SOIR and NOMAD: Characterization of planetary atmospheres

Transcription

1 SOIR and NOMAD: Characterization of planetary atmospheres S. Robert*, S. Chamberlain*, A. Mahieux*, R. Drummond*, I. Thomas*, V. Wilquet*, A.C. Vandaele* and J.-L. Bertaux * BIRA-IASB, Belgian Institute for Space Aeronomy, Belgium LATMOS - UVSQ/CNRS/IPSL ; Institut Pierre Simon Laplace, Université de Versailles-Saint-Quentin Guyancourt, France

2 Outline Planetary atmospheres SOIR intrument Principles Strategy Some results NOMAD instrument Description Scientific objectives Scientific preparation

3 Outline Planetary atmospheres: Venus - Mars SOIR intrument Principles Strategy Some results NOMAD instrument Description Scientific objectives Scientific preparation

4 Planetary atmospheres Orbital Distance (UA) Orbital period (yrs) Rotation period (h) Equ. Radius (km) Obliquity ( ) Mass (rel. To Earth) Gravity (m/s 2 ) Density (kg/m 3 ) Venus days 243 days Earth Mars

5 Planetary atmospheres Venus Earth Mars Main constituents Photochemical products CO 2 96,5% N 2 3,5% SO 2 Ar H 2 O OCS He HCl Kr HF 150 ppm 70 ppm 30 ppm 15 ppm 12 ppm 0,6 ppm 25 ppb 5 ppb N 2 O 2 H 2 O Ar CO 2 Ne He CH 4 Kr N 2 O Xe HCl 78,1% 20,9% <4% 0,93% 350 ppm 18 ppm 5 ppm 1,7 ppm 1,1 ppm 0,3 ppm 87 ppb 1 ppb CO 2 N 2 Ar H 2 O Ne Kr Xe 95,3% 2,7% 1,6% 0,03% 2,5 ppm 0,3 ppm 0,08 ppm CO, H 2 SO 4, SO, O 2 H 2, CO, O 3 O 2, CO, NO, O 3

6 The atmosphere of Venus The atmosphere is divided in three regions: Troposphere Mainly composed of CO 2 From 0 to 50 km Calm zone almost no wind Mesosphere From 50 to 100 km Thermosphere Mainly composed of CO 2 (96%) From 100 km Cloud layer Zone studied by the SOIR instrument ( km)

7 The atmosphere of Mars The thin atmosphere is divided in three regions: Troposphere From 0 to 40 km CO 2 and H 2 O seasonal cycles Large quantities of dust Mesosphere From 40 to 100 km Mainly composed of CO 2 (97%) Thermosphere From 100 km Significant aerosol loading

8 Outline Planetary atmospheres SOIR intrument Principles Strategy of observations Some results NOMAD instrument Description Scientific objectives Scientific preparation

9 Solar occultation principle Self calibrated measurements: transmittances obtained by dividing measured spectra by full sun spectra Altitude range probed: 65 km to 165 km To Sun VEX Orbit 232 Order 129 Venus Atmosphere Cloud top

10 Solar occultation principle Self calibrated measurements: transmittances obtained by dividing measured spectra by full sun spectra Altitude range probed: 65 km to 165 km To Sun VEX Orbit 232 Order 129 Venus Atmosphere Cloud top

11 SPICAV/SOIR instrument Solar Occultation in the InfraRed Infrared spectroscopy (2.29 µm to 4.43 µm) Altitude range probed: 65 km to 165 km Echelle grating spectrometer (94 useful orders) Acousto Optical Tunable filter (AOTF) for order selection AOTF Echelle grating Detector optics and detector Collimation and camera lens together in 1 parabolic mirror Instrument resolution: cm -1 Spectral sampling: cm -1 D. Nevejans et al., Applied Optics 45 (21), (2006)

