1. SOIR data workshop SOIR Instrument description and data calibration A.C. Vandaele, R. Drummond, A. Mahieux, S. Robert, V. Wilquet SOIR Team @ Belgian Institute for Space Aeronomy (IASB-BIRA)

2. SOIR data workshop Overview  Venus  Characteristics  Atmosphere  Venus Express  SOIR  Solar occultation  Instrument description  Telemetry  Calibrations  Echelle grating  AOTF  Detector  Optics  Spectrum construction  Geometry

3. SOIR data workshop Overview  Venus  Characteristics  Atmosphere  Venus Express  SOIR  Solar occultation  Instrument description  Telemetry  Calibrations  Echelle grating  AOTF  Detector  Optics  Spectrum construction  Geometry

4. SOIR data workshop The Venus orbit Credits: Celestia

5. SOIR data workshop Venus : Characteristics Characteristics Radius Mass Sidereal day Year duration Axis inclination Distance to the Sun Surface temperature Surface pressure Earth 6371.0 km (1.00) 5.97 10 24 kg (1.00) 1 day 365.15 days 23.44° 1 AU 287 K (14°C) 1 atm Venus 6051.8 km (0.95) 4.87 10 24 kg (0.82) -243 days 224.65 days 177.3° 0.723 AU 730 K (457°C) 92 atm

6. SOIR data workshop Venus : Atmosphere subdivisions  Troposphere  Poorly known region  High temperatures and pressures  Low wind  Cloud layer  Aerosols H 2 SO 4  Wind ~ 300 km/h retrograde  Mesosphere  Transition zone  Aerosol haze  Thermosphere  Large differences between day and night  Temperature  chemistry  Subsolar – antisolar circulation  Region studied by SOIR

7. SOIR data workshop Venus : Atmospheric composition  Main compound: carbon dioxide CO 2  96.5 % up to ~110 km  Uniform  Transformed by solar UV into CO (> 110 km)  Quantity decreases with altitude, replaced by CO and O  Little water  Variable quantity  HDO/H 2 O fraction 140 x larger than on Earth  H 2 SO 4 in the regions close to the cloud layer  products SO 2, SO, OCS, H 2 CO  Halogens  HCl, HF

8. SOIR data workshop Venus: Temperatures Combination of Zasova model 1997 and Hedin 1983 Day profile

9. SOIR data workshop Venus: Atmospheric circulation  Zonal retrograde circulation  Winds at the cloud top ~ 300 km/h  3 day rotation period  Subsolar – antisolar circulation  Higher altitude > 130 km  Explained by the larger temperature gradient between day and night sides

10. SOIR data workshop Overview  Venus  Characteristics  Atmosphere  Venus Express  SOIR  Solar occultation  Instrument description  Telemetry  Calibrations  Echelle grating  AOTF  Detector  Optics  Spectrum construction  Geometry

11. SOIR data workshop Venus Express: Mission description  Launched from Baïkonour in November 2005  Reached Venus in May 2006  Apoapsis  North pole  Distance ~ 250 km  Periapsis  South pole  Distance ~ 65 000 km  Already two mission extensions  Should end in December 2012  Maybe until 2014? Sun N

12. SOIR data workshop Venus Express: Payload  7 instruments  ASPERA  MAG  PFC  SPICAV/SOIR  VeRA  VIRTIS  VMC Credits: European Space Agency

13. SOIR data workshop Overview  Venus  Characteristics  Atmosphere  Venus Express  SOIR  Solar occultation  Instrument description  Telemetry  Calibrations  Echelle grating  AOTF  Detector  Optics  Spectrum construction  Geometry

14. SOIR data workshop SOIR: Solar occultation - Animation Credits: Celestia

15. SOIR data workshop SOIR: solar occultation – Measurement principle To Sun Venus VEX Atmosphere Orbit 232 – Order 129 Side view View from Venus Express N Transmittance

16. SOIR data workshop To Sun Venus VEX Atmosphere Orbit 232 – Order 129 Side view View from Venus Express N Transmittance SOIR: solar occultation – Measurement principle

