Radiometric performance of Clouds and the Earth´s Radiant Energy system (CERES) instrument sensors aboard EOS Terra and Aqua spacecraft

Clouds and the Earth´s Radiant Energy System (CERES) instruments were designed to measure the reflected shortwave and emitted longwave radiances of the Earth´s radiation budget and to investigate the cloud interactions with global radiances for the long-term monitoring of Earth´s climate. The three scanning thermistor bolometer sensors on CERES measure broadband radiances in the shortwave (0.3 to 5.0 micrometer), total (0.3 to >100 micrometer) and in 8 - 12 micrometer water vapor window regions. Four of the CERES instruments (Flight Models1 through 4) fly aboard Earth Observing System (EOS) Terra and Aqua platforms with two instruments aboard each spacecraft, in 705 KM sun-synchronous orbits of 10:30 AM and 1:30 PM equatorial crossing time. The CERES data products consist of geolocated instantaneous unfiltered radiances through temporally and spatially averaged Top of the Atmosphere (TOA) and Surface fluxes. These CERES data products have achieved a higher level of calibration accuracy and stability than the previous ERBE products. This improvement was attained through the development of a rigorous and comprehensive radiometric validation protocol comprising of studies covering different spatial, spectral and temporal time scales. The in-flight calibration of CERES sensors are carried out using the internal calibration module (ICM) comprising of blackbody sources and tungsten lamp, and a solar diffuser plate known as the Mirror Attenuator Mosaic (MAM). The ICM and MAM calibration results are instrumental in understanding the ground to flight shift and in-flight drifts in CERES sensors´ gains.