12 Spectra recorded by SOIR 1 orbit 4 diffraction orders H 2 O CO 2 & HCl Wavenumber (cm -1 ) CO 2 CO

13 Venus: CO 2 laboratory

14 Sounding various altitudes G.S. CO Diffraction order: 166 ± km G.S. CO Diffraction order: 149 ± km

15 SOIR on VEX: strategy of observation 4 different diffraction orders measured during each occultation Targeting different species simultaneously Targeting different absorption features of the same species with different intensities (covering the whole altitude range) Strong absorption Weak absorption altitude but altitude to go deeper in the atmosphere Study of the spectral dependence of the light extinction due to aerosols (SPICAV-UV and IR when possible) information on the composition and size distribution Of special interest: minor gases vs. CO 2 volume mixing ratio H 2 O and HDO for the D/H ratio aerosols vs. H 2 O and SO 2

16 Inversion method Optimal Estimation Method (Rodgers) using onion peeling approach Density vertical profiles are retrieved from measured spectra Atmospheric line saturation is considered Profiles obtained separately & then combined (up to 8 measurements) From the 2 detector parts (bins) From all CO 2 diffraction orders VEx Temperature profiles : Inversion from CO 2 density assuming Hydrostatic law From CO 2 only above homopause, all species below CO 2 VMR from Keating [1980] and Zasova [2008] models By-products: Total pressure profile Total density profile A. Mahieux et al., JGR 117 E07001 (2012)

17 CO 2 & Temperature profiles 132 selected occultations: CO 2 at high altitude Retrieve CO 2 density Apply the hydrostatic law to calculate temperature profiles 5-20% error on the CO 2 density K on the temperature profiles Change of slope at km A. Mahieux et al. PSS, (submitted), 2014

18 Venus Atmosphere from SOIR at the Terminator Database of densities and temperatures is created: VAST Bins of latitude Plot the mean values of density and temperature profiles together with standard deviation Latitude bin AM PM Total A B AM C D PM A. Mahieux et al. PSS, (submitted), 2014

19 Carbon monoxide Produced by photodissociation of CO 2 on the day side in the upper atmosphere of Venus by solar UV radiation CO recombination into CO 2 is very slow CO and O 2 observed abundances cannot be explained Faster recombination processes through catalytic cycles involving chlorine (ClOx) or hydrogen (HOx) oxides have been proposed Study short-term variability A.C. Vandaele, PSS, (submitted), 2014 ; V.A. Krasnopolsky, Icarus, th International HITRAN Conference (united with the 12 th ASA conference) June Venus 2014 workshop 2-6 June 2014

20 Hydrogen halides (HCl, HF) Active species involved in three of the main chemical cycles: the CO 2 cycle ; the sulfur oxidation cycle ; the polysulfur cycle. HCl VMR in the different latitude bins, based on the retrievals done on the order 130 ( cm -1 ) Latitude bin H 35 Cl H 37 Cl H 19 F Total At latitudes <70, no latitudinal variations At latitudes > 70 and altitude km, depletion of HCl At latitudes > 70 and altitude km, increase of HCl A. Mahieux et al. PSS, (submitted), 2014

21 Hydrogen halides (HCl, HF) 2 HCl isotopologues observed in the same spectra 37 Cl / 35 Cl isotopic ratio can be measured On Earth: On Venus: ± A. Mahieux et al. PSS, (submitted), 2014 ; L.S. Rothman et al. JQSRT, 2013

22 Sulfur dioxide SO 2 is a key species of the Venus atmosphere Its origin is probably volcanic outgassing, even if no clear evidence of recent volcanic activity has been detected up to now Clouds (30-70 km) are made of H 2 SO 4 hydrated droplets Exchange of SO 2 between upper and lower atmosphere is not fully understood, but undoubtedly involves convection transport, presumably in conjunction with Hadley cell transport Above the clouds, it is involved in two main cycles: sulphur oxidation cycle and polysulfur cycle (hypothetical) Destroyed on the dayside through photolysis, followed by oxidation Latitude bin SO Total 142 Geo-temporal location of SO 2 measurements weak latitude/altitude variation of the minimum VMR in the km region Profiles have been averaged by latitude bins (N- S and AM-PM symmetry) Averages calculated on pressure scale A. Mahieux et al. PSS, (submitted), 2014

