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

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

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

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

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)

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)

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

The PLEIADES satellites San Francisco

The PLEIADES satellites Himalaya (Everest Mount)

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

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

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

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

The Moon seen by PLEIADES

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

The Moon seen by PLEIADES

The Moon seen by PLEIADES

The Moon seen by PLEIADES

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%

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

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 2013-2014

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

Results from GIRO Absolute comparison between PLEIADES and GIRO  

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

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

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)

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  

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

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…

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 ?)