- Email: [email protected]
Earth global mosaic observations with NIMS-Galileo
Plunet. Spate Sci.. Vol. 41. No. 7. pp. 551-561. 1993 Printed in Great Britain.
00324633/9? $6.00 +O.OO t’ 1993 Pergamon Press Ltd
Earth global mosaic observations with NIMS-Galileo P. Drossart,’ J. Rosenqvist,’ Th. Encrenaz,’ E. Lellouch,’ R. W. Carlson,’ K. H. Baines,’ P. R. Weissman,’ W. D. Smythe,’ L. W. Kamp,’ F. W. Taylor,3 A. D. Collard,’ S. B. Calcutt’ and R. Thompson’ ’ DESPA (CNRS-URA264). Observatoire de Paris. F-92195 Mcudon. France ‘Jet Proptrlsion Laboratory. Pasadena. CA 91109. U.S.A. ‘Clarcndon Laboratory, Oxford University, Parks Road. Oxford OXI 3PU. U.K. ‘Laboratory for Planetary Studies. Cornell University, Ithaca, NY 14853. U.S.A.
Abstract. During the Earth-l Galileo flyby (December 1990). the Near-Infrared Mapping Spectrometer (NIMS) experiment investigated the illuminated side of the Earth in the spectral range 0.7-5.2 pm. Mosaics of the entire terrestrial globe were recorded with a spatial resolution ranging from 100 to 500 km. From these spectra. information is retrieved upon the largescale temperature structure in the stratosphere and in the mesosphere (O-70 km altitude range) from the inversion of the CO, bands at 4.3 and 4.8 pm. These data also permit monitoring of the cloud temperatures. and derivation of the abundances of several minor atmospheric constituents (HzO. CO. NzO. CH, and 0,). These observations constitute a continuation of the study of the atmospheres of the three planets (i.e. Venus, the Earth and Jupiter) targeted by the Galileo spacecraft during its mission. Observing these atmospheres with the NIMS instrument in the near-infrared will provide a unique data set, useful for comparative planetary studies.
Introduction The Earth- I Grrlilc~) flyby. in December 1990. provided a ncv+ opportunity to investigate the atmospheric composition and structure of the Earth on a large scale from infrared imaging spectroscopy. using the NIMS exper-
below I pm and 0.026 pm above. NIMS is a “pushbroom” imager. with one dimension of spatial scanning, yielding a linear image 20 pixels (IO mrad) in height : the orthogonal dimension is scanned through spacecraft scan-platform motion. generating swathes that are mosaiced to form larger images. The IFOV is 0.5 mrad.
The observations Figure I shows the geometry of the Gdiko Earth-l encounter. Closest approach occurred on 8 December 1990 at 20:35 U.T.C. at an altitude of 954 km. NIMS data were recorded at the time of closest approach (limb scans) and in the following hours (mapping of Australia and Antarctica, and global mosaics). Figure 2 shows one of the I? global mosaics’ observing sequence. The global Earth mosaics were recorded in order to monitor the large-scale structure and composition of the terrestrial atmosphere. In what follows. we concentrate on a preliminary analysis of the global mosaics, because an understanding of the atmospheric effects (clouds and gaseous absorptions) has to be achieved before attempting the interpretation of the surface variability which can be observed on the Australian and Antarctic maps.
Description of the NIMS atmospheric spectra
imc‘nt. The NIMS instrument is a grating spectrometer (Carlson (21t/l.. 1991). consisting of a 23 cm telescope. a diffraction grating spectrometer and I7 radiatively cooled photodiode detectors. This combination of detectors (7 Si, 15 InSbr and grating positions (24) covers the spectral range
from
0.7 to 5.2 [lrn. with a spectral
~‘o,~,.c~\/~(J/~~/~~,~~~~, to : P. Drossart
resolution
of 0.013 ,nm
An example of a NIMS spectrum is shown in Fig. 3. It is characterized by a reflected sunlight component. which dominates below 3 pm. and a thermal emission increasing above 3 pm. Because the dynamics of the detectors have been optimized for Jupiter observations. many spectra are saturated in the short-wavelength part of the spectrum; the limit at which saturation occurs in the reflected sunlight component corresponds to an albedo of about 0.05. Below 3 pm. the solar reflected component can be used
P. Drossart it nl. : Earth plobal mosaic observations
with NIMS-~Gcdileo
Galileo - Earth encounter
Limb studies
Lunar phase studies (NIMS, PPR)
Galileo
to determine the column dcnsitv ofwater vapour and CO,. v,,hich exhibit se\,eral absorpt;on hands in this spectral range. However. scattering cfrects at-estrong. especially in the prcsencc of clouds. To check I‘or the cio~d opacit) \\ilhin the NIMS obser\~~ttions. the albcdo ari:itions in the I .c) /rm CO band arc‘ uwi : ;lt thi< \+avciength. the HIO absorption is IOU. and the cfl.ect ol‘a cln~~d (incrc;lsc in the albedo and decrcahe in the column density of CO,. o\ving to a reflection at higher altitude) is to enhance the refectance. in principle. the cOiunin densit!, ofCO> could be used as an estimate of‘ the cl~~u&tc\p altitude. but the saturation of the continuum nc‘:~r the CO> absorption prccludcs this determination in most NIMS spectra. The continuum at 0.7 /ml i\ u\u;111! wturatcrt in the NIMS spectra. and cannot bc u\cd I’c)I. tht\ purpohc. in the thermal emission rcglon. the c~nttnuum level at _S jm giws a niciisurcnicnt 01‘ the temperature 01‘ ltic surface. or the temperature of the : = I le\ci of an>, o\crlying clouds. The thermal spectrum 15 dominated by the absorption due to the strong I’: hand of C‘O:. A weaker CO, band at 3.85 j(rn. as dell 25 9gnatures of(‘O and 0, betkveen 4.6 and 4.75 Itm. t\+o N ,(I bands at 3.9 and 4.55 Inn. CH, around 3.5 /em. and wwral \\eak H:O spcctral fi-atures arc also present. ah shown in Fig. 3. Hecause. ;I\ mentioned above. CO, ia constant and uniformly mixed in the atmosphere. the CO, absorption< can be inwrted to
