Performance stability of the Clouds and Earth's Radiant Energy System (CERES) instrument sensors on board the Aqua and Terra spacecraft

Abstract

The Clouds and Earth’s Radiant Energy System (CERES) instruments measure the earth-reflected shortwave energy as well as the earth-emitted thermal energy, which are two components of the earth’s energy budget. These measurements are made through four instruments on two spacecraft as part of the Earth Observing System (EOS) mission - Flight Models 1 and 2 onboard the Terra spacecraft, and Flight Models 3 and 4 onboard the Aqua spacecraft. Each instrument comprises of three sensors that measure the radiances in different spectral regions- a shortwave channel that measures energy in the 0.3 to 5 micron wavelength band, a total channel that measures all the incident energy (0.3- <100 microns) and a window channel that measures the water-vapor window region of 8 to 12 microns. The required accuracy of the CERES sensors is achieved through pre-launch ground-based calibrations as well as on-orbit calibration activities. Onorbit calibration is carried out using the Internal Calibration Module (ICM) that consists of a quartz-halogen tungsten lamp, blackbodies, and a solar diffuser plate known as the Mirror Attenuator Mosaic (MAM). The ICM calibration provides information about the change in the CERES sensors’ broadband radiometric gains on-orbit from the pre-launch values. Several validation studies are conducted in order to monitor the behavior of the instruments in various spectral bands. The CERES Edition-3 data products incorporate the latest upgrades to the calibration techniques. In this paper, we present the on-orbit performance stability as well as some validation studies using the CERES Edition-3 data products from all four instruments.