干旱区生态环境知识资源中心

Records of top-of-the-atmosphere albedo over several sites around the globe indicate that the formulae given in Rao and Chen (1996) to determine the post-launch calibration of the visible (channel I, 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 overestimate the in-orbit degradation of the two channels, resulting in spurious upward trends in the albedo time series. Therefore, the calibration formulae have been revised to minimize the upward trends, utilizing a 3-year (1995-1997) record of albedo measurements over a calibration site (21-23 degrees N, 28-29 degrees E) in the southeastern Libyan desert. Formulae for the calculation of the revised calibration coefficients as a function of elapsed time in orbit are given. The revised calibration formulae presented here, and those presented in Rao and Chen (1996), yield radiance/albedo values within 5% (relative) of each other for about 900 days after launch in channel 1 and for about 500 days in channel 2.