First observations of the planetary Fourier spectrometer at Mars

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Advances in Space Research 36 (2005) 1074–1083

First observations of the planetary Fourier spectrometer at Mars

V. Formisano a,*, V. Cottini a, M. Giuranna a, D. Grassi a, I. Khatuntsev a,d,N. Ignatiev a,d, A. Maturilli a, G. Piccioni b, B. Saggin c,

L. Zasova a,d, The rest of PFS TEAM 1

a Istituto di Fisica dello Spazio Interplanetario INAF-IFSI, Planetology, Via del Fosso del Cavaliere 100, 00133 Roma, Italyb Istituto Astrofisica Spaziale INAF-IASF, Via Fosso del Cavaliere 100, 00133 Roma, Italy

c Politecnico di Milano, Dipartimento di Meccanica, Sede di Lecco, Italyd Space Research Institute of Russian Academy of Sciences (IKI) Profsojuznaja 84/32, 117997 Moscow, Russia

Received 28 February 2005; received in revised form 30 June 2005; accepted 1 July 2005

Abstract

The first results of the Planetary Fourier Spectrometer (PFS) orbiting the planet Mars are reviewed and discussed here, with ref-erence to a set of studies being published elsewhere. An average global spectrum ranging from 200 to 8200 cm�1 is discussed bycomparing it to the ISO SWS Martian spectrum and to the global synthetic spectrum computed using only CO2, CO, H2O gases.PFS is able to measure the vertical temperature–pressure profile in the Martian atmosphere and the temperature of the soil. The SWchannel shows the major CO2 bands at 4.3 and 2.7 lm. The bottom of the first band shows very clearly the non LTE emission of thehigh atmospheric CO2 gas, and the dust content in the atmosphere. In one of the first orbit passing over the Olympus Mons, thetemperature field retrieved shows abnormal adiabatic cooling in the atmosphere above the mountain, while the soil temperatureof the volcano is higher than the latitudinal profile expectation because of a better illumination from the sun. Many solar linesare observed, a few of them are studied and compared to ISO observations.� 2005 COSPAR. Published by Elsevier Ltd. All rights reserved.

Keywords: Infrared; Mars; Atmosphere

1. Introduction

Launched on June 3, 2003, Mars Express went intoorbit around Mars on December 25, 2003, and was thefirst successful European Planetary mission.

The Planetary Fourier Spectrometer (PFS in the fol-lowing), one of the seven experiment on board thespacecraft, was first switched-on on January 10, 2004,

0273-1177/$30 � 2005 COSPAR. Published by Elsevier Ltd. All rights reser

doi:10.1016/j.asr.2005.07.018

* Corresponding author. Tel.: +39 06 4993 4362.E-mail address: [email protected] (V. Formisano).

1 S. Atreya, F. Billebaud, M.I. Blecka, L. Colangeli, F. Esposito,S. Fonti, G. Hansen, H. Hirsh, A. Jurewicz, E. Lellouch, J. LopezMoreno, B. Moshkin, P. Orleanski, E. Palomba, M. Rataj,R. Rodrigo, D. Titov.

and started since then its routine operations for eachorbit: calibrations, Mars observations, calibrationsagain. The observed spectra, although showing someeffects of the micro-vibrations present on board, gaveus immediately the flavour of a data set extremely richof information. The team could immediately arrangefor a number of publications aiming to describe theexperiment, its performance and its scientific valida-tion. In particular we refer to the experiment descrip-tion (Formisano et al., 2005a) and to its calibrations(Giuranna et al., 2005a,b). The method of tempera-ture–pressure vertical profile retrieval in the Martianatmosphere is described in Grassi et al. (2005a),and the method of fast synthetic spectra computationis presented in Ignatiev et al., 2005. A number of

ved.

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V. Formisano et al. / Advances in Space Research 36 (2005) 1074–1083 1075

scientific results were also obtained, and they were veryappropriate for a scientific validation of the experimentand of the data obtained. This task is the aim of thispaper, in which we shall review some of the results pre-sented in these papers (see Formisano et al., 2005b,Grassi et al., 2005b, Zasova et al., 2005), add someunpublished data, with the aim, once again, to bringto the attention of the scientific community the charac-teristics of PFS data and to validate its scientific capa-bilities and use.

