Retrieval of atmospheric 03, HNO3,CFC-1 1, and CFC-1 2 profiles from MIPAS-B-89limb emission spectra
Thomas v. Clarmann, Hermann Oelhaf, and Herbert Fischer
During the night from May 17 to May 18, 1989, the first of four flights of the Michelson Interferometer forPassive Atmospheric Sounding, Balloon-borne version (MIPAS-B) instrument took place from the CentreNational d'Etudes Spatiales balloon-launching site at Aire-sur-l'Adour (France, 440 N latitude). Fromapproximately 33 km float altitude, stratospheric and tropospheric limb infrared emission spectra havebeen recorded by this novel type of fast-scanning interferometer. Although the measured spectra did notreach the expected quality and the a priori information on the corresponding viewing directions wascoarse, the data were processed successfully with a retrieval algorithm specially adapted for application tonoisydata. Mixingratio profiles of ozone, nitric acid, CFC-11, and CFC-12 havebeen retrieved from limbsequences of wide spectral intervals by nonlinear least-squares fitting in combination with a layer-by-layer onion-peeling approach. A rigorous error analysis has been carried out by means of Monte Carlocalculations.
Knowledge of the distribution of numerous atmo-spheric trace gases is necessary to understand strato-spheric ozone destruction. Simultaneous measure-ments of these chemically coupled trace constituentsare an essential precondition for determining theirrole in the mechanism of ozone depletion. Mostrelevant gases emit infrared radiation in their vibra-tional-rotational bands because of their thermal exci-tation. Thus emission spectroscopy is a powerfultool to satisfy this scientific demand of simultaneousmeasurements, especially under nighttime or polarwinter conditions. The limb-sounding concept alsoprovides good vertical resolution. The MichelsonInterferometer for Passive Atmospheric Sounding(MIPAS) is a novel type of Fourier spectrometer thathas been developed for this purpose in particular.Its first test flight on board a balloon-borne platformtook place from the launching site of the CentreNational d'Etudes Spatiales at Aire-sur-l'Adour(France, 440 N latitude) during the night from May 17
The authors are with the Institut fur Meteorologie und Klimafor-schung, Kernforschungszentrum Karlsruhe GmbH and the Univer-sitat Karlsruhe, Postfach 3640, D-76021 Karlsruhe, Germany.
to May 18, 1989. This mission of the MIPAS instru-ment was an important step for its further develop-ment and proved its suitability for simultaneous tracegas measurements. This success led to another flightat Aire-sur-l'Adour in May 1990 and two launcheswith the improved instrument from Esrange nearKiruna, Sweden, in the course of the 1991-1992European Arctic Stratospheric Ozone Experiment(EASOE). Unfortunately, the balloon gondola wasdestroyed completely during its last mission. Thispaper deals with the scientific output of the 1989campaign only: Altitude distributions of 03, HNO3,CFC-11, and CFC-12 have been retrieved from asequence of stratospheric and tropospheric limb spec-tra.
Experiment
Atmospheric nighttime emission measurements havebeen carried out with the cooled Fourier spectrom-eter MIPAS. The most distinctive subsystem of theballoon-borne MIPAS instrument is a double-pendu-lum interferometer, which, in contrast with the stan-dard Michelson design, uses a rotational rather thana translational movement of retroreflectors. Thisstructural feature leads to a quite compact design ofthe instrument and permits us to reduce the scantime per interferogram to only 3.7 s. Thus theexperiment becomes less sensitive to an unstable line
of sight but requires co-addition of interferograms ofthe same geometrical situation improve the signal-to-noise ratio. The optical bandwidth of the 1989version of the instrument covered the 690 cm-' to960 cm-' range. An apodized spectral resolution of0.11 cm-' has been achieved. The instrument wasequipped with a three-mirror telescope that provideda geometrical vertical resolution at the limb of betterthan 3 km and with a two-axis line of sight stabiliza-tion system. From a mean floating altitude of 32.7km a sequence of limb emission spectra has beenrecorded that corresponds to tangent altitudes fromapproximately 3 km to 32 km. A description of thetechnical concept of the instrument, experimentaldetails, and data preprocessing can be found in Refs.1-4 and in Table 1.