rctriwc ;I possible thermal vertical atmospheric structure :rbo\~ the surface or the cloud. Once the thermal profile is known, information can be retrieved about the abundances of the other minor species. Ali these species (CO. M’ater vapour. N 4). (‘H, and 0:) are expected to be nonuniforml\~ m~wd \\ith altitude. it is not possible to retrieve their \cr;ic;II distl-ibution from the NIMS data. because the solution \\ould not be unique. In order to derive their abundances. \Jc haw thus assumed. for each molecule. a nominal rclativc vertical distribution. taken from Houghton (‘I (I/. (IW6). and WC have determined their mixing ratio> at the surli~cc 2s ;I free multiplicative parameter. F-or ;I first-order modclling of the NIMS spectrum. we h;l\c used a simple radiative transfer program developed for the analysis 01‘ the atmospheres of Mars and Venus (C‘ombcs 1’1r/l.. I99 I : Rosenqvist P/ t/l.. 1992 ; Carison cf (I/.. 1901 ). it is ;I semi-empirical band model taken from Wallace PI ul. ( 1974) which takes into account the gaseous absorptions by H :O. C02. CO, CH,. N20 and 03, the \,lewing geonictr!. and does not include any scattering elrect. The cmi\slvit! ofthc surface is derived from Fiobert (I 98X) and the atmosphere is vertically divided into 25 layers of3 km. In ;I first approximation. the surface albedo is supposed to be constant between I and 5 jlrn; this assumption has no Incidence upon the retrieval of the thermal profile and the vertical density distributions. The
POlN?EA C3.1 pacldy:lll2/1990 N.ElWNGMOS_-10
13:48:49
NIMS
iSDF:kcif-vetl-ud CENTRAL BODY:EARTH
1MINI:m.elwngmOs-10 EPHE~~plf/epNEARTH-O7059O.t PERIAPSIS:90-342120:35:31.21 THDREEE SO-342120:34:11.000
*CDS 1036:OO:O
AC~V~~~~WNGM~S_-lO
a~nlight ( 1.9pm. Fig. la) and in the thermal emission (4.6 jrm. f-is. Ah). .A comparison has been made between a NIMS mos~~ic (GMOSI6A). centrcd on the Pacific Ocean. and cl”~~sl-simultaneous SSI images (El WC)61 7 anti IX IWO6l XI (Fig. 4c), which show a very good corrd~ttion. This tmpiics that the al&do does not show strong \;triations hctwcun the visible and the nc~r-infrared range. ,As a consoq~xncc. the NIMS mosaic at 1.9 pm (Fig. 4a) C:III 1~ uuxi to give a good representation of the cloud sIrucIurc. the clo~ld patterns being associated with high \:~IIIc\ of the albedo. On the other hand, comparison of
554
P. Drossart et nl. : Earth global mosaic observations
with ~IMS-G~~/~~~,~~
Wovelength (pn)
Fig. 3. Example of a NIMS spectrum. Absorptions
Fig. 3a and b shows a clear anticorrelation : regions of high al&do are associated with regions of low temperature. Nevertheless, it must be noticed that there is no simple quantitative relationship between the cloud albedo and the upper cloud temperature. First, due to the instrumental saturation outside the HZ0 band at short wavelengths, albedo contrasts in Fi?. 4a are plotted within an H,O band, and can therefore be partly affected by l-t,0 cariations. Moreover. clouds of similar albedos have diKerent temperature in the NIMS data (okvinp to a different altitude of the upper cloud layer). The thermal radiation at 4.6 /lrn comes from either the surface or from the overlapping cloud. the cloud being colder than the surface. The NlMS global mos;rics in the thermal range thus provide cloud temperature information.
As mentioned above. the inversion of the two CO? bands at 4.3 and 4.X jrrn allows the deternljn~lti~~rl oi’~ltmo~pheri~ temperature profiles in the stratosphere and the mesosphere. in particular the outgoing radiation in the Y, CO, band at 4.3 /ml iomes From altitudes ranging from about 5 to 70 km. A global mosaic at 4.3 /ml thus provides a direct mapping of the mesosphcric temperatures. In fact, these altitudes being higher than the clouds. no perturbation by cloud opacity is present at this wavelength, and no cloud is visible at this ivavelength. This etrect is illustrated in Fig. 5. which clearly shows an enhancement of the stratospheric temperatures 111the southern polar regions. Figure 6 shows three examples of NIMS spectra recorded respectively at mid-latitudes (30 S), high latitudes (50 S) and at the South Pole. The corresponding thermal profiles (Fig. 7) exhibit a thermal enhancement
by atmospheric gases are indicated
at the South Pole in the stratosphere, of the order of 30+ 15K at an altitude of 20 km. in agreement with previous observations of the stratospheric thermal structure near summer solstice (Houghton et ul., 1986).
An intriguing “hotspot” anomalous feature is apparent near the western coast of South America in the vicinity of northern Chile (Fig. 8). When compared with a spectrum of the open ocean (Fig. 9). this feature appears as an enhancement ofintensity mainly in thecontinuum thermal emission beyond 3 /ml and, at a lower level, within the gaseous H-0 and CO2 absorption. This feature covers many NIMS pixels (approximately 8 pixels E-W by 15 pixels No-S in El WNCJMOS-IOA) and, from examination of several global mosaics. is found to be fixed to the rotating Earth. By checking the position of the clouds, in comparison with 1.r) itrn images. it can be shown that only the eastern part of South America. eastward of the hotspot. is cloudy. The illt~rpret~ltion of the spectra given in Fig. 8b shows that the ~~~ntinL]uIn enhancement can only be modelled by a temperature increase of the surface by about 20K compared with the ocean temperature, Therefore, the most plausible interpretation of this hotspot is the summer heating over the Chilean Andes, which are viewed in summer. close to noon. The high altitude of these mountains is also responsible for the enhancement within the shoulder of the CO: bands, owing to a lower gaseous column density over the high-altitude regions. Comparison with the temperature observed in spectra recorded in the cloud-free area northward of the hotspot show that the temperatures are intermediate between the ocean and hotspot temperatures.
P. Drossltrt
cl trl. : Earth global mosaic observations
with NIMS-Grrlileo
Fig. 4. NIMS global mosaic EIWNGMOS16 (a) at I.9 kern (b) at 4.6 {lrn. (c) Two SSI images (ElWO617 and El WO618) taken nearly simultaneously are shown to allow comparison with (a)
P. Drossart
Fig. 5. NIMS globai mosaic
El WNGMOSIO-a
ef ui. : Earth global mosaic observations
with NIMS-Grr&o
at 4.35 /ml
Fig. 8. (a) NIMS global mosaic Ei WNGMOSIO-c at 4.55 iirn: (b) synthetic spectra (I) for a surfxc temperature T,. (2) for a surface tcmpcraturc T,+?OK. (3) for ;I surface located at 4 km altitude, with temperature T,+20K: (c) NIMS observed spectra \vithin (upper curve) and oursidc (lower curve) the bright spot of the image (a). The difference between both spectra IS hcst modcllcd by the spectra ( 1) and (3) of Fig. 8b (Cnr7rb7ucd on p. 558) Fig. IO. NIMS global mosaic EIWNGMOSIO-c to the West of the bright spot (2). still visible at
at 3.3 )rm. The specular the same position
reflection
as in Fig.