1.1. Experiment characteristics and present global

coverage

The Planetary Fourier Spectrometer (PFS) for theMars Express mission is an infrared spectrometer opti-mized for atmospheric studies. This instrument has aShort Wavelength (SW) channel that covers the spectralrange from 1700 to 8200 cm�1 (1.2–5.5 lm) and a LongWavelength (LW) channel that covers 250–1700 cm�1

(5.5–45 lm). Both channels have a uniform spectral res-olution of 1.3 cm�1, while the sampling is every 1 cm�1.The instrument Field Of View (FOV) is about 1.6�(FWHM) for the Short Wavelength channel (SW) and2.8� (FWHM) for the Long Wavelength channel (LW)corresponding to a spatial resolution of 7 and 12 kmwhen Mars is observed from an height of 250 km.

The interferometer design (see Formisano et al., 2005a)is very robust against slight misalignments in harsh envi-ronments compared with the classical Michelson-typeinterferometer. Furthermore, mechanical vibrations,present on board, affect the main radiation beam and

Fig. 1. PFS coverage of the planet Mars after one year of operations i

the reference channels used to drive the experiment, inthe same way, so that meaningful measurements can stillbe taken.

Double sided interferograms are taken, as they pres-ent the advantage of being relatively insensitive to phaseerrors (an important problem when computing the spec-trum of Mars).

It is important to add in this preliminary presentationof the PFS experiment and its results, information aboutthe coverage of the planet Mars achieved up to date, andthe perspectives for the entire mission.

Fig. 1 shows the coverage of the planet achieved inJanuary 2005, one year after starting of operations. Atthis date more than 140000 measurements were col-lected, each measurement consisting of an interferogramfor the Long Wavelength channel plus an interferogramfor the Short Wavelength channel. The footprint of theLW channel is shown in red in the figure (if with solarillumination), while the footprint of the SW channel isshown in yellow. The footprints in grey indicate no solarillumination. The coverage of the planet is very good,and in the extended mission we aim to achieve fourtimes the same coverage.

Fig. 2 shows the Latitude – Local time coverage, animportant aspect of the coverage of Mars as the studyof diurnal variation of several parameters will be animportant scientific objective. The local time coverageis rather good, but it is biased by season, i.e., seasonand local time are strongly linked. At the moment equa-torial regions at midnight have no measurements, butwe shall make use of the pointing mirror in the future,in order to fill this gap, as the pericenter of the orbit

n orbit in a longitude–latitude map. Horizontal axis is longitude.

Fig. 2. Latitude, local time coverage of the PFS observations after one year in orbit.

1076 V. Formisano et al. / Advances in Space Research 36 (2005) 1074–1083

although it moves over all latitudes in time, does nevercover the midnight regions at the equator.

2. An average spectrum of PFS

In order to scientifically validate the PFS data, wehave computed an average spectrum to be comparedwith ISO SWS measurements of Mars. The details ofhow this average was computed are given in the paperby Formisano et al. (2005b). Here, we note simply thatthe 16 orbits considered were distributed over all longi-tudes range, latitudes being between �50� and +45�. Inlocal time the data were between 1200 and 1400 LT. Theselection of the data was done by choosing high SNRspectra from un-calibrated data. In the following weshall also compare PFS results with a synthetic spec-trum, computed with radiative transfer modelling ofthe Martian atmosphere, and line by line computation.The computed spectra were with only CO2, H2O andCO gases or with also aerosols (dust and H2O ice parti-cles). The global spectra of both PFS and ISO are shownin Fig. 3. PFS radiance is larger than ISO from 1600 upto 3200 cm�1, while ISO�s radiance is larger above3750 cm�1. The first aspect is understood in terms ofhigher ground temperature of the planet Mars for PFSobservations with respect to ISO; the second aspect isexplained in terms of higher albedo for the ISO observa-tions. The average Martian soil temperature for the PFSaverage observations was 275.5 K. Indeed a Planckianof 275.5 K fits rather well the LW channel spectrum

(not shown here for brevity). Note that the Planckiancurve fits well also the measured spectrum between1750 and 2350 cm�1 and indeed the thermal contribu-tion in the synthetic spectrum shown in Fig. 3 is dueto the mentioned temperature. At wave-numbers greaterthan the last value the solar radiance dominates. TheISO ground temperature was 240 K (see Formisanoet al., 2005b).