Although this first flight was only thought to be atechnological one, and the noise equivalent power didnot reach the expected value, the measured spectracould be evaluated with a specially adapted retrievalalgorithm as will be shown in the following sections.
Data Analysis
For data analysis a hydrostatic model atmosphere hasbeen constructed from the onboard temperature andpressure measurements with the algorithms de-scribed in Ref. 5. This temperature profile was
Table 1. MIPAS-B Instrument Parameters for the Flight on17-18 May 1989
Parameter Value
Overall mass 360 kgOverall envelope 300 cm x 100 cm x 100 cm
(excluding trifilar suspensionand crash pads)
Scan time per interferogram 3.7 sUnapodized spectral resolu- 0.05 cm-'
quencyA/D converter word length 14 bitDetector Si:Ga, 1 mm x 1 mm with cone
condenserBias voltage 11 VFeedback resistor 50 MflResponsivity (output preamp)a 8 x 105 V/WFlight noise equivalent 4 x 10-12 W/\H/i
powerzField of view 17 arcminAperture stop diameter 190 mmEtendue 3.5 x 10-3 sr cm2
Beam splitter KCl with Sb2S3 coatingOptical efficiency 11%Modulation efficiency 60%Flight noise equivalent radi- 1 x 10-7 W/(cm2 sr cm-')
ancea
aValues that were improved significantly in the subsequentMIPAS-B experiments in 1990 and 1992.
found to be consistent with all available radiosondemeasurements at adjacent stations (Lyon, Bordeaux,and Madrid) up to 29 km of altitude. The finaltemperature profile was obtained by combining theslightly smoothed onboard measurements below 29km, the US-76 Standard Atmosphere6 above 33 km,and a linear interpolation between 29 and 33 km.
The limb sequence consists of 12 averaged spectrarecorded at elevation angles from approximately - 5.3'to - 0.8° (corrected; see below) and covers the altituderange from approximately 3.0 km to 32.0 km. Sixspectra in an altitude range from 7.0 to 32.0 kmproved to be evaluable. Because of the malfunctionof the line of sight stabilization system, the remainingsix spectra were related to tangent heights below 6km and were influenced by clouds such that a success-ful quantitative evaluation has not yet been possible.7
Retrieval calculations have been performed withthe Retrieval of Atmospheric Trace Gas Profiles (RAT)software package, which is partly described in Ref. 8.For this application the standard layer-by-layer onion-peeling method9"10"'1 has been chosen to control thesuccessive nonlinear least-squares fitting of calcu-lated to measured spectra of each tangent altitude.Forward line-by-line calculations have been carriedout by FASCOD2,12 which includes the LOWTRANprogram' 3 as a subroutine. The FASCOD2-versionused here has been modified such that the calculationof chlorofluorocarbon (CFC) bands is possible.'4The most recent available spectroscopic information[CFC-11 and CFC-22, pseudo-lines from the ATMOSdatabase;' 5 other gases, HITRAN database,'6 withupdates' 7 for CFC-12 (Ref. 18) for O3 and C02] hasbeen used for these calculations. The temperaturedependence of CFC-12 is given by cross-section spec-tra for six temperatures. The cross-section spec-trum for the actual temperature of each atmosphericlayer and the requested spectral meshpoints werecalculated by a third-order spline function. For bothlowest tangent heights the LOWTRAN cirrus model'9has been applied. Also, the aerosol contribution hasbeen modeled by the LOWTRAN subroutine.' 3 Allforward calculations have been carried out for localthermodynamic equilibrium conditions, because non-local thermodynamic equilibrium effects are assumedto be of minor importance in the altitude rangeexamined and for the spectral bands considered. Toapproximate both the effects of instrumental lineshape and the Filler apodization function,20 whichhad been applied to measured interferograms, calcu-lated monochromatic spectra were convolved with asinc2 function.