23 Aerosols The continuum is obtained by fitting the baseline of a spectrum by a second degree polynomial as a function of the wavenumber. Transmittances Extinction : t ln( T ) ln( I / I 0) N ext With N 1 i t dzi ext, z i 1 dz t aerosol optical depth T the transmittance N # of atmospheric layers i #ing of layers above layer N dz i length of light path within layer i I atmospheric intensity I 0 full sun intensity β i local extinction within layer i N

24 Aerosols Mie theory Bimodal distribution SPICAM-UV and SOIR data Altitude (km) Composition (%H 2 SO 4 ) R 1 (µm) R 2 (µm) s 1 s 2 Density (# /cm 3 ) Density 1 (# /cm 3 ) Density 2 (# /cm 3 ) V. Wilquet et al., JGR, 114, E00B42, 2009

25 Rovibrational assignment 1. Selection of the spectra (wrt noise level) 2. Selection of possible assignments 3. Association between the experimental peaks and the selected assignments Within half the pixel width (~ half of cm -1 ) Lines from adjacent orders are marked as well

26 Outline Planetary atmospheres SOIR intrument Principles Strategy Some results NOMAD instrument Description Scientific objectives Scientific preparation

27 ExoMars Trace Gas Orbiter 2016 TECHNOLOGY OBJECTIVE Entry, Descent, and Landing (EDL) of a payload on the surface of Mars. SCIENTIFIC OBJECTIVE To study martian atmospheric trace gases and their sources. Provide data relay services for landed missions until Launch window 7 th -27 th Jan 2016 Mars orbit insertion Science Operations 19/10/ martian year Nov 2017 Oct 2019 End of Mission 31/12/2022

28 Trace Gas Orbiter (TGO) payload NOMAD High resolution occultation and nadir spectrometers Atmospheric composition (CH 4,O 3, trace species, isotopes) dust, clouds, P&T profiles UVIS ( mm) /D ~ 250 SO Limb Nadir IR ( mm) /D ~ 10,000 SO Limb Nadir IR ( mm) /D ~ 20,000 SO CaSSIS High-resolution camera Mapping of sources; landing site selection ACS Suite of 3 high-resolution spectrometers Near IR ( mm) /D ~ 20,000 Atmospheric chemistry, aerosols, surface T, structure IR (Fourier, 2 25 mm) /D ~ 4000 (SO)/500 (N) Mid IR ( mm) /D ~ 50,000 SO Limb Nadir SO Nadir SO FREND Collimated neutron detector Mapping of subsurface water All Power Resolution /D calculated at mid-range

29 The NOMAD spectrometer suite 3 channels - UV & IR - Solar Occultation, Limb & Nadir LNO SO UVIS to Sun or limb nadir

30 NOMAD : 3 channels SO Solar Occultation IR : mm Resolution ~ 0.15 cm -1 Resolving power = LNO Nadir, Limb, Solar Occultation IR : mm Resolution ~ 0.3 cm -1 Resolving power = UVIS Nadir, Limb, Solar Occultation UV-vis : nm Resolution ~ 1-2 nm

31 NOMAD : Science Objectives Chemical composition Detection of a broad suite of trace gases and key isotopes CO 2, CO, O 3 CH 4 related : CH 4, 13 CH 4, CH 3 D, C 2 H 2, C 2 H 4, C 2 H 6, H 2 CO Escape processes : H 2 O, HDO D/H Volcanism related : SO 2, H 2 S, HCl Villanueva et al., 2008 Mars Climatology & Seasonal cycles 3D spatial & temporal variability of trace gases and aerosols Climatology of O 3 and UV radiation levels O 3 - SPICAM-UV/Mars Express (Y. Willame) Sources & Sinks Analyse correlation trace gases dust clouds T&P Use GCM for interpretation GCM simulation (F. Daerden)