The larger ISO radiance above 3750 cm�1 is under-stood in terms of higher soil albedo and lower dustopacity with respect to PFS average. Indeed the sub-so-lar region for the ISO observation was over the Tharsisregion, a region with higher albedo per se, but also a re-gion of higher elevation, which necessarily means lowerdust opacity. The different dust/water ice content in theatmosphere between the two observations is also re-vealed by two other features: the radiance inside theCO2 band at 2.7 lm, which is clearly higher in thePFS observation, and a band observed between 3100and 3500 cm�1 which is due to water ice. The possibilityto use the radiance inside the two big CO2 bands formeasuring the atmospheric dust content was proposedby Titov et al. (2000). We shall discuss the details ofthe two major CO2 bands later.

Fig. 3 shows also a comparison of the PFS averagespectrum with a synthetic spectrum computed for a soiltemperature of 275.5 K and an albedo of 0.2 constantover the range. We see in Fig. 3 that between 1600and 1750 cm�1 the observed radiance tends to be largerthan the computed one. This fact is due to the very lowresponsivity of PFS SW channel in this range. The

Fig. 3. PFS LW channel (dark green curve) and SW channel (black curve) comparison with ISO SWS spectrum of Mars (light green curve) and asynthetic spectrum (red curve). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of thisarticle.)


experiment was not designed to be able to detect radi-ance in this range, so any capability of PFS below2000 cm�1, is a sort of gift/surprise from optical ele-ments not efficient enough. A posteriory this is consid-ered as a very positive result because mechanicalvibrations destroy this same wavenumber range in theLW channel. The radiance, however, below 1750 cm�1

wavenumbers, has a much larger error bar.The synthetic spectrum shows both main CO2 bands

much deeper than observed: the amount of dustincluded was not enough. Non Local ThermodynamicalEquilibrium (LTE) effects, on the other hand, can pro-duce emission from the upper atmosphere, which canbe observed by PFS in the 2200–2400 cm�1 band (seeLopez-Valverde et al., 2005).

A large difference between synthetic and measuredspectra exists between 3000 and 3500 cm�1. In principlethis difference could be due either to soil features or toaerosols. We think that both effects are probably pres-ent, but certainly water ice clouds are important andperhaps dominant, as we can deduce from several othersynthetic spectra (not shown here for brevity) that wehave computed with different ice opacities.

The radiance profile inside the 4.3 lm CO2 band isgiven in Fig. 4(a). Here, we note that ISO radiance isnegative at the center, meaning that the ISO spectrumhad a zero radiance level problem. The ISO data areshown here smoothed over 11 points to reduce the noise,but the effect on spectral resolution is minor. The radi-ance variation observed in the ISO spectrum was inter-preted (see Lellouch et al., 2000) as due to non LTE

effects in the Martian atmosphere. In order to have theISO minimum above the zero level, a radiance valueof 0.007 ergs/(s sr cm2 cm�1) must be added. We notethat the minimum radiance in all four curves is observedat 2370 cm�1. The synthetic spectrum (no dust) is equalto zero there, ISO has �0.005 , and PFS has 0.01 ergs/(s sr cm2 cm�1). Adding the zero offset, the difference be-tween ISO and PFS becomes 0.008 ergs/(s sr cm2 cm�1).The inclusion of dust in the computation of the syntheticspectrum introduces a small value in the bottom of theband, but PFS exhibits certainly more dust than in thecomputation. Note that non LTE effects seem to gener-ate up to 0.017 ergs/(s sr cm2 cm�1); the difference ISO-PFS at the band minimum is half this value and can bedue to either stronger non LTE effects (all PFS data areat 13:00–14:00 local time, the maximum of the dailythermal variation) or to dust contribution.

The radiance inside the 2.7 lm band (shown inFig. 4(b)) is a measure of the aerosols content in theatmosphere. In the PFS data the radiances in the twoCO2 bands (3580–3635 cm�1) and (3690–3740 cm�1)clearly differ. This could be due to spectral propertiesof the dust grains, as suggested by Fedorova et al.(2002).

It should be noted that in the case of ISO, dust opac-ity was evaluated to be 0.2, while in the PFS case, usingFig. 2 of Titov et al. (2000), we obtain an average valueof 0.5, in agreement with other findings of PFS data.PFS average dust opacity at 1100 cm�1 in this periodwas 0.3, (see Zasova et al., 2005, and Grassi et al.,2005b) which would indicate a ratio between 2.7 and

Fig. 4. (a) The bottom of the CO2 band at 4.3 lm. ISO SWS is the blue line, PFS the black line, light blue is synthetic with no dust, red is syntheticwith dust in the atmosphere. (b) CO2 band at 2.7 lm for the same four spectra of (a). (For interpretation of the references to colour in this figurelegend, the reader is referred to the web version of this article.)


