The post-launch calibration of the visible (channel 1:approximate to 0.58-0.68 mu m) and near-infrared (channel 2: approximate to 0.72-1.1 mu m) channels of the Advanced Very High Resolution Radiometer (AVHRR) on the NOAA-14 spacecraft is described. The southeastern part of the Libyan desert (21-23 degrees N latitude; 28-29 degrees E longitude) is used as a radiometrically stable calibration target to determine the 'slope'-the inverse of the gain-of the AVHRR, expressed in units of W (m(-2) sr(-1) mu m(-1) count(-1)), in the two channels in the course of 1995. The variation of the 'slope' with time during 1995 indicates that channel 1 has degraded at the annual rate of 7.7 per cent; and channel 2 at the rate of 10.5 per cent. Comparison of the AVHRR 'slopes' immediately after launch of NOAA-14 with the results of pre-launch calibration performed in September/October 1993 indicates that channel 2 experienced a deterioration of approximate to 18 per cent (relative) immediately after launch while channel 1 was not appreciably affected. Formulae are given for the calculation of the post-launch calibration coefficients for the two channels.
