Validation studies performed on Clouds and the Earth's Radiant Energy system (CERES) instrument sensors aboard EOS Terra and Aqua spacecraft

Abstract

Clouds and the Earth's Radiant Energy system (CERES) sensors provide accurate measurements for the long-term monitoring of the Earth's radiation budget components. 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. Currently four of the CERES instruments (Flight Models 1 through 4 [FM1 - FM4]) are flying aboard EOS Terra and Aqua platforms with two instruments aboard each spacecraft. The sensor calibrations are performed with onboard blackbody sources and a tungsten lamp as well as a solar diffuser plate known as the Mirror Attenuator Mosaic (MAM). The calibration results collectively depict the ground to orbit shifts and the on-orbit drifts in the sensor reponses. Deep convective clouds and tropical ocean are used as validation targets to understand the sensors' stability on-orbit. With two CERES instruments on the same platform, comparison of measurements from similar sensors viewing the same geolocation are performed. The different calibration and validation studies performed on CERES bring to light the radiometric gain and spectral variation of the sensors from pre and post launch. This paper discusses briefly the contribution of each calibration and validation study in understanding CERES sensors' behavior. It also shows the results from these studies which enabled to correct the data products with a calibration stability of better than 0.2%.