In a first step auxiliary information had to bedetermined: The actual spectral resolution was ob-tained from several optically thin lines in high-altitude spectra, where instrumental degrading pre-dominates pressure broadening of the Voigt lines.Only in a few cases, when low-altitude spectra wererecorded after telecontrolled instrument adjusting,the spectral resolution had to be determined byleast-squares fitting of calculated to measured spectra.
Thus field of view effects2' on the spectral resolutionare considered implicitly and only remain as a higher-order error in instrumental line shape uncertainty.
Minor baseline corrections were necessary becauseof calibration uncertainties. These were due to apartly obstructed field of view when deep spacemeasurements were recorded during this first flight.Also, small corrective adjustments of the frequencyshift have been carried out.
A malfunction of the gondola stabilization systemrequired the correction of the viewing angles. Forspectra from 7.0- to 21.0-km tangent altitude, theviewing angles have been retrieved directly from theCO2 lines in the spectra (Fig. 1). For these altitudesthe initially guessed temperature profile has beenmaintained. For both uppermost lines of sight theviewing angle correction has been calculated fromboth the result at 21 km and the data of the onboardgyrometer and inclinometer, by means of whichrelative line of sight information was obtained.Temperatures have been retrieved from the spectrafor the corresponding altitudes.
Because of the determination of the viewing anglefrom spectral information rather than from a prioriinformation, the line of sight is defined as the centerof gravity of the contribution function, i.e., the direc-tion of maximum radiance impact, and not as thegeometrical center of the noninfinitesimal field ofview. Thus nonlinearity of radiance profiles resultingfrom pressure decrease with altitude are consideredimplicitly, as are the effects resulting from averagingspectra of slightly different elevation angles. Higher-order effects from changing gradients of trace gasmixing ratio profiles2223 in combination with thenoninfinitesimal field of view are small and remainuncorrected.
Noise caused by the filter characteristics reducedthe evaluable spectral range from 740 cm-' to 940cm-'. In the range from 740 cm-' to 795 cm-',line-by-line calculations did not fit well to measured
v*d MIPAS-B-89
-0 O A) AJAAAAAA 6h A 6. NA
925.0 927.5 930.0 93Z5 935.0 937.5 940.0
Wavenumber (cm-')
Fig. 1. Comparison of measured and calculated emissions by CO2lines that have been used for viewing angle corrections. Thebroad underlying feature centered at approximately 929 cm-1 is apart of the CFC-12 band. This example shows the measured andcalculated best-fit spectra and residuals for the 16.8kM tangentaltitude.
spectra because of uncertainties in Q branch model-ing (line mixing effects) and problems concerning thecontinuum, which might be attributed to far-wingeffects from the 15-,um C02 band. Thus data analy-sis has been restricted to a suitable spectral rangebetween 795 and 940 cm-'. For temperature retriev-als and viewing angle corrections CO2 lines near 940and 810 cm-' have been used. Determinations ofthe cloud base altitude and cloud thickness have beencarried out for both of the lowest tangent altitudeswithin the whole spectral range of 795 to 940 cm-'.We do not claim to retrieve true cloud quantities,because this inversion problem is not unique. Also,the results suffer considerably from the assumptionof spherical symmetry. However, we use standard-ized cloud parameters, which lead to a strong con-tinuum emission in modeled spectra and thus makethem fit very well to the measured ones. The resultsare relatively independent of the true cloud param-eters in the investigated cases. This approach en-ables one to evaluate spectra that obviously contain asignificant cloud contribution. 7
On the basis of the derived temperature profile andthe corrected viewing angles, altitude distributions ofHNO3, CFC-12, CFC-11, and O3 have been retrievedwith an algorithm combining onion peeling and non-linear least-squares fit.8
Analysis of the 1989 data has been a comparativelydifficult task. Spectra of high tangent altitudes wererather noisy, despite the co-adding of up to 60 inter-ferograms for each final spectrum. This is due to thesmall air mass as well as to the reduced performanceof the detector and the detector optics during thisfirst flight. The limited quality of high-altitude spec-tra required us to evaluate simultaneously wholeemission bands instead of single spectral features, touse as much redundant information as possible.Therefore a fully automatic retrieval algorithm couldnot be used for both of the highest tangent altitudesbecause of huge computer storage requirements andlimited computer capacity. Powell's direction setmethod, which makes use of the conjugate directionsconcept,24 in combination with Brent's parabolic inter-polation method25 for one-dimensional search in eachdirection, turned out to be most useful for interactiveminimization of residuals of measured and calculatedspectra. These algorithms are discussed in Ref. 8.
