AERO NOMICA ACTA

i s s n 0 0 6 5 - 3 7 1 3

I N S T I T U T O A E R O N O M I E S P A T I A L E 0 Ê B E L G I Q U E 3 - Avenue Circulaire

B - 1180 B R U X E L L E S

AERO NOMICA ACTA

A - N° 3 6 7 - 1992

Second flight of the spacelab grille spectrometer during the Atlas-1 mission by

M. DE MAZIERE, C. MULLER, C. LIPPENS, J. VERCHEVAL, D.FONTEYN

R. ARMANTE, C. CAMY-PEYRET, V. ACHARD, J. BESSON, J. MARCAULT, D. HENRY, N. PAPINEAU, J.P. MEYER,

D. FRIMOUT

B E L G I S C H I N S T I T U U T V O O R R U I M T E - A E R O N O ' M I E

FOREWORD

This text will be published in the ATLAS 1 Geophysical Research Letters special issue.

AVANT-PROPOS

Ce texte sera publié dans le numéro spécial ATLAS 1 de Geophysical Research LetLeis special issue.

VOORWOORD

Deze tekst zal in de ATLAS 1 Geophysical Research Lette special issue verschijnen.

VORiORT

Dieser Tekst wird in den ATLAS 1 Geophysical Reserch Lette

special issue publiziert werden.

SECOND FLIGHT OF THE SPACELAB GRILLE SPECTROMETER DURING THE MISSION

by

M . DE MAZIERE (*), C. MULLER (*) , ^C . LIPPENS (*), J . VERCHEVAL (*), D. FONTEYN (*)

R. ARMANTE (**), C. CAMY-PEYRET (**,***), V . ACHARD (**) , J . BESSON (**) J. MARCAULT (**), D. HENRY (**) , N. PAPINEAU (****), j.p. MEYER (*****)'

D. FRIMOUT ( * * * * • * )

Abstract

The SPACELAB grille spectrometer on its second space flight tnnk advantage of the favorable timeline and of the extra day to perform more than 65 successful solar occultation runs. It succeeded in obtaining spectra pertinent to its ten target molecules in the full range of altitudes available to the solar infrared occultation technique. These ten molecules are H ² 0 , CO, C 0 ² , C H ⁴ , NO, NO,,, N O , HC1, HF and 0.. A preliminary analysis of an HC1 observation is presented showing no significant change of upper atmospheric hydrogen chloride in comparison with previous data.

Résumé

Lors de son second vol, le spectromètre à grille SPACELAB a bénéficié d'un programme d'opération favorable et d'un jour supplémentaire pour observer avec succès au-dessus de 65 occultations.

Des données concernant les dix molécules cibles ont été obtenues dans l'intervalle complet des altitudes accessibles à la technique d'occulation infrarouge solaire. Ces dix molécules sont : H O , CO, CO C H ⁴ , NO, N 0 ² , N ² 0 , HC1, HF et 0 ³ . Une analyse préliminaire d'une observa- tion de HC1 est présentée et ne montre pas de changement significatif de l'acide chlohydrique dans l'atmosphère supérieure par rapport aux données antérieures.

* Institut d'Aéronomie Spatiale de Belgique, 3, Avenue Circulaire B-1180 Bruxelles, Belgium.

