Raising the bar in vicarious radiometric calibration

Vicarious calibration uses stable, mostly natural objects for calibration. VITO develops vicarious Cal/Val methodologies for optical instruments and tunes these algorithms in operational systems. By exploring new solutions, we seek to continuously improve calibration methodologies.

For the ESA led PROBA-V mission, we have developed our sensor generic, vicarious radiometric calibration tool suite. It features a combination of calibration methods that allow us to perform absolute, inter-band and multi-temporal calibrations. Its remarkable performance led to the tool being implemented in the Sentinel-3 Mission Performance Center (MPC) for OLCI L1 radiometric verification. 

PROBA-V sensor calibration using moon observations

The moon’s surface changes only very little over time. This makes it ideal for vicarious calibration. Although brightness of the moon varies, the photometric stability of the lunar surface enables us to characterise these cyclic variations with high precision.

Every month, PROBA-V records two lunar images just before and after full moon. We then automatically process these images into a single stability value per observation. An automated workflow takes care of conversion to radiance, pixel integration and oversampling estimation. VITO has its own implementation of the USGS ROLO model and is involved in the joint GSICS-CEOS Lunar Calibration initiative.