Spectra of lower tangent altitudes have been evalu-ated the Levenberg-Marquardt nonlinear least-squares fitting,26 ,27 allowing the simultaneous re-trieval of mixing ratios of several gases in case ofoverlapping bands. To keep the results as stable aspossible, a layer model has been used instead of a levelmodel.28 The layer model has been deduced from a43-level model. The only quantities that can beretrieved with a certain degree of uniqueness are gasamounts in layers between a pair of adjacent tangentaltitudes. For reasons of comparability with otherexperiments, the most probable (i.e., reasonablysmooth) mixing ratio profiles defined by the levels
aVMR, volume mixing ratio; 1VCA, integrated vertical column amount between the given and the next level or the given level and the topof the atmosphere, respectively. For CFC's no IVCA's are given for both uppermost layers, because the values in the 21.0-km columnindicate the total mass above this level. The mixing ratios are obtained from the scaling of the whole profile above 21.0 km. The largeerrors are explained in the discussion of the results.
corresponding to the given tangent altitudes of theexperiment are listed in Table 2. Nevertheless, itshould be kept in mind that the only results thatgenerally can be given are integrated vertical columnamounts for layers, unless there are a priori con-straints on the shape of trace gas profiles between the
FASCOD2 calculations
Q~1~6
d] -1w
tangent altitude levels. The measured spectra andbest-fit spectra are shown in Fig. 2.
Error Analysis
In certain altitude regions gas concentrations andspectral radiances are related to each other in a highly
nonlinear manner. When one uses the onion-peeling technique for evaluating limb-sounding mea-surements, error propagation can only be roughlyestimated by classical Gaussian error analysis, whichrequires an analytical formulation of the retrievalproblem instead of a numerical one. An approxi-mately linear dependence between the measurementsand the retrieved quantities is required to transformnormally distributed errors of auxiliary quantities tonormally distributed errors of resulting parameters.As a consequence, the covariance matrix for the totalinversion problem is not available, nor should it beinterpreted as the actual squared standard errors ofthe parameter estimation.
Therefore error analysis has been carried out witha strategy that is closely related to the Monte Carlomethod (Ref. 29, p. 529-532): First, uncertainties ofa priori and auxiliary information have been esti-mated (see Table 3). These are baseline offset, spec-tral shift and resolution, temperature, viewing angle,and observer altitude. Observer altitude containsuncertainties that arise from pressure variations atthe observer level and influences of temperatureuncertainties on barometric calculation of the ob-server altitude. For both of the lowest tangentheights uncertainties in standardized cloud base alti-tude and standardized cloud thickness have also beenestimated by sensitivity studies. Assumptions onuncertainties of baseline offset and spectral shift andresolution have been estimated directly from themeasured spectra. The standard deviation of tem-perature was calculated from the MIPAS onboardmeasurements and radiosonde temperature informa-tion, representing both random errors of measure-ment and temperature inhomogeneities of the atmo-sphere.
