08/07/2013 The Image Quality Center for PROBA-V: How to maintain the image performance after launch? Sindy Sterckx IQC Image Quality center IQC-RC IQC-GC Stefan Adriaensen Wouter Dierckx Stefan Livens Sindy Sterckx Iskander Benhadj Geert Duhoux Supported by ACS 08/07/2013 © 2013, VITO NV 2 IQC –Radiometric Calibration » Reliable, accurate and consistent measurements » Variations in the characteristics of the instrument are likely to occur in orbit due to » outgassing phenomena during launch » aging of the optical parts,… » In-flight calibration » with on-board calibration devices such as lamps, solar diffuser panels, LEDs,.. » Vicarious calibration techniques : Calibration against a non-standard reference by (source) making use of natural (or artifical sites) 08/07/2013 © 2013, VITO NV 3 Radiometric Performance Requirements » 5 % absolute accuracy » 3 % relative accuracy »inter-band »multi-temporal 08/07/2013 © 2013, VITO NV 4 RC – IQC: Vicarious Calibration Concept Absolute OSCAR* (Optical Sensor Calibration with simulated Radiances) » Relies on combination of various vicarious calibration methods to reduce uncertainty in the calibration results and to verify the different requirements Antarctica/ Greenland Temporal Oceans Sun Deserts DC Clouds Multi Angular 08/07/2013 © 2013, VITO NV Glint Interband *Sterckx et al. IJRS, in5 Press Desert calibration Target: stable, homogenous desert sites Method: compare TOA radiances to simulated values Usage : Operational absolute calibration for all bands , cross mission calibration, multi-temporal PROBA-V image 26/06 08/07/2013 © 2013, VITO NV Adriaensen et al., 2012 (CEOS report); Govaerts et al., RSL 2013 6 Rayleigh calibration Target: stable, homogenous oceans Method: compare TOA radiances to simulated values, using NIR band to retrieve aerosol optical depth Usage : Operational absolute calibration, for RED and BLUE combine with inter-band to transfer results to NIR, SWIR 08/07/2013 © 2013, VITO NV 7 Sterckx et al. TGARS, 2013 Rayleigh calibration Application to VGT 08/07/2013 © 2013, VITO NV 8 Deep Convective Clouds calibration Target: reflection of deep convective clouds over oceans Method: Compare PROBA-V TOA data to simulated data using RED band as reference band to retrieve cloud optical thickness” Usage: inter-band (absolute if combined) 08/07/2013 © 2013, VITO NV PROBA-V image 24/06 9 Sun Glint Calibration » Target: white specular reflection of sun over oceans » Method: compare PROBA-V TOA data to simulated data » Usage : inter-band (absolute) reference: RED band to retrieve wind speed. 08/07/2013 © 2013, VITO NV 10 Lunar Calibration Moon = stable over thousands of years Usage : stability monitoring Implementation : • Compute integrated irradiance • Convert integrated irradiance to full disc reflectance and compare with a lunar reflectance model • Monthly acquisition at same phase PROBA-V image 23/06 angle to reduce uncertainty Other usage :  MTF  Dark current validation  Straylight assessment 08/07/2013 © 2013, VITO NV 11 Experimental calibrations : the linearity check Integration time changes in steps over homogenous areas PROBA-V image 17/06 08/07/2013 © 2013, VITO NV 12 Vicarious Calibration Concept Statistically combine results of different methods to reduce uncertainty reconcile methods temporal: time series averaging over sites 08/07/2013 © 2013, VITO NV 13 RC- Image Quality Center: HMI • • • • fully automated image workflows and statiscal processing View at the database using Graphical User Interface Full traceability new instrument calibration parameters updates Automated distribution towards PF 08/07/2013 © 2013, VITO NV 14 First results on Libya-4 desert site …… 08/07/2013 © 2013, VITO NV 15 Instrument Programming Center (IPC) • Communication with Mission Control Center (MCC) for acquisitions • with specific instrument settings • over non-nominal sites • with maneuvers 08/07/2013 © 2013, VITO NV 16 Instrument Programming Center (IPC) • validate requests against resource constraints • send request to the Mission Control Center (MCC) • monitors their uploading and execution 08/07/2013 © 2013, VITO NV 17 IPC – IQC HMI Calibration request status follow-up IQC workflows automatically started 08/07/2013 © 2013, VITO NV 18 IQC Image Quality center IQC-RC IQC-GC Stefan Adriaensen Wouter Dierckx Stefan Livens Sindy Sterckx Iskander Benhadj Geert Duhoux Supported by ACS 08/07/2013 © 2013, VITO NV 19 Geometric calibration objectives Main objective of the In-flight GC is : To assure that the geolocation accuracy requirements for the PROBA-V end products can be met 08/07/2013 © 2013, VITO NV 20 In-flight geometric calibration » major challenges : » » » » » 3 camera’s VNIR and SWIR detectors mounted on different locations VNIR and SWIR with different Ground Sampling Distances (GSD) SWIR detector composed of 3 overlapping detectors No active onboard thermal control 08/07/2013 © 2013, VITO NV 21 IQC – Geometric Calibration » Estimate and monitor on a regular basis :  The exterior orientation (boresight misalignement angles)  The interior orientation deformations (CCD viewing direction vectors) » To account for  distortions within one orbit (time since exit from eclipse)  slow varying errors (seasonal effects) (sun beta angle) » To update the ICP to guarantee the geometrical system accuracy of the system corrected products. 08/07/2013 © 2013, VITO NV 22 GC- Image Quality Center: HMI 08/07/2013 © 2013, VITO NV 23 Geolocation error: preliminary results Scatter plot of absolute geolocation error (m) BLUE band 08/07/2013 © 2013, VITO NV 24 Conclusions » Pre-flight studies showed that the mission requirement speciﬁcations for the radiometric calibration, i.e., 5% absolute and 3% relative should be realistic achievable goals for the PROBA-V missions although no on-board calibration devices are available » The calibration concept of combining different vicarious calibration methods which cover different parts of the dynamic range of the sensor (dark oceans versus bright clouds), and which are using different references minimizes biases or systematic errors which may occur if only one method is used. » Preliminary radiometric calibration results are very promising » Preliminary geolocation assessment results : » mandatory requirements already achieved » realization of the goal requirements = a realistic goal, achievable by the end of commissioning 08/07/2013 © 2013, VITO NV 25 Thank you! IQC-RC : Sindy Sterckx [email protected] IQC-GC : Iskander Benhadj [email protected] VITO – Flemish Institute for Technological Research Boeretang 200, B-2400 Mol, Belgium 08/07/2013 © 2013, VITO NV 26