Xa
point (I) is seen
P. Drossart
et al. : Earth global mosaic observations
with NIMS-Galileo
Wavelength
(pm)
Fig. 6. Example of NIMS spectra in the 4.3 pm band of CO2 : mid-latitude South-latitude at 50”s (2 : dashed line) and South Pole (3 : solid line)
(1 : dashed-dot
line), high
3
240
260
Temperature Fig. 7. Thermal profiles retrieved visible at the South Pole
from the three spectra
Another spot is visible near the centre of the disc in Fig. IO. It corresponds exactly to the specular reflection point, for which the solar incidence and reflection angles are equal. As expected. this spot is not seen in the thermal emission (in Fig. 8). since this phenomenon is due to the reflection of the sunlight from the ocean. The specular point is seen in several images of the sequence of global mosaics, except when its position is covered by a cloud,
(K) shown in Fig. 6. A thermal
enhancement
is
or is over the land, in agreement with the expected iour of the specular reflection point.
Abundance
of atmospheric
behav-
compounds
As mentioned above, the reflected sunlight component is difficult to use for retrieving abundances because of the
P. Drossart ef a/. : Earth global mosaic observations
558
(61
::
I,,,,
N3
,
3.5
*
of scattering
effects.
in particular
when
clouds
are present. A better analysis can be pcrf-ormed in the thermal part of the spectrum 3 S {cm) \%%crc the \oliir component is very small or negligible. and whore scatterinf effects are less important.
,
4.5
Wavelength
importance
I,,
4
,
,
(
,
f
with
(
NIMS-Gnlilt~
-.I
5
(pm)
Examples of‘ fits areshown in Figs c)and I 1. As indicated above. the CO2 vertical distribution is known to be constant, with a mixing ratio of 350 ppm. Thus. the CO? band at 4.3 Llrn is used to derive the T(z) profile. The other minor species are known to have nonuniform vertical
P. Drossart
cf (11.: Earth global mosaic observations
with NIMS-Galileo
559
Lot=1 1.6N/Long=132.2W
H20
A \‘I
co2
Tp=270K/z=4km
I
r
J,I
‘1
03
I’
\
,“\\
CO
0
3
3.5
4
’
1
I’
4.5
Wavelength
5
(/XII)
Fig. 9. Example of best tits obtained for a NIMS spectrum above the Pacific at the indicated position. The multiplicative factors of the nominal vertical distributions (see Table I) arc. rcspectivcly. 0.3. 0.1. 17.4 and 0.9 for H ?O. CO. 0,. CH, and N,O
We have used nominal relative distributions for these species (Table I and Fig. 12) taken from Houghton (~1rrl. (1986) and we have estimated their abundances by multiplying these relative vertical distributions by a
distributions.
unique free parameter. Figure I I. corresponding to a 100 x 100 km’ area of Pacific Ocean. shows the best global fit of the thermal spectrum. In Fig. I I. an observed spectrum in the region 4.74.8 pm. located in Texas. is com-
L
.- - /-A I
,
4.2
4.3
4.4
,
,
4.5
Wavelength
,
4.6
I
,
4.7
(JUTI)
Fig. I I. NIMS spectrum of the North American arca located at (Lat. = 35.X N. Long. = 94.4 W) in the 4.1 4.X /m spectral region. The N,O mixing ratio with the altitude is half the nominal vertical distributton. Full lint: observed spectrum. Dashed line: no CO and 0,. Dasheddotted lint: best fit. The mulripllcati\c factors of the nominal vertical distributions (see Table I) are. rcspectivcly. I and IO I.o,r CO and 0 i
560
P. Drossart
Table 1. Nominal Altitude
(km)
vertical distributions
of several atmospheric
CO, (ppm)
H20 (ppm)
350 350 350 350 350 350 350 350 350 350
3000.0 1000.0 2.0 2.0 3.0 2.0 3.0 2.0 7.0 0.7
0 IO 30 30 40 50 60 70 X0 90
constituents
range
Lat. < 35 25 < Lat. -$ 60 Lat. > 60
Number
of spectra
CO
0;
II 5 4
I.5 1.6 I.5
3.0 3.1 5.3
0, (PPm)
CH, @pm)
N 4 (ppm)
0.1
0.05 0.05 0.1 7.0 7.0 3.0 0.4 0.1 0.05 0.0
1.3
0.6 0.2 0.1 0.1 0.05 0.01 0.0 0.0 0.0 0.0
CH, N,O 2.0 2.0 1.6
with fits with and without CO and 0,. For this typical spectrum, the mixing ratio of CH,. CO, O3 and N,O as a function of altitude is represented by a multiplicative factor of the nominal distribution. indicated in brackets in Fig. 12. A preliminary step was to select 20 spectra over all the visible Earth hemisphere. This set of spectra was chosen to be a good representation of the latitudinal and longitudinal range of the available hemisphere. The preliminary aim of this study is to measure the abundance of each
2
I.2 I.2 1.0 0.7 0.4 0.1 0.1 0.1 0.1
constituent as a function of latitude. Table 2 shows the results in terms of multiplicative factor of the nominal vertical distributions. The accuracy of the measurement is estimated to be within a factor of 2. Thus, the signal-tonoise ratio is not high enough to conclude firmly on any latitudinal variation. However, if we take into account only the best-fit values of the spectra, several remarks can be drawn. There is possible evidence for a positive gradient of the ozone abundance from the equator to the South Pole. This result is consistent with previous obsrvations from different experiments such as BUV;Nirrzhus 4 (Hilsenrath ef al.. 1981) or SBUVl’Ninrhrrs 7 (Bhartia et al.. 1984). The relatively low signal-to-noise ratios of the spectra do not provide information on the CO variations observed by Reichle ct al. (1982) from the Space Shuttle. Finally, a slight decrease of the CH, and N20 abundances from the equator and tropical latitudes to the southern latitudes is marginally observed. Both results are consistent with the data from the SAMS experiment aboard the Nittzhus 7 satellite (Jones. 1984; Holton and Choi. 1988).
