Calibration of satellite sensors after launch.

A method is presented for calibrating satellite radiometers that measure radiance of sunlight scattered from the earth-atmosphere system. The calibrations are made after satellite launch. The calibration source is the radiance of sunlight scattered by the atmospheric gas above oceans inasmuch as aerosols and the surface scatter much less light than the gas under restricted conditions. Calibration coefficients are given for two Visible Infrared Spin-Scan Radiometers (VISSR) carried by Geostationary Operational Environmental Satellites during the years 1980–1983. The gain of the first VISSR during 1980 and part of 1981 varied significantly by ±12%. The second VISSR started observations after 5 Aug. 1981. Its daily values of gain ranged by only ±2% from its mean value during a period of three summers, which shows the stability of the calibration method as well as that of the satellite sensor. The accuracy of the calibration coefficients was estimated by comparing values of aerosol optical thickness measured by VISSR with those measured from the ground. The good agreement between the two sets of data demonstrated the accuracy of the calibration method.