
0.0473
0.0472
0.0450
0.0432
0.0433
0.0434
0.0425
0.0428
0.0422
0.0420
0.0420
0.0410
0.0411
0.0395
0.0386
0.0376
0.0367
0.0367
0.0361
0.0358
0.0354
0.0351
0.0355
0.0348
0.0339
0.0342
0.0543
0.0545
Pres.
4.56
4.64
4.89
5.32
5.67
4.89
5.06
5.21
5.24
5.61
5.73
5.75
6.18
6.14
6.34
6.95
7.16
7.84
8.31
8.44
8.06
7.90
7.79
7.93
7.77
6.19
6.70
6.30
6.48
6.16
5.93
5.11
6.27
6.18
6.42
6.41
6.49
6.61
6.50
6.64
6.51
6.20
6.12
5.97
6.05
5.97
6.07
6.02
6.01
6.21
6.08
5.90
6.06
6.23
6.36
Alt.
5.56
2.74
2.21
1.38
0.73
2.22
1.86
1.58
1.52
0.85
0.64
0.59
-.13
-.07
-.39
-1.30
-1.60
-2.50
-3.09
-3.25
-2.78
-2.59
-2.44
-2.62
-2.42
-.15
-.94
-.32
-.60
-.09
0.28
-.02
-.27
-.12
-.51
-.49
-.62
-.80
-.65
-.84
-.34
-.16
-.04
0.21
0.09
0.22
0.06
0.13
0.15
-.18
0.03
0.33
0.08
-.20
-.42
MARINER 6 AND 7 ULTRAVIOLET SPECTROMETER EXPERIMENT
TABLE I continued
Mariner 6, Phase Angle = 62.5
Lat.
2.7
2.5
2.4
2.2
2,0
1,8
1.6
1.5
1.5
I.I
1.0
0.8
0.7
0.5
0.4
0.2
O.l
-.0
-.2
-.3
-.4
-.5
-.7
-.8
-.9
-I.0
-l.l
-1.2
-1.3
-1.4
-1.5
-1,6
Lon.
~
20.6
20.1
19.7
19.3
18,9
18.5
18,0
17,6
17.2
16.8
16.4
16.0
15.6
15.1
14.7
14,3
15,9
13.5
15.1
12.7
12.3
11.9
11.5
II,I
I0.7
I0.3
9,9
9.6
9.2
8,8
8.4
8,0
0.637
0.641
0.646
0.651
0.655
0,660
0.664
0,668
0.672
0,676
0.680
0.684
0.688
0.691
0.695
0,698
0.702
0.705
0.708
0.711
0.714
0.717
0.720
0,723
0.726
0,729
0.731
0,734
0.756
0,739
0.741
0.743
Uo
0.809
0.805
0.802
0.798
0,794
0,790
0,786
0.782
0.778
0.774
0.770
0.766
0.761
0.757
0.755
0,749
0,744
0,740
0.755
0.731
0.726
0.722
0.717
0.712
0.708
0.703
0,698
0.694
0.689
0.684
0.679
0,674
R
0.0347
0.0349
0.0338
0.0325
0.0322
0.0310
0,0323
0.0311
0.0513
0.0315
0.0506
0.0505
0.0304
0.0296
0,0308
0,0297
0,0285
0.0300
0.0287
0.0299
0.0284
0.0295
0.0303
0.0289
0,0298
0.0286
0,0293
0,0300
0.0298
0,0309
0.0307
0,0302
Pres.
6.58
6.73
6.42
6.07
6,04
5,71
6,21
5.88
5.98
6.13
5.88
5.91
5.93
5.71
6.17
5,84
5,47
6,07
5.65
6.13
5.63
6.10
6.42
5.97
6.34
5,97
6,26
6,57
6.55
7,04
7.01
6,87
Alt.
-.75
-.98
-,51
0.05
0,10
0,66
-,18
0.38
0.21
-.04
0.37
0.53
0.29
0,67
-,12
0,45
1,10
0,06
0.77
".04
0.80
0.00
-.51
0.22
-,38
0,22
-,26
-,74
-.70
"I,43
-1.38
-I,18
Mariner 6, Phase Angle = 90.9
-12.7
-13.1
-13.5
-13.9
-14.3
-14.6
-15,0
-15.3
-15.5
-15.8
-16,1
-16.3
-16.5
-14.0
-14.2
-14-4
10
42.7
41.6
40.3
39.0
37,8
36,7
35.6
34,5
33,5
32.5
31,6
30.7
29.8
27,4
26,5
25,8
0.224
0.971
0.243
0.966
0,266 0,960
0.288
0.953
0,309
0,946
0.328
0,939
0.346
0,933
0.364
0.926
0.380
0,919
0.396
0.912
0,411
0.905
0.425
0,898
0.440
0,891
0.458
0.877
0.471
0,869
0,483
0,863
0.0559
0.0552
0.0514
0.0516
0.0505
0.0488
0.0464
0,0444
0,0446
0.0452
0.0437
0.0462
0.0451
0.0425
0,0408
0.0408
3.97
4.26
4.20
4.60
4.79
4,85
4,77
4,69
4.98
5.32
5,26
6.00
5,99
5.74
5.55
5.74
4.29
3.60
3.74
2.84
2,42
2,29
2.46
2,64
2,04
1.37
1.48
0.18
0.19
0.61
0,94
0.61
259
260
CHARLES
W. HORD
TABLE I continued
Mariner 6, Phase Angle = 90.9
Lat.
-14.6
-14.8
-14.9
-15.1
-15.2
-15.4
-15.5
-15.7
-15.8
-15.9
-16.0
-16.1
-16.3
-16.4
-16.5
-16.5
-16.6
-16.7
-16.8
-16.9
-17.0
-17,0
-17.1
-17.2
-17.2
-17.3
-17.3
-17.4
-17.4
-17.5
-17.5
-17.5
-17.6
-17.6
-17.6
-17.7
-17.7
-17.7
-17.7
-17.8
-17.8
-17.8
-17.8
-17.8
-17.8
-17.8
-17.8
-17.8
-17.8
-17.8
-17.8
-17.8
-17.8
-17.8
-17.8
-17.8
Lon.
25.0
24.3
23.5
22.8
22.1
21.4
20.8
20.1
19.4
18.8
18.4
17.5
16.9
16,3
15,6
15.0
14.4
13,8
13.3
12.7
12.1
11.5
11.0
10.4
9.9
9.3
8.8
8.2
7.7
7.1
6.6
6.1
5.6
5.1
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.1
359.6
359.1
358.6
357.7
357.2
356.7
356.3
355.8
355.3
354.9
354.4
354.0
~
Uo
0.495
0.506
0,517
0.528
0.538
0,548
0.558
0.567
0.577
0.586
0.591
0,603
0,612
0,620
0.628
0.636
0.644
0.652
0.659
0.666
0.674
0,681
0.688
0.694
0.701
0.708
0.714
0.720
0.726
0.732
0.738
0.744
0.750
0.756
0.761
0.766
0.772
0.777
0.782
0.787
0.792
0.797
0.802
0.806
0.811
0.816
0.820
0.828
0.833
0.837
0.841
0.845
0.849
0.853
0.856
0.860
0.856
0.849
0,842
0.835
0,828
0.822
0,815
0.808
0,801
0.794
0.790
0,781
0.774
0.767
0.760
0.753
0.746
0.740
0.733
0,726
0.719
0.712
0,706
0.699
0.692
0.685
0.678
0.671
0.665
0.658
0.651
0.644
0.637
0.630
0.624
0.617
0.610
0.603
0.596
0.589
0.583
0.576
0.569
0.562
0.555
0.548
0.542
0.528
0.521
0.514
0.508
0.501
0.494
0.487
0.480
0.473
R
0.0415
0.0412
0,0408
0.0390
0,0381
0.0379
0.0369
0.0564
0.0364
0,0369
0.0369
0.0367
0.0362
0.0350
0.0338
0.0353
0.0325
0.0322
0.0317
0.0301
0.0301
0.0298
0.0292
0.0294
0.0287
0.0289
0.0285
0.0280
0.0283
0.0275
0.0273
0.0265
0.0257
0.0262
0.0259
0.0259
0.0261
0.0253
0.0252
0.0251
0.0240
0.0242
0.0241
0.0235
0.0238
0.0222
0.0224
0.0212
0.0215
0.0208
0.0205
0.0201
0.0194
0.0197
0.0193
0.0195
Pres.
