1. PLEIADES Lunar Observations Sophie Lachérade, Bertrand Fougnie
CNES
Ouahid Aznay
CS-SI
Lunar WS – 2nd December 2014, Darmstadt

2. Summary General description of the Pleiades sensors and system
PLEIADES calibration
The Moon seen by PLEIADES (maneuver and images)
Data pre-processing (dark signal, IFOV, integration step, satellite position)
Operation of the GIRO : status
Pleiades results from GIRO

3. The PLEIADES satellites
System of two satellites: PLEIADES-1A (PHR1A) and PLEIADES-1B (PHR1B)
launched in December 2011 and 2012
→ continuity of the SPOT missions
Applications: civilian and military such as cartography, geology, risks

4. The PLEIADES satellites
System of two satellites: PLEIADES-1A (PHR1A) and PLEIADES-1B (PHR1B)
launched in December 2011 and 2012
→ continuity of the SPOT missions
Applications: civilian and military such as cartography, geology, risks
Pushbroom sensor, Altitude 695 km, Swath 20 km, very agile Satellite
Blue
Green
Red
PIR
5 x Arrays
XS = 1500 detectors
PAN = 6000 detectors
sensor

5. The PLEIADES satellites
System of two satellites: PLEIADES-1A (PHR1A) and PLEIADES-1B (PHR1B)
launched in December 2011 and 2012
→ continuity of the SPOT missions
Applications: civilian and military such as cartography, geology, risks
Pushbroom sensor, Altitude 695 km, Swath 20 km, very agile Satellite
Spectral : PANchromatic + 4 spectral bands (B0-Blue, B1-Green, B2-Red, B3-NIR)

6. The PLEIADES satellites
System of two satellites: PLEIADES-1A (PHR1A) and PLEIADES-1B (PHR1B)
launched in December 2011 and 2012
→ continuity of the SPOT missions
Applications: civilian and military such as cartography, geology, risks
Pushbroom sensor, Altitude 695 km, Swath 20 km, very agile Satellite
Spectral : PANchromatic + 4 spectral bands (B0-Blue, B1-Green, B2-Red, B3-NIR)

7. The PLEIADES satellites
System of two satellites: PLEIADES-1A (PHR1A) and PLEIADES-1B (PHR1B)
launched in December 2011 and 2012
→ continuity of the SPOT missions
Swath 20 km, very agile Satellite
Applications: civilian and military such as cartography, geology, risks
Pushbroom sensor, Altitude 695 km, Swath 20 km, very agile Satellite
Spatial resolution: 70cm PAN and 2.8m XS

8. The PLEIADES satellites
San Francisco

9. The PLEIADES satellites
Himalaya (Everest Mount)

10. The PLEIADES calibration
AMETHIST for inter-detector normalization
Steady-Mode for Radiometric SNR assessment
Geometric auto-calibration for focal plane cartography
PICS observation and extra-terrestrial observations for absolute calibration

11. The PLEIADES calibration
Goal: absolute calibration < 5% - Drift monitoring < 1%
Reflectance based calibration
→ Absolute calibration coefficients based on a synergy of the results obtained with the different methods and sites
Estimated performance :
Absolute : 3%
Temporal stability : < 0.5%
PICS observation and extra-terrestrial observations for absolute calibration

12. Summary General description of the Pleiades sensors and system
PLEIADES calibration
The Moon seen by PLEIADES (maneuver and images)
Data pre-processing (dark signal, IFOV, integration step, satellite position)
Operation of the GIRO : status
Pleiades results from GIRO

13. The Moon seen by PLEIADES
Operational PLEIADES Lunar Observations
Regularly Scheduled at the Phase Angles: ±40° (±0.5°)
Monitoring of the temporal drift of the spectral bands (initial need)
Cross-calibration of PLEIADES-1A and PLEIADES-1B
Non-scheduled PLEIADES Orbital Lunar Observations (POLO)
Taking Advantage of the High Level of Agility of the Spacecraft
→Intensive Observation of the Moon as Frequently as Each Orbit
Lunar Phase Angle Range of the POLO Dataset: [-115°;+115°]
Study of the phase angle dependence of the lunar irradiance
Study of the sensitivity of the PLEIADES ground processing on lunar calibration results
Lunar Observations as of November 28, 2014: PLEIADES-1A/PLEIADES-1B: 197/1155

