Characterization of the clouds and the Earth's radiant energy system (CERES) sensors on Terra and Aqua spacecraft

Abstract

The Clouds and the Earth's Radiant Energy System (CERES) instruments measure the two key components of the Earth's Radiation Budget, the reflected shortwave and the emitted longwave energy. The CERES instrument consists of three scanning thermistor bolometers that measure the broadband radiances in the shortwave (0.3 to 5.0 micrometer), total (0.3 to >100 micrometer) and 8-12 micrometer water vapor window regions. Four CERES instruments (Flight Models 1 through 4) are flying aboard EOS Terra and Aqua platforms with two instruments aboard each spacecraft. The accuracy requirements of the CERES sensors are achieved through the prelaunch calibrations and on-orbit calibration activities. The CERES detector gain and the response function are determined by the prelaunch ground calibrations. The post launch calibration of CERES sensors are carried out using the internal calibration module (ICM) comprising of blackbody sources and quartz-halogen tungsten lamp, and a solar diffuser plate known as the Mirror Attenuator Mosaic (MAM). The ICM calibration results are instrumental in determining the changes in CERES sensors' gains after launch from the pre-launch determined values and the on-orbit gain variations. In addition to the broadband response changes derived from the on-board blackbody and the tungsten lamp, the shortwave and the total sensors show a spectral change in responsivity in the shorter wavelength region below one micron that were brought to light through vicarious studies. The spectral change was attributed to the instrument operational modes and the corrections were derived using the sensor radiance comparisons. This paper covers the on-orbit behavior of CERES sensors and the determination of the sensor response changes utilizing the in-flight calibration and the radiance comparisons. The corrections for the sensor responses were incorporated in the radiance calculations of CERES Edition3 data products.