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The radiometric performances of the Planetary Fourier Spectrometer for Mars exploration
\ PERGAMON
Planetary and Space Science 36 "0888# 330Ð349
The radiometric performances of the Planetary Fourier Spectrometer for Mars exploration E[ Palombaa\ \ L[ Colangelia\ V[ Formisanob\ G[ Piccionic\ N[ Cafarob\ V[ Morozd a
Osservatorio Astronomico di Capodimonte\ Via Moiariello 05\ 79020 Napoli\ Italy Istituto di Fisica dello Spazio Interplanetario\ CNR\ Via Fosso del Cavaliere\ 99022 Roma\ Italy c Istituto di Astro_sica Spaziale!Reparto di Planetolo`ia\ CNR\ Via Fosso del Cavaliere\ 99022 Roma\ Italy d IKI!Space Research Institute of the Russian Academy of Science\ Profsojuznaja 73:21\ 006709 Moscow\ Russia b
Received 04 January 0887^ received in revised form 0 September 0887^ accepted 07 October 0887
Abstract The {Planetary Fourier Spectrometer| "PFS# is a Fourier transform interferometer\ operating in the range 0[1Ð34 mm[ The instrument\ previously included in the payload of the failed mission Mars ?85\ is proposed for the future space mission Mars Express\ under study by ESA[ The present paper is aimed at presenting the radiometric performances of PFS[ The two channels "LW and SW# forming PFS were analysed and characterised in terms of sensitivity and noise equivalent brightness[ To cover the wide spectral range of PFS\ di}erent blackbodies were used for calibration[ The built!in blackbodies\ needed for the in!~ight calibrations\ were also characterised[ The results show that the LW channel is comparable with IRIS Mariner 8 in terms of noise equivalent brightness[ The SW channel performances\ while satisfactorily\ could be improved by lowering the sensor operative temperature[ A simple model of the Mars radiance is used in order to calculate the signal!to!noise ratio on the spectra in typical observation conditions[ The computed signal!to!noise ratio for the LW channel varies between 329 and 39\ while for the SW channel it ranges from 049 to 29[ The radiometric analyses con_rm that PFS performances are compliant with the design requirements of the instrument[ PFS is fully validated for future remote exploration of the atmosphere and the surface of Mars[ Þ 0888 Elsevier Science Ltd[ All rights reserved[
0[ Introduction The {Planetary Fourier Spectrometer| "hereafter PFS# is a Fourier transform interferometer\ operating in the range 0[1Ð34 mm\ that was included in the payload of the Mars ?85 space mission[ Unfortunately\ this mission failed just after the launch in November 0885 and the scienti_c payload was lost[ Nevertheless\ the spare model of PFS is still available and is proposed to become the ~ight version for a future mission to Mars\ presently under study by ESA] Mars Express[ This renewed interest for PFS makes it important to report the results of cali! bration measurements\ performed on the available model in the performance veri_cation phase of the instrument[ In a previous paper Palomba et al[ "0886# reported the results of spectroscopic measurements\ obtained with various models produced during the PFS study and devel! opment program[ However\ a complete characterisation of the instrument must account for radiometric measure! ments\ too[ The aim of the present work is to report the
Corresponding author[ Fax] 99 28 70 34509^ e!mail] palombaÝ astrna[na[astro[it:palombaÝcosmic[na[astro[it
results of radiometric calibration sessions\ performed in parallel with spectroscopic tests to fully characterise PFS[ The ground!based spectroscopic and radiometric measurements\ once coupled with in!~ight calibration data which will be available thanks to PFS built!in cali! brated sources\ will form a set of reference data necessary to handle and calibrate correctly the PFS results[ The scienti_c goals of PFS are described in detail in previous papers to which we refer the reader "e[g[ For! misano et al[\ 0882\ 0885\ 0886#[ Here we recall brie~y that PFS is designed to achieve the primary goal of study! ing the Martian atmosphere[ Through inversion methods "Smith\ 0869^ Chahine\ 0857\ 0861#\ the spectral pro_le of dominant features will be used to obtain a detailed description of temperature _eld and pressure pro_le[ A global long term monitoring of the three!dimensional temperature _eld in the lower atmosphere "from the sur! face up to 39 km# will be possible[ Measurements of the minor constituent "e[g[ water vapour# variations and search for traces of other components are envisaged[ The optical properties of the aerosol "dust\ ice and hazes# will be studied in order to determine their chemical com! position and size distribution[ As far as surface studies are concerned\ PFS can provide hints about the temperature
9921Ð9522:88:, ! see front matter Þ 0888 Elsevier Science Ltd[ All rights reserved[ PII] S 9 9 2 1 Ð 9 5 2 2 " 8 7 # 9 9 0 1 4 Ð 0
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distribution\ as well as the thermal inertia from the daily thermal variations[ The PFS is also sensitive to re~ected solar energy at the shorter wavelengths and can provide surface compositional information[ The spectroscopic coverage of selected areas should allow us to place restric! tions on the mineralogical composition of the surface layer\ to determine the nature of condensed materials\ as well as their seasonal variations in composition[ The results reported in the present paper have been obtained on the PFS ~ight spare version "labelled PFS96# at the Istituto di Fisica dello Spazio Interplanetario "IFSI*CNR#\ before the production of the ~ight model[ The obtained data demonstrate that the overall charac! teristics of the instrument are compatible with the design speci_cations and can achieve the planned scienti_c goals[ In Section 1\ we describe the experimental set!up and the approach followed to perform radiometric measurements on PFS96[ The approach to data analysis is reported in Section 2\ while the results are presented in Section 3[ Finally\ Section 4 is devoted to a discussion of the infor! mation derived from the experimental data about the PFS performances for the application to Mars study[ 1[ Experimental We recall that PFS is a Fourier spectrometer based on a double!pendulum design\ formed by two parallel channels covering the spectral ranges SW 0[1Ð3[7 mm and LW 3[7Ð34 mm "see Formisano et al[\ 0882\ 0885\ 0886 for more details#[ The instrument design speci! _cations are summarised in Table 0[ The LW channel is equipped with a pyro!electric sensor "LiTaO2#\ able to convert temperature gradients with respect to time into alternate current "AC#[ It should be pointed out that the LW channel works as a di}erential instrument] the higher the temperature di}erence between the sensor and the
target\ the higher the recorded signal^ if the two tem! peratures are equal then the signal measured is almost null[ The SW sensor is a photo!conductive PbSe semi! conductor^ to minimise the thermal noise "photon generation by high temperature# it is cooled at a tem! perature between 134 and 140 K[ The temperature for both the sensors is set and controlled by the PFS main electronics[ To perform quantitative radiometric measurements\ PFS was placed on a bench in a thermo!vacuum chamber of about 0599 l[ The chamber has six ~anges and a win! dow for visual inspection of the internal set!up[ The pumping group "pre!vacuum plus cryogenic pump# allows a high vacuum of about 09−6 mbar to be achieved[ The chamber temperature can be varied from ¦099 to −59>C overall\ via a gas compression!expansion process[ The temperature of the instrument\ and of the sensors in particular\ was continuously controlled and monitored "engineering data#[ Several interferogram acquisitions were performed by pointing PFS at di}erent calibrated blackbodies\ whose temperature was _xed and monitored "engineering data#[ The PFS spectral range is so wide and the technical characteristics of the two channels are so di}erent that di}erent calibrated blackbodies had to be used for the SW and LW spectral ranges[ Moreover\ two main sessions of measurements were performed on PFS\ before and after mechanical vibration tests needed to qualify the instru! ment for launch and ~ight stresses[ For the LW channel\ four calibration blackbodies were used before the vibration] one simulating Mars "hereafter BB0#\ one simulating the deep space "hereafter BB1#\ the module A!LW "the LW built!in blackbody# and another blackbody "BB2#[ Thanks to the operation of the PFS scanner "i[e[ the pointing device# it was possible to per! form sequential measurements on the di}erent black!
