THE CLOUDS AND THE EARTHS RADIANT ENERGY SYSTEM (CERES) SENSORS AND PREFLIGHT CALIBRATION PLANS

The Clouds and the Earth's Radiant Energy System (CERES) spacecraft se nsors are designed to measure broadband earth-reflected solar shortwav e (0.3-5 mu m) and earth-emitted longwave (5->100 mu m) radiances at t he top of the atmosphere as part of the Mission to Planet Earth progra m. The scanning thermistor bolometer sensors respond to radiances in t he broadband shortwave (0.3-5 mu m) and total-wave (0.3->100 mu m) spe ctral regions, as well as to radiances in the narrowband water vapor w indow (8-12 mu m) region. The sensors are designed to operate for a mi nimum of 5 years aboard the NASA Tropical Rainfall Measuring Mission a nd Earth Observing System AM-1 spacecraft platforms that are scheduled for launches in 1997 and 1998, respectively. The flight sensors and t he in-flight calibration systems will be calibrated in a vacuum ground facility using reference radiance sources, tied to the international temperature scale of 1990. The calibrations will be used to derive sen sor gains, offsets, spectral responses, and point spread functions wit hin and outside of the field of view. The shortwave, total-wave, and w indow ground calibration accuracy requirements (1 sigma) are +/-0.8, /-0.6, and +/-0.3 W m(-2) sr(-1), respectively, while the correspondin g measurement precisions are +/-0.5% and +/-1.0% for the broadband lon gwave and shortwave radiances, respectively. The CERES sensors, in-fli ght calibration systems, and ground calibration instrumentation are de scribed along with outlines of the preflight and in-flight calibration approaches.