** ONERA, BP 72, F-92322 Chàtillon Cedex, France.

*** LPMA/CNRS, 4, Place Jussieu, F-75252 Paris Cedex 05, France

Samenvatting

Tijdens zijn tweede ruimtevlucht h e e f t de S P A C E L A B raster- (Grille) spectrometer, nuttig gebruik gemaakt v a n de gunstige timeline en v a n de toegekende extra dag om gedurende meer dan 65 zonsoccultaties succesvolle w a a r n e m i n g e n te d o e n . Het instrument slaagde erin atmo- sferische spectra te registreren met informatie over de 10 b e o o g d e m i n d e r h e i d s g a s s e n , over het v o l l e d i g e h o o g t e b e r e i k dat h a a l b a a r is met de techniek v a n infrarood spectrometrie tijdens z o n s o c c u l t a t i e s . Deze 10 m o l e c u l è n zijn : ^ 0 , C O , CO,,, C H 4 > N O , N 0 2 , N 2 0 , H C 1 , HF en 0 r Een èerste analyse v a n een waarneming v a n H C 1 wordt v a s t g e s t e l d : ze toont geen beduidende v e r a n d e r i n g in de h o e v e e l h e i d H C 1 in de h o g e r e s t r a t o s f e e r , in vergelijking met vroegere g e g e v e n s .

Z u s a m m e n f a s s u n g

Dank dem günstigen A r b e i t s p l a n und dem z u s ä t z l i c h e n F l u g t a g , ist

das G i t t e r s p e k t r o m e t e r in der Lage g e w e s e n , b e i seinem zweiten Flug,

mehr als 65 O k k u l t a t i o n e n zu b e o b a c h t e n . D a t e n b e t r e f f e n d die z e h n

u n t e r s u c h t e n M o l e k ü l e w u r d e n e r h a l t e n . Sie b e z i e h e n sich auf dem g a n z e n

H ö h e b b e r e i c h wo die Technik der O k k u l t a t i o n der infraroten Sonnen-

strahlung anwendbar ist. Die zehn M o l e k ü l e sind : H 2 0 , C O , C 0 2 , C H 4 > N O ,

N 2 0 , H C l , HF u n d 0 3 . Eine vorläufige A n a l y s e einer HCl Beobachtung w i r d

v o r g e s t e l l t . Sie z e i g t keine bedeutsame Ä n d e r u n g der K o n z e n t r a t i o n der

Chlorsäure in der o b e r e n Atmosphäre im V e r g l e i c h e mit früheren

Ergebnissen v o r .

INTRODUCTION

The purpose of the ATLAS missions, onboard the American Space Shuttle, is to study the evolution of atmospheric properties over an entire solar cycle. The grille spectrometer, which already flew onboard Spacelab-1 and was used for several balloon and airplane observations since 1972, measures vertical concentration profiles of trace gases. It uses the method of infrared absorption spectrometry during sunrise or sunset periods, with the sun as the source of light. The largest amount of absorbing molecules is observed along the optical path through the Earth atmosphere at various tangent altitudes from the stratosphere up to the lower thermosphere, leading to concentration profiles with an instrumental vertical resolution of about 4 km.

This paper gives a balance of the grille spectrometer observa- tions performed during the ATLAS-1 flight, and presents an example of data retrieval. Because of the strong interaction between chlorine and stratospheric ozone, a preliminary analysis of a vertical profile of hydrogen chloride has been chosen.

EXPERIMENT

The grille spectrometer flew for the first time in space

(Lemaitre et al, 1984) onboard SPACELAB-1, with a launch on November 28,

1983. The flight came up to its objectives (see final review by Girard

et al., 1988) despite an orbit entirely sunlit during the last six days

of the ten days mission and numerous technical difficulties uncountered

for this spacelab test flight. Still, this mission provided an early

data base very useful for comparisons with later flights. On the basis

of the SPACELAB-1 grille experience, the scientific program (spectral

windows, altitude range for each window) was optimized for the ATLAS-1

mission (Camy-Peyret et al., 1992).

During the design of the final ATLAS-1 timeline in the middle of 1991, the ATLAS-1 investigators and the NASA engineers agreed on an attitude timeline divided into solar, plasmas, astronomical and earth observation periods, with the objective of maximizing observation opportunities for the suite of payload instruments. The crew and P.I.

teams were extensively trained in procedures designed to overcome possible mission contingencies and to return to the scheduled timeline as soon as possible. The telemetry and telecommand links between the payload and the ground based stations were also greatly improved due to the presence of two relay satellites and a new organization of the NASA Payload Operation Center.

