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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)
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SOIR data workshop Overview Venus Characteristics Atmosphere Venus Express SOIR Solar occultation Instrument description Telemetry Calibrations Echelle grating AOTF Detector Optics Spectrum construction Geometry
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SOIR data workshop Overview Venus Characteristics Atmosphere Venus Express SOIR Solar occultation Instrument description Telemetry Calibrations Echelle grating AOTF Detector Optics Spectrum construction Geometry
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SOIR data workshop The Venus orbit Credits: Celestia
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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
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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
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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
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SOIR data workshop Venus: Temperatures Combination of Zasova model 1997 and Hedin 1983 Day profile
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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
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SOIR data workshop Overview Venus Characteristics Atmosphere Venus Express SOIR Solar occultation Instrument description Telemetry Calibrations Echelle grating AOTF Detector Optics Spectrum construction Geometry
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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
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SOIR data workshop Venus Express: Payload 7 instruments ASPERA MAG PFC SPICAV/SOIR VeRA VIRTIS VMC Credits: European Space Agency
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SOIR data workshop Overview Venus Characteristics Atmosphere Venus Express SOIR Solar occultation Instrument description Telemetry Calibrations Echelle grating AOTF Detector Optics Spectrum construction Geometry
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SOIR data workshop SOIR: Solar occultation - Animation Credits: Celestia
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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
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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
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SOIR data workshop SOIR: Solar occultation – Example of measured spectra 4 different diffraction orders measured during each occultation Orbit 486 (20070820) HDOH2OH2OCO 2 CO
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SOIR data workshop SOIR: Solar occultations – Measurements map
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SOIR data workshop Overview Venus Characteristics Atmosphere Venus Express SOIR Solar occultation Instrument description Telemetry Calibrations Echelle grating AOTF Detector Optics Spectrum construction Geometry
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SOIR data workshop SOIR: Optical description (1) Credits: IASB/BIRA
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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
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SOIR data workshop Overview Venus Characteristics Atmosphere Venus Express SOIR Solar occultation Instrument description Telemetry Calibrations Echelle grating AOTF Detector Optics Spectrum construction Geometry
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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
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SOIR data workshop 60 Slit position during an occultation 60 km Venus Bin 1Bin 2 Spectral Spatial
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SOIR data workshop Overview Venus Characteristics Atmosphere Venus Express SOIR Solar occultation Instrument description Telemetry Calibrations Echelle grating AOTF Detector Optics Spectrum construction Geometry
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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
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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.
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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.
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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.
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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
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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
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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.
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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
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SOIR data workshop Acousto Optical Tunable Filter: Characteristics – Order width vs. AOTF FWHM
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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
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SOIR data workshop Detector: Flat field (2)
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SOIR data workshop Detector: Sample interval
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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:
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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
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SOIR data workshop Instrumental Line Shape (ILS) (1) From Solar lines and/or Atmospheric lines
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SOIR data workshop Instrumental Line Shape (ILS) (2)
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SOIR data workshop Instrumental Signal to Noise ratio (1) From transmittance corresponding to high altitude (no absorption)
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SOIR data workshop Instrumental Signal to Noise ratio (2)
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SOIR data workshop Overview Venus Characteristics Atmosphere Venus Express SOIR Solar occultation Instrument description Telemetry Calibrations Echelle grating AOTF Detector Optics Spectrum construction Geometry
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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.
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SOIR data workshop Overview Venus Characteristics Atmosphere Venus Express SOIR Solar occultation Instrument description Telemetry Calibrations Echelle grating AOTF Detector Optics Spectrum construction Geometry
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SOIR data workshop Geometry: The onion peeling approach
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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
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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
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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:
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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
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SOIR data workshop Thank you for your attention
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