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

OMEGA calibration plan 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

OMEGA IN THE CALIBRATION TANK

THE OPTICAL BENCH

Spectral calibration (lambda.dat)

List of spectral calibration performed using the monochromator SWIR (2,5 ms & 5ms) VNIR (100 &200) ms Tspectro Tdet (IR) Position in the FOV -90°C -195°C 3 -80°C center -70°C -191°C -198°C -200°C -197°C -193°C -188°C Tspectro T det (IR) Position in the FOV -90°C 20°C 5 1 (center) -80°C -195°C -70°C 3 -95°C

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

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

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

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)

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

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

Photometric response of OMEGA 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)

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

3. geometric calibration

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

Azimuth, spacecraft motion "Site", scanning mirror

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

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

(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

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

 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

REGISTRATION EFFECTS along the azimuth

4. Stray light

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

5. Reference samples

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

Calcite Montmorillonite Gypsum Diopsite Fayelite Labradorite Magnetite wavelength (micrometers)