Table 0 Main design characteristics for the SW and LW channels of PFS
Mirror displacement Displacement time Speed Measurement time Optical path di}erence Spectral resolution Wavenumber range Wavelength range Resolving power Nominal reference source wavelength Beamsplitter material Field of view Throughput
LW
SW
2 4 9[5 3[985 25 1[92 111Ð1972 34Ð3[7 0930 0[1 CsI 9[924 9[933
2 4 9[5 3[985 25 1[92 1972*7222 3[7Ð0[1 3055 0[1 CaF1 9[906 9[995
mm s mm s−0 s mm cm−0 cm−0 mm mm rad cm1 sr
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bodies[ Each session of measurements consisted of several acquisitions according to the following sequence] BB0ÐBB0ÐBB2ÐBB0ÐBB0ÐBB1ÐBB0ÐBB0ÐA!LW In di}erent sequences the blackbodies and the LW detec! tor temperature varied[ A summary of the sequences and the temperature ranges measured is shown in Table 1[ A total number of 2 sessions\ each consisting of about 19 sequences was collected[ After vibrations the scanner was not operative for the LW session\ so that measurements were performed on BB0 only[ In the case of the SW channel\ a blackbody "BBSW# and the module A!SW "the SW built!in blackbody# were used[ The BBSW is formed by a source illuminating an aluminium screen\ whose re~ectivity and emissivity are known quantities "Moroz\ personal communication#[ Two sessions of measurements were performed\ one before and one after vibrations[ In each session about 09 sequences\ in which measurements of the two sources
were alternatively repeated\ were acquired[ In di}erent sequences the BBSW temperature was changed\ as indi! cated in Table 1[ In some cases the internal dark walls of the chamber were observed to monitor the background level[ The SW detector temperature was stable between 134[4 and 135[5 K in the _rst session and between 138[8 and 140[2 K in the second one[ Thus\ we can exclude variations in the PbSe sensitivity due to temperature e}ects[ In order to perform a thorough characterisation of the PFS radiometric performances\ given the wealth of available data a selection of the sessions more appro! priate for the data analysis was done[ Many inter! ferograms had to be discarded because their intensity exceeded the full span of the analog to digital converter "ADC# "hereafter\ such interferograms will be referred to as saturated interferograms#[ In the case of LW\ this happened especially when BB0 or BB1 were at tem! perature ³069 K[ This problem was subsequently solved by changing the pyroelectric preampli_er hardware
Table 1 Summary of the PFS radiometric calibration campaign[ For each session of measurement there are indicated all the temperature ranges of interest LW channel
SW channel Temperature ranges "K#
1 Sessions before the vibration Session A 19 Sequences of measurement
Session B 19 sequences of measurement
0 Session before the vibration Td "171[5Ð182[4# TIB "170[6Ð181[1# TBB0 "026Ð185# TBB1 "091Ð108# TBB2 "174Ð182# TA!LW "168Ð178#
09 Sequences of measurement
Td "134[4Ð135[5# TBBSW "0617Ð1207#
Td "174[5Ð177[9# TIB "173[4Ð176[9# TBB0 "068Ð167# TBB1 "82Ð064#
0 Session after the vibration 12 Sequences of measurement
Temperature ranges "K#
0 Session after the vibration Td "173[9Ð182[9# TIB "179[0Ð182[9# TBB0 "033Ð111#
09 Sequences of measurement
Td "138[8Ð140[2# TBBSW "1057Ð1252#
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reducing the gain by a factor two[ We have also noticed that several BB0 spectra\ taken immediately after BB1 spectra\ show an intensity reduction with respect to the other BB0 spectra in the sequence[ This is probably due to a decrease of the detector temperature during the measurement of BB1 "which is at temperature much less than that of BB0#] a sort of {memory e}ect|[ For this reason BB0 spectra recorded immediately after BB1 acquisitions were discarded in our analysis[ An accurate analysis of this phenomenon is beyond the scope of this work\ however we can assume that it would be of limited importance during mission operations\ when huge ther! mal gradients respect to time will be rare[ On the other hand\ an overall knowledge of the e}ect will be desirable in order to calibrate correctly the data returned from the orbiter[ Moreover\ in our analysis we have assumed negligible the temperature variations of the LW detector[ 2[ Data analysis The spectrum of a blackbody\ Sbb"n#\ measured by the LW channel as a function of the wavenumber\ n\ can be expressed as] Sbb"n# R"n#ðB"Tins\n#−B"Tbb\n#Ł
"0#
where R"n# is the sensitivity function of the LW channel\ B"T\n# is the Planck function and Tins and Tbb are the instrument and the blackbody temperature\ respectively[ If the instrument temperature is constant while observ! ing blackbodies at di}erent temperatures\ from eqn "0# it is possible to compute the sensitivity function of the LW channel] Sbbi"n#−Sbbj"n# R"n# ðB"Tbbj\n#−B"Tbbi\n#Ł
S"n# R"n#
while B"Tins\n# can be expressed as]
Sbb"n# ¦B"Tbb\n# R"n#
"3#
Thus\ from eqns "1#\ "2# and "3#\ we obtain] I"n#
Sbb0"n#−S"n# ðB"Tbb1\n#−B"Tbb0\n#Ł¦B"Tbb0\n# Sbb0"n#−Sbb1"n# "4#
This relation can be used to determine the spectral radi! ance for module A!LW or BB2 from their spectra and\ then\ their temperature to be compared with the engin! eering data[ Similarly\ the instrument temperature can be computed starting from the spectral radiance\ Iins"n#] Iins"n#
Sbb0"n# ðB"Tbb1\n#−B"Tbb0\n#Ł¦B"Tbb0n# Sbb0"n#−Sbb1"n# "5#
where Sins"n# is zero "see eqn "0##[ The noise equivalent brightness\ NEB"n#\ of the instru! ment is given by the standard deviation\ s\ expressed in radiometric units\ of the spectral radiance for a given source] "6#
NEB"n# s"I"n##
Following Hanel et al[ "0860#\ the error on I"n# derives\ primarily\ from the ~uctuations of S"n# "see eqn "4#\ thus the NEB"n#\ can be written as] NEB0"n# s"S"n##
B"Tbb1\n#−B"Tbb0\n#Ł Sbb0"n#−Sbb1"n#
X
"1#
In a _rst approach "AP0#\ we have used for Sbbi"n# and Sbbj"n# the averages of spectra measured within each sequence "see Section 1# for the two blackbodies BB0 and BB1[ Alternatively\ it is possible to use for Sbbi"n# and Sbbj"n# the average spectra of the BB0 blackbody at two di}erent temperatures "approach AP1#[ In this case\ we have considered for Sbbi"n# the BB0 average spectrum corresponding to the sequence in which it reached the maximum temperature and we have used as Sbbj"n#\ in turn\ all the average spectra relative to sequences with di}erent BB0 temperatures[ For n!sequences\ we com! puted n!0 di}erent sensitivities and we took the average[ Starting from eqn "0#\ the spectral radiance of a black! body\ I"n#\ can be retrieved from its spectrum S"n# as] I"n# B"Tins\n#−
B"Tins\n#
"2#
sðSi"n#−S Þ"n#Ł1 i
n−0 R"n#
"7#
where the i!index runs over all the considered spectra and S"n# is the average spectrum[ Þ For comparison\ an alternative approach has been applied to calculate the NEB"n# function[ For the k!th spectrum a smooth function\ SMk"n#\ has ben computed\ by a running average over nine points of the spectrum\ and the ~uctuations of the spectrum around SMk"n# have been considered[ Thus\ the k!th NEB"n# has been obtained by]
NEB1k"n#
X
ðSk"n#−SMk"n#Ł1 R"n#
"8#
The _nal NEB1"n# is the average of the NEB1k"n# func! tions calculated for the spectra taken into account in the computation[ We modelled the Martian spectral radiance\ Ltot"n#\ as the combination of two terms] the re~ected sunlight\ Lref"n#\ and the grey body emission\ Lem"n#[ So that]
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Ltot"n# Lref"n#¦Lem"n# A
r1 D
B"TS\n#¦oB"TM\n# 1
"09#
where A is the bolometric albedo "i[e[ the fraction of solar radiation re~ected in all directions# of the Martian surface\ r 3[55 09−2 AU is the radius of the Sun\ D 0[41 AU is the Mars mean heliocentric distance\ TS 4799 K is the Sun photosphere temperature\ TM and oM are the Mars surface temperature and emissivity[ In order to compute the signal!to!noise ratio\ S:N\ three cases were considered "Kei}er et al[\ 0865\ 0866^ Pleskot and Miner\ 0870^ Lumme and James\ 0873#] a bright region in spring "A 9[16\ TM 119 K#\ a dark region in summer "A 9[05\ TM 189 K# and the south polar cap in winter "A 9[68\ TM 039 K#[ The Martian radiance\ shown in Fig[ 0\ was calculated for the three sets of parameters and making the approximation that oM 0 "although emissivity changes with wavelength and surface material#[ The S:N is given by] S:N"n#
Ltot"n# NEB"n#
"00#
For the SW channel\ the spectrum recorded by looking at a source with radiance I"n# is given by] S"n# R"n#I"n#¦D"n#
"01#
where D"n# is the thermal noise\ that can be measured in dark conditions by pointing at the chamber walls or at the BBSW\ once switched o}[ The radiance of BBSW is] V I"Tbbsw\n# B"Tbbsw\n#ral"n#o p
"02#
334
of BBSW and V 1[5333 09−3 sr " ratio between the area of the exit hole of the source and the distance of the hole from the aluminium screen#[ Starting from eqn "01#\ the sensitivity function for the SW channel is] R"n#
S"n#−D"n# I"n#
"03#
eqns "7#\ "8# and "01#\ used to compute the NEB and S:N functions for the LW\ are still valid for the SW case[ Finally\ the radiance of the module A!SW can be deter! mined from] I"n#
S"n#−D"n# R"n#
"04#
3[ Results 3[0[ The LW channel For the LW channel we have performed the data analy! sis on two di}erent sessions of measurement\ hereafter A and B\ before the vibration tests[ They consisted of 19 di}erent sequences each\ in which BB0 and BB1 tem! peratures were varied[ For session A\ it was possible to compute the sensitivity by the two approaches\ AP0 and AP1 "see Section 2#[ Instead\ AP1 only was applied to session B as the interferograms of BB1 were saturated due to its low temperature "³069 K#[ Out of the 19 sequences forming session A we selected 2 of them\ characterised by fully unsaturated interferograms\ to apply AP0[ An average of the three sensitivity deter! minations was _nally computed and is shown in Fig[ 1[ The R"n# function has a maximum of about 9[21 Digital
where Tbbsw is the BBSW temperature\ ral"n# is the re~ect! ivity of the aluminium screen\ o 9[88 is the emissivity