6.08
6.18
6.24
5.94
5.87
5.95
5.83
5.85
5.97
6.24
6.33
6.45
6.42
6.19
5.97
5.95
5.81
5.82
5.77
5.37
5.48
5.48
5.37
5.53
5.41
5.55
5.50
5.41
5.62
5.43
5.45
5.25
5,07
5.32
5.28
5.36
5.52
5.31
5.34
5.38
5.05
5.22
5.24
5.10
5.26
4.76
4.89
4.58
4.76
4.57
4.51
4.41
4.20
4.38
4.29
4.44
Aft.
0.04
-.12
-.22
0.26
0.39
0.25
0.45
0.42
0.22
-.22
-.36
-.56
-.51
-.14
0.22
0.26
0.49
0.48
0.56
1.27
1.07
1.08
1.27
0.99
1.21
0.96
1.04
1.20
0.83
1.18
1.14
1.50
1.85
1.37
1.45
1.30
1.00
1.39
1.34
1.26
1.90
1.57
1.52
1.80
1.49
2.48
2.22
2.86
2.49
2.90
3.03
3.25
3.73
3.32
3.54
3.17
MARINER 6 AND 7 ULTRAVIOLET SPECTROMETER EXPERIMENT
TABLE I continued
Mariner 6, Phase Angle = 90.9
Lat.
Lon.
U
~o
R
0.0194
0.0190
Pres.
Alt.
4.44
4.37
3.17
3.33
-17.7
-17.7
353.5
353.1
0.864
0.867
0.467
0.460
-17.7
352.6
0,871
0.453
0.0187
4,31
3.48
-17.7
352.2
0.874
0.0186
4.34
3.41
-17.6
351.7
0,878
0.0180
4.14
3.88
-17.6
-17.6
-17.6
-17.5
-17.5
-17,5
351.3
350.8
350.4
350.0
349.5
349.1
0.881
0,884
0,887
0.890
0.893
0.896
0.446
0.439
0.432
0.426
0.419
0,412
0.405
0.398
0.0184
0.0180
0.0176
0.0175
0.0167
0.0174
4.36
4.28
4.17
4.18
3.92
4.27
3.37
3.54
3.80
3.79
4.42
3.57
Mariner 7, Phase Angle = 46.3
-35.6
-36.2
-36.8
-37.4
-37.9
-38.5
-39.0
-39.5
-40.0
-40.5
-41.0
-41.5
-42,0
-42.4
-42.9
=43.3
-43.8
-44.2
-44.6
-45.1
-45.5
-45.9
-46.3
-46.7
-47,1
-47,5
-47.9
-48.2
-48.6
-49.0
-49.4
-49.7
-50.I
50.4
49.7
49.0
48.3
47.7
47.1
46.5
45.9
45.3
44.7
44.2
43,6
43,1
42.6
42.1
41.6
41.0
40.5
40.1
39.6
39.1
38.6
38.1
37.6
37.2
36.7
36.2
35.8
35.3
34.9
34.4
33.9
33.5
0.317
0.330
0.343
0.355
0.367
0.578
0.389
0.400
0.410
0.420
0.429
0.438
0.447
0.456
0.464
0.472
0.480
0,488
0.495
0.503
0.510
0.517
0.524
0.530
0.537
0,543
0.549
0.556
0.562
0,567
0.573
0,579
0.584
0.615
0,620
0,624
0,628
0.632
0.655
0,639
0,641
0.644
0.646
0.648
0.650
0,652
0.654
0.655
0,656
0.658
0.658
0.659
0.660
0,661
0.661
0.661
0.662
0.662
0.662
0,662
0,661
0.661
0.661
0.660
0.660
0.659
0.0711
0.0678
0,0652
0.0623
0.0605
0.059~
0.0577
0,0555
0.0528
0,0501
0.0480
0.0462
0.0451
0.0440
0.0430
0.0414
0.0389
0.0388
0.0389
0.0386
0.0387
0.0385
0.0385
0.0387
0.0392
0.0401
0.0397
0.0401
0.0405
0.0417
0.0425
0.0425
0.0421
7.49
7.31
7.21
7.01
6.96
6.98
6.92
6.73
6.44
6.13
5.90
5.70
5.62
5.54
5.45
5.25
4.88
4.95
5.04
5.06
5.16
5.19
5.27
5.37
5.55
5.83
5.80
5.98
6.13
6.46
6.72
6.81
6.77
-2.04
-1.81
-1.67
-1.39
-1.32
-1.34
-1.25
-.98
-.53
-.04
0.33
0.68
0.82
0.97
1.13
1.50
2.24
2.10
1.90
1.88
1.67
1.63
1.47
1.27
0.94
0.46
0.50
0.21
-.04
-.57
-.97
-1.09
-1.04
-50.5
33.0
0.589
0.658
0.0413
6.67
-.88
-50.8
32.6
0.595
0.658
0.0409
6.64
-.85
-51.2
-51.5
-51.9
-52.2
32.1
31.7
31.2
0.600
0.605
0.610
0~614
0.657
0.656
0.655
0.0405
0.0406
0.0403
0.0386
6.61
6.69
6.67
6.32
-.80
-.92
-.88
30.8
0-~54
-.35
261
262
CHARLES W. HORD
T A B L E I continued
Mariner 7, P h a s e Angle = 46.3
Lat.
Lon.
U
~
-52.6
-52.9
-53.3
-53.6
-53.9
-54.3
-54.6
-54,9
-55.3
-55.6
-55.9
-56.2
-56.6
-56.9
-57.2
-57,5
-57.8
30.3
29.9
29.4
29,0
28.5
28.0
0.619
0.624
0.628
0.633
0.637
0.641
0,645
0.649
0.653
0.657
0.661
0.665
0.668
0.672
0.676
0.679
0.682
0.653
0.651
0.650
0.649
0.647
0.646
0,645
0,643
0,641
0.640
0.638
0.636
0.634
0.632
0.630
0.628
0.626
27.6
27.1
26.7
26,2
25.8
25.3
24,8
24.4
23.9
25.4
22.9
R
0.0390
0.0400
0.0388
0.0385
0.0386
0.0389
0.0390
0.0375
0,0374
0.0370
0.0375
0.0375
0.0383
0.0576
0.0384
0.0395
0.0407
Pres.
Alt.