pared
0
on Earth
0.1 0.05 0.03 0.05 0.08 0.1 0.8 2.0 10.0
3.5 2.4 I.5
with NIMS-Galileo
CO @pm)
Table 2. Qualitative latitudinal variation of several atmospheric constituents from the NIMS experiment. The value indicated below is the multiplicative factor of the nominal dtstributions shown in Table I. The uncertainty is a factor of 2 Latitudinal
et al. : Earth global mosaic observations
4
6
8
10
Mixing ratio Fig. 12. Nominal vertical distributions of CO, N20. CH, and 0,. The numbers in the brackets indicate the multiplicutivc factors of the nominal vertical distributions derived from the best fit of the spectrum presented in FIN. I I
P. Drossart er al. : Earth global mosaic observations with NlMS-Gff~j~~~~) Conclusions
The preliminary analysis of the Earth-I NIMS global mosaics gives us a first idea of the information which can be retrieved from this imagirlg spectroscopy in the nearinfrared range for the analysis of the terrestrial atmosphere. The main interest in the near-infrared part of the NIMS data (reflected solar component. below 3 pm) has been to derive a mapping of the cloud structure. This information complements that provided by the visible images. Surface temperature variations have been observed as a large-scale hotspot localized over the South American Andes, with a temperature enhancement about 20K larger than the low-altitude surface temperatures. Another remarkable feature is the specular reflection point over the ocean which is observed in a sequence of observations over the Pacific Ocean. From the continuum temperature at 5 pm, a thermal map of the clouds can be retrieved. The CO1 absorption bands permit the retrieval of the thermal profile in the stratosphere and the mesosphere, and a monitoring of the mesospheric temperatures can be achieved by the use of the NIMS mosaic at 4.3 [irn. These measurements may be of high interest for the Earth observations (Chahine, 1991). Finally, information can be derived about the abundances of water vapour. CO. CH,, N,O and O?. Latitudinal variations of the ozone abundance have been observed by comparing a few clear areas chosen at different latitudes. in agreement with current 0; observations. These studies have been pursued since the Galileo Earth2 encounter in December 1992, with a different observing geometry. The observations of the Earth by NIMS are a continuation ofthe studies of planetary atmospheres in the near-infrared by imaging spectrometer. after the studies of the tenuous Martian atmosphere with the instrument ISM on the Pl?~)b~).sspacecraft (Bibring Et ~1.. 1989) and of the Venusian atmosphere (Carlson cf a/.. 1991). In the future, Jupiter will be studied by NIMS during the Galileo mission after 1995. Then. Saturn and Titan will also be observed by the imaging spectrometer VIMS onboard the Cassini spacecraft. Observations of the Earth with NIMS will therefore provide a framework for future interpretations of less well-known atmospheres.
References Bhartia, P. I<., Klenk. K. F., Wong, C. K. and Gordon, D., llltcrco~lparls(~n of the ,%‘whzr.s7 SBUV’TOMS total ozone
data xts with Dobson and MY.7results. f. +W@JX Rcs. 89, T’19 _ -- 5247. I%4
561
Bibring, J.-P., Combes, M., Langevin, Y., So&Rot, A., Cara, C., Drossart, P.. Encrenaz, Th., Erard, S., Forni, O., Gondet, B., Ksanfomality, L., Lellouch, E., Masson, P., Moroz, V., Rocard, F., Rosenqvist, J. and Sotin, C., Results from ISM experiment. Nuture, Lnnd. 341, 591-593. 1989. Carlson, R. W., Baines, K. H., Encrenaz, Th., Taylor, F. W., Drossart, P., Kamp, L. W., Pollack, J. B., Lellouch, E., Collard, A. D., Calcutt, S. B., Grinspoon, D., Weissman. P. R., Smythe, W. D., Ocampo, A. C.. Danielson, G. E., Fanale, F. P., Johnson, T. V., Kieffer. H. H., Matson, D. L., McCord, T. B. and Soderblom, L. A., Galileo Infrared Imaging Spectroscopy Measurements at Venus. .%ic,ncP 253, 1541.. 1.548. 1991. Carlson, R. W., Weismann, P. R., Smythe, W. D. and Mahoney, J. C., Near infrared Mapping Spectrometer experiment on Guliiw. Spuci~ Sri. Rrr. 60, 457. 1992. Chahine, M. T., The hydroio_pical cycle and its influence on climate. Nature. Land. 359, 373-380. 1992. Combes, M., Cara, C., Drossart. P.. Encrenaz, Th., Lellouch. E., Rosenqvist, J., Bibring, J.-P., Erard, S., Gondet, B.. Langevin, Y., Soufflot, A., Moroz, V. I., Grygoriev, A. V., Ksanfomality, L. V., Nikolsky, Yu. V., Sanko, N. F., Titov, D. V., Forni, O., Masson, P. and Sotin, C., Martian atmosphere studies from the iSM experiment. Phet. Spwc Sci. 39, 189-197. 1991. Flobert, J. F., TlrC;.ss &I I’l~rkwsitC Pm% VI, 76. 1988. Hilsenrath, E. and Schlesinger, B. M., Total ozone seasonal and interannual variations derived from the 7 year Nimbus-4 BUV data set. J. ~rop/?~~. Rm. 86, t2,087-12.096. 1981. Holton, J. R. and Woo-Kap Choi, Transport circulation deduced from SAMS trace species data. J. rtfn~~ Sci. 45, 1929-1939,
1988. Houghton, J. T., Taylor, F. W. and Rodger, C. D., Rrnzotr Sounding of A ttnosphwes. Cambridge Planetary Science
Series (edited by W. I. Axford. R. Greelcy and G. Hunt). Cambridge University Press. Cambridge. 1986. Husson, Iv., Chedin. A., Scott, N. A., Bailly, D., Gtaner, C., Lacome, N.. Lbvy, A., Rossetti, C.. Tarrago, G.. Camy-Peyret, C., Flaud, J. M., Bauer, .4., Colmont, J. M., Monnanteuil, N., Hilico, J. C.. Pierre, G., Loete, M., Champion, J. P., Rothman, L. S., Brown, L. R.. Orton. C., Varanasi, P., Rinsland, C. P., Smith, M. A. H. and Goldman, A., The GEISA spectroscopic line parameters data bank in 1984. Ann. Grr~p/~~.s.4, 1855 190. 1986. Jones, R. L., Satellite measurements of atmospheric composition: three years observations of CH, and N,O. A&. S/xiw Rvs. 4, I:! I--l 30. 1984. Reichle, H. G. Jr. Beck, S. M., Haynes, R. E.. Hesketh, W. D., Holland, J. A., Hypes. W. D., Orr, H. D. III. Sherrill, R. T., Wallio, H. A., Casas, J. C.. Saylor, M. S. and Gormsen, B. B., Scicvw 218, 1024. 1076. 1981. Rosenqvist, J., Drossart, P., Combes, M., Encrenaz, Th., Lellourh, E., Bibring, J.-P., Erard, S., Langevin, Y. and Chassefi&e. E., Minor constituents in the Martian atmosphere from the ISM. Plrohm cxpcrimcnt. /(.ff~ci.s98. 2i4-270, 1992. L., Prather, M. and Belton, M. J. S., The thermal of .lupitcr. ilstroplzy.~. J. 193, 481-493. 1974.