Fig[ 0[ Expected radiance from Mars for three di}erent conditions[
Fig[ 1[ Sensitivity of the LW channel computed by the two di}erent approaches] AP0 "continuous line# and AP1 "dotted line#[ The errors on each curve are lower than 5) in the 199Ð0199 cm−0 interval[
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Units "erg s−0 cm−1 sr−0 cm#−0 at around 349 cm−0 and is ×9[19 Digital Units "erg s−0 cm−1 sr−0 cm#−0 in the range 299Ð0999 cm−0[ To compute the sensitivity by AP1\ we considered the average BB0 spectra from 2 di}erent sequences in session A and from 09 sequences in session B[ The resulting R"n# function matches that obtained by AP0 "see Fig[ 1#\ within the experimental errors[ The periodic oscillation superimposed on the general behav! iour of both sensitivity curves is attributed to the dichroic mirror optical properties[ The measurements performed on BB0 after the vibration tests were analysed by AP1[ The ratio between sensitivities obtained before and after the vibrations is about 9[7\ fairly constant with wavenumber[ This slight worsening in the overall instrument sensitivity "present also for the SW channel\ see below# is probably due to a little optical misalignment produced by the vibration tests[ By inserting the sensitivity computed by AP0 into eqns "7# and "8# we obtained the NEB0 and NEB1 functions[ Only sequences where three or four spectra of BB2 and module A!LW are available were considered[ The _nal NEB0 is an average over 06 di}erent determinations[ To retrieve the average NEB1\ three sequences of the A session were considered and BB0 and BB1 spectra were used[ The results shown in Fig[ 2 look very similar and are close to the theoretical curve calculated on the basis of the instrument design and the measured spectral response of the optical components "Hirsch\ 0885#[ The NEB remains below 0 erg s−0 cm −1 sr−0 cm up to 0299 cm−0 and reaches a minimum of about 9[2 erg s−0 cm−1 sr−0 cm\ between 249 and 349 cm−0[ The S:N for the LW channel\ derived from eqn "00# for the three Mars environment cases presented in Section
Fig[ 2[ Average NEB0 "dotted line# and NEB1 "continuous line# for the LW channel[
Fig[ 3[ The LW S:N for di}erent temperatures of the Martian surface[
2\ is shown in Fig[ 3[ The maximum values are 39\ 199 and 399\ for T 039\ 119 and 189 K\ respectively\ and fall in the spectral range 249Ð499 cm−0[ The S:N remains larger than 09 up to 0199 cm−0 for TM 119 K and up to 0699 cm−0 for TM 189 K\ while for the coldest regions the S:N is larger than 0 in the 199Ð0999 cm !0 spectral range[ Finally\ we have computed the spectral radiance of BB2 and of the module A!LW by using eqn "4# and that of the instrument by using eqn "5#[ For this purpose we chose the same three sequences of the A session used in the previous analysis[ Then\ we have _tted the obtained pro_les by a Planck function in the spectral region of high NEB "i[e[ 399Ð799 cm−0#[ As an example\ the retrieved radiance of module A!LW is shown in the top of Fig[ 4^ it is well matched by a Planck function at T 179[0 K\ as evidenced by the ratio of the two curves in the bottom of the same _gure[ The temperatures derived by this approach for BB2\ the module A!LW and the instrument\ have an error of less than 1) and are compared in Table 2 with the engineering data[ The determined instrument temperature must be considered as an {e}ective| value\ which accounts for the contributions to the radiance of both the detector and the rest of the instrument "Hanel et al[\ 0881#[ For this reason it is compared with the temperature of the detector and of the PFS interferometer block "an average of data over eight check points of the optical bench#[ In general\ the retrieved temperatures are in good agreement[ In some cases a little di}erence is found\ probably due to the fact that the instrument tem! perature is not actually constant as assumed[ Moreover\ wider BB0 and BB1 temperature variations imply larger uncertainties in the A!LW\ BB2 and instrument tem! perature determination "see\ e[g[\ sequence 2 in Table 2#[
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Fig[ 4[ The computed module A!LW radiance "top# and its ratio by a Planck function at 179[0 K "bottom#[
3[1[ The SW channel Six series of spectra\ recorded for di}erent BBSW tem! peratures\ have been chosen for our analysis\ while other four series have been excluded\ as the interferograms were saturated[ The obtained SW average sensitivity is shown in Fig[ 5[ It reaches a maximum value of 9[6 Digital Units "erg s−0 cm−1 sr−0 cm#−0\ around 1399 cm−0\ and is above 9[0 Digital Units "erg s−0 cm−1 sr−0 cm#−0 up to 4499 cm−0[ Many features are visible between 1799 and 2999 cm−0\ probably due to contamination residues present in the thermovacuum chamber[ Among the data collected after vibration\ four di}erent sequences have been selec!
336
ted[ The sensitivity function is very similar to that com! puted before the vibration tests\ but the maximum around 1299Ð1399 cm−0 is slightly lower] 9[4 Digital Units "erg s−0 cm−1 sr−0 cm#−0[ In Fig[ 6 the NEB0 and NEB1 functions computed by using only unsaturated spectra at the highest gain of the detector ampli_er are shown[ The NEB0 is lower than 9[0 erg s−0 cm−1 sr−0 cm up to 4599 cm−0 and reaches a minimum of 1[1×09−1 erg s−0 cm−1 sr−0 cm around 1699 cm−0[ The NEB1 has a similar shape\ but is lower by a factor of 2 in the spectral region 1999Ð1499 cm−0^ it reaches a minimum value around 0[0×09−1 erg s−0 cm−1 sr−0 cm around 1399 cm−0 and remains below 0×09−0 erg s−0 cm−1 sr−0 cm up to 5999 cm−0[ We recall that the theoretical NEB\ computed for a PbSe detector tem! perature of 084 K\ reaches a minimum of 3×09−2 erg s−0 cm−1 sr−0 cm "Hirsch\ 0885#[ The discrepancy by a factor 2 with measurements is primarily a consequence of the worsening in the S:N\ as the actual detector temperature "around 135 K# is higher than the value assumed for the computation "084 K#[ Indeed\ this temperature di}erence implies a decrease by a factor 1 of the PbSe detector output "Palomba\ 0884# and a noise increase of a factor 0[0\ by assuming a Johnson noise[ These factors lead to a S:N reduction of about 1[1 and\ thus\ an equivalent increase in NEB[ Moreover\ in our measurements we have noted that\ by increasing the gain of the detector ampli_er\ the NEB decreases and the interferogram peak intensity increases[ This suggests a direct relation] the higher the signal the lower the NEB[ For this reason\ in the computation of the NEB "see Fig[ 6# and of the S:N "reported in Fig[ 7# we have used only unsaturated measurements at the highest detector gain[ As for the LW range\ we have considered the radiance from the Mars surface shown in Fig[ 0\ to compute the S:N function[ The maximum S:N for the polar and for the bright regions is obtained at 3299Ð3399 cm−0 with a value of 049 and 49 for the two cases\ respectively[ For the dark regions the thermal contribution prevails over the re~ected one in the spectral range 1999Ð2999 cm−0\ where S:N reaches a maximum of about 049 around 1499 cm−0[ These results con_rm that the higher the albedo\ the higher the S:N[ However\ it should be pointed out the importance of the thermal radiance for the SW spectral region\ especially in the range 1999Ð 2999 cm−0[ The last example is particularly instructive\ as it indicates the possibility of measuring spectra at very good S:N on low albedo regions at high tem! perature "T ¼ 189 K#[ With the previous information\ it has been possible to retrieve the absolute spectrum of the built!in SW lamp\ i[e[ the module A!SW[ It is characterised by a nearly constant brightness pro_le between 0 and 1 erg s−0 cm−1 sr−0 cm in the spectral range 2999Ð7999 cm−0\ with a cut! o} at 1349 cm−0[ This trend is con_rmed by measure! ments after vibrations[
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E[ Palomba et al[ : Planetary and Space Science 36 "0888# 330Ð349 Table 2 Comparison between retrieved and engineering temperatures of BB2\ TBB2\ module A!LW\ TA!LW\ and the LW detector\ Td[ The temperature measured on the interferometer block\ TIB\ is also reported Sequence 0
1
2
0
Td TIB TBB2 TA!LW Td TIB TBB2 TA!LW Td TIB TBB2 TA!LW
Engineering data "K#
Retrieved temperature "K#
171[7429[93 171[0929[0 175[2929[0 167[1929[00 168[8929[00 171[6029[97 170[7929[0 175[5929[0 167[4929[00 179[1929[0 171[4629[93 170[99[6929[0 176[1929[0 168[9929[00 179[6929[00
170[8929[6 171[8929[8 170[1929[5 179[4920 171[0920[1 179[09200 168[9923 17023 167[9923
Values measured at two di}erent checking points[
Fig[ 5[ Sensitivity of the SW channel[
Fig[ 6[ Comparison between NEB0 "dotted line# and NEB1 "continuous line# for the SW channel[
4[ Discussions and conclusions The most relevant function derived from the radio! metric measurements that characterises the PFS per! formances\ is the noise equivalent brightness[ For the LW channel it is well within the design limits and is comparable to that of the IRIS instrument on board Mariner 8 "Hanel et al[\ 0861#[ This corresponds to a maximum S:N on a single spectrum of some hundreds\ by observing the hottest regions of Mars\ and of about 39\ for the coldest areas[ On the contrary\ the NEB obtained for the SW channel is slightly worse than expected and should be improved by reducing the sensor operative temperature[ The maximum S:N for a single
spectrum in the SW channel is about 049\ for the highest albedo regions\ and about 29\ for the darkest regions[ High S:N is needed for atmospheric studies\ such as the determination of the 01C:02C\ 05O:07O and 05O:06O isotopic ratios\ the estimate of upper limits for possible minor constituents and the discerning of their bands[ This can be accomplished by summing over an adequate number of spectra\ as done e[g[ by Maguire "0866# for the IRIS spectra\ which can increase the S:N by a factor of tens[ The wide spectral range covered at high spectral resolution by PFS "Palomba et al[\ 0886# will allow new investigations in this sense[ Moreover\ the retrieving of the temperature pro_le will be possible by means of inver!
