Toward a wider use of the Moon for In-flight Characterization GSICS Annual Meeting 29th Feb.- 4th March 2016, Tsukuba, Japan Toward a wider use of the Moon for In-flight Characterization An Overview Bertrand Fougnie1, Sophie Lachérade1 Jack Xiong2 Pepe Phillips3, Thierry Marbach3 Marc Bouvet4 Stefan Adriaensen5 1 CNES 2 NASA-GSFC 3 EUMETSAT 4 ESA-ESTEC 5 VITO

Summary Current Calibration over the Moon Used as a PICS for Monitoring (ROLO) Radiometric properties of the Moon Current (past) use of the Moon Feedback from MODIS/VIIRS Feedback from PARASOL Feedback from Pleiades Feedback from Proba-V Expected/Future use of the Moon – under investigation Post-EPS : 3MI and Metimage Sentinel Missions : Sentinel-3 and Sentinel-2

Introduction The main current use of the Moon Moon for monitoring Used by many (if not all) sensors through specific or opportunist acquisitions But regular acquisitions Monthly for fixed phase angle Need model to consider libation or phase dependency Definitively a powerful use Many other characterization have been tested  MODIS, VIIRS, Pleiades, Proba-V, PARASOL… among many others Radiometric : cross-calibration, interband, MTF, straylight, response versus scan Geometrical : registration Highlight benefits for future uses which are under investigation 3MI, Metimage Sentinel-3, Sentinel-2

Moon for monitoring By “construction”, the Moon is a perfectly stable target (inherent property) The integrated irradiance from lunar disk (apparent property) varies with the geometry of the scene : respective positions between sensor/moon/sun the considered spectral band  Use of ROLO model to normalize results to a reference Approach used by many sensors to monitor the degradation or evolution Lachérade et al., SPIE, 2014 Xiong et al., SPIE, 2013 PHR-1A

Some of the properties of the moon… Stability, but also other properties  Out-of-Atmosphere Reference spectrum convenient for interband calibration convenient for calibration of absorption bands (harder through vicarious tech.)  Bright target over perfectly dark background ideal dark for in-flight checking of the background level offset, artifact, cross-talk… perfect bright/dark transition for in-flight checking of the artifacts PSF, MTF, straylight, ghosts, optical leak… optimized contrast line for in-flight checking of geometry band-to-band registration  Stable target during large portion of the sensor orbit ability to view several times the “same” moon checking response versus scan or within field-of-view, multi-gain sensitivity study

Current Use for MODIS/VIIRS MODIS and VIIRS Radiometric Calibration Stability RSB (MODIS and VIIRS) TEB (MODIS and VIIRS) DNB (VIIRS) Spatial Characterization Along-scan and along-track BBR (MODIS and VIIRS) Along-track MTF (MODIS and VIIRS) Calibration Inter-comparison (MODIS and VIIRS) Interband Characterization (MODIS and VIIRS) Others Optical Leak Characterization (MODIS) Electronic Crosstalk Assessment (MODIS) MODIS VIIRS

Current Use for MODIS/VIIRS Interband checking

Current Use for MODIS/VIIRS MTF estimation Spatial characterization (Band-to-band Registration) Edge response function Xiong et al., SPIE, 2013 Wang et al., CALCON, 2015

Current Use for MODIS/VIIRS Before correction Optical leak Electronic crosstalk Terra B35 From B31 to B32-36 Xiong et al., SPIE, 2013 Band 27 Jan 2002

Past Use for PARASOL PARASOL Interband normalization Full image 2004-2013 : opportunity for 1 moon acquisition during decommissioning Small target, only 8 images Sufficient to detect anomaly (offset) Interband checking for absorption bands (763-O2, 9-H2O) Tentative to check response within field-of-view More acquisitions were needed… Interband normalization Full image Region of interest Fougnie, Pers. Comm., 2014

Current Use for Pleiades Monitoring Check consistency with acquisition geometry Moonflower experiment Cross-calibration with ODIS/VIIS : Simultaneous Lunar Acquisition (LSO) Phase angle matching Xiong et al., SPIE, 2015 Lachérade et al., SPIE, 2014 PHR-1B vs VIIRS PHR-1B vs MODIS

Current Use for Proba-V Follow-on Végétation 1 & 2, developed by ESA Proba : Launched in May 2013 Land surface VEGETATION instrument = 4 bands from blue to SWIR , 300m, 2000km No on-board device – Only vicarious calibration methods Lunar acquisitions for monitoring Assessment of straylight : checking consistency with the expected level Dark current validation MTF estimation Sterck et al., 2014 Proba-V

Expected Future Use for Sentinel ESA mission – operational service for the European Copernicus Program S2A : Launched in June 2015 Land surface MSI imager MSI = 13 bands from 440 to 2200nm, 10/20/60m, 290km On-board diffuser (nominal) + Vicarious calibration methods MSI Sentinel-2