Wallace,
structure of the atmosphere
00324633/9? $6.00 +O.OO t’ 1993 Pergamon Press Ltd
Earth global mosaic observations with NIMS-Galileo P. Drossart,’ J. Rosenqvist,’ Th. Encrenaz,’ E. Lellouch,’ R. W. Carlson,’ K. H. Baines,’ P. R. Weissman,’ W. D. Smythe,’ L. W. Kamp,’ F. W. Taylor,3 A. D. Collard,’ S. B. Calcutt’ and R. Thompson’ ’ DESPA (CNRS-URA264). Observatoire de Paris. F-92195 Mcudon. France ‘Jet Proptrlsion Laboratory. Pasadena. CA 91109. U.S.A. ‘Clarcndon Laboratory, Oxford University, Parks Road. Oxford OXI 3PU. U.K. ‘Laboratory for Planetary Studies. Cornell University, Ithaca, NY 14853. U.S.A.
Abstract. During the Earth-l Galileo flyby (December 1990). the Near-Infrared Mapping Spectrometer (NIMS) experiment investigated the illuminated side of the Earth in the spectral range 0.7-5.2 pm. Mosaics of the entire terrestrial globe were recorded with a spatial resolution ranging from 100 to 500 km. From these spectra. information is retrieved upon the largescale temperature structure in the stratosphere and in the mesosphere (O-70 km altitude range) from the inversion of the CO, bands at 4.3 and 4.8 pm. These data also permit monitoring of the cloud temperatures. and derivation of the abundances of several minor atmospheric constituents (HzO. CO. NzO. CH, and 0,). These observations constitute a continuation of the study of the atmospheres of the three planets (i.e. Venus, the Earth and Jupiter) targeted by the Galileo spacecraft during its mission. Observing these atmospheres with the NIMS instrument in the near-infrared will provide a unique data set, useful for comparative planetary studies.
Introduction The Earth- I Grrlilc~) flyby. in December 1990. provided a ncv+ opportunity to investigate the atmospheric composition and structure of the Earth on a large scale from infrared imaging spectroscopy. using the NIMS exper-
below I pm and 0.026 pm above. NIMS is a “pushbroom” imager. with one dimension of spatial scanning, yielding a linear image 20 pixels (IO mrad) in height : the orthogonal dimension is scanned through spacecraft scan-platform motion. generating swathes that are mosaiced to form larger images. The IFOV is 0.5 mrad.
The observations Figure I shows the geometry of the Gdiko Earth-l encounter. Closest approach occurred on 8 December 1990 at 20:35 U.T.C. at an altitude of 954 km. NIMS data were recorded at the time of closest approach (limb scans) and in the following hours (mapping of Australia and Antarctica, and global mosaics). Figure 2 shows one of the I? global mosaics’ observing sequence. The global Earth mosaics were recorded in order to monitor the large-scale structure and composition of the terrestrial atmosphere. In what follows. we concentrate on a preliminary analysis of the global mosaics, because an understanding of the atmospheric effects (clouds and gaseous absorptions) has to be achieved before attempting the interpretation of the surface variability which can be observed on the Australian and Antarctic maps.
Description of the NIMS atmospheric spectra
imc‘nt. The NIMS instrument is a grating spectrometer (Carlson (21t/l.. 1991). consisting of a 23 cm telescope. a diffraction grating spectrometer and I7 radiatively cooled photodiode detectors. This combination of detectors (7 Si, 15 InSbr and grating positions (24) covers the spectral range
from
0.7 to 5.2 [lrn. with a spectral
~‘o,~,.c~\/~(J/~~/~~,~~~~, to : P. Drossart
resolution
of 0.013 ,nm
An example of a NIMS spectrum is shown in Fig. 3. It is characterized by a reflected sunlight component. which dominates below 3 pm. and a thermal emission increasing above 3 pm. Because the dynamics of the detectors have been optimized for Jupiter observations. many spectra are saturated in the short-wavelength part of the spectrum; the limit at which saturation occurs in the reflected sunlight component corresponds to an albedo of about 0.05. Below 3 pm. the solar reflected component can be used
P. Drossart it nl. : Earth plobal mosaic observations
with NIMS-~Gcdileo
Galileo - Earth encounter
Limb studies
Lunar phase studies (NIMS, PPR)
Galileo
to determine the column dcnsitv ofwater vapour and CO,. v,,hich exhibit se\,eral absorpt;on hands in this spectral range. However. scattering cfrects at-estrong. especially in the prcsencc of clouds. To check I‘or the cio~d opacit) \\ilhin the NIMS obser\~~ttions. the albcdo ari:itions in the I .c) /rm CO band arc‘ uwi : ;lt thi< \+avciength. the HIO absorption is IOU. and the cfl.ect ol‘a cln~~d (incrc;lsc in the albedo and decrcahe in the column density of CO,. o\ving to a reflection at higher altitude) is to enhance the refectance. in principle. the cOiunin densit!, ofCO> could be used as an estimate of‘ the cl~~u&tc\p altitude. but the saturation of the continuum nc‘:~r the CO> absorption prccludcs this determination in most NIMS spectra. The continuum at 0.7 /ml i\ u\u;111! wturatcrt in the NIMS spectra. and cannot bc u\cd I’c)I. tht\ purpohc. in the thermal emission rcglon. the c~nttnuum level at _S jm giws a niciisurcnicnt 01‘ the temperature 01‘ ltic surface. or the temperature of the : = I le\ci of an>, o\crlying clouds. The thermal spectrum 15 dominated by the absorption due to the strong I’: hand of C‘O:. A weaker CO, band at 3.85 j(rn. as dell 25 9gnatures of(‘O and 0, betkveen 4.6 and 4.75 Itm. t\+o N ,(I bands at 3.9 and 4.55 Inn. CH, around 3.5 /em. and wwral \\eak H:O spcctral fi-atures arc also present. ah shown in Fig. 3. Hecause. ;I\ mentioned above. CO, ia constant and uniformly mixed in the atmosphere. the CO, absorption< can be inwrted to