The use of a NASA provided high pressure nitrogen vessel (GN2) for cooling the detectors by Joule-Thomson expansion, and a new procedure against overheating of the instrument electronics consisting of radiative cooling keeping the heliostat open, allowed to run more occultation observations than during the SPACELAB-1 mission. The calibration, performed about four hours after launch, confirmed correct operation of the instrument. After correction of a few target errors due to the launch delay, the observations followed nominally except for the sunrises that were affected by late sun acquisition due to the fact that a wrong positioning of its multi-layer insulation hindered the heliostat from correct pointing. The real-time data quality was good, permitting optimization of the scientific program through uplink of some new spectral windows and new altitude ranges for each window. Emission observations were attempted, but the signal did not allow any reliable analysis : after two trials it was decided to cancel all emission runs in order to save ressources.

Figure 1 shows the geographical distribution of the observations

for each species.

-180 -150 -120 -90 -60 -30 0 30 60 90 120 150 180

EiiL__kâ- * Geographical distribution of trace observations : CH H O

CO and ( X L . 4 2 '

Fi fi- lb - • Geographical distribution of tracé species observations

HC1, HF, CL, NO, NO. and N„0.

SAMPLE ANALYSIS

The occultation performed during the sunset in orbit 124 (54°S, 153'E) is chosen as an example of an absorption run because of the importance of hydrogen chloride measurements in the middle atmosphere.

In particular, HC1, in the 40 to 50 km altitude range is a good indicator of the total active chlorine in the stratosphere (W.M.O., 1985).

^ c

The spectral window covers the H J °C1 line at 2944.9 cm" 1 , some lines of CH 4 , and a few solar lines. The HC1 profile has been derived between 30 and 55 km, using 9 consecutive spectra (numbered 33 to 40) just before loss of sun. The measurements below 30 km were perturbed by the Pinatubo aerosols obscuring the lower part u£ the acmosphere.

Figure 2 shows spectra obtained in this altitude range. Two independent retrieval methods were used in this work. The first one is based on an algorithm proposed by Mill, starting from the lower level and iterating to the highest tangent height available spectrum. The second one uses a least squares global fit method : all the spectra are included simultaneously in order to retrieve the vertical concentration profiles together with the background. Identical parameters of the instrumental function are used in both computations. The concentration values and uncertainty limits resulting from both methods are in good mutual agreement. The tangent heights used in the computation are derived from the orbital analysis performed by Marshall Space Flight Center orbit engineers during and at the end of the flight and are still preliminary.

Figure 3 shows the agreement obtained between observed and

computed spectra around the HC1 line. Because of uncertainties remaining

on the orbit parameters, retrievals have been made for the nominal

values of the tangent heights, and for a tangent height uncertainty

equal to plus or minus 1 km. The final values reported in Table 1 and on

Figure 4 are combined envelopes and uncertainties of both methods at any

given level. A preliminary uncertainty analysis of the retrieved HC1

profile has been performed including the measurement noise. The 68 %

wavenumber (cm-1)

Fi fi- 2 - ' s Pectra recorded at sunset 124 The amplitude of the signal

is shown versus wavenumber (cm ), nominally for spectrum 33-

the others are successively shifted downwards by 200

amplitude units. Several solar absorption features appear in

the spectral range. The HC1 line at 2944.9 cm" 1 is indicated

by the arrow. The tangent altitudes of the line of sight to

the sun's center of this absorption line are 55.7, 48.5, 41 2

and 33.8 km for spectra 33, 35, 37 and 39, respectively.'

SS observation of HCL - orbit 124 (54*S,153'E)

2944.6 2944.8 2945 2945.2 2945.4 2945.6

0.6 0.4 0.2

* — '

_ca 0 ."D

VI

-0.2 - QS •0.4 - -0.6 -

' ^ 4 4 2944.4 2944.6 2944.8 2945

Wawnumber (cm-1) ^{2945.2 2945.4 2945.6}

The uppe^ graph shows part of spectrum 37 versus wavenumber

(in cm ) as the continuous line, the dashed line

representing the computed spectrum. The lower graph shows the

relative difference between computed and observedd values

(residual in %).

