PLEIADES Lunar Observations Sophie Lachrade Bertrand Fougnie CNES

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

Summary 2 • 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-1 A (PHR 1 A) and PLEIADES-1 B (PHR 1 B) launched in December 2011 and 2012 → continuity of the SPOT missions • Applications: civilian and military such as cartography, geology, risks 3

The PLEIADES satellites • System of two satellites: PLEIADES-1 A (PHR 1 A) and PLEIADES-1 B (PHR 1 B) 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 5 x Arrays XS = 1500 detectors PAN = 6000 detectors sensor 4 Blue Green Red PIR

The PLEIADES satellites • System of two satellites: PLEIADES-1 A (PHR 1 A) and PLEIADES-1 B (PHR 1 B) 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 (B 0 -Blue, B 1 -Green, B 2 -Red, B 3 -NIR) 5

The PLEIADES satellites • System of two satellites: PLEIADES-1 A (PHR 1 A) and PLEIADES-1 B (PHR 1 B) 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 (B 0 -Blue, B 1 -Green, B 2 -Red, B 3 -NIR) 6

The PLEIADES satellites • System of two satellites: PLEIADES-1 A (PHR 1 A) and PLEIADES-1 B (PHR 1 B) 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: 70 cm PAN and 2. 8 m XS 7

The PLEIADES satellites San Francisco 8

The PLEIADES satellites Himalaya (Everest Mount) 9

The PLEIADES calibration AMETHIST for inter-detector normalization Geometric auto-calibration for focal 10 plane cartography Steady-Mode for Radiometric SNR assessment 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 Ø Estimated performance : ØAbsolute : 3% ØTemporal stability : < 0. 5% PICS observation and extra-terrestrial observations for absolute calibration

Summary 12 • 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-1 A and PLEIADES-1 B 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-1 A/PLEIADES-1 B: 197/1155 13

The Moon seen by PLEIADES 14

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

The Moon seen by PLEIADES

Data pre-processing 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) Step 2: 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 J 2000 coordinates of the Spacecraft are computed using the acquisition date (based on the MSLIB). Step 4: 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

GIRO - status Ø Sample from the operational dataset SENSOR Spectral range Nb of spectral bands Spatial resolution Acquisition Dates Lunar Phase angle Number of measurements PLEIADES-1 A Vis-Nir 4 2. 80 m 2012 ± 40° 10 PLEIADES-1 B Vis-Nir 4 2. 80 m 2013 -2014 ± 40° 10 Ø Spectral responses : converted to Net. CDF (EUMETSAT tool) Ø PHR lunar measurements converted to Net. CDF (CNES tool) Ø GIRO 4 rd release downloaded and operated (linux platform) 21

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

Results from GIRO Absolute comparison between PLEIADES and GIRO 23

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

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

Results Cross-calibration based on lunar observations : status Ø March 2014 – GSICS annual meeting - cross-calibration between PLEIADES, MSG and MODIS - no management of the spectral response differences (band-to-band calibration) Ø Summer 2014 - Cross-calibration realised between PLEIADES, OLI, MODIS (AQUA and TERRA) - Different types of calibration methods (w/o ROLO): → Simultaneous Lunar Observations (SLO) q 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) 26

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

Direct comparison of Aqua MODIS and Pleiades calibration (same phase angles, not constraint to SLO) – SPIE Europe 2014 n 9241 Same PA Aqua MODIS W/O ROLO Terra MODIS W/O ROLO Same PA Aqua MODIS with ROLO Terra MODIS with ROLO 28

Results Cross-calibration based on lunar observations : status Ø 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… 29

Conclusions • GIRO successfully operated in CNES on PHR 1 A and PHR 1 B 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 ? ) 30