9 lm of 1.66, in agreement with the ratio of 2.5, usuallyquoted, between the visible and thermal infrared (seeClancy et al., 1995, and references therein).

In concluding this section, it is important to add thatthe behaviour of the Noise Equivalent Radiance for thetwo channels is such that (see Giuranna et al., 2005a,b)the SNR for the CO2 15 lm band is larger than 150 for asingle measurement, and that the radiation inside the 4.3

and 2.7 lm band are measured with a SNR larger than100 (thanks to the averaging of 1680 spectra).

3. Results from the LW channel

The long wavelength channel (LWC) covers thethermal region between 250 and 1700 cm�1. Spectral


resolution is in the order of 2 cm�1 for apodized spec-tra, sampled with a 1 cm�1 step. The instantaneousfield of view (FOV) of LWC has a diameter of12.2 km at the nominal height of the MEX pericenter(250 km). A complete description of the instrumentand its radiometric performances can be found in thepapers by Formisano et al. (2005a) and Giurannaet al. (2005a).

The PFS spectra can be analyzed on an individual ba-sis following the methods and tools presented by Grassiet al. (2005a). The algorithm computes the effects ofmultiple scattering by atmospheric aerosols. Retrievalof atmospheric fields is limited to: (a) surface tempera-ture; (b) air temperature vs. altitude (up to 45–50 kmabove the surface), (c) dust and (d) water ice integratedcontents. Dust concentration is assumed to scale expo-nentially with altitude, according to a decay height of10 km, but this parameter is kept variable and it is anoutput of the retrieval iteration. Results presented in thiswork were achieved assuming the water ice particlesconcentration vs. altitude to be described by an expo-nential shape, with a 10 km decay height.

The most serious issue rises from the assumptionsmade to define the value of Psurf (atmospheric pressureat the surface), to be adopted in the definition of a suit-able temperature vs. pressure grid during evaluation ofsynthetic spectra. Values foreseen by models were usedtogether with altimetry provided by MOLA (MarsGlobal Surveyor experiment) data. In the future, weshall make use of the SW channel data to obtain ourown measured Psurf. The non-saturated CO2 bands in re-flected solar radiation wavelengths (e.g., 5000, 6350 and

Fig. 5. Blow up of the 15 lm CO2 band. Note the

6950 cm�1) allow actually the retrieval of the integratedcontent of CO2 (i.e., Psurf), with an error in the order of0.25 mbar or lower.

3.1. Atmospheric temperatures

In Fig. 5, we present the details of the CO2 15 lmband: the bottom of the band shows clearly severalQ-branches, the main one being due to O16C12O16

(usually called 626 isotopic molecule), the others beingdue to all the CO2 isotopic molecules. Note in particularthat on the left of the 626 large Q-branches at 668 cm�1,the Q-branches for the isotopic molecules O16C12O18 at663 cm�1 and O16C12O17 at 665 cm�1 are well resolved.This fact will allow us in the future to evaluate the abun-dances of these isotopic molecules. In Fig. 6, we show aLW single spectrum measured by PFS fitted with thesynthetic spectrum resulting from the temperature pro-file retrieval process. Putting together all the tempera-ture profiles from one orbit (the spacecraft trajectoryis essentially always north south along a meridian) weobtain the atmospheric temperature fields. Fig. 7 showsthe retrieved air thermal field in orbit 37. The generalbehaviour in the panel is similar, in the regions far fromthe relief, to the GCM (Global Circulation Model).When comparing the details, however, it is found thatthe thermal field measured by our instrument is some-what warmer (10–15 K) than the EMCD (EuropeanMars Circulation Dataset) expectations for MGS (MarsGlobal Surveyor) dust scenario. This discrepancy hasprobably to be ascribed to the different dust load inthe atmosphere. Adopting value for dust opacity ratio

many Q-branches and their isotopic satellites.

Fig. 6. The 15 lm CO2 band fitted with a synthetic spectrumcomputed according to the temperature profile retrieved.


svis/sIR � 2, PFS measurements exceed model assump-tions by a factor �2–2.5. The capability of Martian aer-osol to raise the average air temperature is wellestablished since Mariner 9 IRIS observations (Conrath,1975) and further confirmed by Thermal Emission Spec-trometer (TES) measurements (Smith et al., 2000). Thetemperature fields retrieved by PFS in the first �5 kmabove the surface should be taken with caution as the er-ror bar could be larger there.