Gaussian distributions of standard deviations ac-cording to the estimated uncertainties have beengenerated for each auxiliary quantity except for theviewing angles and standardized cloud parameters,which are formally treated in the same way as the gasconcentrations; they are retrieved from the spectrarather than provided in an a priori manner. Syn-thetic random normal distributions were generatedwith a random number generator (Ref. 29, p. 191-199) and the Box-Muller transformations By this
means, 14 sets of auxiliary quantities, each of themhaving been superimposed by its individual artifi-cially generated random error vector, have beenconstructed.
Second, retrieval calculations for viewing anglesand trace gas calculations have been repeated. Eachrespective spectral interval has been divided into 14subintervals, all the same size. Each subinterval
I
Ld
0
U0
35.0 -
30.0-
25.0 -
20.0 -
15.0-
10.0-
Li0
03 35.0-
30.0-
25.0-
20.0-
15.0-
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1 1 1-7 i0c- 10-5 10-4
VOLUME MIXING RATIO
35.0-
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S x+ US CFC-11
I ..... r:'; v \:
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10 0 10-12 10-1lo- 10 lVOLUME MIXING RATIO
"'to' i';'
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I.'1 10 lo 10- 1c-
VOWME MIXING RATIO
Is II.........................1..- 1 1LUME MIX"NG RIOI flCT 110- lu-1° 10
Fig. 3. Retrieved altitude distributions of O3, HNO 3, CFC-11, andCFC-12 compared with results from ATMOS and other experi-ments. Large error bars reflect not only the noise in the spectrabut also uncertainties in assumed parameters as, most important,elevation angles.
was combined with one set of perturbed auxiliaryquantities. For each subinterval an onion-peelingretrieval calculation has been carried out, resulting in14 profiles of estimated parameters for each gas thathas been evaluated within this spectral subinterval.Provided the relation between radiance and param-eters is not too far from linearity and the informationcontent of all subintervals is roughly the same, theaverage of these 14 profiles turned out to be more orless identical with the resulting profile of the originalretrieval calculation. The resulting standard devia-tions are taken for the estimated total l-retrievalerrors.
This procedure is carried out for all parameters inthe same order as the original retrieval calculations.All 14 input data sets are updated after each step withdistributions of already processed data to includecovariance effects that are due to overlapping bandsof various gases. Fourteen different HNO3 resultsare, for example, used as input data when CFCconcentrations are retrieved. By this means, theimpact of HNO3 uncertainties on CFC results isconsidered.
These estimated retrieval errors implicitly includeerrors from auxiliary and a priori information, spec-tral noise, onion-peeling error propagation, and covari-ance effects. Even nonsystematic errors in line dataare included implicitly by the use of more than onetransition. Nonlinearity of the inverse radiativetransfer algorithm and the possible existence of sec-ondary minima of residuals could lead to an underes-timation of errors with classical error analysis but aretreated in a correct manner by this Monte Carloapproach.
Calibration errors, which appear as multiplicativefactors on the whole spectrum, errors in band inten-sity, and other purely systematic errors are notincluded in this error analysis because they aremostly small compared with nonsystematic errors ofthe MIPAS-B-89 experiment. For CFC-11 pseudo-lines the uncertainty of the integrated band intensityis given as ± 10% (Ref. 15), resulting in a possible biasof retrieved mixing values of the same size. For theother gases only uncertainties of intensities of spec-tral lines are available, which can be taken as upperlimits of uncertainties of integrated band intensities.These are 4-10% for 03 (Ref. 31) and ±15% forCFC-12 (Ref. 32). In the case of HNO3 , a range of±5-20% is given,33 the lower value seeming moreprobable in the spectral region used here. The line-to-line variance of intensity errors is implicitly re-flected by the error estimation described above, andonly systematic uncertainties of the integrated bandintensities have to be taken into account additionally.Thus in most cases any possible biasing of resultsshould be smaller than the line data uncertaintieslisted above.