6.47
6.80
6.53
6.53
6,60
6.73
6.81
6,48
6,49
6,44
6.62
6.67
6.94
6.80
7.08
7.42
7.80
-.59
-I.08
-.68
-.68
-.78
-.98
-I.10
-,59
-.61
-.53
-.81
-.89
-1.29
-I.08
-1.48
-1.95
-2.46
Mariner 7, Phase Angle = 90.7
-19.8
-20.4
-2|.4
-22.3
-23.3
-24.1
-24.9
-25.7
-26.4
-27.1
-28.4
-29.0
-29.6
-30.2
-30.7
-31,~
-3!.7
-32.2
-32.7
-33.1
-33,6
-34.0
-34.4
734.8
-35,2
-35.6
-35,9
-36,3
-36.6
-37.0
-37.3
-37.6
-37.9
353.8
353.2
352.3
351.5
350.6
349.8
349.0
348,2
347.4
346,7
345.2
344.5
343.9
343.2
342.5
341,8
341.2
340.5
339.8
339.2
338.6
337.9
337.3
336.6
336,0
335.4
334,8
334.1
333.5
352.9
332.3
331.6
331.0
0.225
0.238
0.260
0.281
0.301
0.320
0.338
0.355
0.371
0.387
0.416
0.429
0.443
0.455
0.467
0,479
0,491
0.502
0.512
0.523
0,533
0.543
0.553
0.562
0.571
0.580
0,589
0.597
0.606
0,6|4
0.622
0.630
0.637
0.971
0.968
0.962
0.956
0.949
0.943
0.936
0.929
0.923
0.916
0.903
0.896
0.890
0.883
0.876
0,870
0.863
0.856
0.850
0.843
0.836
0.830
0.823
0.816
0.810
0.803
0.797
0.790
0.783
0.777
0.770
0.763
0.757
0.0588
0.0574
0.0549
0.0523
0.0503
0.0481
0.0461
0,0445
0.0433
0.0420
0.0401
0.0387
0.0376
0.0369
0.0360
0,0351
0.0344
0.0336
0.0327
0.0324
0.0320
0.0312
0.0316
0.0304
0.0303
0.0298
0.0291
0.0294
0.0282
0.0280
0.0283
0.0276
0.0272
4.51
4.42
4.53
4.57
4.64
4.62
4.58
4,58
4.61
4.61
4.63
4.55
4.49
4.49
4,44
4.40
4.37
4.31
4.22
4.27
4,30
4.20
4.40
4.22
4.29
4.26
4.17
4.34
4.10
4,14
4.30
4.21
4.17
3.49
3.23
2.98
2.88
2.74
2.79
2.86
2,86
2.80
2.81
2.76
2.98
3.07
3.06
3.18
3.28
3.35
3.48
3.68
3.58
3.49
3.73
3,27
3.69
3,52
3.60
3,81
3.41
3.97
3.87
3.50
3.72
3.81
MARINER 6 AND 7 ULTRAVIOLET SPECTROMETER EXPERIMENT
TABLE I continued
Mariner 7, Phase Angle = 90.7
Lat.
Lon.
~
;~o
R
Pres.
Alt.
-38.2
-38.5
-38.8
-39.1
-39.3
-39.6
-39.8
-40,I
-40.3
-40.6
-36.5
-36.7
-36.9
-37.1
-37.2
-37.4
-37.5
-37.7
-37.8
-38.0
-38.2
-38.4
0.645
0.652
0.659
0.666
0.673
0.680
0.686
0.693
0,699
0.705
0.695
0.700
0.706
0.711
0.716
0.721
0.725
0.730
0.735
0.739
0.748
0.752
0.750
0.744
0.737
0.730
0.724
0.717
0.710
0,704
0.697
0.691
0.651
0.644
0.637
0.631
0.624
0.618
0.611
0.604
0.598
0.591
0.578
0.571
3.90
4.01
3.73
3.93
3,85
3.58
0.756
0.760
0.764
0.768
0.772
0.565
0.558
0.551
0.545
0.538
0.0268
0.0264
0.0265
0.0260
0,0258
0.0260
0.0260
0.0266
0e0259
0.0264
0.0271
0.0266
0.0271
0.0273
0.0280
0.0285
0.0297
0.0506
0.0309
0.0312
0.0311
0.0316
0.0314
0.0316
0.0316
0.0322
0.0308
4.13
4.09
4.20
4.12
4.15
4.27
4.37
4.62
4.47
4,69
5.04
4.95
5.17
5.31
5.63
5.88
6.37
6.75
6.94
7.13
7.27
7.54
7.57
-38.8
-38.9
330.4
329.8
329.2
328.5
327.9
327.3
326.7
526.1
325.5
524.9
318.0
317.4
316.8
316.3
315.7
315.2
314.6
314.0
313.5
312.9
311.8
311.2
310.7
310.1
309.6
309.0
508.5
-39.0
•3 9 . 1
307.9
507.4
0.776
0.780
0.532
0.525
0.0307
0.0310
-39.1
306.8
0.783
0.518
0.0307
7.92
7.91
•3 9 . 2
•3 9 . 3
306.3
305.7
0.787
0.790
0.512
0.505
0.0310
0.0300
8.12
7.80
-2.85
-2.46
•39.4
•39.4
•39.5
39.5
,39.6
39.6
39.7
39.7
39.7
39.8
39.8
39,8
39.8
39.8
39.8
305.2
304.6
304.1
303.5
303.0
302.4
301.9
301,3
300.8
300.3
299.7
299.2
298.7
298.1
297.6
0.794
0.797
0.800
0.803
0.806
0.809
0.812
0.815
0.818
0.821
7,28
7.21
7.27
7.21
-2.07
-2,27
-2.08
-2.20
-2,35
-2.22
-2.13
-1.78
-1.91
-1.83
-1,86
-1.77
-1.66
-1.75
-1.67
39.8
39.8
297.1
296.5
0.836
0.838
0.400
0.593
0.0291
0.0292
0.0287
0.0287
0.0288
0.0284
0.0280
0.0272
0.0272
0.0269
0.0268
0,0264
0.0260
0.0260
0,0257
0.0258
7.50
7.65
7.51
7.60
7.72
7.62
7.55
7.29
7.39
7.33
0,826
0.829
0.831
0.834
0.499
0.492
0.485
0,479
0.472
0.466
0.459
0.452
0.446
0.439
0.433
0,426
0.419
0.413
0,406
7.32
7.11
-1.81
-1.53
39.8
296.0
0.840
0.386
0.0245
295.5
0.843
0.380
0.0245
39.8
294.9
39.8
294.4
39.8 t 295.9
39.7
293,4
0.845
0.847
0,849
0.851
0.373
0.367
0,360
0.353
0.0244
0.0245
0.0254
0.0235
6.91
7.01
7.02
7.04
6.75
6.84
-1.24
39.8
-38.5
-38.6
-38.7
0.825
0.0251
3.35
2.78
3.11
2.64
1.92
2.09
1.66
1.38
0.81
0.37
-.42
-I.01
-1.29
-1.56
-1.74
-2.12
-2.15
7.75
-2.39
7.84
8.15
7.71
-2.51
7.72
-2.36
-2.61
7.35
-2.90
-2.33
-2.59
-1.38
-1.40
-1.43
-I.00
-1.15
263
264
C H A R L E S W . tt01~D
TABLE
I continued
M a r i n e r 7, P h a s e A n g l e = 90.7
Lat.
-39.7
-39.7
-59.6
-39.6
-59.5
-59.5
-59.4
-59.4
-59.5
-59.5
-59.2
-59.1
-59.0
-59.0
-58.9
-58.8
-58.7
-58.6
-58.5
-58.4
-58.5
-58.2
-38.1
Lon.
292.9
292.5
291.8
291.5
290.8
290.5
289.8
289.5
288.8
288.5
287.8
287.5
286.8
286.5
285.8
285.5
284.8
284.5
285.8
285.4
282,9
282.4
281o9
~
0.855
0.854
0.856
0.858
0.860
0.861
0.865
0.864
0.866
0.867
0.868
0.869
0.871
0.872
0.875
0.874
0.875
0.876
0.877
0.~77
0.878
0.879
0.879
~o
R
0.547
0.340
0.554
0.527
0.520
0.514
0.507
0.500
0.294
0.287
0.281
0.274
0.267
0.261
0.254
0.248
0.24I
0.254
0.228
0.221
0.215
0.208
0.202
small v a l u e of k for this region. I n the
Hellas d a t a o b t a i n e d for the l a t i t u d e a n d
longitude r a n g e from -39?6, 29173 to
-3871, 28179 t h e Minnaert p a r a m e t e r s
were k = 0.83 =~ 0.04 a n d R 0 = 0 . 0 5 5 . A
s u m m a r y of ultraviolet Minnaert p a r a m e t e r s is given in T a b l e I I .