Expected Future Use for Sentinel ESA mission – operational service for the European Copernicus Program S3A : launched in February 2016 Oceanography and land monitoring Altimetry + 2 optical sensors OLCI and SLST (follow-on MERIS and AATSR) OLCI = 21 bands from 410 to 1020nm, 300m, 1270km SLSTR = 11 bands from 550 to 12 000nm, 500m/1km, 1400km On-board diffusers + Black body (nominal) + Vicarious calibration methods Sentinel-3A OLCI SLSTR

Expected Future Use for Sentinel Sentinel expected characterization Too late for S2a and S2B -> to be considered for 2C Too late for S3a and S3B -> to be considered for 3C Commissioning (possibly regular acquisitions)  motivated, not decided, still under investigation Configuration Need for a manoeuver A few acquisitions for commissioning Which optimal phase angle for each goal ? Characterization Radiometric stability (1% over the lifetime) – only possible if regular acquisition Absolute calibration (better than 2%) – will be possible in a couple of years Interband calibration (better than 1%) Straylight (1-2% at 50SSD from transition) MTF Flat field equalization

Future Use for Post-EPS / Metop-SG Program EPS-SG (EUMETSAT polar system) launch 2021 3 satellites METOP-SG A : optical and sounder imagers IASI-NG, Metimage, RO, MWS, Sentinel-5, 3MI 3 satellites METOP-SG B : microwave imager Metimage VII Visible Infrared Imager Meteorology, Hi-res cloud products, aerosols, surface temperature On-board diffuser + space view EPS-SG Metimage

Future Use for Post-EPS / Metop-SG Metimage On-board device to support in-flight calibration (including monitoring) Moon intrusion occasionally captured in the cold space port during lifetime Characterization Currently documented for Commissioning (possibly regular) Need at Beginning Of Life (BOL) more favorable phase angle than moon intrusion Remove scan angle dependent artefacts from the space port view Possible simultaneous lunar observation (SLO) with 3MI Configuration Need for a manoeuver A few acquisitions for commissioning Which optimal phase angle for each goal ?

3MI: Multi-Viewing, -Channel, -Polarisation Imager Dedicated to aerosol characterisation for: - Climate monitoring - Air quality monitoring and forecasting - Numerical Weather Prediction 2D Push-broom radiometer (2200 km swath, 4 km pixel at nadir) Provides images of the Earth TOA outgoing radiance using: - Multi-view (10 to 14 views; angular sampling in the order of 10°) - Multi-channel (12 channels from 410 to 2130 nm) - Multi-polarisation (9 channels with -60°, 0°, +60° polarisers) POLDER heritage (PARASOL follow-on) 3MI

3MI Acquisition Detectors Wheel Filters Optical heads 3MI image 2000 km cross-track along-track 3MI image 1 view: all spectral channels (about 22 seconds) up to 14 views: N = 7 (about 5 minutes) c View 1 c View N c View 2N Detectors Wheel Optical heads Filters Vsat Target

Moon View Benefit for 3MI 3MI has no onboard calibration facility – Vicarious Methods monitoring and calibration (including during commissioning time) will use the so-called vicarious calibration methods i.e. based on statistical use of reference scenes final accuracy depends on various parameters a significantly large number of acquisitions are required to reduce the uncertainty of each method many radiometric aspects may limit the accuracy : the spectral knowledge, the straylight contamination, the polarization sensitivity, the linearity, etc… absorption bands (763 nm, 910 nm, or SWIR-1370 nm) may have less accurate performances because of the difficulty to predict the observed signal The benefit for a moon view would be multiple : No atmospheric absorption allowing an immediate accurate inter-channel calibration (crucial for absorption bands) Estimation of the system MTF (bright target over a perfectly dark background) Diagnosis/validation of the stray-light correction performance (small target) Cross-calibration with many sensors : METimage but also VIIRS, MODIS, Sentinel-3... In general much effort will be saved for vicarious calibration on spectral assessment, absolute calibration, variation within the field-of-view, and cross-calibration could be used to check the registration performances for polarized triplets and spectral bands or optical heads

Conclusion The moon is extensively used for monitoring This requires regular acquisitions (scheduled or occasional) Many other characterizations can be used for radiometric and geometrical purposes Cross-calibration, Interband checking (absorption bands), absolute (coming), MTF estimation, straylight level checking or estimation, registration, response versus scan… Moon is definitively a target that can be considered as an on-board device Moon acquisition has to be considered as much as possible in the design of future system Systematic acquisition is not the only approach : occasional viewing during (de)commissioning are also very precious We (will) always learn something when viewing the moon Thanks to all the contributors and co-authors…