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OMEGA GROUND CALIBRATION

OMEGA GROUND CALIBRATION. B. Gondet,Saint Louis, 21/05/2008. Optical test bench OMEGA was mounted on a two axis platform 0.1 mrad in both site and azimuth (0.1 IFOV) Cold sink for regulating the operating temperatures light sources: - monochromator (spectraPro 275)

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OMEGA GROUND CALIBRATION

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  1. OMEGA GROUND CALIBRATION B. Gondet,Saint Louis, 21/05/2008

  2. Optical test bench • OMEGA was mounted on a two axis platform • 0.1 mrad in both site and azimuth (0.1 IFOV) • Cold sink for regulating the operating temperatures • light sources: • - monochromator (spectraPro 275) • the grating can be set as a mirror • - tungsten ribbon lamp (Russia) • brightness temperature from 2500 K to 2850 K • five filters with different transmission profiles • pinhole point source (steps of 0.05 IFOV) • sample holder • - black body, from 325 K to 1400 K (Galaï – 1200 BB) • circular aperture covering 4 IFOV’s • - grid of 4 x 4 IFOV-sized black bodies (Galileo) • - cold plate, from 150 K to 293 K • OMEGA calibration plan • spectral calibration • photometric calibration • influence of detector temperature • and spectrometer temperature • linearity • geometric calibration • co-alignment, registration • stray light • reference targets

  3. OMEGA IN THE CALIBRATION TANK

  4. THE OPTICAL BENCH

  5. Spectral calibration • (lambda.dat)

  6. List of spectral calibration performed using the monochromator SWIR (2,5 ms & 5ms) VNIR (100 &200) ms

  7. Procedure and examples of results for SWIR Tspectro = -90°C Tdet = -195°C Tspectro = -70°C Tdet = -195°C

  8. SWIR-L spectral calibration as a function of position in the FOV right of FOV Nanometers left of FOV Spectel number

  9. Spectral match between OMEGA Earth spectrum, and "MODTRAN"  simulated SWIR-L SWIR-C

  10. 2. radiometric calibration mtfYYMM_25.dat (2.5 msec, release of year YY, month MM) mtfYYMM_50.dat ( 50 msec, release of year YY, month MM)

  11. Operational parameters Hot Black body source temperature, varying from 9°C to 1175°C Cold BB temperature from 10°C down -120°C IR detector temperature from –201°C to –188°C (-195°C nominal) Integration time = 2,5 ms, 5 ms & 10ms for SWIR = 100 ms & 200 ms for VNIR Test at several positions in the FOV

  12. DETERMINATION OF THE PHOTOMETRIC FUNCTION (C CHANNEL) low S/N 197°C 295°C 368°C 523°C saturation Signal in DN divided by the corresponding black body flux

  13. S/N ratio for observations of Mars Phase = 0°, surface temperature = 250 K Bright region Photometric response of OMEGA SWIR L SWIR C VIS Dark region Wavelength (µm) Wavelength (µm)

  14. INFLUENCE OF THE TEMPERATURE OF THE SPECTROMETER 200 K 190 K 175 K Solid line: 5 msec Dashed lines: 2.5 msec Wavelength (µm) For OMEGA, photons remove electrons from pre-charged wells The available dynamics decreases rapidly with the temperature of the spectrometer beyond 4.5 µm, in particular for long integration times (5 msec) This is essential for the detection of sulfates

  15. 3. geometric calibration

  16. Geometric calibration SLIT "SITE" = yaw: SCANNING MIRROR motion Point Source (ribbon lamp, grid Officine Galileo) "AZIMUTH" = pitch: spacecraft motion

  17. Azimuth, spacecraft motion "Site", scanning mirror

  18. Geometric calibration files • IFOV for each spectel, for each of the 128 spatial directions • 2. perpendicular to the slit ("azimuth") direction • - for each channel, relative variation of the viewing direction along the spectrum, for each IFOV within the entire 128 px FOV • - spectral registration for the 3 channels, and each of the 128 positions • 3. along the slit ("site") direction • - relation between the IR swath position and the VNIR column number • - spectral registration for the 3 channels, and each of the 128 directions

  19. IFOV = f(wavelength), at the center of the FOV

  20. (Y,λ) maps of a point source scanned in azimuth SWIR-C SWIR-L 12 pixels VNIR l l l l .45 µm 1. µm 2.5 µm 5 µm

  21. (i,j) (i,j-/+n) (i-/+m,j-/+n) IRC IRL VIS

  22. REGISTRATION : creation of false feature in case the viewing direction of # spectels would be as follows…  …we would end up with a misinterpretated spectral feature

  23. REGISTRATION EFFECTS along the azimuth

  24. 4. Stray light

  25. Measurements made: ± 30° ("site") ± 40° ("azimuth") Source: ribbon lamp, full power No stray light detected

  26. 5. Reference samples

  27. Samples used: "ISM " samples "NASA" samples "Lecce" samples Source: Ribbon lamp Integration times: 2.5 ms, 5 ms, 10 ms (SWIR) 100 ms, 200 ms (VNIR) Number of files acquired : 140

  28. Calcite Montmorillonite Gypsum Diopsite Fayelite Labradorite Magnetite wavelength (micrometers)

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