D u e to t h e large phase angles of
the Mariner o b s e r v a t i o n s c o m p a r e d w i t h
g r o u n d - b a s e d observations, an e x a c t comparison of the 3050A reflectances is not
possible. E x c l u d i n g unusual p h o t o m e t r i c
properties, it is e x p e c t e d t h a t the E a r t h b a s e d m e a s u r e m e n t s of the geometric
albedo should be of the s a m e order as the
Minnaert constant, R0, for the range of k
values found. E a r t h - b a s e d d a t a o b t a i n e d
b y I r v i n e et al. (1968) indicate an a v e r a g e
geometric albedo ~ 0 0 5 at 3050Jk E a r t h b a s e d r o c k e t d a t a o b t a i n e d in the 25503300_~ w a v e l e n g t h region b y B r o a d f o o t
a n d Wallace (1970) give a geometric albedo
~0.09 at 3050A. I n this e x p e r i m e n t , the
M a r t i a n polar caps were included in the
i n s t r u m e n t field of view. A p a r t of the
intensity measured by Broadfoot and
0.0226
0.0226
0.0222
0.0219
0.0218
0.0217
0.0217
0.02'14
0.0210
0.0206
0.0202
0.0195
0.0190
0.0182
0.0178
0.0174
0.0167
0.0167
0.0162
0.0165
0.0161
0.0157
0.0155
Pres.
Alt.
6.55
6.60
6.52
6.42
6.46
6.49
6.54
6.52
6.59
6.29
6.19
5.84
5.79
5.47
5.56
5.27
5.05
5.09
4.95
5.05
5.00
4.92
4.76
-.71
-.78
-.66
-.51
-.57
-.61
-.70
-.67
-.46
-.50
-.14
0.45
0.55
1.10
1.50
1.47
1.95
1.82
2.15
1.94
1.99
2.15
2.48
Wallace m a y be a t t r i b u t e d to the considerably b r i g h t e r polar cap which has the
effect of bringing their o b s e r v a t i o n s into
closer a g r e e m e n t w i t h the Mariner ultraviolet s p e c t r o m e t e r results. T h e Mariner
d a t a indicate t h a t t h e c o m b i n a t i o n of
desert reflectance, showing a m o n o t o n i c
increase in reflectance w i t h decreasing
w a v e l e n g t h , c o m b i n e d w i t h a polar cap
reflectance, with the b r o a d ozone absorption centered at 2550 ~ ( B a r t h a n d H o r d ,
TABLE I [
MINNAERT PARASIETERS
UVS data
Mariner 6 Aurorae
Sinus, Margaritifer
Sinus
Mariner 6 Deuealionis
P~egio
Mariner 7 DeucMionis
Regio, Pandorae
Fretum
Mariner 7 Hellas
k
Ro
0.71 ± 0.02
0.037
0.69 ± 0.06
0.031
0.31 ± 0.01
0.022
0.83 ± 0.04
0.055
MARINER 6 AND 7 ULTRAVIOLET SPECTROMETER EXPERIMENT
~65
.I0
0
0
ILl
fJ
Z
l'-fO
0
0
0
.05
0
0
0
0
I
I
I
I
.--I
ILl
t',"
0
!
I
1
I
I
2600
3100
I
3600
WAVELENGTH (A)
F1G. 4. M a r i n e r 7 Mars reflectance as a f u n c t i o n of w a v e l e n g t h o b t a i n e d a t l a t i t u d e -1978 a n d
l o n g i t u d e 353?8, w i t h /x0 ~ 0.971, /x = 0.225, a n d a p h a s e angle of 4-6?3. T h e d a t a p o i n t s o b t a i n e d
e,~¢ery 4.3 A a t a resolution of 20 A h a v e been c a l i b r a t e d a n d d i v i d e d b y t h e solar flux, a n d are p r e s e n t e d
here a t 100A resolution c o n s i s t e n t w i t h t h e 3050A reflectance d a t a .
1971), would tend to give the constant
reflectance as a function of wavelength
observed by Broadfoot and Wallace. An
earlier rocket experiment performed by
Evans (1965) seems to qualitatively match
the spectral shape observed by the Mariner
spectrometer for the nonpolar regions of
Mars. Evans' experiment used photographic methods while Broadfoot and
Wallace used photoelectric detection as
did the Mariner ultraviolet spectrometer.
Results from the Orbiting Astronomical
Observatory (OAO) ultraviolet experiment
o~
give geometric albedos of 0.0401 at 3215 A
and 0.0428 at 2800 A (Caldwell, 1970) using
photoelectric detection methods.
SPECTRAL REFLECTANCE
Analysis of the Mariner ultraviolet
spectrometer (UVS) data has shown that
the illuminated disk of Mars has two
characteristic ultraviolet spectral reflectances. These two spectral types, associated
with the polar and nonpolar regions of the
planet, have been discussed (Barth and
Hord, 1971).
2000
n~
>-
Jo o o
Z
la.I
I--..
z
0
2500
:3000
3500
4000
o
WAVELENGTH ( A )
FIG. 5. Mariner 7 s p e c t r u m o b t a i n e d w i t h t h e s p e c t r o m e t e r field o f view including t h e b r i g h t limb
o f Mars. This s p e c t r u m was o b t a i n e d a t l a t i t u d e - 2 9 ° a n d l o n g i t u d e 307 °, w i t h a p h a s e angle of 46?3
a n d a solar incidence angle equal to 55 °.
266
CHARLES W. HORD
o4
2000 -
~r
>bz
tu
bz
I000-
0
I
I
I
I
I
2500
I
I
I
3000
1
!
1
I
I
I
3500
o
WAVELENGTH (A)
I
I
I
I
I
4000
FIG. 6. Mariner 7 spectrum obtaincd alt latitude -39?0 and longitude 286?8, with #0 = 0.267,
/z = 0.871, and a phase angle of 90?7.
Figure 4 shows t h e n o n p o l a r Mars
reflectance in t h e w a v e l e n g t h region f r o m
2600 to 3600A, o b t a i n e d b y dividing a
c a l i b r a t e d s p e c t r u m of Mars b y t h e solar
flux. I n this w a v e l e n g t h interval, each of
the 400 n o n p o l a r spectra has the s a m e
basic spectral s h a p e as shown in Fig. 4.
D u e to the large v a r i a t i o n in the solar flux
o v e r t h e long w a v e l e n g t h channel (1900-
4300/~), the i n s t r u m e n t s e n s i t i v i t y was set
to cause a full-scale m e a s u r e m e n t a t a b o u t
3600/~ for m o s t of the s p e c t r a o b t a i n e d
w h e n observing t h e i l l u m i n a t e d disk of
Mars. This was done in order to o b t a i n
necessary sensitivity at shorter w a v e lengths. H o w e v e r , several s p e c t r a were
o b t a i n e d which were c o m p l e t e l y on scale
t h r o u g h o u t the spectral r a n g e 2500 to
1.25
O
1.00
O
O
.75
0
0
0
0
0
I
I
I
I
I
o
o
I
I
o
0
0
"
.50
.25
0
3000
I
5500
I
I
|l
I
I
4000
o
WAVELENGTH
(A)
FXG. 7. Ratio of terminator to limb intensities obtained by dividing the spectrum in Fig. 6 by that
in Fig. 5.
MARINER 6 AND
7 ULTRAVIOLET SPECTROMETER EXPERIMENT
267
4300J~. Figure 5 shows one of several the airmass along the instrument line of
ultraviolet spectra measured with the sight. Near the bright limb of the planet,
field of view of the instrument crossing the where the emission angle was large, the
bright limb of Mars. In this particular airmass is better represented by the more
geometry the long dimension of the UVS accurate Chapman function (see e.g., Hord
slit made an angle of 55 ° with the tangent et al., 1970). In this discussion, the airmass
to the limb and the field of view is only will be represented by the secant factor,
partially filled with the bright disk of 1//t, as this assumption does not alter the
Mars. This measurement at the bright limb conclusions reached here. Pressure is
with the field of view underfilled allowed directly proportional to column density
an on-scale (at all wavelengths) spectrum and therefore to optical thickness for a
to be obtained at the bright limb. Figure 6 homogeneous atmosphere, independent of
shows one of the spectra taken near the temperature structure, so that
evening terminator which are also fully
P = (Po/ro) r.
