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

2. 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

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
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

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. 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)

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 µm µm 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

25. 4. Stray light

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

27. 5. Reference samples

28. 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

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