<title>Ground through on-orbit transfer of the International Temperature Scale of 1990 (ITS-90): radiometeric scale using the CERES thermistor bolometers and built-in flight calibration systems</title>

Abstract

The Clouds and Earth's Radiant Energy System (CERES thermistor bolometers were calibrated using filtered radiances, characterized on an International Temperature Scale of 1990 (ITS-90) derived absolute radiometric scale. Longwave filtered radiances were characterized using the optical and geometric surface properties of the reference Narrow-Field-of-View Blackbody (NFBB), the NFBB temperature measurements from the ITS-90 calibrated platinum resistance thermometers (PRT) embedded in the blackbodies, and the spectral responses of the CERES bolometers. Shortwave filtered radiances were characterized using the cryogenically-cooled Transfer Active Cavity Radiometer (TACR) which was an ITS-90 transfer standard, and using the spectral responses of the bolometers. In ground vacuum facilities, the ITS-90, temperature-based radiometric scale was transferred to the CERES bolometers. As ITS-90 transfer standards, the bolometers were used to characterize the emitted filtered radiances from in-flight systems: (1) the internal calibration module (1CM) which consisted of anodized aluminum blackbodies and tungsten lamp sources; and (2) mirror attenuator mosaic (MAM) which was an aluminum solar diffuser plate, built into the bolometer instrumentation. From the ground [October 1995] through the on-orbit phases [December 1998 -July 1999] of the Tropical Rainfall Measuring Mission (TRMM) Spacecraft CERES instrument mission, the stabilities of the bolometers' responses were assessed from periodical observations of the in-flight calibration systems radiances. Each CERES instrument package consisted of broadband shortwave [0.3 jim to 5.0 .tm], broadband total [0.3 pm to >100 .tm], and narrowband window [8 pm and 12 rim], scanning thermistor bolometer sensor units; and of inflight calibration systems.Between the ground and initial on-orbit calibrations, the TRMM CERES bolometers and the builtin, flight calibration system sources maintained their filtered radiance measurement ties to ITS-90 at the 0.2 Wm2sr' precision level. On-orbit calibration studies indicate that the radiance measurements were stable at the 0.2 Wm2sr' precision level. The ground and on-orbit calibration results are presented and discussed.