CERES on Terra

      CERES is a broadband scanning thermistor bolometer package with extremely high radiometric measurement precision and accuracy. The Terra spacecraft carries two identical instruments: one operates in a cross-track scan mode and the other in a biaxial scan mode. The CERES Terra cross-track scanning data greatly extends the CERES data from the Tropical Rainfall Measuring Mission (TRMM) to achieve complete global measurements by adding mid-latitude and polar observations. TRMM data is restricted by its orbit to roughly cover 40S to 40N. Terra crosstrack data also adds observations at different times of day than TRMM (and later Aqua) in order to increase the accuracy of measuring the large diurnal cycle of the radiation fields from day to night. Finally, the CERES Terra biaxial scan mode provides new observations of the angular radiation fields in order to greatly improve the accuracy of the final fluxes of solar and thermal energy used to derive the Earth's radiation balance.

      Each CERES instrument has three channels--a short-wave channel for measuring reflected sunlight, a longwave channel for measuring Earth-emitted thermal radiation in the 8-12 µm "window" region, and a total channel for total radiation. Onboard calibration hardware includes a solar diffuser, a tungsten lamp system with a stability monitor, and a pair of blackbody sources. Cold space and internal calibration looks are performed during each normal Earth scan.