The most complex situation is observed in the regionaround the Olympus Mons. In this case EMCD wouldrepresent a poor reference, being that the model doesnot currently include mesoscale phenomena.

A useful comparison can be performed between theair temperatures retrieved close and far away from thedome at a given altitude.

Fig. 7. Thermal field from orbit 37 passing over Olympus Mons. Num

(a) The most interesting structure is represented bythe air temperature minima centered around45 km of altitude and 20N latitude. Lower bound-aries of the cold region lie at an altitude of �35–40 km, where PFS data can still provide some use-ful information, even if just from the tails ofweighing functions. No similar structure is visiblein the thermal field expected from the model, usedas a priori during retrieval. Consequently, we areconfident about the actual occurrence of theminima.

(b) The air on the lowest atmospheric levels in thesouthern flank of the dome (more directly exposedto direct Sun light due to combination of localtopography and Sun zenith angle) shows valuesup to 220 K, even when the less reliable altituderange closer to the surface is neglected. Numbersof about 20 K lower are observed on the northernflank when the same altitudes above the surfacesare taken into account. These fields are related tomoderate vertical thermal gradients, in the orderof 1.5–2 K/km, to be compared with an indicativeadiabatic thermal gradient for Mars in the order of4.5 K/km (Zurek et al., 1992). Higher thermal gra-dients are measured only in the lowest levels ofatmosphere.

(c) A heating branch is observed around 16.5N,extended up to 40–45 km. This structure is strictlycorrelated with the topographic profile, being thatthe vertical temperature gradient seems quite con-stant over the volcano�s shield.

(d) Air temperatures at the boundaries of the volcanoshield present local minima from the surface up to30 km. Namely, cooling branches seem to be pres-ent at 12N and 24N.

bers in the figure represent the temperature, in units of Kelvin.

Fig. 9. Altimetry and dust content in the orbit passing over Olympus.


All structures identified above indicate the need formeso-scale modelling of the Martian atmosphere, withpossible consequences on a global scale. In other wordsobservations over local altimetry features are importantbecause they may have consequences for the globalplanetary circulation.

3.2. Surface temperatures

Fig. 8 shows the surface temperatures trend measuredby PFS during an Olympus Mons pass. The Sun eleva-tion above the reference geoid and the topographic pro-file are also reported for comparison. The general trenddriven by Solar illumination dependence on latitude hasa remarkable anomaly above the dome, represented byan exceeding warming of about 10 K extended between15N and 21N. On the other hand, the surface tempera-ture measured around 23S seems significantly lowerfrom the long scale trend. A complete simulation of sur-face temperatures, including geometrical conditions,surface thermal inertial (taken, e.g., from TES measure-ments, Mellon, 2002), a digital terrain model and aero-sol opacity is currently under development. From aqualitative point of view, a major role in temperaturedriving is played by surface orientation (being theSouthern flank of the dome being better exposed tothe Sun) and dust, with its shielding effect towardincoming Solar energy.

3.3. Integrated dust content

The integrated dust content is presented in Fig. 9for the passage over Olympus. The effect of differentatmosphere thickness due to dome rise is well evidentwith low dust opacities near the dome�s summit. Oncean exponential decay of dust concentration withheight is assumed, the fit of PFS-retrieved dust con-tent vs. MOLA topography allows a crude estimate

Fig. 8. Soil temperature, Sun elevation and altimetry in the orbitpassing over Olympus.

of dust scale height. The retrieved values are subjectto a number of error sources (limited statistics, dustcontent uncertainties, finite size of FOV) which maylead to cumulative effects that are hard to quantify.The results points toward a figure for the scale heightaround 10 km, on the southern side (11.9 ± 1.9 km) aswell as on the northern (9.6 ± 2.7 km) flank of thevolcano (note that the dust scale height is a freeparameter in the retrieval procedure, and it is opti-mised with the other quantities while retrieving thetemperature–pressure profile (see Grassi et al.,2005a). The extrapolated value of integrated dust atzero altitude is also quite symmetric in latitude, being0.16 ± 0.02 for the southern side and 0.19 ± 0.07 forthe northern flank.