Because the results are integral column amountsfor layers rather than mixing ratios for infinitesimallevels, the null-space error analysis3 4 can be leftundone in a limb-sounding scenario like this. Thus
the error bars characterize the absorber amount inthe layer between adjacent tangent heights ratherthan mixing ratios at given levels.
Ozone Results
As proposed by Oelhaf and Fischer,35 ozone has beenanalyzed in the 810 cm-' region. In the wholealtitude range from 7 km to 32 km, onion-peelingretrievals could be carried out because of the clearfeatures of the ozone in the spectra. Error barsincrease for lower tangent altitudes because of theshape of the ozone mixing ratio profile: The peaks ofa standard ozone profile in terms of mixing ratio anddensity are at altitudes of approximately 35 km andapproximately 23 km, respectively. Variations ofozone in lower altitudes have a weak impact on thespectrum only. Thus the sensitivity of the spectra totropospheric ozone is low, and huge error bars areobtained. Nevertheless the overall profile that isretrieved fits quite well to previous measurements3 6 37
and proves the applicability of MIPAS-B to nighttimemeasurements of stratospheric ozone (for results, seeFig. 3 and Table 2). Detailed spectra are shown inFig. 4.
Nitric Acid Results
Under certain polar winter conditions, reactions onthe surface of nitric acid trihydrate (HNO3 x 3H20)particles release molecular chlorine and HOC, whichare photochemically converted into their reactiveradical forms such as atomic Cl or ClO in the polarstratosphere. Thus the feasibility of sunlight-inde-pendent HNO3 measurements is important in thecontext of polar stratospheric clouds. In the chemis-try of the mid-latitudinal stratosphere, nitric acidacts as the main reservoir and sink for NO2 and NO.
HNO3 profile retrievals have been carried out in the860-875 cm-' spectral region within the P branch ofthe V5 band. The Q and R branches of the v5 band aswell as the 2v9 band proved to be inappropriate for
o
_ i-
-~0
L_
-0 d ul
MIPAS-B-89A FASCQD2 -Z~~~~~~~~~~~~I
825.0824.0Wavenumber (cm-')
Fig. 4. Example of least-squares best fit within the 03 band:These relatively weak lines had to be used for the ozone retrievalcalculation to avoid too much overlapping of the CO2 bands. Themeasured and calculated spectra refer to a tangent altitude of 16.8km and contain 03, C02 , and H20 lines as well as weak contribu-tions of CFC-22 and C2H6.
retrieval calculations. In particular, the calculatedQ branches of the 2vg band can hardly be comparedwith the measured spectra (see Fig. 5). The informa-tion content of the measured spectra permitted anonion-peeling-type retrieval for all given tangent alti-tudes. The MIPAS-B-89 experiment demonstratedthe feasibility of HNO3 nighttime measurements andled to operation of the MIPAS under polar winterconditions during the EASOE campaign in 1992.
In the altitude region of the stratospheric HNO3maximum the error bars are significantly smallerthan 20% despite the very uncertain auxiliary infor-mation and the only mediocre quality of the spectracompared with later MIPAS-B experiments. Theinformation content of the high-altitude spectra islimited because of the small gas amounts within theline of sight. As for ozone, the retrievability ofmixing ratios below the density maximum is limitedbecause of a broadened contribution function. Re-sults are in very good agreement with the findings offormer experiments (see Fig. 3, Refs. 37-39).
Chlorotluorocarbon Results
Chlorofluorocarbons are halogenated source gasesthat are photolyzed by the sunlight in the strato-sphere. They provide the middle atmosphere withchlorine and fluorine, which cause catalytic ozonedestruction or are converted to buffering reservoirand sink gases by reaction with methane and nitrogendioxide.