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data reported in the present work and by Palomba et al[ "0886#\ some improvement is still possible in the sensor performances\ while the overall design and optical struc! ture appear fully compatible with the scienti_c goals to be achieved] investigation of mineralogy\ climate and atmospheric chemistry of Mars[ Acknowledgements We thank E[ Zona for his technical assistance during experiment execution and Dr M[S[ Robinson for his use! ful comments about the manuscript[ This work was sup! ported by MURST\ CNR and ASI[ Ernesto Palomba received support under a contract from Osservatorio Astronomico di Capodimonte[ Fig[ 7[ The SW S:N for di}erent Martian surface conditions[
References sion methods applied to both the 556 cm−0 bending and the 1936 cm−0 stretching bands of CO1\ taking also into account the scattering e}ects due to the aerosols dispersed in the atmosphere[ High sensitivity and high spectral resolution are sim! ultaneously needed in order to discriminate the diagnostic features of di}erent minerals forming the Martian soil or aerosols\ which are weak and often occur spectrally very close[ Furthermore\ a high S:N o}ers the possibility of detecting weak features\ in absorption or emission\ due to trace minerals mixed in the surface rock deposits or suspended in the atmosphere[ As an example\ we recall that KAO "Kuiper Airborne Observatory# observations of Mars at a S:N comparable to that of PFS in the LW channel allowed Pollack et al[ "0889# to identify several spectral features of carbonates and sulfates\ for the aero! sol constituents\ or hydrates and silicates\ for the surface\ in the 4[3Ð09[4 mm spectral range[ Moreover\ Wagner and Schade "0885# computed that a 2) carbonate content in an analogue soil mixture\ for a 144 K Mars surface temperature\ produces a 9[94 relative strength in the 3 mm band[ This means that a minimum S:N of 19 is necess! ary to detect that feature[ Again for carbonates\ Calvin et al[ "0883#\ by analysing Mariner 5 and 6 spectra with highly variable "4Ð049# S:N\ found a 4[3 mm band assigned to hydrous carbonates[ All the previous require! ments are well within the capabilities of the instrument[ In addition\ although at the limit of the PFS sensitivity\ it should be stressed that it is possible to detect in emiss! ivity the Christensen and the Reststrahlen features of an iron!substituted montmorillonite clay at a 04) content in a Martian analogue soil mixture with a S:N of at least 099 "Roush and Orenberg\ 0885#[ In conclusion\ PFS for its radiometric and spec! troscopic performances appears as a suitable instrument for future remote exploration of Mars[ According to the
Calvin\ W[M[\ King\ T[V[V[\ Clark\ R[\ 0883[ Hydrous carbonates on Mars<] evidence from Mariner 5:6 infrared spectrometer and ground! based telescopic spectra[ J[ Geophys[ Res[ 88\ 03548Ð03564[ Chahine\ M[T[\ 0857[ Determination of the temperature pro_le in an atmosphere from its outgoing radiance[ J[ Opt[ Soc[ Am[ 47\ 0523Ð 0526[ Chahine\ M[T[\ 0861[ A general relaxation method for inverse solution of the full radiative transfer equation[ J[ Atmos[ Sci[ 18\ 630Ð636[ Formisano\ V[\ Moroz\ V[\ Amata\ E[\ Baldetti\ P[\ Bellucci\ G[\ Chion! chio\ G[\ Matteuzzi\ A[\ Orfei\ R[\ Piccioni\ G[\ Carusi\ A[\ Coradini\ A[\ Cerroni\ P[\ Capaccioni\ F[\ Adriani\ A[\ Viterbini\ M[\ Angrilli\ F[\ Baglioni\ P[\ Bianchini\ G[\ Fanit\ G[\ Bussoletti\ E[\ Fonti\ S[\ Mancini\ D[\ Colangeli\ L[\ Grigoriev\ A[\ Moshkin\ B[\ Zasova\ L[\ Sanko\ N[\ Nikolsky\ Y[V[\ Gnedykh\ V[\ Kiselev\ A[\ Khatuntsev\ I[\ Gonharov\ S[\ Titov\ D[\ Hirsch\ H[\ Arnold\ G[\ Orleansky\ P[\ Combes\ M[\ Michel\ G[\ Rodrigo\ R[\ Lopez Moreno\ J[J[\ Rod! rigues Gomez\ J[\ Olivares\ I[\ 0882[ Planetary Fourier spectrometer] an interferometer for atmospheric studies on board Mars 83 mission[ Il Nuovo Cimento 05\ 464Ð477[ Formisano\ V[\ Moroz\ V[\ Hirsch\ H[\ Oleansky\ P[\ Michel\ G[\ Lopez Moreno\ J[J[\ Amata\ E[\ Bellucci\ G[\ Piccioni\ G[\ Chionchio\ G[\ Carusi\ A[\ Coradini\ A[\ Cerroni\ P[\ Capria\ M[T[\ Capaccioni\ F[\ Adriani\ A[\ Viterbini\ M[\ Angrilli\ P[\ Bianchini\ G[\ Saggin\ B[\ Fonti\ S[\ Bussoletti\ E[\ Mancini\ D[\ Colangeli\ L[\ Grigoriev\ A[\ Moshkin\ B[\ Gnedykh\ V[\ Matsygorin\ I[A[\ Patsaev\ D[\ Nikolsky\ Y[V[\ Titov\ D[\ Zasova\ L[\ Khatuntsev\ I[\ Kiselev\ A[\ Arnold\ G[\ Driesher\ H[\ Blecka\ M[I[\ Rodrigo\ R[\ Rodriguez Gomez\ J[\ 0885[ Infrared spectrometer PFS for the Mars 83 orbiter[ Adv[ Space Res[ 06\ 01"50#Ð"01#53[ Formisano\ V[\ Moroz\ V[\ Angrilli\ F[\ Bianchini\ G[\ Bussoletti\ E[\ Cafaro\ N[\ Capaccioni\ F[\ Capria\ M[T[\ Cerroni\ P[\ Chionchio\ G[\ Colangeli\ L[\ Coradini\ A[\ Di Lellis\ A[\ Fonti\ S[\ Orfei\ R[\ Palomba\ E[\ Piccioni\ G[\ Saggin\ B[\ Ekonomov\ A[\ Grigoriev\ A[\ Gnedykh\ V[\ Khatuntsev\ I[\ Kiselev\ A[\ Matsygorin\ I[A[\ Moshkin\ B[\ Nechaev\ V[\ Nikolsky\ Y[V[\ Patsaev\ D[\ Russakov\ A[\ Titov\ D[\ Zasova\ L[\ Blecka\ M[I[\ Jurewicz\ A[\ Michalska\ M[\ Novosielsky\ W[\ Orleansky\ P[\ Arnold\ G[\ Hirsch\ H[\ Driesher\ H[\ Lopez Moreno\ J[J[\ Rodrigo\ R[\ Rodriguez Gomez\ J[\ Michel\ G[\ 0886[ PFS] a Fourier spectrometer for the study of Martian atmosphere[ Adv[ Space[ Res[ 08\ "01#66Ð"01#79[ Hanel\ R[A[\ Schlachman\ D[R[\ Vanous\ D[\ 0860[ Nimbus 3 Mich! elson interferometer[ Appl[ Opt[ 09\ 0265Ð0271[ Hanel\ R[A[\ Conrath\ B[J[\ Hovis\ W[A[\ Kunde\ V[G[\ Lowman\ P[D[\ Maguire\ W[\ Pearl\ J[C[\ Pirraglia\ J[\ Prabhakara\ C[\ Schlachman\
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B[\ Levin\ G[\ Straat\ P[\ Burke\ T[\ 0861[ Investigation of the Martian environment by infrared spectroscopy experiment on the Mariner 8[ Icarus 06\ 312Ð331[ Hanel\ R[A[\ Conrath\ B[J[\ Jennings\ D[E[\ Samuelson\ R[E[\ 0881[ Exploration of the Solar System by Infrared Remote Sensing[ Cam! bridge University Press[ Hirsch\ H[\ 0885[ Private communication[ Kie}er\ H[H[\ Martin\ T[Z[\ Chase\ S[C[ Jr[\ B[M[\ Miner\ E[D[\ Pallu! coni\ F[D[\ 0865[ Martian North Pole summer temperatures] dirty water ice[ Science 083\ 0230Ð0233[ Kei}er\ H[H[\ Martin\ T[Z[\ Peterfreund\ A[R[\ Jakosky\ B[M[\ Miner\ E[D[\ Palluconi\ F[D[\ 0866[ Thermal and albedo mapping of Mars during the Viking primary mission[ J[ Geophys[ Res[ 71\ 3138Ð 3180[ Lumme\ K[\ James\ P[B[\ 0873[ Some photometric properties of the Martian south polar cap region during the 0860 apparition[ Icarus 47\ 252Ð265[ Maguire\ W[C[\ 0886[ Martian isotopic ratios and upper limits for possible constituents as derived from Mariner 8 infrared spec! trometer data[ Icarus 21\ 74Ð86[ Palomba\ E[\ 0884[ Graduation thesis[
Palomba\ E[\ Colangeli\ L[\ Formisano\ V[\ Piccioni\ G[\ Cafaro\ N[\ Moroz\ V[\ 0886[ The spectroscopy performances of the planetary Fourier spectroemter for the Mars ?85 mission[ Planet[ Space Sci[ 34\ 398Ð307[ Pleskot\ L[M[\ Miner\ E[D[\ 0870[ Time variability of Martian bolo! metric albedo[ Icarus 34\ 068Ð190[ Pollack\ J[B[\ Roush\ T[\ Witterborn\ F[\ Bregman\ J[\ Wooden\ D[\ Stoker\ C[\ Toon\ O[B[\ Rank\ D[\ Dalton\ B[\ Freedman\ R[\ 0889[ Thermal emission spectra of Mars "4[3Ð09[4 mm#] evidence for sulfates\ carbonates\ and hydrates[ J[ Geophys[ Res[ 84\ 03484Ð 03516[ Roush\ T[\ Orenberg\ J[B[\ 0885[ Estimated detectability limits of iron! substituted montmorillonite clay on Mars from thermal emission spectra of clay!palagonite physical mixtures[ J[ Geophys[ Res[ 090\ 15000Ð15007[ Smith\ W[L[\ 0869[ Iterative solution of the radiative transfer equation for the temperature and absorbing gas pro_le of an atmosphere[ Appl[ Opt\[ 8\ 0882Ð0888[ Wagner\ C[\ Schade\ U[\ 0885[ Measurements and calculations for esti! mating the spectrometric detection limit for carbonates in Martian soil[ Icarus 012\ 145Ð157[
Planetary and Space Science 36 "0888# 330Ð349
The radiometric performances of the Planetary Fourier Spectrometer for Mars exploration E[ Palombaa\ \ L[ Colangelia\ V[ Formisanob\ G[ Piccionic\ N[ Cafarob\ V[ Morozd a