4. Signatures of solar spectrum

We have looked at 10 solar lines studying theirintensity relative to the continuum given in the Table1 in CGS units (ergs/(s sr cm2 cm�1)). Indeed theintensity of a solar line relative to the continuumshould remain constant in time if the line is not vari-able (as we have assumed) and if there are no system-atic errors in our measurements. The lines considered(see Table 1) range from wavenumber 2468 to3012 cm�1. Their intensity with respect to the contin-uum span from 2.1% to 8.5%. Although there is a sys-tematic difference in the continuum due to higher soiltemperature for PFS (as already commented above)the solar line intensities are essentially identical forPFS and for ISO, and indeed on average the deviationseems to be only 0.02%. The overshoot is present inthe PFS data only for the most intense lines. It isinteresting to note that if we consider the average er-ror on the lines intensities as due to noise, then wehave a SNR of the order of 3000 in the wavenumberrange considered here (for this average of 1680 PFSmeasurements).

Table 1Solar lines intensity

ISO data PFS data

Line (cm�1) Continuum % Continuum % Overshoot Differences FWHM (cm�1)

2468 0.440 4.9 0.735 4.2 No 0.7 1.72557 0.436 2.5 0.667 2.4 No 0.1 2.02587 0.430 6.5 0.641 7.1 Yes �0.6 1.32669 0.428 2.1 0.597 1.8 No 0.3 1.82673 0.425 2.8 0.592 2.0 No 0.8 1.72704 0.421 3.1 0.574 3.3 No �0.2 1.32716 0.418 3.1 0.566 4.0 Yes �0.9 1.02719 0.416 3.1 0.563 3.0 No 0.1 1.82747 0.404 2.2 0.537 2.4 Yes �0.2 1.23012 0.270 8.5 0.355 8.4 Yes 0.1 1.6

Average 0.02

Fig. 10. PFS spectrum compared with our assembled solar spectrum: almost all lines observed in this region are solar.


The last column in the table gives the FWHM ofthe lines studied. This quantity is useful to check thespectral resolution of PFS: on average the FWHMis of the order of 1.5 cm�1. This is not in disagree-ment with the quoted spectral resolution of 1.3 cm�1

resulting from studies of synthetic spectra fitting PFSmeasurements, as we have not necessarily selected sin-gle solar lines. It may very well be that some of thelines are multiple solar lines, in which case we donot expect the FWHM to be representative of thePFS spectral resolution.

Finally, we have compared a measured PFS spec-trum in the range 6000–6200 cm�1 with the solar spec-trum assembled by Fiorenza and Formisano (2005)for PFS. The measured spectrum gives the intensityof the solar radiation reflected by the planet, thereforeaffected by atmospheric gases, dust and by the soilmineralogy. It is also important to note that, whilein the study of the 10 solar lines discussed above,

the thermal radiation was still important, in the wave-number range considered here (6000–6200 cm�1) thetemperature of the soil is not important and the albe-do may be considered constant, being the range rathershort. The results are shown in Fig. 10. We see thatessentially all the observed lines in this range appearto be solar in origin. It is important also to note thatthe solar spectrum in this region has many major linesand was never measured before from space. On Earththe saturated water bands in the atmosphere do notallow to study solar lines in this wave-number range.There are 41 solar lines identified in this portion ofthe spectrum which are also observed by PFS, whileonly 6 lines in the PFS spectrum do not correspondto solar lines, and 3 solar lines (minor) are not seenby PFS (possibly because of insufficient spectral reso-lution). It also should be noted that the relative inten-sity of the measured lines corresponds very well to theintensity of the assembled solar spectrum.


5. Conclusions

PFS first results have been reviewed here. PFS workswell and produces interesting results in the range ofwave-numbers explored. A comparison with the SWSISO spectrum has been performed and has demon-strated that we certainly get good measurements to thelower radiance intensity level (features down to 0.1% le-vel in the 1680 measurements average spectrum, havebeen shown to be significant). Finally the details of thesolar spectrum seem to appear very well in the PFS spec-trum as measured from space for the first time.

Acknowledgements

The PFS experiment has been built at the Instituto diFisica dello Spazio Interplanetario (IFSI) of InstitutoNazionale di Astrofisica (INAF), and has been fundedby the Italian Space Agency (ASI) in the context of theItalian participation to theMars Express mission of ESA.

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Documents

First observations of the planetary Fourier spectrometer at Mars