Below 21 km the information content of the mea-sured spectra permitted onion-peeling profile retriev-als for CFC's by analysis of their emission bands at850 cm-' (CFC-11) and 920 cm-' (CFC-12). TheCFC profiles above 21 km have been scaled as a wholeby analysis of the 3.4° spectrum. MIPAS-B-89 spec-tra of these high tangent altitudes do not contain
C,)
Tc 0o d.
0U:
Ic1 8 -
0
enough information about CFC's to permit the deter-mination of their altitude distributions. Forwardcalculations for CFC-12 have been carried out withtemperature-dependent cross sections.'7 For CFC-11a band model based on pseudolines, provided byBrown et al.,15 has been used. The results agreequite well with previous measurements,37' 40 if thelong-term increase of CFC's since then is taken intoaccount (see Fig. 3 and Table 2). Correspondingspectra are shown in Figs. 6 and 7.
Discussion
Despite the handicap of the nonoptimum quality ofspectra and the lacking of a priori knowledge on theviewing direction the MIPAS-B-89 limb emissionspectra have turned out to be evaluable, if an appropri-ate retrieval strategy is used. The RAT softwarepackage proved to be a most helpful tool for thispurpose. The retrieved profiles are in good agree-ment with the sunlight absorption measurements ofthe ATMOS experiment, which do not provide night-time or polar winter results. The weaker signal-to-noise ratio had to be compensated for by the redun-dant evaluation of many transitions of the samespecies. For this purpose, it would be helpful if morereliable line data for HN03 were available. This isespecially true for the region between the v5 and 2v9 Qbranches, where the interaction of both bands isstrongest.
Further improvements could be obtained with amore sophisticated model for the temperature andpressure dependence of CFC cross sections. Analy-sis of small spectral features of CFC-22, C2H6, NH3,ClONO2, and water vapor is in progress but is notvery promising because of the limited quality of thedata of this first technological experiment.
A CCl4 profile has not been retrieved, because theCCl4 band at approximately 795 cm-' is superim-posed by a strong CO2 Q branch, which cannot bemodeled properly by FASCOD2. The consideration
0
coI
860.0 870.0 880.0 890.0 900.0Wavenumber (cm-']
910.0 920.0
Fig. 5. Example of least-squares best fit calculated for HNO3bands. Within the P- and Q-branch regions of the HNO3 vs bandaround 870 cm-', good consistency between the calculated andmeasured spectra could be obtained. Because of less reliable linedata in the other regions, where the v5 and 2v9 bands areinteracting, large residuals remain. Note different scaling of theordinate in the spectra and residual plots, which has been neces-sary because of the large discrepancies in the 2v Q branchregion. The spectra refer to the 16.8-km tangent altitude.
c -
iV)
0
921.5 9220 9225 923.0 923.5Wavenumber (cm-')
924.0
Fig. 6. Example of least-squares best fit with CFC-12 crosssections' 4 17 in combination with FASCOD2 line-by-line modelingfor other gases. Thus the temperature dependence of the CFC-12absorption coefficients could be included. There are also weakcontributions of H20 and CO2. The spectra refer to the 16.8-kmtangent altitude.
Fig. 7. Example of least-squares best fit with aline band model,' 5 which implicitly regards the tendence of the CFC-11 absorption coefficients, in cFASCOD2 line-by-line modeling for other gases.contributions of HNO3, 03, H20, and minor featiOCS. The spectra refer to the 16.8-km tangent a
of CO2 line mixing effects that will biFASCOD3 (Ref. 41) would permit analyEband.
Replacing the assumption of spherihby a more sophisticated forward algaresult in a gain in accuracy, especially ving spectra of lower altitudes.
Conclusion and Outlook
The MIPAS concept proved to be a pomthe simultaneous measurement of atmcconstituents. In spite of the malfunctsubsystems during this first technologic,tra of scientific value have been recordievaluated. Altitude distributions of Itrace gases have been retrieved. Mostshortcomings during this first flight cccompensated for by a highly sophisticstrategy.