Osservatorio Astronomico di Capodimonte\ Via Moiariello 05\ 79020 Napoli\ Italy Istituto di Fisica dello Spazio Interplanetario\ CNR\ Via Fosso del Cavaliere\ 99022 Roma\ Italy c Istituto di Astro_sica Spaziale!Reparto di Planetolo`ia\ CNR\ Via Fosso del Cavaliere\ 99022 Roma\ Italy d IKI!Space Research Institute of the Russian Academy of Science\ Profsojuznaja 73:21\ 006709 Moscow\ Russia b
Received 04 January 0887^ received in revised form 0 September 0887^ accepted 07 October 0887
Abstract The {Planetary Fourier Spectrometer| "PFS# is a Fourier transform interferometer\ operating in the range 0[1Ð34 mm[ The instrument\ previously included in the payload of the failed mission Mars ?85\ is proposed for the future space mission Mars Express\ under study by ESA[ The present paper is aimed at presenting the radiometric performances of PFS[ The two channels "LW and SW# forming PFS were analysed and characterised in terms of sensitivity and noise equivalent brightness[ To cover the wide spectral range of PFS\ di}erent blackbodies were used for calibration[ The built!in blackbodies\ needed for the in!~ight calibrations\ were also characterised[ The results show that the LW channel is comparable with IRIS Mariner 8 in terms of noise equivalent brightness[ The SW channel performances\ while satisfactorily\ could be improved by lowering the sensor operative temperature[ A simple model of the Mars radiance is used in order to calculate the signal!to!noise ratio on the spectra in typical observation conditions[ The computed signal!to!noise ratio for the LW channel varies between 329 and 39\ while for the SW channel it ranges from 049 to 29[ The radiometric analyses con_rm that PFS performances are compliant with the design requirements of the instrument[ PFS is fully validated for future remote exploration of the atmosphere and the surface of Mars[ Þ 0888 Elsevier Science Ltd[ All rights reserved[
0[ Introduction The {Planetary Fourier Spectrometer| "hereafter PFS# is a Fourier transform interferometer\ operating in the range 0[1Ð34 mm\ that was included in the payload of the Mars ?85 space mission[ Unfortunately\ this mission failed just after the launch in November 0885 and the scienti_c payload was lost[ Nevertheless\ the spare model of PFS is still available and is proposed to become the ~ight version for a future mission to Mars\ presently under study by ESA] Mars Express[ This renewed interest for PFS makes it important to report the results of cali! bration measurements\ performed on the available model in the performance veri_cation phase of the instrument[ In a previous paper Palomba et al[ "0886# reported the results of spectroscopic measurements\ obtained with various models produced during the PFS study and devel! opment program[ However\ a complete characterisation of the instrument must account for radiometric measure! ments\ too[ The aim of the present work is to report the
Corresponding author[ Fax] 99 28 70 34509^ e!mail] palombaÝ astrna[na[astro[it:palombaÝcosmic[na[astro[it
results of radiometric calibration sessions\ performed in parallel with spectroscopic tests to fully characterise PFS[ The ground!based spectroscopic and radiometric measurements\ once coupled with in!~ight calibration data which will be available thanks to PFS built!in cali! brated sources\ will form a set of reference data necessary to handle and calibrate correctly the PFS results[ The scienti_c goals of PFS are described in detail in previous papers to which we refer the reader "e[g[ For! misano et al[\ 0882\ 0885\ 0886#[ Here we recall brie~y that PFS is designed to achieve the primary goal of study! ing the Martian atmosphere[ Through inversion methods "Smith\ 0869^ Chahine\ 0857\ 0861#\ the spectral pro_le of dominant features will be used to obtain a detailed description of temperature _eld and pressure pro_le[ A global long term monitoring of the three!dimensional temperature _eld in the lower atmosphere "from the sur! face up to 39 km# will be possible[ Measurements of the minor constituent "e[g[ water vapour# variations and search for traces of other components are envisaged[ The optical properties of the aerosol "dust\ ice and hazes# will be studied in order to determine their chemical com! position and size distribution[ As far as surface studies are concerned\ PFS can provide hints about the temperature
9921Ð9522:88:, ! see front matter Þ 0888 Elsevier Science Ltd[ All rights reserved[ PII] S 9 9 2 1 Ð 9 5 2 2 " 8 7 # 9 9 0 1 4 Ð 0
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distribution\ as well as the thermal inertia from the daily thermal variations[ The PFS is also sensitive to re~ected solar energy at the shorter wavelengths and can provide surface compositional information[ The spectroscopic coverage of selected areas should allow us to place restric! tions on the mineralogical composition of the surface layer\ to determine the nature of condensed materials\ as well as their seasonal variations in composition[ The results reported in the present paper have been obtained on the PFS ~ight spare version "labelled PFS96# at the Istituto di Fisica dello Spazio Interplanetario "IFSI*CNR#\ before the production of the ~ight model[ The obtained data demonstrate that the overall charac! teristics of the instrument are compatible with the design speci_cations and can achieve the planned scienti_c goals[ In Section 1\ we describe the experimental set!up and the approach followed to perform radiometric measurements on PFS96[ The approach to data analysis is reported in Section 2\ while the results are presented in Section 3[ Finally\ Section 4 is devoted to a discussion of the infor! mation derived from the experimental data about the PFS performances for the application to Mars study[ 1[ Experimental We recall that PFS is a Fourier spectrometer based on a double!pendulum design\ formed by two parallel channels covering the spectral ranges SW 0[1Ð3[7 mm and LW 3[7Ð34 mm "see Formisano et al[\ 0882\ 0885\ 0886 for more details#[ The instrument design speci! _cations are summarised in Table 0[ The LW channel is equipped with a pyro!electric sensor "LiTaO2#\ able to convert temperature gradients with respect to time into alternate current "AC#[ It should be pointed out that the LW channel works as a di}erential instrument] the higher the temperature di}erence between the sensor and the
target\ the higher the recorded signal^ if the two tem! peratures are equal then the signal measured is almost null[ The SW sensor is a photo!conductive PbSe semi! conductor^ to minimise the thermal noise "photon generation by high temperature# it is cooled at a tem! perature between 134 and 140 K[ The temperature for both the sensors is set and controlled by the PFS main electronics[ To perform quantitative radiometric measurements\ PFS was placed on a bench in a thermo!vacuum chamber of about 0599 l[ The chamber has six ~anges and a win! dow for visual inspection of the internal set!up[ The pumping group "pre!vacuum plus cryogenic pump# allows a high vacuum of about 09−6 mbar to be achieved[ The chamber temperature can be varied from ¦099 to −59>C overall\ via a gas compression!expansion process[ The temperature of the instrument\ and of the sensors in particular\ was continuously controlled and monitored "engineering data#[ Several interferogram acquisitions were performed by pointing PFS at di}erent calibrated blackbodies\ whose temperature was _xed and monitored "engineering data#[ The PFS spectral range is so wide and the technical characteristics of the two channels are so di}erent that di}erent calibrated blackbodies had to be used for the SW and LW spectral ranges[ Moreover\ two main sessions of measurements were performed on PFS\ before and after mechanical vibration tests needed to qualify the instru! ment for launch and ~ight stresses[ For the LW channel\ four calibration blackbodies were used before the vibration] one simulating Mars "hereafter BB0#\ one simulating the deep space "hereafter BB1#\ the module A!LW "the LW built!in blackbody# and another blackbody "BB2#[ Thanks to the operation of the PFS scanner "i[e[ the pointing device# it was possible to per! form sequential measurements on the di}erent black!