14. The Moon seen by PLEIADES

15. The Moon seen by PLEIADES
The focal plan is made by 5 linear arrays
Raw images
The Moon: more than 4 Million of pixels !
Equalization
Before ground processing
After ground processing

16. The Moon seen by PLEIADES

17. The Moon seen by PLEIADES

18. The Moon seen by PLEIADES

19. Data pre-processing
Native view of the moon
Detector number
DIFOV < 0.5%
Step 1: Equalization (Dark signal correction + Non-uniformity correction)
Dark signal estimated on each lunar image
Dark signal: average of the first 100 lines and the last 100 lines to take into account the temporal evolution of the dark signal in the image
Correction of the non uniformity response of the detectors
Using dedicated images: Amethist (90° yaw steering)
Step2: Resampling step
The image of the Moon is natively « round »
No resampling required, no oversampling to be considered
Consideration of a very light cross-track IFOV variation when integrating irradiances → Impact on integrated irradiance estimated < 0.15%

20. Data pre-processing Step 3: Computation of the Satellite position
Orbit information are supplied by DORIS. Then J2000 coordinates of the Spacecraft are computed using the acquisition date (based on the MSLIB).
Step4: Integration of the Lunar Irradiances
Sum of all pixels of the image (after checking that residual dark current mean = 0)
– weighted by the IFOV variation factor
– converted in irradiance unit using fixed calibration coefficients
* The operational absolute coefficients are applied after the calibration step at CNES

21. Number of measurements
GIRO - status
Sample from the operational dataset
Spectral responses : converted to NetCDF (EUMETSAT tool)
PHR lunar measurements converted to NetCDF (CNES tool)
GIRO 4rd release downloaded and operated (linux platform)
SENSOR
Spectral range
Nb of spectral bands
Spatial resolution
Acquisition Dates
Lunar Phase angle
Number of measurements
PLEIADES-1A
Vis-Nir 4
2.80m
2012
±40° 10
PLEIADES-1B

22. Simulated Irradiances
Results from GIRO
SRF
Satellite position
Simulated Irradiances
GIRO
Sensor Irradiances
Comparisons
Absolute Comparisons
Relative comparisons:
Temporal drift monitoring
Cross-band calibration
Cross-calibration

23. Results from GIRO
Absolute comparison between PLEIADES and GIRO

24. Results from GIRO Drift monitoring of the PLEIADES system PHR-1A
PHR-1B

25. Results from GIRO Inter-band calibration of the PLEIADES system PHR-1A
PHR-1B

26. Results Cross-calibration based on lunar observations : status
March 2014 – GSICS annual meeting
- cross-calibration between PLEIADES, MSG and MODIS
- no management of the spectral response differences (band-to-band calibration)
Summer 2014
- Cross-calibration realised between PLEIADES, OLI, MODIS (AQUA and TERRA)
- Different types of calibration methods (w/o ROLO):
→ Simultaneous Lunar Observations (SLO)
Same day and same phase angles (within ±0.5°, 1° or 2°)
→ Same Phase Angles (no time constraint)
In both cases, management of the spectral response differences using a spline function
(Using MODIS/OLI spectral band irradiances to simulate their irradiances in the PLEIADES spectral bandwidths)

27. Spectral interpolation Sensor_to_Cal vs Ref Sensor
Results
Cross-calibration based on lunar observations : status
Measured Irr
for Ref Sensor
Comparison = ∆Ak
Lunar Irradiance
Computed Irr
for Cal sensor
Spectral interpolation
I_ROLO_CAL
Measured
Irr for Cal sensor
Cross-calibration
Sensor_to_Cal vs Ref Sensor
I_ROLO_REF

28. Direct comparison of Aqua MODIS and Pleiades calibration (same phase angles, not constraint to SLO) – SPIE Europe 2014 n9241
Same PA
Aqua MODIS W/O ROLO
Same PA
Aqua MODIS with ROLO
Terra MODIS W/O ROLO
Terra MODIS with ROLO
Same PA
Same PA 28

29. Results Cross-calibration based on lunar observations : status
Automn 2014
- cross-calibration between PLEIADES, MODIS and VIIRS
- Reflexions on the calibration method:
cannot directly compare Irr_cal and Irr_ref_reech
→ Activity on-going…

30. Conclusions
GIRO successfully operated in CNES on PHR1A and PHR1B dataset
Development of cross-calibration methods which give good results BUT could be improved to remove the equivalent solar irradiance dependence on the calibration results (use of the Albedo ?)