New Radcalnet Site at Gobabeb, Namibia: Installation of the Instrumentation and First Satellite Calibration Results

A new permanently instrumented radiometric calibration site for high/medium resolution imaging satellites in the visible/near-IR has been set up in Gobabeb, Namibia in July 2017. The station location has been decided after a global analysis of satellite data assessing surface spatial homogeneity, cloud coverage, temporal variability, atmospheric turbidity etc. which has been compared with insitu data (surface reflectance, BRDF etc.) from a field campaign which took place in late 2015. The instrumentation automatically measures atmospheric (aerosol optical thickness etc.) and surface conditions (BRDF) from 414 nm to 1600 nm in 12 narrow spectral bands. The data processing is performed at CNES and includes the calibration of the photometer itself using in-situ measurements, and the simulation of the top-of-atmosphere radiance seen by any optical sensor over-passing the site, thus calibrating the sensor. This paper describes the instrument location, measurement protocol, calibration principle and calibration results of satellites Sentinel2A and Sentine12B.