PROBA-V Commissioning: Radiometric Calibration

The Belgian-ESA Proba-V(egetation) satellite is to be launched in April 2013. The aim of the Proba-V mission is to ensure data product continuity with SPOT-VEGETATION, which ends its operations in 2014. While developed in the frame of ESA’s In Orbit Demonstration (IOD) technological program, Proba-V is an operational mission providing the user community daily with global land coverage data in four multispectral bands at both 1/3 km and 1 km resolution. This user community requires reliable and consistent measurements over time in order to detect and quantify changes in the Earth’s environment. To this end, the radiometric calibration requirements for PROBA-V specify 5 % absolute and 3 % relative accuracies. To guarantee this high quality over the full lifetime of PROBA-V, in-flight calibration algorithms have to be in place which fully consider the specific properties of the PROBA-V platform and its instrument design characteristics. Due to size, weight and power constraints, no onboard calibration devices are available. Therefore the PROBA-V in-flight radiometric calibration has to rely solely on vicarious calibration methods. The radiometric calibration after launch will be performed by the PROBA-V Image Quality Center (IQC) located at VITO. To this end, VITO developed the Optical Sensor Calibration with simulated Radiance (OSCAR) facility. It will be used for the vicarious calibration activities of PROBA-V. OSCAR encompasses various calibration methods based on the exploitation of reflected radiance by clouds, atmospheric molecules, sun glint and bright desert surfaces. It achieves its calibration results through a combination of the results of these methods. The consistency with SPOT-VGT, essential for a continuity mission, will be verified through inter-calibration over stable desert sites. The vicarious calibration methods implemented in the OSCAR facility have been throughout tested and validated on various satellite data and detailed error assessments have been performed. These analyses showed that the mission requirement specifications for the radiometric calibration are realistic achievable goals. The Cal/Val commissioning phase will start after the platform and instrument verification and validation phase and is scheduled to be a three-month activity, running in the summer months of 2013. At the Calcon 2013 conference, the Cal/Val activitity will be ongoing. This will allow to present preliminary results and give a firsthand and very up-to-date view on the status of the in-flight calibration and the end-to-end image-quality assessment