Table 0 Main design characteristics for the SW and LW channels of PFS
Mirror displacement Displacement time Speed Measurement time Optical path di}erence Spectral resolution Wavenumber range Wavelength range Resolving power Nominal reference source wavelength Beamsplitter material Field of view Throughput
LW
SW
2 4 9[5 3[985 25 1[92 111Ð1972 34Ð3[7 0930 0[1 CsI 9[924 9[933
2 4 9[5 3[985 25 1[92 1972*7222 3[7Ð0[1 3055 0[1 CaF1 9[906 9[995
mm s mm s−0 s mm cm−0 cm−0 mm mm rad cm1 sr
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bodies[ Each session of measurements consisted of several acquisitions according to the following sequence] BB0ÐBB0ÐBB2ÐBB0ÐBB0ÐBB1ÐBB0ÐBB0ÐA!LW In di}erent sequences the blackbodies and the LW detec! tor temperature varied[ A summary of the sequences and the temperature ranges measured is shown in Table 1[ A total number of 2 sessions\ each consisting of about 19 sequences was collected[ After vibrations the scanner was not operative for the LW session\ so that measurements were performed on BB0 only[ In the case of the SW channel\ a blackbody "BBSW# and the module A!SW "the SW built!in blackbody# were used[ The BBSW is formed by a source illuminating an aluminium screen\ whose re~ectivity and emissivity are known quantities "Moroz\ personal communication#[ Two sessions of measurements were performed\ one before and one after vibrations[ In each session about 09 sequences\ in which measurements of the two sources
were alternatively repeated\ were acquired[ In di}erent sequences the BBSW temperature was changed\ as indi! cated in Table 1[ In some cases the internal dark walls of the chamber were observed to monitor the background level[ The SW detector temperature was stable between 134[4 and 135[5 K in the _rst session and between 138[8 and 140[2 K in the second one[ Thus\ we can exclude variations in the PbSe sensitivity due to temperature e}ects[ In order to perform a thorough characterisation of the PFS radiometric performances\ given the wealth of available data a selection of the sessions more appro! priate for the data analysis was done[ Many inter! ferograms had to be discarded because their intensity exceeded the full span of the analog to digital converter "ADC# "hereafter\ such interferograms will be referred to as saturated interferograms#[ In the case of LW\ this happened especially when BB0 or BB1 were at tem! perature ³069 K[ This problem was subsequently solved by changing the pyroelectric preampli_er hardware
Table 1 Summary of the PFS radiometric calibration campaign[ For each session of measurement there are indicated all the temperature ranges of interest LW channel
SW channel Temperature ranges "K#
1 Sessions before the vibration Session A 19 Sequences of measurement
Session B 19 sequences of measurement
0 Session before the vibration Td "171[5Ð182[4# TIB "170[6Ð181[1# TBB0 "026Ð185# TBB1 "091Ð108# TBB2 "174Ð182# TA!LW "168Ð178#
09 Sequences of measurement
Td "134[4Ð135[5# TBBSW "0617Ð1207#
Td "174[5Ð177[9# TIB "173[4Ð176[9# TBB0 "068Ð167# TBB1 "82Ð064#
0 Session after the vibration 12 Sequences of measurement
Temperature ranges "K#
0 Session after the vibration Td "173[9Ð182[9# TIB "179[0Ð182[9# TBB0 "033Ð111#
09 Sequences of measurement
Td "138[8Ð140[2# TBBSW "1057Ð1252#
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reducing the gain by a factor two[ We have also noticed that several BB0 spectra\ taken immediately after BB1 spectra\ show an intensity reduction with respect to the other BB0 spectra in the sequence[ This is probably due to a decrease of the detector temperature during the measurement of BB1 "which is at temperature much less than that of BB0#] a sort of {memory e}ect|[ For this reason BB0 spectra recorded immediately after BB1 acquisitions were discarded in our analysis[ An accurate analysis of this phenomenon is beyond the scope of this work\ however we can assume that it would be of limited importance during mission operations\ when huge ther! mal gradients respect to time will be rare[ On the other hand\ an overall knowledge of the e}ect will be desirable in order to calibrate correctly the data returned from the orbiter[ Moreover\ in our analysis we have assumed negligible the temperature variations of the LW detector[ 2[ Data analysis The spectrum of a blackbody\ Sbb"n#\ measured by the LW channel as a function of the wavenumber\ n\ can be expressed as] Sbb"n# R"n#ðB"Tins\n#−B"Tbb\n#Ł
"0#
where R"n# is the sensitivity function of the LW channel\ B"T\n# is the Planck function and Tins and Tbb are the instrument and the blackbody temperature\ respectively[ If the instrument temperature is constant while observ! ing blackbodies at di}erent temperatures\ from eqn "0# it is possible to compute the sensitivity function of the LW channel] Sbbi"n#−Sbbj"n# R"n# ðB"Tbbj\n#−B"Tbbi\n#Ł
S"n# R"n#
while B"Tins\n# can be expressed as]
Sbb"n# ¦B"Tbb\n# R"n#
"3#
Thus\ from eqns "1#\ "2# and "3#\ we obtain] I"n#
Sbb0"n#−S"n# ðB"Tbb1\n#−B"Tbb0\n#Ł¦B"Tbb0\n# Sbb0"n#−Sbb1"n# "4#
This relation can be used to determine the spectral radi! ance for module A!LW or BB2 from their spectra and\ then\ their temperature to be compared with the engin! eering data[ Similarly\ the instrument temperature can be computed starting from the spectral radiance\ Iins"n#] Iins"n#
Sbb0"n# ðB"Tbb1\n#−B"Tbb0\n#Ł¦B"Tbb0n# Sbb0"n#−Sbb1"n# "5#
where Sins"n# is zero "see eqn "0##[ The noise equivalent brightness\ NEB"n#\ of the instru! ment is given by the standard deviation\ s\ expressed in radiometric units\ of the spectral radiance for a given source] "6#
NEB"n# s"I"n##
Following Hanel et al[ "0860#\ the error on I"n# derives\ primarily\ from the ~uctuations of S"n# "see eqn "4#\ thus the NEB"n#\ can be written as] NEB0"n# s"S"n##
B"Tbb1\n#−B"Tbb0\n#Ł Sbb0"n#−Sbb1"n#
X
"1#
In a _rst approach "AP0#\ we have used for Sbbi"n# and Sbbj"n# the averages of spectra measured within each sequence "see Section 1# for the two blackbodies BB0 and BB1[ Alternatively\ it is possible to use for Sbbi"n# and Sbbj"n# the average spectra of the BB0 blackbody at two di}erent temperatures "approach AP1#[ In this case\ we have considered for Sbbi"n# the BB0 average spectrum corresponding to the sequence in which it reached the maximum temperature and we have used as Sbbj"n#\ in turn\ all the average spectra relative to sequences with di}erent BB0 temperatures[ For n!sequences\ we com! puted n!0 di}erent sensitivities and we took the average[ Starting from eqn "0#\ the spectral radiance of a black! body\ I"n#\ can be retrieved from its spectrum S"n# as] I"n# B"Tins\n#−
B"Tins\n#
"2#
sðSi"n#−S Þ"n#Ł1 i
n−0 R"n#
"7#
where the i!index runs over all the considered spectra and S"n# is the average spectrum[ Þ For comparison\ an alternative approach has been applied to calculate the NEB"n# function[ For the k!th spectrum a smooth function\ SMk"n#\ has ben computed\ by a running average over nine points of the spectrum\ and the ~uctuations of the spectrum around SMk"n# have been considered[ Thus\ the k!th NEB"n# has been obtained by]
NEB1k"n#
X
ðSk"n#−SMk"n#Ł1 R"n#
"8#
The _nal NEB1"n# is the average of the NEB1k"n# func! tions calculated for the spectra taken into account in the computation[ We modelled the Martian spectral radiance\ Ltot"n#\ as the combination of two terms] the re~ected sunlight\ Lref"n#\ and the grey body emission\ Lem"n#[ So that]
E[ Palomba et al[ : Planetary and Space Science 36 "0888# 330Ð349
Ltot"n# Lref"n#¦Lem"n# A
r1 D
B"TS\n#¦oB"TM\n# 1
"09#
where A is the bolometric albedo "i[e[ the fraction of solar radiation re~ected in all directions# of the Martian surface\ r 3[55 09−2 AU is the radius of the Sun\ D 0[41 AU is the Mars mean heliocentric distance\ TS 4799 K is the Sun photosphere temperature\ TM and oM are the Mars surface temperature and emissivity[ In order to compute the signal!to!noise ratio\ S:N\ three cases were considered "Kei}er et al[\ 0865\ 0866^ Pleskot and Miner\ 0870^ Lumme and James\ 0873#] a bright region in spring "A 9[16\ TM 119 K#\ a dark region in summer "A 9[05\ TM 189 K# and the south polar cap in winter "A 9[68\ TM 039 K#[ The Martian radiance\ shown in Fig[ 0\ was calculated for the three sets of parameters and making the approximation that oM 0 "although emissivity changes with wavelength and surface material#[ The S:N is given by] S:N"n#
Ltot"n# NEB"n#
"00#
For the SW channel\ the spectrum recorded by looking at a source with radiance I"n# is given by] S"n# R"n#I"n#¦D"n#
"01#
where D"n# is the thermal noise\ that can be measured in dark conditions by pointing at the chamber walls or at the BBSW\ once switched o}[ The radiance of BBSW is] V I"Tbbsw\n# B"Tbbsw\n#ral"n#o p
"02#
334
of BBSW and V 1[5333 09−3 sr " ratio between the area of the exit hole of the source and the distance of the hole from the aluminium screen#[ Starting from eqn "01#\ the sensitivity function for the SW channel is] R"n#
S"n#−D"n# I"n#
"03#
eqns "7#\ "8# and "01#\ used to compute the NEB and S:N functions for the LW\ are still valid for the SW case[ Finally\ the radiance of the module A!SW can be deter! mined from] I"n#
S"n#−D"n# R"n#
"04#
3[ Results 3[0[ The LW channel For the LW channel we have performed the data analy! sis on two di}erent sessions of measurement\ hereafter A and B\ before the vibration tests[ They consisted of 19 di}erent sequences each\ in which BB0 and BB1 tem! peratures were varied[ For session A\ it was possible to compute the sensitivity by the two approaches\ AP0 and AP1 "see Section 2#[ Instead\ AP1 only was applied to session B as the interferograms of BB1 were saturated due to its low temperature "³069 K#[ Out of the 19 sequences forming session A we selected 2 of them\ characterised by fully unsaturated interferograms\ to apply AP0[ An average of the three sensitivity deter! minations was _nally computed and is shown in Fig[ 1[ The R"n# function has a maximum of about 9[21 Digital
where Tbbsw is the BBSW temperature\ ral"n# is the re~ect! ivity of the aluminium screen\ o 9[88 is the emissivity