(3)
on-scale due to the decreased solar illumination. Figure 7 shows the reflectance near This assumption is made at the beginning
the terminator relative to the bright limb and its accuracy will be evaluated at the
reflectance and was obtained by dividing end of the analysis. In the absence of a
the spectrum in Fig. 6 by the Fig. 5 turbid atmosphere, r 0 = 0.032 for Po =
spectrum. A similar relative spectral 6.0rob if the major constituent is carbon
reflectance is obtained by dividing any of dioxide. Ground reflectance is represented
the spectra taken near the terminator by by the Minnaert function in Eq. (2). The
any of the limb spectra. The spectral Minnaert parameters R o and k are taken to
shapes are very nearly identical shortward be constant for this analysis, an assumption
of about 3600A and show the character- which can be tested a posteriori.
istie shape of the other nonpolar spectra.
Atmospheric extinction is assumed to be
Longward of 3500 A the terminator to limb due to scattering only so that pure
intensity ratio increases monotonically, absorption is neglected. Taking into acwith wavelength, and illustrates the dif- count extinction and multiple scattering,
ferent photometric properties in this the measured reflectance at 3050 A is
wavelength region. The terminator spectrum was obtained in the visually bright
Hellas region which accounts for the
increase in ratio at longer wavelengths.
+ Ro/to~/t~-1 exp (-rM)}
(4)
PHOTOMETRIC MODEL
In the following analysis, Mariner 6 and
7 infrared spectrometer pressure data
(Herr et al., 1970) are combined with
ultraviolet data in order to give a more
realistic model of the 3050 A reflectance of
Mars. The ultraviolet reflectivity is assumed to consist of two components; an
atmospheric part, (p/4) (r//t), and a ground
contribution, R0/t0k/t k-~. For the atmospheric part, p is the atmospheric scattering
phase function, T is the vertical scattering
optical depth, and r//t is the optical depth
along the instrument line of sight. The
phase function, p, depends upon the
scattering angle, ~, which is the supplement
of the phase angle. In the factor r//t, 1//t is
where [1 - exp ( - r M ) ] / r M and exp ( - r M )
are attenuation factors associated with the
atmospheric and surface parts of the
reflectance. Total airmass, M, of the
incident and outward optical paths is
1//to + 1//t. The multiple scattering factor,
f, is a function of/t, t*0, ~, r as well as of the
ground reflectance and the form of the
phase function. Including the factor f
makes Eq. (4) exact for the model selected.
In practice, the magnitude of f can be
estimated by comparison with exact solutions for simplified cases. For the small
values of R 0 and r encountered on Mars,
the strongest dependence o f f is on r. The
f a c t o r f i s greater than unity by an amount
of order 7. In this analysis f is taken to be
268
CHARLES W. HORD
u n i t y which causes the optical thickness
to be o v e r e s t i m a t e d b y a small amount.
W h e n Eq. (4) is solved for optical
thickness and substituted into Eq. (3), the
pressure as a function of the 3 0 5 0 ~
reflectance, R, is
p_Po 1 . [Ro/~0k/~k-I-RA]
where R A is defined as pl(4[xM). E q u a t i o n
(5), with values for the constants rolPo,
R 0, k, and the phase function, p(~),
constitute an algorithm for conversion of
ultraviolet reflectance into pressure.
MARINER INFRARED AND
ULTRAVIOLET PRESSURES
In the normalization of these d a t a to a
single occultation m e a s u r e m e n t (Barth
and Hord, 1971), only one p a r a m e t e r can
be specified, n a m e l y rop(~)/Po, assuming
no ground reflectance. Mariner infrared
spectrometer pressure measurements (Herr
et al., 1970) provide the o p p o r t u n i t y to
u n d e r s t a n d more a b o u t the Mars physical
p a r a m e t e r s used in Eq. (5) and provide a
test of the assumptions involved. The
p r i m a r y assumptions are a uniform ground
reflectance and homogeneous scattering
atmosphere.
A total of 23 infrared measurements
from Mariner 6 and 35 from Mariner 7 were
c o m p a r e d with corresponding ultraviolet
measurements. Due to an offset in the
fields of view of the two instruments,
m e a s u r e m e n t s of" similar areas were made
at subsequent times. The set of 58 infrared
measurements which lie along the ultraviolet viewing p a t h were selected for
comparison. A corresponding set of 58
ultraviolet measurements, which correspond best in latitude and longitude with
the infrared measurements, were also
selected. Differences in spatial resolution
a n d position observed on the planet have
not been t a k e n into account in this
analysis. The long dimension of the infrared
s p e c t r o m e t e r slit, orientated perpendicular
to the Sun, was 2?0 compared with 2?3 for
the ultraviolet spectrometer. I n the narrow
dimension, the effective infrared field of
view was a b o u t half the size of the 0?23
ultraviolet dimension.
Using these 58 measurements the parameters ro/Po, Ro, k, and p(~) for the
scattering angles observed (~ = 89 °, 118 °,
134 °) were varied in order to minimize the
root mean square (rms) error defined b y
rms
-'Y
[ W (p(UVS)_
~.~ ~ i
/'='
L. . . .
:v-
p(IRS)~]
--i
/
/
1/2
,
J
where p~uvs) and p~nts) are the ultraviolet,
Eq. (5), and infrared pressure measurements. Using nonlinear least squares
techniques, the sensitivity of the rms error
to each of the p a r a m e t e r s of Eq. (5) could
be tested. W i t h this procedure the phase
function and optical d e p t h p a r a m e t e r s
were not well separated and the Minnaert
parameter, k, did not have a strong effect
on the rms error. The p a r a m e t e r s obtained
by this analysis were rop(89o)/Po = 0.0111,
p(118°)/p(SW ') --0.qd,
p(134°)/p(89 °)
1.18, R0 = 0.015, and k ~ 1. This choice of
p a r a m e t e r s gave an rms error of 9% taking
into account the degrees of freedom used
in specif~'ing five parameters. The agreement is good considering t h a t pressure
measurements used in this analysis varied
b y more t h a n a factor of two. On a large
scale, the agreement between the ultraviolet and infrared techniques is good, with
the exception of the swath near Aurorae
Sinus. I t is notable t h a t this is a region
where chaotic terrain was observed b y the
Mariner television e x p e r i m e n t (Sharp et
al., 1971 ). This is also the region n o t e d b y
N e u g e b a u e r et al. (1971), where the
observed albedo did not give the predicted
surface t e m p e r a t u r e , as measured b y the
Mariner 6 infrared r a d i o m e t e r experiment.
I t is suggested t h a t the assumption of
h o m o g e n e i t y of' ultraviolet atmospheric
scattering m a y be violated here and m a y
be related to the different appearance of
this region. On a finer scale, differences
between the ultraviolet and infrared observations a~.'e evident.. Most notable is the
Hellas region where the general trends of
the ultraviolet and infrared d a t a agree b u t
where infrared pressures show much larger
fluctuations in the terrain t h a n is seen in
MARINER 6 AND 7 ULTRAVIOLET SPECTROMETER EXPERIMENT
the ultraviolet. Ultraviolet pressures determined from Eq. (5) are listed in Table I. A
total of 337 pressure measurements were
made.
The inability to separate phase function
and optical depth normalizations results
from the small optical depth of the
scattering atmosphere. A small optical
depth causes the attenuation factors
[1 - exp (-rM)]/-rM and exp (-TM) to show
only small variation for the range of air
masses, M, involved. Large values of air
mass were encountered near the bright limb
while the ultraviolet spectrometer was
changing from high gain, used for observing
the Mars upper atmosphere, to low gain,
for observations of the disk reflectance.
Some observations made immediately after
changing gain have larger air mass values
and are consistent with the interpretation
given here. However, the large variation of
M over the instrument field of view near
the bright limb, coupled with the strong
effect of viewing geometry uncertainties,
limits the sensitivity of these measurements
for separation of optical thickness and
phase function normalizations. In the 1971
Mariner 9 ultraviolet spectrometer experiment, observations will be made continuously across the bright limb at 4km
intervals with a resolution of the order of
the lower atmosphere scale height. These
limb data, coupled with observations
nearer the terminator than were obtained
by Mariner 6 and 7, can provide a basis for
separating the 70 and p normalizations.
