The Legacy of SPICAV on Venus Express

Transcription

1 The Legacy of SPICAV on Venus Express Jean-Loup Bertaux 1 and the SPICAV team jean-loup.bertaux@latmos.ipsl.fr (1) LATMOS, UVSQ, CNRS, 11 Boulevard d Alembert,78280,Guyancourt France Venus 2016 Conference Express SPICAV April 2016

2 SPICAV or SPICAV/SOIR =SOIR + SPICAV UV_IR SOIR (A.C Vandaele) SPICAV UV_IR

3 SPICAV / VEX Flawless operation throughout whole VEX mission IR: µm AOTF spectrometer Two pixels polarization +Z (nadir) UV: nm spherical grating imaging spectrometer with slit mechanism Acousto-Optic Tunable filter= scanning specrometer (IKI)

4 SPICAV UV channel Spectral Range : nm Mechanical slit at the focal plane of offaxis mirror Narrow Part : resolution 1.5 nm Wide Part : resolution 10 nm Intensified CCD with 384 (spectral) and 288 (spatial) pixels 4/15/2016 Svalbard Meeting 5

5 SPICAV Observations Nadir (IR and UV) mapping composition above cloud deck (day side) + polarization (particles) Night :sounding surface in windows (R>1000); H 2 O contents below clouds Solar occultations (IR and UV) vertical profiles of minor constituents, isotopes, and atmosphere structure above clouds probing top of cloud deck Limb (UV and IR) UV airglow ( nm) H Lyman α and NO O 21 emission at 1.27 µm Stellar occultations (UV, IR < 1 µm) Vertical profiles atmospheric density SO 2, H 2 O above km (cloud top) Aerosol vertical structure * Star Sun Nadir Venus Night side Sun VEX Limb * Star Orbit

6 SPICAV UV Targets (number of observations)

7 SPICAV Ultra-Violet observations Spectrum of the star : outside the atmosphere through the atmosphere Atmospheric Transmission ratio CO 2 Venus Express spacecraft Line of sight star VENUS

8 Star Occultation Ex SPICAM star occultation: Browse images from 0A/1A archive (5 tempo-spectra representing stacked spectra through time records) Observation in 5-band mode star star Stray light time NO limb emission Nitric oxide lambda Raw data level 0A Clean data level 1A Electronic noise and Dark charge removed

9 Data Processing for SPICAV UV Imaging spectrometer: 5 spectra ( nm) each second for minutes observations Level 0: raw data file, ADU units (in binary format) + geometry in ASCII format 2 files per observation. Catalogue existing Processing Level 0 to Level 1A: Produce Clean ADU data: level 1A 1. Flag matrix with detection of erroneous data, missing data, cosmics and saturated pixels, error bar (ADU) 2. Concatenated with geometry in FITS (Flexible Image Transport System) format Processing Level 1A to Level 1B: calibrated data in physical units (star spectrum, spectral radiance ) -PRNU correction, stray light decontamination (MAJOR Effort), transformation between ADU in physical units, error bar propagation, but no separation of contamination (NO emission) Processing Level 1B to Level 2a,2b to be detailed in next slide

10 SPICAV high-level data products Data products level L2a: Atmospheric spectral transmission from SPICAV Star Occultation data (Nitric oxide subtracted) Absolute spectral radiance from SPICAV Nadir data (day side, night side) Spectral Albedo from SPICAV Nadir data day side by dividing by solar flux Note: this step requires Data products level L2b: Density profiles of CO 2, O 3 and aerosols from SPICAV Star Occultation data Temperature profiles from SPICAV Star Occultation data SO 2 vertical quantity from SPICAV Nadir data O 3 and aerosols vertical quantity from SPICAM Nadir data

11 Star O055/HR5056: Alfa Virginis, SPICA!!! Level 1, mode Z (full CCD) 21 images averaged Orbit 2718_A01 PRNU Internal stray light: photons not at the right place! - Scattering on mirror (minor) - Scattering on grating? - Scattering in M g F 2 window Internal stray light Star spectrum PSF Model hypothesis: - core+ halo - Core gaussian contains the good photons - isotropic scattering away from center= f(r) r, radial distance in pixels from nominal position: - halo-bad photons which must be subtracted

12 Possible origin of stray light (about 20-25% of signal)/1 HT1 module le gain de Gerbe=pulse=photo-event l intensificateur Intensifier Hamamatsu Colle fibre-ccd Thomson CCD TH 7863 SPICAM sapphire Window Not existing in SPICAV HT V v e Gerbe de 10 4 électrons La gerbe de photons produit des électrons dans les pixels du CCD sur environ 6-9 pixels 1 photo-event PELTIER COOLER MgF 2 window HT2 5 kv 0.5 mm Lecture du CCD: 1 ADU 100 électrons CsTe cathode Micro Channel Plate MCP phosphore 1 e= beaucoup de photons verts Fiber optics window Gain=G= nombre d ADU total pour un pulse (0.001 à 20 selon HT1 )