17. SOIR data workshop SOIR: Solar occultation – Example of measured spectra  4 different diffraction orders measured during each occultation Orbit 486 (20070820) HDOH2OH2OCO 2 CO

18. SOIR data workshop SOIR: Solar occultations – Measurements map

19. SOIR data workshop Overview  Venus  Characteristics  Atmosphere  Venus Express  SOIR  Solar occultation  Instrument description  Telemetry  Calibrations  Echelle grating  AOTF  Detector  Optics  Spectrum construction  Geometry

20. SOIR data workshop SOIR: Optical description (1) Credits: IASB/BIRA

21. SOIR data workshop Spectral direction: 320 pixels Spatial direction: 256 pixels Crystal SOIR: Optical description (2) Acousto-optic filter Echelle grating Infrared detector Reflective surfaces 250 µm

22. SOIR data workshop Overview  Venus  Characteristics  Atmosphere  Venus Express  SOIR  Solar occultation  Instrument description  Telemetry  Calibrations  Echelle grating  AOTF  Detector  Optics  Spectrum construction  Geometry

23. SOIR data workshop SOIR telemetry – Constraints on the combination of detector lines Detector: 320 x 256 pixels 32 illuminated rows  Telemetry = equivalent of 8 spectra/second  If 4 orders/second  2 spectra/order = 2 ‘bins’ Spectral Spatial

24. SOIR data workshop 60 Slit position during an occultation 60 km Venus Bin 1Bin 2 Spectral Spatial

25. SOIR data workshop Overview  Venus  Characteristics  Atmosphere  Venus Express  SOIR  Solar occultation  Instrument description  Telemetry  Calibrations  Echelle grating  AOTF  Detector  Optics  Spectrum construction  Geometry

26. SOIR data workshop SOIR: Calibrations  Need to obtain different calibrations  In flight calibration of almost all characteristics  Echelle grating  Blaze function  Acousto-optic filter  Transfer function  Tuning relation wavenumber – acousto-optic frequency  Detector  Non-uniformity of the detector pixels  Pixel to wavenumber relation  Sample interval  Instrument  Sensitivity  Resolution  Signal to noise ratio

27. SOIR data workshop Echelle grating: Blaze function (1)  The efficiency of the grating in terms of refracted angle  Is maximum when the refracted angle = incident angle Pyo, Tae-Soo. 2003. Blaze Function and the Groove Shadowing Effect.

28. SOIR data workshop Echelle grating: Blaze function (2) Diffraction order Mahieux, A. et al, 2008. In-flight performance and calibration of SPICAV/SOIR on-board Venus Express. Applied Optics, 47(13), 2252–65.

29. SOIR data workshop Acousto Optical Tunable Filter: Characteristics  Calibrations:  1. AOTF bandpass function  T AOTF = f(, ,  FWHM )  2. Tuning function  0 = f(RF)  3. Bandwidth   FWHM = f() Mahieux, A. et al, 2008. In-flight performance and calibration of SPICAV/SOIR on-board Venus Express. Applied Optics, 47(13), 2252–65.

30. SOIR data workshop Acousto Optical Tunable Filter: Characteristics – Bandpass function (1)  Calibration using miniscans  Using deed solar lines (from Hase et al. 2009)  Radiofrequency of AOTF chosen to correspond to well defined solar lines  Different frequency steps (1 kHz to 20 kHz) around that RF  Lots of miniscans for a lot of different solar lines over the entire spectral range covered by SOIR  Performed routinely to follow aging of the crystal Mahieux, A. et al. 2009. A New Method for Determining the transfer function of an Acousto Optical Tunable Filter. Optics Express, 17, 2005–2014.  Usual transfer function for AOTF

31. SOIR data workshop B Acousto Optical Tunable Filter: Characteristics – Bandpass function (2) Mahieux, A. et al. 2009. A New Method for Determining the transfer function of an Acousto Optical Tunable Filter. Optics Express, 17, 2005–2014. A One solar line @ 2948.7 cm -1

32. SOIR data workshop  Sum of 5 sinc 2  With all parameters varying linearly with  = I i, 0i(i≠0), FWHM i Acousto Optical Tunable Filter: Characteristics – Bandpass function (3) Mahieux, A. et al. 2009. A New Method for Determining the transfer function of an Acousto Optical Tunable Filter. Optics Express, 17, 2005–2014.