Fig[ 0[ Expected radiance from Mars for three di}erent conditions[
Fig[ 1[ Sensitivity of the LW channel computed by the two di}erent approaches] AP0 "continuous line# and AP1 "dotted line#[ The errors on each curve are lower than 5) in the 199Ð0199 cm−0 interval[
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Units "erg s−0 cm−1 sr−0 cm#−0 at around 349 cm−0 and is ×9[19 Digital Units "erg s−0 cm−1 sr−0 cm#−0 in the range 299Ð0999 cm−0[ To compute the sensitivity by AP1\ we considered the average BB0 spectra from 2 di}erent sequences in session A and from 09 sequences in session B[ The resulting R"n# function matches that obtained by AP0 "see Fig[ 1#\ within the experimental errors[ The periodic oscillation superimposed on the general behav! iour of both sensitivity curves is attributed to the dichroic mirror optical properties[ The measurements performed on BB0 after the vibration tests were analysed by AP1[ The ratio between sensitivities obtained before and after the vibrations is about 9[7\ fairly constant with wavenumber[ This slight worsening in the overall instrument sensitivity "present also for the SW channel\ see below# is probably due to a little optical misalignment produced by the vibration tests[ By inserting the sensitivity computed by AP0 into eqns "7# and "8# we obtained the NEB0 and NEB1 functions[ Only sequences where three or four spectra of BB2 and module A!LW are available were considered[ The _nal NEB0 is an average over 06 di}erent determinations[ To retrieve the average NEB1\ three sequences of the A session were considered and BB0 and BB1 spectra were used[ The results shown in Fig[ 2 look very similar and are close to the theoretical curve calculated on the basis of the instrument design and the measured spectral response of the optical components "Hirsch\ 0885#[ The NEB remains below 0 erg s−0 cm −1 sr−0 cm up to 0299 cm−0 and reaches a minimum of about 9[2 erg s−0 cm−1 sr−0 cm\ between 249 and 349 cm−0[ The S:N for the LW channel\ derived from eqn "00# for the three Mars environment cases presented in Section
Fig[ 2[ Average NEB0 "dotted line# and NEB1 "continuous line# for the LW channel[
Fig[ 3[ The LW S:N for di}erent temperatures of the Martian surface[
2\ is shown in Fig[ 3[ The maximum values are 39\ 199 and 399\ for T 039\ 119 and 189 K\ respectively\ and fall in the spectral range 249Ð499 cm−0[ The S:N remains larger than 09 up to 0199 cm−0 for TM 119 K and up to 0699 cm−0 for TM 189 K\ while for the coldest regions the S:N is larger than 0 in the 199Ð0999 cm !0 spectral range[ Finally\ we have computed the spectral radiance of BB2 and of the module A!LW by using eqn "4# and that of the instrument by using eqn "5#[ For this purpose we chose the same three sequences of the A session used in the previous analysis[ Then\ we have _tted the obtained pro_les by a Planck function in the spectral region of high NEB "i[e[ 399Ð799 cm−0#[ As an example\ the retrieved radiance of module A!LW is shown in the top of Fig[ 4^ it is well matched by a Planck function at T 179[0 K\ as evidenced by the ratio of the two curves in the bottom of the same _gure[ The temperatures derived by this approach for BB2\ the module A!LW and the instrument\ have an error of less than 1) and are compared in Table 2 with the engineering data[ The determined instrument temperature must be considered as an {e}ective| value\ which accounts for the contributions to the radiance of both the detector and the rest of the instrument "Hanel et al[\ 0881#[ For this reason it is compared with the temperature of the detector and of the PFS interferometer block "an average of data over eight check points of the optical bench#[ In general\ the retrieved temperatures are in good agreement[ In some cases a little di}erence is found\ probably due to the fact that the instrument tem! perature is not actually constant as assumed[ Moreover\ wider BB0 and BB1 temperature variations imply larger uncertainties in the A!LW\ BB2 and instrument tem! perature determination "see\ e[g[\ sequence 2 in Table 2#[
E[ Palomba et al[ : Planetary and Space Science 36 "0888# 330Ð349
Fig[ 4[ The computed module A!LW radiance "top# and its ratio by a Planck function at 179[0 K "bottom#[
3[1[ The SW channel Six series of spectra\ recorded for di}erent BBSW tem! peratures\ have been chosen for our analysis\ while other four series have been excluded\ as the interferograms were saturated[ The obtained SW average sensitivity is shown in Fig[ 5[ It reaches a maximum value of 9[6 Digital Units "erg s−0 cm−1 sr−0 cm#−0\ around 1399 cm−0\ and is above 9[0 Digital Units "erg s−0 cm−1 sr−0 cm#−0 up to 4499 cm−0[ Many features are visible between 1799 and 2999 cm−0\ probably due to contamination residues present in the thermovacuum chamber[ Among the data collected after vibration\ four di}erent sequences have been selec!
336
ted[ The sensitivity function is very similar to that com! puted before the vibration tests\ but the maximum around 1299Ð1399 cm−0 is slightly lower] 9[4 Digital Units "erg s−0 cm−1 sr−0 cm#−0[ In Fig[ 6 the NEB0 and NEB1 functions computed by using only unsaturated spectra at the highest gain of the detector ampli_er are shown[ The NEB0 is lower than 9[0 erg s−0 cm−1 sr−0 cm up to 4599 cm−0 and reaches a minimum of 1[1×09−1 erg s−0 cm−1 sr−0 cm around 1699 cm−0[ The NEB1 has a similar shape\ but is lower by a factor of 2 in the spectral region 1999Ð1499 cm−0^ it reaches a minimum value around 0[0×09−1 erg s−0 cm−1 sr−0 cm around 1399 cm−0 and remains below 0×09−0 erg s−0 cm−1 sr−0 cm up to 5999 cm−0[ We recall that the theoretical NEB\ computed for a PbSe detector tem! perature of 084 K\ reaches a minimum of 3×09−2 erg s−0 cm−1 sr−0 cm "Hirsch\ 0885#[ The discrepancy by a factor 2 with measurements is primarily a consequence of the worsening in the S:N\ as the actual detector temperature "around 135 K# is higher than the value assumed for the computation "084 K#[ Indeed\ this temperature di}erence implies a decrease by a factor 1 of the PbSe detector output "Palomba\ 0884# and a noise increase of a factor 0[0\ by assuming a Johnson noise[ These factors lead to a S:N reduction of about 1[1 and\ thus\ an equivalent increase in NEB[ Moreover\ in our measurements we have noted that\ by increasing the gain of the detector ampli_er\ the NEB decreases and the interferogram peak intensity increases[ This suggests a direct relation] the higher the signal the lower the NEB[ For this reason\ in the computation of the NEB "see Fig[ 6# and of the S:N "reported in Fig[ 7# we have used only unsaturated measurements at the highest detector gain[ As for the LW range\ we have considered the radiance from the Mars surface shown in Fig[ 0\ to compute the S:N function[ The maximum S:N for the polar and for the bright regions is obtained at 3299Ð3399 cm−0 with a value of 049 and 49 for the two cases\ respectively[ For the dark regions the thermal contribution prevails over the re~ected one in the spectral range 1999Ð2999 cm−0\ where S:N reaches a maximum of about 049 around 1499 cm−0[ These results con_rm that the higher the albedo\ the higher the S:N[ However\ it should be pointed out the importance of the thermal radiance for the SW spectral region\ especially in the range 1999Ð 2999 cm−0[ The last example is particularly instructive\ as it indicates the possibility of measuring spectra at very good S:N on low albedo regions at high tem! perature "T ¼ 189 K#[ With the previous information\ it has been possible to retrieve the absolute spectrum of the built!in SW lamp\ i[e[ the module A!SW[ It is characterised by a nearly constant brightness pro_le between 0 and 1 erg s−0 cm−1 sr−0 cm in the spectral range 2999Ð7999 cm−0\ with a cut! o} at 1349 cm−0[ This trend is con_rmed by measure! ments after vibrations[
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E[ Palomba et al[ : Planetary and Space Science 36 "0888# 330Ð349 Table 2 Comparison between retrieved and engineering temperatures of BB2\ TBB2\ module A!LW\ TA!LW\ and the LW detector\ Td[ The temperature measured on the interferometer block\ TIB\ is also reported Sequence 0
1
2
0
Td TIB TBB2 TA!LW Td TIB TBB2 TA!LW Td TIB TBB2 TA!LW
Engineering data "K#
Retrieved temperature "K#
171[7429[93 171[0929[0 175[2929[0 167[1929[00 168[8929[00 171[6029[97 170[7929[0 175[5929[0 167[4929[00 179[1929[0 171[4629[93 170[99[6929[0 176[1929[0 168[9929[00 179[6929[00
170[8929[6 171[8929[8 170[1929[5 179[4920 171[0920[1 179[09200 168[9923 17023 167[9923
Values measured at two di}erent checking points[
Fig[ 5[ Sensitivity of the SW channel[
Fig[ 6[ Comparison between NEB0 "dotted line# and NEB1 "continuous line# for the SW channel[
4[ Discussions and conclusions The most relevant function derived from the radio! metric measurements that characterises the PFS per! formances\ is the noise equivalent brightness[ For the LW channel it is well within the design limits and is comparable to that of the IRIS instrument on board Mariner 8 "Hanel et al[\ 0861#[ This corresponds to a maximum S:N on a single spectrum of some hundreds\ by observing the hottest regions of Mars\ and of about 39\ for the coldest areas[ On the contrary\ the NEB obtained for the SW channel is slightly worse than expected and should be improved by reducing the sensor operative temperature[ The maximum S:N for a single
spectrum in the SW channel is about 049\ for the highest albedo regions\ and about 29\ for the darkest regions[ High S:N is needed for atmospheric studies\ such as the determination of the 01C:02C\ 05O:07O and 05O:06O isotopic ratios\ the estimate of upper limits for possible minor constituents and the discerning of their bands[ This can be accomplished by summing over an adequate number of spectra\ as done e[g[ by Maguire "0866# for the IRIS spectra\ which can increase the S:N by a factor of tens[ The wide spectral range covered at high spectral resolution by PFS "Palomba et al[\ 0886# will allow new investigations in this sense[ Moreover\ the retrieving of the temperature pro_le will be possible by means of inver!