13 Possible origin of stray light (about 20-25% of signal)/2 HT1 module le gain de Gerbe=pulse=photo-event l intensificateur Intensifier Hamamatsu Colle fibre-ccd Thomson CCD TH 7863 SPICAM sapphire Window Not existing in SPICAV 4.5 mm HT V v Gerbe de 10 4 électrons La gerbe de photons produit des électrons dans les pixels du CCD sur environ 6-9 pixels Core PELTIER COOLER MgF 2 window CsTe cathode Halo stray light Micro Channel Plate HT2 5 kv 0.5 mm phosphore 1 e= beaucoup de photons verts Fiber optics window Stray light Lecture du CCD: 1 ADU 100 électrons Gain=G= nombre d ADU total pour un pulse (0.001 à 20 selon HT1 ) Hypothèse du stray light: diffusion sur la face d entrée du MgF 2

14 From Level 0 to 1A to 1B Level 1B: absolute spectral flux of target 0 Raw vs Clean star spectrum ADU=f(pixel) 1A Calibrated star spectrum Conversion to physical units and wavelength assignment Spectral Flux=f(λ)

15 SPICAV high-level data products Data products level L2a: Atmospheric spectral transmission from SPICAV Star Occultation data (Nitric oxide subtracted) Absolute spectral radiance from SPICAV Nadir data (day side, night side) Spectral Albedo from SPICAV Nadir data day side by dividing by solar flux Data products level L2b: Density profiles of CO 2, O 3 and aerosols from SPICAV Star Occultation data Temperature profiles from SPICAV Star Occultation data SO 2 vertical quantity from SPICAV Nadir data Example for SPICAM/MEX

16 The variable PI mood versus public Archiving Step 1: Some people outside the team is going to steal my data! Step 2: nobody is interested by my data! Step 3: I am going to die. What to do? Step 4. Legacy to future generations: Public archiving. Put cleaned data, calibrated, as a legacy to future generations and comparison with future missions (Akatsuki, ) Step 5. Even now, some smarter people than me or my team could find something that we did not find? (it actually happened on SPICAM )

17 Plan of SPICAV Availability at PSA PSA archive: Level 0A UV and 0B IR : data for the whole mission available on PSA (last dataset Ext. 4 Release 3 sent in 04/2015) Level 1A UV : dataset Ext. 4 Release 3 available now Level 1A IR : datasets Ext. 1-4 available Near future (2 months): a tool will be delivered to produce Level 2A calibrated from level 1B, without the decontamination of stray light. Middle 2017: delivery to PSA for ingestion of high-level products Level 2a and Level 2B

18 Some outstanding Venus questions Establish an average UV albedo and connect to Virtis UV check for calibration stability Correlation between UV markings of VMC (365 nm) and SPICAV albedo (nadir and zig-zags) Scattering phase function from spot pointing analysis. Wind velocity at 115 km altitude from NO successive maps correlation Slow variations of cloud top altitude (star occ)

19 CO 2 absorption Absolute calibration of SPICAV UV with known stars Marcq says: UV albedo has decreased, as well as SO2 column above ~70 km. Based on constant calibration Need to be checked versus analysis of numerous star observations UV albedo of UV absorber UV albedo of UV absorber has a minimum around 340 nm? Better identification of UV absorber, Bob Carlsson

20 Time variations of constant density altitude?? To be analyzed in detail!!! Geography? A.Piccialli et al. Planetary and Space Science (2015)

21 Winds tracked by NO emission night side MTP-101

22 Solar scans with SPICAV UV (non Venus Science) Solar UV maps (spectroheliograms) will be used to validate by Fontenla (LASP, Boulder) his model of solar UV output as a function of activity (co-operation lead by Eric Quémerais) A few maps at every MTP, weekly basis One during the transit of Venus for comparison with ISS

23 Highlights of SPICAV-UVIR Nightside temperature profiles Bertaux, Montmessin, Piccialli Discovery of ozone Montmessin SO 2 nadir at ~70 km : two regimes, time trend Marcq UV albedo: a trough and a trend (?) Marcq NO maps night side winds? Jean-Claude Gérard Fisrt observation of UV day glow Chaufray The H night bulge of the exosphere Chaufray Clouds and polarimetry Rossi Advances in CO 2 spectroscopy in the near IR Anna Fedorova Mapping of H 2 O 0-30 km night side, constant 30 ppm Bezard, Fedorova Geographic Mapping of H 2 O at cloud top Anna Fedorova Size of cloud particles in haze (multi lambda solar occ) Anna Fedorova SO2 solar/stellar occultation Denis Beliyaev/Montmessin Sun disc UV maps Eric Quémerais.

24 SPICAV UV Targets (number of observations)

25 Conclusions: Plan for future Not enough scientists in the SPICAV team to extract the whole science from SPICAV data Cleaning, production and archiving of higher level data in progress Stray light, radiometric calibration Products: vertical profiles from star occultation UV albedo spectra =f(t) needs aging of instrument analyzed from star observations.