Lack of separation of 70 and p factors
means t h a t Eq. (5) can be expressed in a
simpler way. Let the attenuation factors
and multiple scattering factor, f, in Eq.
(4) be replaced by average values (f>,
<[1 - exp( 7M)]/7M>, and <exp(-TM)>.
Results of this analysis indicate t h a t
(f> ~ 1.1,
<[1 - exp(-TM)]/TM> ~ 0.9,
and <exp (-TM)> ~ 0.8. If these corrections,
which are of order unity, are assimilated so
that R/(f> --+ R, 7([1 - e x p ( - T M ) ] / T M >
-+ 7, and Ro(exp (--~M)> -+ Ro, then Eq.
(4) can be written
R = (p14)(71t~) + R o t , o~t~~-~.
(7)
This form displays the essential dependence
of 3050A reflectance on atmospheric
269
scattering and ground reflectance. Equation (7) may be combined with the pressure
relation, Eq. (3), giving
Po
P = 70(p/4i J R , - Ro(~ot~)k].
(S)
In this form, the coupling of the 70 and p
normalizations is evident. I f the phase
function is normalized so that p(89 °) = 1,
then 70= 0.068 for Po = 6rob, which is
about twice the scattering expected from a
pure molecular atmosphere. Also note that
the scattering phase function dependence,
p(~), is more nearly isotropic than Rayleigh.
This behavior is expected for particulate
matter at the large scattering angles
observed (see e.g. Deirmendjian, 1969). It
is probable that the particulate scatterer
has a forward peaked phase function so
that p(89 °) is likely to be less than one in
order to satisfy the phase function normalization relation
4~
p ( ; ) d ~ = ~0.
(9)
I f the single scattering albedo, &0, is less
than unity, i.e. if pure absorption occurs,
then p(89 °) may be even smaller. I f p(89 °)
is less than one, then To > 0.068.
Apparent agreement of the ultraviolet
measurements with infrared measurements
suggests the assumption of a homogeneously mixed particulate scatterer is good.
This implies that the particulate scatterers
may have fairly long lifetimes in the
Martian atmosphere and therefore puts a
restriction on particle size (see e.g. Pollack
and Sagan, 1969). Turbulent support may
allow somewhat larger particles to contribute to a uniformly mixed scatterer. The
monotonic increase in ultraviolet refleetance with decreasing wavelength noted
earlier (Barth and Hord, 1971) implies a
small scatterer.
I f these two restrictions are placed on
the particle size, i.e. if the particles must be
large enough to have the observed phase
function dependence but small enough to
be suspended uniformly in the atmosphere,
then the scatterer size may be comparable
to the scattering wavelength, or about
270
CHARLES W. HORD
0.3/~. A n o t h e r possibility t h a t admits to
a n o n u n i f o r m l y mixed scatterer is t h a t
larger particles account for the scattering
and are preferentially stirred up for short
times in the topographically low places on
Mars.
An atmospheric spectral feature observed b y the Mariner infrared spectrometer and identified as a silicate material
(Herr and Pimentel, 1969) m a y be the
nonmolecular scatterer observed in the
ultraviolet. The limb haze observed b y the
Mariner television e x p e r i m e n t does not
appear homogeneous (Leovy et al., 1971)
and is difficult to reconcile with the
ultraviolet d a t a (Cutts, 1971 ).
The concept of measuring surface pressure is based upon measured ultraviolet
intensity being d o m i n a t e d b y scattering
from an optically thin atmosphere against
a small surface background. This possibility has been considered earlier b y E v a n s
(1965), Pollack (1967), and Sagan and
Pollack (1966, 1968).
ALTITUDE ZERO
Although pressure is the more fundamental measurement, relative altitudes
can be inferred from the ultraviolet d a t a if
some assumptions are made a b o u t atmospheric t e m p e r a t u r e structure. Belton and
H u n t e n (1971) and H e r r et al. (1970) have
discussed the use of simple isothermal
models in making pressure-to-altitude
conversions. H e r r et al. chose a single
effective isothermal t e m p e r a t u r e , while
Belton and H u n t e n a d o p t e d an isothermal
model with variable effective t e m p e r a t u r e
in order to b e t t e r represent latitudinal
t e m p e r a t u r e variation. The simpler conversion has been used here with a single
effective isothermal t e m p e r a t u r e of 190°K
corresponding to a 10kin scale height. I f
the true Martian atmosphere is more
nearly adiabatic with a 5 ° K / k m lapse rate
(Belton and H u n t e n , 1971) t h e n an isot h e r m a l average model gives relative
altitudes which are in error b y ~<10% for
the range of pressures encountered.
These authors have selected a value near
the m e a n Mars pressure for their altitude
zero. H e r r et al. (1970) selected 6.0mb for
their altitude zero while Belton and
H u n t e n (1971) selected 5.5mb. I t is suggested t h a t the selection of a normalization
p a r a m e t e r such as this be chosen to convey
physically useful information. The physically useful normalization or choice of zero
altitude on the E a r t h is sea level. B a r t h
(197l) has suggested t h a t a meaningful
normalization on Mars is to choose zero
altitude to occur at the triple pointpressure of water, P 0 = 6.105rob. W i t h
this selection, liquid water is i m m e d i a t e l y
precluded at all altitudes greater t h a n
zero. W a t e r m a y exist at altitudes less t h a n
zero if the t e m p e r a t u r e is greater t h a n 0°C
and equilibrium conditions are reached. I f
Mars pressure is constant over geologic
time, this would provide a unique pressurealtitude conversion reference point.
SUMMARY AND COMPARISON WITH
OTHER MEASUREMENTS
Table I I I shows the subset of Mariner
ultraviolet and infrared s p e c t r o m e t e r d a t a
t h a t were compared. Figures 8, 9, and 10
show the infrared pressures from Table I I I
and the complete set of ultraviolet pressures
d e t e r m i n e d from the comparison in Table I.
Table IV lists the Mariner infrared and
ultraviolet pressure d a t a obtained n o r t h of
Aurorae Sinus. As was the case in Table I I I ,
only the subset of d a t a points which
correspond closely in latitude and longitude
are given. The anomalous region where the
ultraviolet and infrared intereomparison
breaks down, is evident in the left-hand
side of Fig. 10. The p r i m a r y effect of the
solution for five parameters, which minimize the root mean square difference
between nltraviolet and infrared measurements, is the gross shifting of the ultra.violet vertical scale in Figs. 8, 9, and 10. A
residual rms error of 9% is quite small
considering the n u m b e r of components. I f
the sources of error are uneorrelated, it is
correct to infer t h a t errors due to: (l)
relative ultraviolet reflectance, (2) infrared
spectrometer pressures, (3) field of view
differences, (4) assumption of uniform
ground reflectance, and (5) assumption of a
homogeneous scattering atmosphere, all
introduce an error less t h a n 9%.
MARINER 6 AND 7 ULTRAVIOLET SPECTROMETER EXPERIMENT
TABLE
III
MARINER 6, PRESSURE COMPARISON (in rob)
P(UVS)
Lat.
6.23
3.3
Lon.
21.9
P(IRS)
6.23
Lat.
2.7
Lon.