32 Detection Limits Species Current Knowledge NOMAD Detection limits CH ppb 14 ppt H 2 O < 300 ppm (variable ) 2.5 ppb CO ppm 20 ppb HDO D/H =5.6 SMOW 1.7 ppb (i.e. 6 ppm H 2 O) 13 CH 4 CH 3 D CO, CO 2 isot 20 ppt (i.e. 2 ppb CH 4 ) 70 ppt (i.e. 100 ppb CH 4 ) 2 % accuracy HCN 3 ppb 0.06 ppb H 2 CO < 3 ppb 0.1 ppb HO 2 6 ppb H 2 S < 100 ppb 4 ppb C 2 H 2 < 2 ppb 0.3 ppb C 2 H 4 < 500 ppb 3 ppb C 2 H 6 < 400 ppb 0.03 ppb OCS < 70 ppb 0.5 ppb N 2 O NO 2 7 ppb 0.03 ppb SO 2 < 2 ppb 0.1 ppb (UVIS) O 3 50 ppt (UVIS)

33 NOMAD radiative intercomparaison Aim: Comparing each group s radiative transfer code: IAA (Granada, Spain), OU (UK), IAPS (Rome, Italy), GSFC (Washington, USA), BIRA-IASB (Belgium) Agree on conditions (atmospheric state ; geometry ; resolution ; instrument line shape ; surface ) Simulate spectra & understand differences Name (Institute) ARS (IAPS) ASIMUT/ALVL (BISA) KOPRA (IAA) LBLRTM (GSFC) Based on Ignatiev[1] Vandaele[2] Spurr[3] Karlsruhe[4] Clough[5] Villanueva[6] Spectral Range UV - VIS - IR UV VIS IR IR UV VIS IR mm/submm Geometry: layering Plane parallel Spherical Plane parallel Spherical Spherical Plane parallel Geometry: viewing NADIR Limb/NADIR/SO Limb/NADIR/SO Limb/NADIR/SO Scattering yes yes Single Single Non-LTE no no GRANADA model [7] yes [via tables] CO 2 line mixing no yes yes yes Outputs Transmittance Radiance Transmittance Radiance Transmittance Radiance Transmittance Radiance 1. N.I. Ignatiev et al., PSS 53 (2005) 1035 ; 2. A.C. Vandaele, et al., Proc. of the First Atmospheric Science Conference, ESRIN (2006) Frascati, Italy ; 3. R. Spurr, et al., JQSRT 68 (2001) 689 ; 4. wwwimk.fzk.de/asf/ame/publications/kopra_docu/ ; 5. S.A. Clough, et al., JQSRT 91 (2005) 233 ; 6. G.L. Villanueva, et al., JGR 116 (2011) E08012 ; 7. B. Funke et al., JQSRT 113 (2012) 1771.

34 NOMAD radiative intercomparaison - IR BEFORE AFTER 2 main issues identified: 1. Pressure shift definition: 2. Partition functions: TIPS 2003 J. Fischer et al., JQSRT 82 (2003) ; ν: final line position (cm -1 ) ν 0 : line center (cm -1 ) p: pressure (atm) δ p : pressure shift (atm/cm -1 ) T: temperature (K) TIPS2011: A.L. Laraia et al., Icarus 215 (2011) Fortran code available on

35 Synergistic retrievals Aim: Improve characterization of CO and CH 4 using 2 of the instruments onboard TGO Define instruments & scenarios (atmospheric state wrt season & location ; geometry of observation ; resolution ; instrument line shape ; SNR ) Fourier Transform Spectrometer (< ACS-like) Grating spectrometer (< NOMAD-like) Produce batches of 50 spectra (64 scenarios in nadir ; 64 scenarios in SO at 18 tangent heights) FTS Grating Sp.

36 Synergistic retrievals Perform retrievals - Non-synergistic: for each spectrum separately - Synergistic: - For both type of spectra at the same time (synergy Level1/ Level 1) - For both type of spectra one after the other (synergy Level2/Level1) - For both geometries

37 Summary SOIR instrument onboard Venus Express (2006-): - High resolution - Self-calibrated technique - SO geometry < SNR < 3000 Provides vertical information on a broad series of species Contributes to a better understanding of the dynamics of the atmosphere at the terminator NOMAD instrument onboard Trace Gas Orbiter (2016-): - High resolution - UV-Visible and IR measurements - Nadir, limb and SO geometries - SNR ~ 1000 in nadir and SNR ~ 4000 in SO May provide vertical profiles on a broad series of species May map the surface and enable climatology developments

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