4 -~ Concentration of hydrogen chloride versus altitude. The ATLAS

I Grille values are represented by the closed circles and

corresponding uncertainty limits, with the arrows excluding

the effect of the + 1 km altitude uncertainty. Other data are

TABLE 1 : Results from the sunset in orbit 124.

ALTITUDE (km)

TEMPERATURE (K)

NUMBER DENSITIES (cm' 3 )

HCl MIXING RATIO (ppbv) ALTITUDE

(km)

TEMPERATURE

(K) AIR HC1

HCl MIXING RATIO (ppbv) 55 250 1 10 x 10 1 6 (3.7 + 1.4) x i o

3 4 + 1.3

50 263 2 01 (6.7 + 1.5)

3 34 + 0.75

45 258 3 90 (1.22 + 0.15) x 10 8 3 12 + 0.38 40 240 8 25 (2.15 + 0.18)

2 61 + 0.22 35 230 1 77 x 1 0 1 7 (3.95 + 0.10)

2 22 + 0.06 30 224 3 82 (6.99 + 0.46)

1 83 + 0.12

The error resulting from the + 1 km tangent height altitude uncertainty is of

order of + 14% and is not included in the above uncertainty limits that only

represent the 68% statistical confidence intervals.

statistical confidence intervals are given in Table 1. The inclusion of the +/" 1 km tangent height uncertainty increases the uncertainty on the retrieved values as indicated on Figure 4 and in Table 1.

Also shown in Figure 4 for comparison are the HC1 vertical concentration profiles derived by ATMOS during the SL-3 flight in April-May 1985 (Zander et al., 1990) and during the BIC-2 balloon campaign in the second half of June 1983 (W.M.O, 1985). At the lowest altitude level of this retrieval, the actual Grille data join data taken during a balloon flight of a similar grille spectrometer in 1975 (De Mazi6re et al., 1989).

The overall data set does not give a clear indication of any steady long-term trend in the HC1 stratospheric concentration. However, HC1 is known to vary with season and latitude and the BIC-2 results have large uncertainties. Therefore, restricting the comparison to the ATMOS '85 and GRILLE '92 data, an increase of the HC1 concentration becomes apparent, which is of order 18 to 28% between 35 and 45 km at which altitudes the relative uncertainties of both data sets are smallest and non-overlapping.

It has been verified by us that the slight difference between the HITRAN '92 parameters used by us and the ones used in the ATMOS '85 retrieval for the HC1 R2 line cannot account for this increase. One must keep in mind however that erroneous estimation of the tangent altitudes of the spectra by only + 1 km may alter this conclusion significantly, as shown in Fig. 4. So care should be exercised and more HC1 observa- tions analysed before generalizing this early conclusion.

CONCLUSIONS

During the ATLAS-1 mission, the grille spectrometer has

performed more than 65 solar occultation runs. The analysis of the

The first preliminary results on HC1 at 54° S seem to indicate an increase of order 20 to 25% at about 40 km altitude in comparison with 1985. This conclusion needs to be confirmed by analysis of more observations and better determination of the orbital parameters.

ACKNOWLEDGMENTS

We wish to thank M. Ackerman, for his help in obtaining and interpreting data and in preparing this article, and E. Falise and J.

Schmitz, for their support in data handling. We would like to acknow-

ledge the ETCA team, for its contribution in preparing the Grille

software and instrumentation, and the NASA and ESA support teams. Thanks

are due to F. Karcher of Etablissements d'Etudes et de Recherches

Météorologiques (EERM, Météo Franr.i», Toulouse) for providing the

vertical pressure and temperature profiles used for the retrievals. The

French agencies, Centre National d'Etudes Spatiales (CNES) and Ministère

de l'Environnement, and the Belgian Ministry of Science Policy have

supported this project.

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