Inter-satellite calibration linkages for the visible and near-infared channels of the Advanced Very High Resolution Radiometer on the NOAA-7, -9, and -11 spacecraft

The post-launch degradation of the visible (channel 1:≈0· 58–0·68μm) and near-infrared (channel 2: ≈ O·72–1·1 μm) channels of the Advanced Very High Resolution Radiometer (AVHRR) on the NOAA–7, –9, and –11 Polar-orbiting Operational Environmental Satellites (POES) was estimated using the south-eastern part of the Libyan desert as a radiometrically stable calibration target. The relative annual degradation rates, in per cent, for the two channels are, respectively: 3·6 and 4·3 (NOAA–7) 5·9 and 3·5 (NOAA–9); and 1·2 and 2·0 (NOAA–11). Using the relative degradation rates thus determined, in conjunction with absolute calibrations based on congruent path aircraft/satellite radiance measurements over White Sands, New Mexico (U.S.A.), the variation in time of the absolute gain or ‘slope’ of the AVHRR on NOAA–9 was evaluated. Inter-satellite calibration linkages were established, using the AYHRR on NOAA–9 as a normalization standard. Formulae for the calculation of calibrated radiances and albedos (AYHRR usage), based on these interlinkages, are given for the three AYHRRs.