Vicarious Radiometric Calibration

Rayference is actively involved in the development of advanced methods for the radiometric calibration of satellite data based on simulated radiances over well characterized targets such as deep convective clouds, sea surface or bright deserts. Within the EC FP7 Quality Assurance for Essential Climate Variables (QA4ECV), Rayference has provide expertise on radiation transfer modelling to assess the impact of sand dune Ridge alignment effects on surface BRF over the Libya-4 CEOS Calibration Site. Such information contributes to determine how reliable and traceable quality information can be provided for satellite and ground-based measurements.

This expertise has been further exploited within the Fidelity and Uncertainty in Climate Data Records from Earth Observation (FIDUCEO) H2020 project that set new standards of accuracy and rigour in the generation of Fundamental Climate Data Records (FCDRs) and Climate Data Records (CDRs), with defensible uncertainty and stability information. FIDUCEO’s ambition was to develop a widely applicable metrology of Earth Observation (EO), since we see the metrological approach as the most fruitful means to establish traceable, uncertainty-quantified evidence for climate and environmental change from space assets. Metrology brings hard-won rigour and clarity to EO, which is intrinsically a measurement science. Rayference contribution to that project was to support the development of reverse engineering methods for the recovery of the original sensor spectral response of the Meteosat First Generation radiometer. A series of papers entitled " Climate Data Records from Meteosat First Generation" have been published on that work.

Rayference developed a Deep Convective Cloud Reference Model for Vicarious Calibration to increase the capabilities of the currently-in-use operational vicarious calibration system for reflective solar bands used at EUMETSAT for the calibration of MSG/SEVIRI solar channels. The study focuses on i) the identification in satellite images of Deep Convective Cloud targets suitable for calibration purposes, ii) the definition of the microphysical properties of a standard deep convective cloud target to establish the vicarious reference signal and iii) a methodology to implement this new type of calibration.

Rayference contributed to S2RadVal project for the radiometric calibration verification of the Sentinel-2/MSI instrument in case of low radiance values. The proposed approach is based on a comparison of Sentinel-2 signal over coastal waters and theoretical TOA signal simulated in the same conditions (geometries, atmosphere, sea surface reflectance). The performance of the method requires to accurately account for sea surface reflectance, the atmospheric effects and select an appropriate radiative transfer model.

Do not hesitate to contact us for additonal information on our radiometric calibration activities.