21.9
Difference
0
6.58
2.7
20.6
6.45
2.1
20.7
0.13
6.42
2.4
19.7
5.92
1.7
19.6
0.50
5.71
1.8
18.5
6.50
I.I
18.3
-0.79
5.91
.8
16.0
6.15
0.2
15.9
-0.24
6.17
.4
14.7
6.32
-0.3
14.7
-0.15
6.07
.0
13.5
6.16
-0.7
13.4
-0.09
5.63
-. 4
12.3
5.89
-I. 0
12.2
-0.26
5.97
-. 8
Ii. i
5.82
-i. 4
Ii. 0
O. 15
7.04
-1.4
8.8
5.82
-2.0
8.6
1.22
4.79
-14.3
37.8
4.63
-13.3
38.1
0.16
4.77
-15.0
35.6
4.54
-14.2
35.2
0.23
5.99
-16.5
29.8
5.27
-15.7
30.0
0~72
5.77
-16.8
13.3
5.67
-16.2
13.2
O. i0
5.48
-17.0
11.5
5.46
-16.5
11.4
0.02
5.41
-17.2
9.9
5.46
-16.7
9.7
-0.05
5.45
-17.5
6.6
5.51
-17.0
6.4
-0.06
5.28
-17.6
4.5
5.71
-17.1
4.7
-0.43
5.05
-17.8
1.5
4.96
-17.3
1.6
0.05
5.26
-17.8
359.6
4.95
-17.3
359.7
0.31
4.20
-17.8
355.3
4.66
-17.3
355.2
-0.46
4.44
-17.8
354.0
4.66
-17.3
353.7
-0.22
4.28
-17.6
350.8
4.70
-17.1
350.8
-0.42
4.88
-43.8
41.0
6.26
-47.2
41.4
-1.38
5.04
-44.6
40.1
5.01
-48.3
40.0
0.03
5.55
-47.1
37.2
5.59
-50.6
37.4
-0.04
5.80
-47.9
36.2
6.07
-51.6 "
"36.1
-0.27
6.46
-49.0
34.9
6.43
-52.7
34.8
0.03
6.77
-50.1
33.5
5.50
-53.7
33.4
1.27
6.61
- 51.2
32.1
5.29
-54.7
32.1
i. 32
6,53
-53.3
29.4
5.48
-56.7
29.5
1.05
6.73
-54.3
28.0
5.49
-57.7
28.1
1.24
6.49
-55.3
26.7
6.74
-58.6
26.7
-0.25
6.67
-56.2
25.3
6.38
-59.6
25.3
0.29
7.08
-57.2
23.9
6.72
-60.5
23.9
0.36
4.62
-24.1
349.8
4.91
-26.4
349.7
-0.29
4.61
-26.4
347.4
4.75
-28.3
347.7
-0.14
4.63
-28.4
345.2
4.42
-30.0
345.7
0.21
4.53
-29.0
344.5
4.32
-31.6
343.8
0.21
4.22
-32.7
339.8
4.49
-34.3
340.0
-0.27
4.30
-33.6
338.6
4.16
-35.6
338.1
0.14
4.29
"-35.2
336.0
4.19
-36.7
336.2
0.I0
4.34
-36.3
334.1
4.34
-37.7
334.4
0
4.30
-37.3
332.3
4.05
-38.7
332.5
0.25
-0.I0
4.12
-39.1
328.5
4.22
-40.4
328.7
4.37
-39.8
326.7
4.26
-41.2
326.8
0.II
4.69
-40.6
324.9
4.83
-41.9
324.9
-0.14
7.71
-38.9
308.5
6.57
-40.3
308.6
1.14
7.91
-39.1
306.8
6.55
-40.6
306.8
1.36
7.72
-39.6
303.0
7.59
-41.0
302.8
0.13
7.29
-39.7
301.3
7.I0
-41.1
301.4
0.19
7.28
-39.8
299.2
8.16
-41.2
299.2
-O. 88
-0.39
7.21
-39.8
297.6
7.60
-41.2
297.5
6.91
-39.8
296.0
6.08
-4 i. 2
295.7
O. 83
6.60
-39.7
292.3
6.77
-41.0
292.2
-0.17
-0.28
6.49
-39.5
290.3
6.77
-40.9
290.5
6.39
-39.3
288.8
7. O0
-40.7
288.8
-0.61
5.84
-39.1
287.3
6.59
-40.5
287.1
-0.75
271
272
CHARLES ~V. HORD
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LONGITUDE
Fro. 8• M a r i n e r 6 u l t r a v i o l e t a n d i n f r a r e d s p e c t r o m e t e r pressures, Tile p a t h of t h e c e n t e r of t h e
i n f r a r e d s p e c t r o m e t e r field of v i e w across Mars is i n d i c a t e d b y d a s h e d lines a n d circles d e s i g n a t e
p r e s s u r e m e a s u r e m e n t s . Only t h a t p a r t of t h e i n f r a r e d d a t a w h i c h overlaps w i t h u l t r a v i o l e t m e a s u r e m e n t s is shown. T h e p a t h of t h e c e n t e r of t h e u l t r a v i o l e t s p e c t r o m e t e r fiold of view across Mars is
i n d i c a t e d b y solid lines a n d p r e s s u r e m e a s u r e m e n t s are d e s i g n a t e d b y dots, Tho B a r t h p r e s s u r e
n o r m M i z a t i o n has b e e n u s e d so t h a t zero a l t i t u d e occurs a t t h e triple p o i n t p r e s s u r e o f water.
T a b l e V gives a c o m p a r i s o n of COz
pressures d e t e r m i n e d b y Belton a n d
H u n t e n (1971). T h e i r m e a s u r e m e n t s are
b a s e d u p o n E a r t h - b a s e d m e a s u r e m e n t of
the 1/, b a n d of C02 during t h e 1969
opposition. Figures 11 a n d 12 show the
locations of t h e Belton a n d H u n t e n
m e a s u r e m e n t s a n d the c o m p a r i s o n pressures listed in T a b l e V. The p r o j e c t e d field
of view for these m e a s u r e m e n t s was 8 0 0 k m
square or a b o u t 13 ° of l a t i t u d e or longitude
at the equator• Points in T a b l e V were
g e n e r a t e d b y s i m p l y a v e r a g i n g t h e CO2
pressures in a b o x of 20 ° longitude a n d 20 °
l a t i t u d e centered a t the locations where
Mariner u l t r a v i o l e t m e a s u r e m e n t s were
made. A subset of these averages were
selected which showed the changes in C02
pressure along the u l t r a v i o l e t o b s e r v a t i o n
swaths. More sophisticated weighting
MARINER 6
AND
7 ULTRAVIOLET
SPECTROMETER
m e t h o d s were tried and f o u n d not to
materially improve or worsen the agreement. R e d u c t i o n of box size to l0 ° reduces
the n u m b e r of comparison points significantly and does not show how well the
general features of the two methods agree.
The anomalous region n o r t h of Aurorae
Sinus, n o t e d in comparing the Mariner
infrared and ultraviolet measurements, is
again obvious in the left-hand side of
Fig. l l . General agreement exists in this
region between E a r t h - b a s e d data. of
Belton and H u n t e n and Mariner d a t a of
H e r r et al.
273
EXPERIMENT
Table VI compares altitudes obtained b y
the H a y s t a c k r a d a r facility during the 1967
and 1969 oppositions (Pettengill et al.,
1969; Rogers et al., 1970) with altitudes
inferred from the Mariner ultraviolet
pressure measurements. No scale adjustm e n t has been used so t h a t zero r a d a r
altitude corresponds to the triple point
pressure of water, P 0 = 6 . 1 0 5 m b . The
assumption of an isothermal scale height
of 10km, used to convert the ultraviolet
pressures to altitude, is a d e q u a t e for this
comparison as is seen in Fig. 13. A l0 °
latitude and longitude square centered at
IF-J
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LONGITUDE
FIG. 9. Mariner 7 ultraviolet and infrared spectrometer pressures.
n~
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.....
274
CHARLES
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LONGLTUDE
F r o . 10. M a r i n e r 6 u l t r a v i o l e t a n d i n f r a r e d s p e c t r o m e t e r p r e s s u r e s . T h e a n o m a l o u s c o m p a r i s o n
o c c u r s n o r t h o f A u r o r a e S i n u s in t h e c h a o t i c region.
TABLE IV
MARINER 6, AURORAE SI-*;US REGION
P(UVS)
Lat.
Long.
P(IRS)
Lat.
Long.