rctriwc ;I possible thermal vertical atmospheric structure :rbo\~ the surface or the cloud. Once the thermal profile is known, information can be retrieved about the abundances of the other minor species. Ali these species (CO. M’ater vapour. N 4). (‘H, and 0:) are expected to be nonuniforml\~ m~wd \\ith altitude. it is not possible to retrieve their \cr;ic;II distl-ibution from the NIMS data. because the solution \\ould not be unique. In order to derive their abundances. \Jc haw thus assumed. for each molecule. a nominal rclativc vertical distribution. taken from Houghton (‘I (I/. (IW6). and WC have determined their mixing ratio> at the surli~cc 2s ;I free multiplicative parameter. F-or ;I first-order modclling of the NIMS spectrum. we h;l\c used a simple radiative transfer program developed for the analysis 01‘ the atmospheres of Mars and Venus (C‘ombcs 1’1r/l.. I99 I : Rosenqvist P/ t/l.. 1992 ; Carison cf (I/.. 1901 ). it is ;I semi-empirical band model taken from Wallace PI ul. ( 1974) which takes into account the gaseous absorptions by H :O. C02. CO, CH,. N20 and 03, the \,lewing geonictr!. and does not include any scattering elrect. The cmi\slvit! ofthc surface is derived from Fiobert (I 98X) and the atmosphere is vertically divided into 25 layers of3 km. In ;I first approximation. the surface albedo is supposed to be constant between I and 5 jlrn; this assumption has no Incidence upon the retrieval of the thermal profile and the vertical density distributions. The
POlN?EA C3.1 pacldy:lll2/1990 N.ElWNGMOS_-10
13:48:49
NIMS
iSDF:kcif-vetl-ud CENTRAL BODY:EARTH
1MINI:m.elwngmOs-10 EPHE~~plf/epNEARTH-O7059O.t PERIAPSIS:90-342120:35:31.21 THDREEE SO-342120:34:11.000
*CDS 1036:OO:O
AC~V~~~~WNGM~S_-lO
a~nlight ( 1.9pm. Fig. la) and in the thermal emission (4.6 jrm. f-is. Ah). .A comparison has been made between a NIMS mos~~ic (GMOSI6A). centrcd on the Pacific Ocean. and cl”~~sl-simultaneous SSI images (El WC)61 7 anti IX IWO6l XI (Fig. 4c), which show a very good corrd~ttion. This tmpiics that the al&do does not show strong \;triations hctwcun the visible and the nc~r-infrared range. ,As a consoq~xncc. the NIMS mosaic at 1.9 pm (Fig. 4a) C:III 1~ uuxi to give a good representation of the cloud sIrucIurc. the clo~ld patterns being associated with high \:~IIIc\ of the albedo. On the other hand, comparison of
554
P. Drossart et nl. : Earth global mosaic observations
with ~IMS-G~~/~~~,~~
Wovelength (pn)
Fig. 3. Example of a NIMS spectrum. Absorptions
Fig. 3a and b shows a clear anticorrelation : regions of high al&do are associated with regions of low temperature. Nevertheless, it must be noticed that there is no simple quantitative relationship between the cloud albedo and the upper cloud temperature. First, due to the instrumental saturation outside the HZ0 band at short wavelengths, albedo contrasts in Fi?. 4a are plotted within an H,O band, and can therefore be partly affected by l-t,0 cariations. Moreover. clouds of similar albedos have diKerent temperature in the NIMS data (okvinp to a different altitude of the upper cloud layer). The thermal radiation at 4.6 /lrn comes from either the surface or from the overlapping cloud. the cloud being colder than the surface. The NlMS global mos;rics in the thermal range thus provide cloud temperature information.
As mentioned above. the inversion of the two CO? bands at 4.3 and 4.X jrrn allows the deternljn~lti~~rl oi’~ltmo~pheri~ temperature profiles in the stratosphere and the mesosphere. in particular the outgoing radiation in the Y, CO, band at 4.3 /ml iomes From altitudes ranging from about 5 to 70 km. A global mosaic at 4.3 /ml thus provides a direct mapping of the mesosphcric temperatures. In fact, these altitudes being higher than the clouds. no perturbation by cloud opacity is present at this wavelength, and no cloud is visible at this ivavelength. This etrect is illustrated in Fig. 5. which clearly shows an enhancement of the stratospheric temperatures 111the southern polar regions. Figure 6 shows three examples of NIMS spectra recorded respectively at mid-latitudes (30 S), high latitudes (50 S) and at the South Pole. The corresponding thermal profiles (Fig. 7) exhibit a thermal enhancement
by atmospheric gases are indicated
at the South Pole in the stratosphere, of the order of 30+ 15K at an altitude of 20 km. in agreement with previous observations of the stratospheric thermal structure near summer solstice (Houghton et ul., 1986).
An intriguing “hotspot” anomalous feature is apparent near the western coast of South America in the vicinity of northern Chile (Fig. 8). When compared with a spectrum of the open ocean (Fig. 9). this feature appears as an enhancement ofintensity mainly in thecontinuum thermal emission beyond 3 /ml and, at a lower level, within the gaseous H-0 and CO2 absorption. This feature covers many NIMS pixels (approximately 8 pixels E-W by 15 pixels No-S in El WNCJMOS-IOA) and, from examination of several global mosaics. is found to be fixed to the rotating Earth. By checking the position of the clouds, in comparison with 1.r) itrn images. it can be shown that only the eastern part of South America. eastward of the hotspot. is cloudy. The illt~rpret~ltion of the spectra given in Fig. 8b shows that the ~~~ntinL]uIn enhancement can only be modelled by a temperature increase of the surface by about 20K compared with the ocean temperature, Therefore, the most plausible interpretation of this hotspot is the summer heating over the Chilean Andes, which are viewed in summer. close to noon. The high altitude of these mountains is also responsible for the enhancement within the shoulder of the CO: bands, owing to a lower gaseous column density over the high-altitude regions. Comparison with the temperature observed in spectra recorded in the cloud-free area northward of the hotspot show that the temperatures are intermediate between the ocean and hotspot temperatures.
P. Drossltrt
cl trl. : Earth global mosaic observations
with NIMS-Grrlileo
Fig. 4. NIMS global mosaic EIWNGMOS16 (a) at I.9 kern (b) at 4.6 {lrn. (c) Two SSI images (ElWO617 and El WO618) taken nearly simultaneously are shown to allow comparison with (a)
P. Drossart
Fig. 5. NIMS globai mosaic
El WNGMOSIO-a
ef ui. : Earth global mosaic observations
with NIMS-Grr&o
at 4.35 /ml
Fig. 8. (a) NIMS global mosaic Ei WNGMOSIO-c at 4.55 iirn: (b) synthetic spectra (I) for a surfxc temperature T,. (2) for a surface tcmpcraturc T,+?OK. (3) for ;I surface located at 4 km altitude, with temperature T,+20K: (c) NIMS observed spectra \vithin (upper curve) and oursidc (lower curve) the bright spot of the image (a). The difference between both spectra IS hcst modcllcd by the spectra ( 1) and (3) of Fig. 8b (Cnr7rb7ucd on p. 558) Fig. IO. NIMS global mosaic EIWNGMOSIO-c to the West of the bright spot (2). still visible at
at 3.3 )rm. The specular the same position
reflection
as in Fig.
