# Presentation: 610780

## 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) **
**          ****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

**OMEGA IN THE CALIBRATION TANK**

## THE OPTICAL BENCH 

**THE OPTICAL BENCH **

## Spectral calibration 

- (lambda.dat)

## SWIR (2,5 ms & 5ms)

| Tspectro | T det (IR) | Position in the FOV |
| --- | --- | --- |
|      -90°C |     20°C |        5 |
|      -90°C       |     20°C |  1 (center)       |
|     -80°C |    -195°C |       5 |
|     -80°C |    -195°C |  1 (center) |
|     -70°C |    -195°C |      3 |
|     -95°C |    20°C |      3 |

- VNIR (100 &200) ms

| Tspectro | Tdet (IR) | Position in the FOV |
| --- | --- | --- |
| -90°C | -195°C | 3 |
| -80°C | -195°C | center |
| -70°C | -195°C | 3 |
| -90°C | -191°C | center |
| -90°C | -198°C | center |
| -90°C | -200°C | center |
| -90°C | -197°C | center |
| -90°C | -193°C | center |
| -90°C | -188°C | center |

- List of spectral calibration performed  using the monochromator

## 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

- Spectel number

- Nanometers

- right of FOV

- left of FOV

## SWIR-C

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

- SWIR-L

## 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

## 197°C

**197°C**

**295°C**

**368°C**

**523°C**

**saturation**

**low S/N**

**Signal in DN divided by the corresponding black body flux**

**DETERMINATION OF THE PHOTOMETRIC FUNCTION (C CHANNEL)**

## Photometric response of OMEGA

**VIS**

**SWIR C**

**SWIR L**

**Bright region**

**Dark region**

**    **S/N ratio for observations of Mars
- Phase = 0°, surface temperature = 250 K

**Wavelength (μm)**

**Wavelength (μm)**

## INFLUENCE OF THE TEMPERATURE OF THE SPECTROMETER

**INFLUENCE OF THE TEMPERATURE OF THE SPECTROMETER**

**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 **

**200 K **
**190 K**
**175 K**

**      ****Solid line: 5 msec**
**Dashed lines: 2.5 msec**

**Wavelength (μm)**

## 3. geometric calibration 

##    "SITE" = yaw: SCANNING 

- "AZIMUTH" = pitch: spacecraft motion

-    "SITE" = yaw: SCANNING
-      MIRROR motion

- SLIT

- Point  Source
- (ribbon lamp, grid Officine Galileo)

- Geometric calibration

## Azimuth, spacecraft motion

- "Site", scanning mirror

## Geometric calibration files

- 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

-  12 pixels

-   l	       l		           l		     	      l
- .45 μm        1. μm                    2.5 μm                       5 μm

- (Y,λ) maps of a point source scanned in azimuth

- VNIR

- SWIR-L

- SWIR-C

## IRC

- IRL

- VIS

- (i,j)

- (i,j-/+n)

- (i-/+m,j-/+n)

## 

- 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

## Slide 24

## 4. Stray light 

## 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

## Slide 29

## Calcite

- Montmorillonite
- Gypsum
- Diopsite
- Fayelite
- Labradorite
- Magnetite

- wavelength (micrometers)