33. SOIR data workshop Mahieux, A. et al, 2008. In-flight performance and calibration of SPICAV/SOIR on-board Venus Express. Applied Optics, 47(13), 2252–65. Acousto Optical Tunable Filter: Characteristics – Tuning function  Tuning function  Relation between the radiofrequency applied to the crystal and the central wavenumber of the filtered spectral interval  By-product of the previous analysis  Different for the different bins  Different parts of the crystal

34. SOIR data workshop Acousto Optical Tunable Filter: Characteristics – Order width vs. AOTF FWHM

35. SOIR data workshop Detector: Flat field (1)  Pixel-to-pixel non-uniformity  Obtained:  In the laboratory: by illuminating the detector directly, without passing through the spectrometer, with an homogeneous light source; repeated with different exposure times  In-flight :  Select orders (32) with (almost) no Solar lines (T>0.95)  Large number of repeated observations  High-pass filtering to remove the effect of AOTF, spectrometer, optics…  Depends on  The binning scenario (2x12, 2x16, …)  From bin to bin  Time

36. SOIR data workshop Detector: Flat field (2)

37. SOIR data workshop Detector: Sample interval

38. SOIR data workshop Instrumental Wavenumber calibration  Use of Solar lines in a lot of distinct orders  Correction for Doppler satellite (rec) – Sun (em)  Pixel – wavenumber – order relation  Wavenumber to pixel relation:

39. SOIR data workshop Instrumental Spectral Sensitivity (1)  Spectral dependence of the whole instrument as a function of the incoming light wavelength  Obtained from direct Sun measurements, fullscan observations

40. SOIR data workshop Instrumental Line Shape (ILS) (1)  From Solar lines and/or Atmospheric lines

41. SOIR data workshop Instrumental Line Shape (ILS) (2)

42. SOIR data workshop Instrumental Signal to Noise ratio (1)  From transmittance corresponding to high altitude (no absorption)

43. SOIR data workshop Instrumental Signal to Noise ratio (2)

44. SOIR data workshop Overview  Venus  Characteristics  Atmosphere  Venus Express  SOIR  Solar occultation  Instrument description  Telemetry  Calibrations  Echelle grating  AOTF  Detector  Optics  Spectrum construction  Geometry

45. SOIR data workshop SPICAV/SOIR instrument description: Measurement principles – diffraction order addition  AOTF transfer function: sinc² like  AOTF transfer function shape determination is critical  7 diffraction orders have to be taken into account to correctly reconstruct measurement spectra AOTF transfer function Central order Measured spectrum Mahieux, A. et al, 2008. In-flight performance and calibration of SPICAV/SOIR on-board Venus Express. Applied Optics, 47(13), 2252–65.

46. SOIR data workshop Overview  Venus  Characteristics  Atmosphere  Venus Express  SOIR  Solar occultation  Instrument description  Telemetry  Calibrations  Echelle grating  AOTF  Detector  Optics  Spectrum construction  Geometry

47. SOIR data workshop Geometry: The onion peeling approach

48. SOIR data workshop Geometry – Tangent altitude calculation (1)  The instrument points to the Sun  Pointing direction displaced of 10’ above the centre of the Sun  Account for diffraction

49. SOIR data workshop Geometry – Tangent altitude calculation (2)  Size of the slit is 30’ x 2’ (spectral x spatial)  VEX is inertial pointing  rotation of the slit

50. SOIR data workshop Geometry – Tangent altitude calculation (3)  Use of SPICE to calculate the tangent altitude  From reconstructed kernels delivered by ESOC  Pointing angle for one bin of the slit:  Tangent altitude:

51. SOIR data workshop Spectral inversion: Non linear problem inversion – General concerns (1)  Goal: Solve a non linear system  Relation between the layers  Transmittance calculation  Hypothesis of equivalent constant atmospheric parameters in each layer

52. SOIR data workshop Thank you for your attention