Xa
point (I) is seen
P. Drossart
et al. : Earth global mosaic observations
with NIMS-Galileo
Wavelength
(pm)
Fig. 6. Example of NIMS spectra in the 4.3 pm band of CO2 : mid-latitude South-latitude at 50”s (2 : dashed line) and South Pole (3 : solid line)
(1 : dashed-dot
line), high
3
240
260
Temperature Fig. 7. Thermal profiles retrieved visible at the South Pole
from the three spectra
Another spot is visible near the centre of the disc in Fig. IO. It corresponds exactly to the specular reflection point, for which the solar incidence and reflection angles are equal. As expected. this spot is not seen in the thermal emission (in Fig. 8). since this phenomenon is due to the reflection of the sunlight from the ocean. The specular point is seen in several images of the sequence of global mosaics, except when its position is covered by a cloud,
(K) shown in Fig. 6. A thermal
enhancement
is
or is over the land, in agreement with the expected iour of the specular reflection point.
Abundance
of atmospheric
behav-
compounds
As mentioned above, the reflected sunlight component is difficult to use for retrieving abundances because of the
P. Drossart ef a/. : Earth global mosaic observations
558
(61
::
I,,,,
N3
,
3.5
*
of scattering
effects.
in particular
when
clouds
are present. A better analysis can be pcrf-ormed in the thermal part of the spectrum 3 S {cm) \%%crc the \oliir component is very small or negligible. and whore scatterinf effects are less important.
,
4.5
Wavelength
importance
I,,
4
,
,
(
,
f
with
(
NIMS-Gnlilt~
-.I
5
(pm)
Examples of‘ fits areshown in Figs c)and I 1. As indicated above. the CO2 vertical distribution is known to be constant, with a mixing ratio of 350 ppm. Thus. the CO? band at 4.3 Llrn is used to derive the T(z) profile. The other minor species are known to have nonuniform vertical
P. Drossart
cf (11.: Earth global mosaic observations
with NIMS-Galileo
559
Lot=1 1.6N/Long=132.2W
H20
A \‘I
co2
Tp=270K/z=4km
I
r
J,I
‘1
03
I’
\
,“\\
CO
0
3
3.5
4
’
1
I’
4.5
Wavelength
5
(/XII)
Fig. 9. Example of best tits obtained for a NIMS spectrum above the Pacific at the indicated position. The multiplicative factors of the nominal vertical distributions (see Table I) arc. rcspectivcly. 0.3. 0.1. 17.4 and 0.9 for H ?O. CO. 0,. CH, and N,O
We have used nominal relative distributions for these species (Table I and Fig. 12) taken from Houghton (~1rrl. (1986) and we have estimated their abundances by multiplying these relative vertical distributions by a
distributions.
unique free parameter. Figure I I. corresponding to a 100 x 100 km’ area of Pacific Ocean. shows the best global fit of the thermal spectrum. In Fig. I I. an observed spectrum in the region 4.74.8 pm. located in Texas. is com-
L
.- - /-A I
,
4.2
4.3
4.4
,
,
4.5
Wavelength
,
4.6
I
,
4.7
(JUTI)
Fig. I I. NIMS spectrum of the North American arca located at (Lat. = 35.X N. Long. = 94.4 W) in the 4.1 4.X /m spectral region. The N,O mixing ratio with the altitude is half the nominal vertical distributton. Full lint: observed spectrum. Dashed line: no CO and 0,. Dasheddotted lint: best fit. The mulripllcati\c factors of the nominal vertical distributions (see Table I) are. rcspectivcly. I and IO I.o,r CO and 0 i
560
P. Drossart
Table 1. Nominal Altitude
(km)
vertical distributions
of several atmospheric
CO, (ppm)
H20 (ppm)
350 350 350 350 350 350 350 350 350 350
3000.0 1000.0 2.0 2.0 3.0 2.0 3.0 2.0 7.0 0.7
0 IO 30 30 40 50 60 70 X0 90
constituents
range
Lat. < 35 25 < Lat. -$ 60 Lat. > 60
Number
of spectra
CO
0;
II 5 4
I.5 1.6 I.5
3.0 3.1 5.3
0, (PPm)
CH, @pm)
N 4 (ppm)
0.1
0.05 0.05 0.1 7.0 7.0 3.0 0.4 0.1 0.05 0.0
1.3
0.6 0.2 0.1 0.1 0.05 0.01 0.0 0.0 0.0 0.0
CH, N,O 2.0 2.0 1.6
with fits with and without CO and 0,. For this typical spectrum, the mixing ratio of CH,. CO, O3 and N,O as a function of altitude is represented by a multiplicative factor of the nominal distribution. indicated in brackets in Fig. 12. A preliminary step was to select 20 spectra over all the visible Earth hemisphere. This set of spectra was chosen to be a good representation of the latitudinal and longitudinal range of the available hemisphere. The preliminary aim of this study is to measure the abundance of each
2
I.2 I.2 1.0 0.7 0.4 0.1 0.1 0.1 0.1
constituent as a function of latitude. Table 2 shows the results in terms of multiplicative factor of the nominal vertical distributions. The accuracy of the measurement is estimated to be within a factor of 2. Thus, the signal-tonoise ratio is not high enough to conclude firmly on any latitudinal variation. However, if we take into account only the best-fit values of the spectra, several remarks can be drawn. There is possible evidence for a positive gradient of the ozone abundance from the equator to the South Pole. This result is consistent with previous obsrvations from different experiments such as BUV;Nirrzhus 4 (Hilsenrath ef al.. 1981) or SBUVl’Ninrhrrs 7 (Bhartia et al.. 1984). The relatively low signal-to-noise ratios of the spectra do not provide information on the CO variations observed by Reichle ct al. (1982) from the Space Shuttle. Finally, a slight decrease of the CH, and N20 abundances from the equator and tropical latitudes to the southern latitudes is marginally observed. Both results are consistent with the data from the SAMS experiment aboard the Nittzhus 7 satellite (Jones. 1984; Holton and Choi. 1988).