The scientific output of the MIPAS-Bwill be considerably higher, because tspectra are of much better quality winoise, calibration, and spectral resolispacing of tangent heights leads to a bresolution of the retrieved profiles, and tspectral interval (1170 to 1400 cm-retrieval of further important climaterelevant trace gases: N205, N20, ananalysis of the MIPAS-B-90 data isSemiquantitative analysis of the spectiexistence of N205.3 This is, as far as,first mid-latitude measurement of threservoir gas during the night.
Further improvements in the MIPAachieved for its third and fourth fligh1991-1992 EASOE campaign. Thesedetailed information about how mucatmosphere has been prepared for majo]tion, which might be comparable withozone hole scenarios. The spectra hav(
completely analyzed, but very interesting results,AS-B-89 especially for CONO 2 and N20 5, are expected.
Preliminary analysis suggests strikingly high amountsof the reservoir gas ClONO2 below 20 km in March1992.42,43 Unfortunately, the series of MIPAS-B ex-periments cannot be continued because of the gon-dola crash after the instrument's second flight duringthe EASOE campaign.
Motivated by the success of this first MIPAS-B limbemission experiment, the development of the nextgeneration of balloon-borne MIPAS experiments hasbeen started. Furthermore, there are plans to oper-
8520 ;sL.0 ate a modified MIPAS instrument from high-altitudeaircraft to detect vertical cross sections of trace gas
CFC-11 pseudo- distributions over wide areas. Also, a MIPAS space-mperature depen- borne instrument based on a classical Michelson-typeombination with interferometer is developed for a launch with the first
There are also European Polar Platform under responsibility of thelres of C2 H6 and European Space Agency.titude.
The German Ministry for Research and Technol-ogy has supported the development of the MIPAS
a included in instrument and the campaign. The radiosonde datasis of the CCl4 were made available by the Deutscher Wetterdienst
(German Weather Service). Without the cooperativecal symmetry collaboration of the Centre National d'Etudes Spatia-rithm would les team the entire experiment could not have taken
when evaluat- place.
References and Notes1. P. Burkert, F. Fergg, and H. Fischer, "A compact high-
rerful tool for resolution Michelson Interferometer for Passive Atmospheric)spheric trace Sounding (MIPAS)," IEEE Trans. Geosci. Remote Sensing[on of several GE-21, 345-349 (1983).al flight, spec- 2. H. Fischer, H. Oelhaf, F. Fergg, C. Fritzsche, C. Piesch, D.
ad and partly Rabus, M. SeefeIdner, F. Friedl-Vallon, and W. Vilker, "Limbfobur relevant emission measurements with the balloon version of the Mich-exereentL elson Interferometer for Passive Atmospheric Soundingexperimental (MIPAS)," in Digest of Topical Meeting on Optical Remoteuld be partly Sensing of the Atmosphere, Vol. 4 of 1990 OSA Technical
ited retrieval Digest Series (Optical Society of America, Washington, D.C.,1990), pp. 150-153.
-90 campaign 3. H. Oelhaf, T. v. Clarmann, F. Fergg, H. Fischer, F. Friedl-he measured Vallon, C. Fritzsche, C. Piesch, D. Rabus, M. SeefeIdner, andth respect to W. V6lker, "Remote sensing of trace gases with a balloon borneition. Finer version of the Michelson Interferometer for Passive Atmo-etter altitude spheric Sounding (MIPAS)," in Proceedings of the Tenth;he additional European Space Agency Symposium on European Rocket and
allows te 1Balloon Programmes and Related Research, ESA SP-317- allows the (European Space Agency, Nordwijk, The Netherlands, 1991),I- and ozone- pp.207-213.d CH4. The 4. H. Fischer, F. Fergg, F. Friedl-Vallon, C. Fritzsche, H. Oelhaf,in progress. C. Piesch, D. Rabus, M. Seefeldner, and W. Voelker, "Balloon-
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nung mit Linie-ftir-Linie-Computerprogrammen," Diplomar-
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