Validation of Clouds and the Earth's Radiant Energy System (CERES) instruments aboard EOS-TERRA spacecraft using tropical ocean measurements

Clouds and the Earth's Radiant Energy System (CERES) instruments were designed to provide accurate measurements for the long-term monitoring of Earth's reflected shortwave and emitted longwave radiances as part of it's radiation energy budget. The CERES instrument consists of three scanning thermistor bolometer sensors. The three sensors measure the broadband radiances in shortwave (0.3 - 5.0 micrometers), total (0.3 - >100 micrometers) and 8 -12 micrometer water vapor window regions. Two of the CERES instruments, Flight Models 1 and 2 (FM1 & FM2), were launched as part of Earth System Sciences (ESS) Terra mission on December 18, 1999 and have been operating successfully for the past 24 months. Tropical ocean measurements conducted by Earth Radiation Budget Satellite (ERBS) instrument have shown that the mean longwave radiances remain very stable, with a variation of about 0.7% over the 5 year period. Thus the tropical ocean with all cloud conditions is used as a suitable Earth target for validating the CERES sensor measurements. The longwave radiances measured by the total sensor as well as the window sensor of the same instrument are intercompared to provide a consistency check on the long-term variation of either of the sensors. The variation in longwave radiances for various scene types at the tropical region are also studied for both instruments. This enables a preliminary evaluation of the response of broadband total sensor in various spectral regions.