pared
0
on Earth
0.1 0.05 0.03 0.05 0.08 0.1 0.8 2.0 10.0
3.5 2.4 I.5
with NIMS-Galileo
CO @pm)
Table 2. Qualitative latitudinal variation of several atmospheric constituents from the NIMS experiment. The value indicated below is the multiplicative factor of the nominal dtstributions shown in Table I. The uncertainty is a factor of 2 Latitudinal
et al. : Earth global mosaic observations
4
6
8
10
Mixing ratio Fig. 12. Nominal vertical distributions of CO, N20. CH, and 0,. The numbers in the brackets indicate the multiplicutivc factors of the nominal vertical distributions derived from the best fit of the spectrum presented in FIN. I I
P. Drossart er al. : Earth global mosaic observations with NlMS-Gff~j~~~~) Conclusions
The preliminary analysis of the Earth-I NIMS global mosaics gives us a first idea of the information which can be retrieved from this imagirlg spectroscopy in the nearinfrared range for the analysis of the terrestrial atmosphere. The main interest in the near-infrared part of the NIMS data (reflected solar component. below 3 pm) has been to derive a mapping of the cloud structure. This information complements that provided by the visible images. Surface temperature variations have been observed as a large-scale hotspot localized over the South American Andes, with a temperature enhancement about 20K larger than the low-altitude surface temperatures. Another remarkable feature is the specular reflection point over the ocean which is observed in a sequence of observations over the Pacific Ocean. From the continuum temperature at 5 pm, a thermal map of the clouds can be retrieved. The CO1 absorption bands permit the retrieval of the thermal profile in the stratosphere and the mesosphere, and a monitoring of the mesospheric temperatures can be achieved by the use of the NIMS mosaic at 4.3 [irn. These measurements may be of high interest for the Earth observations (Chahine, 1991). Finally, information can be derived about the abundances of water vapour. CO. CH,, N,O and O?. Latitudinal variations of the ozone abundance have been observed by comparing a few clear areas chosen at different latitudes. in agreement with current 0; observations. These studies have been pursued since the Galileo Earth2 encounter in December 1992, with a different observing geometry. The observations of the Earth by NIMS are a continuation ofthe studies of planetary atmospheres in the near-infrared by imaging spectrometer. after the studies of the tenuous Martian atmosphere with the instrument ISM on the Pl?~)b~).sspacecraft (Bibring Et ~1.. 1989) and of the Venusian atmosphere (Carlson cf a/.. 1991). In the future, Jupiter will be studied by NIMS during the Galileo mission after 1995. Then. Saturn and Titan will also be observed by the imaging spectrometer VIMS onboard the Cassini spacecraft. Observations of the Earth with NIMS will therefore provide a framework for future interpretations of less well-known atmospheres.
References Bhartia, P. I<., Klenk. K. F., Wong, C. K. and Gordon, D., llltcrco~lparls(~n of the ,%‘whzr.s7 SBUV’TOMS total ozone
data xts with Dobson and MY.7results. f. +W@JX Rcs. 89, T’19 _ -- 5247. I%4
561
Bibring, J.-P., Combes, M., Langevin, Y., So&Rot, A., Cara, C., Drossart, P.. Encrenaz, Th., Erard, S., Forni, O., Gondet, B., Ksanfomality, L., Lellouch, E., Masson, P., Moroz, V., Rocard, F., Rosenqvist, J. and Sotin, C., Results from ISM experiment. Nuture, Lnnd. 341, 591-593. 1989. Carlson, R. W., Baines, K. H., Encrenaz, Th., Taylor, F. W., Drossart, P., Kamp, L. W., Pollack, J. B., Lellouch, E., Collard, A. D., Calcutt, S. B., Grinspoon, D., Weissman. P. R., Smythe, W. D., Ocampo, A. C.. Danielson, G. E., Fanale, F. P., Johnson, T. V., Kieffer. H. H., Matson, D. L., McCord, T. B. and Soderblom, L. A., Galileo Infrared Imaging Spectroscopy Measurements at Venus. .%ic,ncP 253, 1541.. 1.548. 1991. Carlson, R. W., Weismann, P. R., Smythe, W. D. and Mahoney, J. C., Near infrared Mapping Spectrometer experiment on Guliiw. Spuci~ Sri. Rrr. 60, 457. 1992. Chahine, M. T., The hydroio_pical cycle and its influence on climate. Nature. Land. 359, 373-380. 1992. Combes, M., Cara, C., Drossart. P.. Encrenaz, Th., Lellouch. E., Rosenqvist, J., Bibring, J.-P., Erard, S., Gondet, B.. Langevin, Y., Soufflot, A., Moroz, V. I., Grygoriev, A. V., Ksanfomality, L. V., Nikolsky, Yu. V., Sanko, N. F., Titov, D. V., Forni, O., Masson, P. and Sotin, C., Martian atmosphere studies from the iSM experiment. Phet. Spwc Sci. 39, 189-197. 1991. Flobert, J. F., TlrC;.ss &I I’l~rkwsitC Pm% VI, 76. 1988. Hilsenrath, E. and Schlesinger, B. M., Total ozone seasonal and interannual variations derived from the 7 year Nimbus-4 BUV data set. J. ~rop/?~~. Rm. 86, t2,087-12.096. 1981. Holton, J. R. and Woo-Kap Choi, Transport circulation deduced from SAMS trace species data. J. rtfn~~ Sci. 45, 1929-1939,
1988. Houghton, J. T., Taylor, F. W. and Rodger, C. D., Rrnzotr Sounding of A ttnosphwes. Cambridge Planetary Science
Series (edited by W. I. Axford. R. Greelcy and G. Hunt). Cambridge University Press. Cambridge. 1986. Husson, Iv., Chedin. A., Scott, N. A., Bailly, D., Gtaner, C., Lacome, N.. Lbvy, A., Rossetti, C.. Tarrago, G.. Camy-Peyret, C., Flaud, J. M., Bauer, .4., Colmont, J. M., Monnanteuil, N., Hilico, J. C.. Pierre, G., Loete, M., Champion, J. P., Rothman, L. S., Brown, L. R.. Orton. C., Varanasi, P., Rinsland, C. P., Smith, M. A. H. and Goldman, A., The GEISA spectroscopic line parameters data bank in 1984. Ann. Grr~p/~~.s.4, 1855 190. 1986. Jones, R. L., Satellite measurements of atmospheric composition: three years observations of CH, and N,O. A&. S/xiw Rvs. 4, I:! I--l 30. 1984. Reichle, H. G. Jr. Beck, S. M., Haynes, R. E.. Hesketh, W. D., Holland, J. A., Hypes. W. D., Orr, H. D. III. Sherrill, R. T., Wallio, H. A., Casas, J. C.. Saylor, M. S. and Gormsen, B. B., Scicvw 218, 1024. 1076. 1981. Rosenqvist, J., Drossart, P., Combes, M., Encrenaz, Th., Lellourh, E., Bibring, J.-P., Erard, S., Langevin, Y. and Chassefi&e. E., Minor constituents in the Martian atmosphere from the ISM. Plrohm cxpcrimcnt. /(.ff~ci.s98. 2i4-270, 1992. L., Prather, M. and Belton, M. J. S., The thermal of .lupitcr. ilstroplzy.~. J. 193, 481-493. 1974.
Wallace,
structure of the atmosphere