4.36
4.89
5.21
5.73
6.18
6.95
8.06
7.93
1.2
--1,9
--2.9
--4.1
--4.9
--5.9
--7.4
--8.3
65.2
59.3
57.4
54.8
53.2
51.0
47.6
45.7
4.59
4.53
4.64
4,96
4.41
4.64
5.08
4.54
1.7
-1.3
--2.5
-3.6
--4.6
--5.6
--7.2
--8.0
65.2
59.6
57.3
55.0
53.0
51.0
47.3
45.6
Diflbrence
--0.23
0.36
0.57
0.77
1.77
2.31
2.98
3,39
W
m
M A R I N E R 6 A N D 7 ULTRAVIOLET SPECTROMETER E X P E R I M E N T
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CHARLES
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M A R I N E R 6 AND 7 ULTRAVIOLET SPECTROMETER EXPERIME~qT
TABLE V
is c a l c u l a t e d w i t h t h e m o d e l (Eq. 4) t o
normalize the Mariner ultraviolet pressures
to t h o s e o f t h e i n f r a r e d s p e c t r o m e t e r , t h e n
EARTH-BASED CO2 PRESSURE
Lat.
Long.
1.2
-1.9
-3.7
-5.6
-7.4
-8.5
12.1
10.8
7.7
5.9
4.0
3.1
1.5
0.1
-0.5
-1.2
-13.5
-15.5
--15.1
--16.5
-17.5
--17.8
65.2
59.3
55.6
51.7
47.6
45.1
36.4
34.6
29.8
26.8
23.2
21.4
17.6
13.9
11.9
9.6
40.3
33.5
22.8
15.6
7.1
354.0
277
P(UVS) P(CO2) Difference
4.36
4.89
5.61
6.34
8.06
7.77
6.30
5.93
6.64
6.05
5.90
6.36
5.88
5.47
6.10
6.57
4.20
4.98
5.94
5.97
5.43
4.44
4.06
3.89
3.56
3.36
3.68
3.80
6.15
6.53
6.70
7.16
6.97
6.57
7.44
6.57
6.41
6.15
4.49
4.44
7.40
7.04
6.70
4.38
0.30
1.00
2.05
2.98
4.38
3.97
0.15
-0.60
0.08
-1.11
-1.07
-0.21
-1.56
1.10
0.31
0.42
-0.29
0.54
--1.46
--1.07
--1.27
0.06
the ultraviolet m e a s u r e m e n t locations was
u s e d to g e n e r a t e r a d a r a l t i t u d e s , i n t h e
s a m e m a n n e r u s e d for t h e c o m p a r i s o n w i t h
E a r t h - b a s e d CO2 p r e s s u r e s . I t is n o t a b l e
t h a t a s y s t e m a t i c difference i n t h e t w o sets
of m e a s u r e m e n t s exists in the region
e x t e n d i n g f r o m C h r y s e to t h e w e s t edge o f
Meridiani Sinus. A systematic decrease in
a l t i t u d e f r o m w e s t t o e a s t across t h i s
r e g i o n is n o t a p p a r e n t i n t h e u l t r a v i o l e t
m e a s u r e m e n t s , or i n e i t h e r of t h e COs
pressure determinations.
T h e m e a n p r e s s u r e b a s e d u p o n t h e 337
u l t r a v i o l e t m e a s u r e m e n t s is 5 . 8 m b . A
m e a n v a l u e of 5 . 3 m b for t h e C02 p r e s s u r e
w a s f o u n d b y H e r r et al., f r o m t h e M a r i n e r
6 and 7 infrared spectrometer data. A
difference i n m e a n p r e s s u r e exists b e c a u s e
o b s e r v a t i o n a l s w a t h s of t h e t w o M a r i n e r
i n s t r u m e n t s were o n l y p a r t i a l l y o v e r l a p ping, even though the ultraviolet measurem e n t s were n o r m a l i z e d t o t h e i n f r a r e d
spectrometer data. Belton and Hunten
r e p o r t a m e a n p r e s s u r e o f 5.5 m b f r o m t h e i r
E a r t h - b a s e d C02 m e a s u r e m e n t s .
I f t h e M a r s g e o m e t r i c a l b e d o a t 3050 A
A - p(180°) [1 - Es(27)] ÷ 2RoE2k+e(27),
8
(10)
w h e r e p ( 1 8 0 °) is t h e p h a s e f u n c t i o n of 180 °
a n d E3 a n d E2k+2 are e x p o n e n t i a l i n t e g r a l s .
The largest phase angle observed by
M a r i n e r u l t r a v i o l e t s p e c t r o m e t e r was 134 °
so t h a t p ( 1 8 0 °) is u n k n o w n . I f p ( 1 8 0 °) ~ 1
a n d n o m i n a l v a l u e s of R 0 = 0.015, ]c ~ 1,
a n d • = 0.066 ( c o r r e s p o n d i n g t o t h e a v e r a g e
u l t r a v i o l e t p r e s s u r e of 5 . S m b ) are s u b s t i t u t e d i n t o E q . (10), t h e n A = 0.035. I n t h i s
m o d e l , a t m o s p h e r i c s c a t t e r i n g , w h i c h is
a c c o u n t e d for b y t h e first t e r m i n E q . (10),
c o n t r i b u t e s 0.026 w i t h t h e r e m a i n d e r d u e
t o g r o u n d r e f l e c t a n c e . T h e Caldwcll (1970)
a n a l y s i s of t h e 0 A O u l t r a v i o l e t s p e c t r u m
of Mars a t t r i b u t e s a sizeable p o r t i o n of t h e
Mars a l b e d o t o a t m o s p h e r i c s c a t t e r i n g
with the surface albedo c o n t r i b u t i o n equal
to 0.7 a t 3 2 1 5 • a n d 0.5 a t 2 8 0 0 ~ . A n a l y s i s
of E a r t h - b a s e d p o l a r i z a t i o n m e a s u r e m e n t s
b y I n g e r s o l l (1971) also i n d i c a t e s a large
atmospheric c o n t r i b u t i o n with surface
TABLE VI
EARTH-BASED RADAR
Lat.
Long.
Alt.
(UVS)
1.2
-0.2
-2.4
12.6
11.3
10.1
8.0
7.0
6.2
4.9
3.8
2.4
1.5
1.0
0.0
-0.7
-0.9
1.5
65.2
62.5
58.3
37.0
35.2
33.5
30.3
28.8
27.3
25.0
22.7
19.7
17.6
16.4
13.5
11.5
10.7
8.4
3.36
2.21
1.86
-0.94
-0.09
-0.27
-0.63
0.16
0.21
0.13
0.08
-0.51
0.38
0.37
0.06
-0.51
-0.38
-1.38
Alt.
(Radar) Difference
2.43
2.20
1.98
3.31
2.07
1.68
1.92
1.46
1.02
0.85
0.59
-0.30
-0.68
--1.15
0.76
--0.61
--1.24
--1.2I
0.93
0.01
-0.12
-4.25
2.16
-I.95
-2.55
--1.62
-0.81
-0.72
-0.51
--0.21
1.06
1.52
0.82
0.10
0.86
0.17
27S
CHARLES
W. HORD
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MARINER 6 AND 7 ULTRAVIOLET SPECTROMETER E X P E R I M E N T
a l b e d o c o n t r i b u t i n g o n l y 0.6 o f t h e t o t a l
p l a n e t a r y a l b e d o a t 3 2 0 0 A . I t will b e
i n t e r e s t i n g t o see i f t h i s m o d e l , w h i c h
indicates that Mars has a very small
g r o u n d r e f l e c t a n c e n e a r 3000 A as w e l l as a
r e l a t i v e l y l a r g e a t m o s p h e r i c s i g n a l , is
confirmed by the Mariner 9 Mars orbiter.
ACKNOWLEDGMENTS
I wish to thank Dr. C. A. Barth for his
vahmble criticism of this work and, of course,
his ultraviolet spectrometer data which makes
this analysis possible. I wotfld also like to thank
Drs. Herr, Pimentel, Horn, Bclton, and Htmten
for the early availability of their data and
valuable discussions. Karen Simmons and Lois
ParmMec made valuable contributions in the
preparation of the data.
This work was supported by NASA grant
NGR-06-003-127.
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