Comparison of Visible Calibrations of GOME and ATSR-2

On board ESA's second European Remote Sensing Satellite (ERS-2), launched in April 1995, two instruments perform measurements of the reflectivity of the Earth at the top of the atmosphere: the Global Ozone Monitoring Experiment (GOME) and the Along Track Scanning Radiometer-2 (ATSR-2). GOME is a spectrometer measuring radiation between 240 nm and 790 nm with a spectral resolution of 0.2–0.4 nm. The ATSR-2 is an imager with four channels in the solar part and three channels in the thermal infrared part of the spectrum. Both instruments observe the Sun via a diffuser plate for relative radiometric calibration, thereby yielding reflectivities. The ATSR-2 channels at 555 and 659 nm overlap with the wavelength range of GOME. In this article, the consistency of the reflectivity calibrations of GOME and ATSR-2 is investigated at both wavelengths, by analyzing data from collocated partly cloudy scenes over the Atlantic Ocean, acquired on 23 July 1995. The main result is that reflectivities measured by both instruments agree well; the ATSR-2 reflectivity differs from the GOME reflectivity by −4.0% at 555 nm and −2.2% at 659 nm (relative differences).