To evaluate, achieve and maintain radiometric stability, it is imperative that these instruments undergo rigorous radiometric calibration and validation. Calibration and validation studies have indicated spectral changes in the reflected solar spectral regions of the shortwave and total sensors. Spectral darkening is detected in the shortwave channel optics, which is more prominent while the instrument operates in RAP mode. This degradation is likely due to instrument scan plan being aligned with the spacecraft direction of motion during part of the RAP scan cycle, which makes the optics more susceptible to increased UV exposure and molecular contamination. Additionally, systematic daytime-nighttime longwave top-of-atmosphere (TOA) flux inconsistency was also detected during validation, which points to the changes occurring in the reflected solar spectral region of total sensor. Sensor corrections are derived and incorporated in the data processing stream in order to account for these changes.
This paper briefly describes the strategy to correct for the sensor response changes and presents the improvements in CERES Edition3 data products, which incorporates these sensor response changes in the computation of shortwave and longwave radiances.