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data reported in the present work and by Palomba et al[ "0886#\ some improvement is still possible in the sensor performances\ while the overall design and optical struc! ture appear fully compatible with the scienti_c goals to be achieved] investigation of mineralogy\ climate and atmospheric chemistry of Mars[ Acknowledgements We thank E[ Zona for his technical assistance during experiment execution and Dr M[S[ Robinson for his use! ful comments about the manuscript[ This work was sup! ported by MURST\ CNR and ASI[ Ernesto Palomba received support under a contract from Osservatorio Astronomico di Capodimonte[ Fig[ 7[ The SW S:N for di}erent Martian surface conditions[
References sion methods applied to both the 556 cm−0 bending and the 1936 cm−0 stretching bands of CO1\ taking also into account the scattering e}ects due to the aerosols dispersed in the atmosphere[ High sensitivity and high spectral resolution are sim! ultaneously needed in order to discriminate the diagnostic features of di}erent minerals forming the Martian soil or aerosols\ which are weak and often occur spectrally very close[ Furthermore\ a high S:N o}ers the possibility of detecting weak features\ in absorption or emission\ due to trace minerals mixed in the surface rock deposits or suspended in the atmosphere[ As an example\ we recall that KAO "Kuiper Airborne Observatory# observations of Mars at a S:N comparable to that of PFS in the LW channel allowed Pollack et al[ "0889# to identify several spectral features of carbonates and sulfates\ for the aero! sol constituents\ or hydrates and silicates\ for the surface\ in the 4[3Ð09[4 mm spectral range[ Moreover\ Wagner and Schade "0885# computed that a 2) carbonate content in an analogue soil mixture\ for a 144 K Mars surface temperature\ produces a 9[94 relative strength in the 3 mm band[ This means that a minimum S:N of 19 is necess! ary to detect that feature[ Again for carbonates\ Calvin et al[ "0883#\ by analysing Mariner 5 and 6 spectra with highly variable "4Ð049# S:N\ found a 4[3 mm band assigned to hydrous carbonates[ All the previous require! ments are well within the capabilities of the instrument[ In addition\ although at the limit of the PFS sensitivity\ it should be stressed that it is possible to detect in emiss! ivity the Christensen and the Reststrahlen features of an iron!substituted montmorillonite clay at a 04) content in a Martian analogue soil mixture with a S:N of at least 099 "Roush and Orenberg\ 0885#[ In conclusion\ PFS for its radiometric and spec! troscopic performances appears as a suitable instrument for future remote exploration of Mars[ According to the
Calvin\ W[M[\ King\ T[V[V[\ Clark\ R[\ 0883[ Hydrous carbonates on Mars<] evidence from Mariner 5:6 infrared spectrometer and ground! based telescopic spectra[ J[ Geophys[ Res[ 88\ 03548Ð03564[ Chahine\ M[T[\ 0857[ Determination of the temperature pro_le in an atmosphere from its outgoing radiance[ J[ Opt[ Soc[ Am[ 47\ 0523Ð 0526[ Chahine\ M[T[\ 0861[ A general relaxation method for inverse solution of the full radiative transfer equation[ J[ Atmos[ Sci[ 18\ 630Ð636[ Formisano\ V[\ Moroz\ V[\ Amata\ E[\ Baldetti\ P[\ Bellucci\ G[\ Chion! chio\ G[\ Matteuzzi\ A[\ Orfei\ R[\ Piccioni\ G[\ Carusi\ A[\ Coradini\ A[\ Cerroni\ P[\ Capaccioni\ F[\ Adriani\ A[\ Viterbini\ M[\ Angrilli\ F[\ Baglioni\ P[\ Bianchini\ G[\ Fanit\ G[\ Bussoletti\ E[\ Fonti\ S[\ Mancini\ D[\ Colangeli\ L[\ Grigoriev\ A[\ Moshkin\ B[\ Zasova\ L[\ Sanko\ N[\ Nikolsky\ Y[V[\ Gnedykh\ V[\ Kiselev\ A[\ Khatuntsev\ I[\ Gonharov\ S[\ Titov\ D[\ Hirsch\ H[\ Arnold\ G[\ Orleansky\ P[\ Combes\ M[\ Michel\ G[\ Rodrigo\ R[\ Lopez Moreno\ J[J[\ Rod! rigues Gomez\ J[\ Olivares\ I[\ 0882[ Planetary Fourier spectrometer] an interferometer for atmospheric studies on board Mars 83 mission[ Il Nuovo Cimento 05\ 464Ð477[ Formisano\ V[\ Moroz\ V[\ Hirsch\ H[\ Oleansky\ P[\ Michel\ G[\ Lopez Moreno\ J[J[\ Amata\ E[\ Bellucci\ G[\ Piccioni\ G[\ Chionchio\ G[\ Carusi\ A[\ Coradini\ A[\ Cerroni\ P[\ Capria\ M[T[\ Capaccioni\ F[\ Adriani\ A[\ Viterbini\ M[\ Angrilli\ P[\ Bianchini\ G[\ Saggin\ B[\ Fonti\ S[\ Bussoletti\ E[\ Mancini\ D[\ Colangeli\ L[\ Grigoriev\ A[\ Moshkin\ B[\ Gnedykh\ V[\ Matsygorin\ I[A[\ Patsaev\ D[\ Nikolsky\ Y[V[\ Titov\ D[\ Zasova\ L[\ Khatuntsev\ I[\ Kiselev\ A[\ Arnold\ G[\ Driesher\ H[\ Blecka\ M[I[\ Rodrigo\ R[\ Rodriguez Gomez\ J[\ 0885[ Infrared spectrometer PFS for the Mars 83 orbiter[ Adv[ Space Res[ 06\ 01"50#Ð"01#53[ Formisano\ V[\ Moroz\ V[\ Angrilli\ F[\ Bianchini\ G[\ Bussoletti\ E[\ Cafaro\ N[\ Capaccioni\ F[\ Capria\ M[T[\ Cerroni\ P[\ Chionchio\ G[\ Colangeli\ L[\ Coradini\ A[\ Di Lellis\ A[\ Fonti\ S[\ Orfei\ R[\ Palomba\ E[\ Piccioni\ G[\ Saggin\ B[\ Ekonomov\ A[\ Grigoriev\ A[\ Gnedykh\ V[\ Khatuntsev\ I[\ Kiselev\ A[\ Matsygorin\ I[A[\ Moshkin\ B[\ Nechaev\ V[\ Nikolsky\ Y[V[\ Patsaev\ D[\ Russakov\ A[\ Titov\ D[\ Zasova\ L[\ Blecka\ M[I[\ Jurewicz\ A[\ Michalska\ M[\ Novosielsky\ W[\ Orleansky\ P[\ Arnold\ G[\ Hirsch\ H[\ Driesher\ H[\ Lopez Moreno\ J[J[\ Rodrigo\ R[\ Rodriguez Gomez\ J[\ Michel\ G[\ 0886[ PFS] a Fourier spectrometer for the study of Martian atmosphere[ Adv[ Space[ Res[ 08\ "01#66Ð"01#79[ Hanel\ R[A[\ Schlachman\ D[R[\ Vanous\ D[\ 0860[ Nimbus 3 Mich! elson interferometer[ Appl[ Opt[ 09\ 0265Ð0271[ Hanel\ R[A[\ Conrath\ B[J[\ Hovis\ W[A[\ Kunde\ V[G[\ Lowman\ P[D[\ Maguire\ W[\ Pearl\ J[C[\ Pirraglia\ J[\ Prabhakara\ C[\ Schlachman\
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B[\ Levin\ G[\ Straat\ P[\ Burke\ T[\ 0861[ Investigation of the Martian environment by infrared spectroscopy experiment on the Mariner 8[ Icarus 06\ 312Ð331[ Hanel\ R[A[\ Conrath\ B[J[\ Jennings\ D[E[\ Samuelson\ R[E[\ 0881[ Exploration of the Solar System by Infrared Remote Sensing[ Cam! bridge University Press[ Hirsch\ H[\ 0885[ Private communication[ Kie}er\ H[H[\ Martin\ T[Z[\ Chase\ S[C[ Jr[\ B[M[\ Miner\ E[D[\ Pallu! coni\ F[D[\ 0865[ Martian North Pole summer temperatures] dirty water ice[ Science 083\ 0230Ð0233[ Kei}er\ H[H[\ Martin\ T[Z[\ Peterfreund\ A[R[\ Jakosky\ B[M[\ Miner\ E[D[\ Palluconi\ F[D[\ 0866[ Thermal and albedo mapping of Mars during the Viking primary mission[ J[ Geophys[ Res[ 71\ 3138Ð 3180[ Lumme\ K[\ James\ P[B[\ 0873[ Some photometric properties of the Martian south polar cap region during the 0860 apparition[ Icarus 47\ 252Ð265[ Maguire\ W[C[\ 0886[ Martian isotopic ratios and upper limits for possible constituents as derived from Mariner 8 infrared spec! trometer data[ Icarus 21\ 74Ð86[ Palomba\ E[\ 0884[ Graduation thesis[
Palomba\ E[\ Colangeli\ L[\ Formisano\ V[\ Piccioni\ G[\ Cafaro\ N[\ Moroz\ V[\ 0886[ The spectroscopy performances of the planetary Fourier spectroemter for the Mars ?85 mission[ Planet[ Space Sci[ 34\ 398Ð307[ Pleskot\ L[M[\ Miner\ E[D[\ 0870[ Time variability of Martian bolo! metric albedo[ Icarus 34\ 068Ð190[ Pollack\ J[B[\ Roush\ T[\ Witterborn\ F[\ Bregman\ J[\ Wooden\ D[\ Stoker\ C[\ Toon\ O[B[\ Rank\ D[\ Dalton\ B[\ Freedman\ R[\ 0889[ Thermal emission spectra of Mars "4[3Ð09[4 mm#] evidence for sulfates\ carbonates\ and hydrates[ J[ Geophys[ Res[ 84\ 03484Ð 03516[ Roush\ T[\ Orenberg\ J[B[\ 0885[ Estimated detectability limits of iron! substituted montmorillonite clay on Mars from thermal emission spectra of clay!palagonite physical mixtures[ J[ Geophys[ Res[ 090\ 15000Ð15007[ Smith\ W[L[\ 0869[ Iterative solution of the radiative transfer equation for the temperature and absorbing gas pro_le of an atmosphere[ Appl[ Opt\[ 8\ 0882Ð0888[ Wagner\ C[\ Schade\ U[\ 0885[ Measurements and calculations for esti! mating the spectrometric detection limit for carbonates in Martian soil[ Icarus 012\ 145Ð157[