On-orbit radiometric calibrations of the Earth Radiation Budget Experiment (ERBE) active-cavity radiometers on the Earth Radiation Budget Satellite (ERBS)

Between November 1984 and July 2002, the Earth Radiation Budget Satellite (ERBS)/Earth Radiation Budget Experiment (ERBE) nonscanning, active cavity radiometers (ACR) were used to measure incoming total solar irradiance, earth-reflected solar irradiance, and earth-emitted outgoing longwave radiation (OLR) irradiance. The ERBE shortwave wide field-of view (SWFOV) and toal wide field-of-view (TWFOV) ACR's measured irradiances from the entire earth disc in the shortwave (0.2-5.0 mum) and total (0.2-100 mum) broadband spectral regions. On-orbit, the ACR's observations of the incoming total solar irradiance, and of reference irradiance from on-board tungsten lamp and blackbodies were used to determine drifts and shifts in the ACR responses/gains. In the cases of the SWFOV ACR, its response/gain changed as much as 8.8% while the TWFOV response was stable at levels better than 0.1%. The precise measurements of gain and offset variations have permitted the generations of ERBE level 1 data products [earth-reflected solar (similar to240 Wm(-2))and earth-emitted (similar to100 Wm(-2)) irradiances] at the precision levels better than 0.3 Wm(-2). In this paper, the ACR radiometric on-orbit calibration approaches and systems are outlined.