Proceedings Article | 2 February 2004
KEYWORDS: Calibration, Satellites, Space operations, Radiometry, Black bodies, Shortwaves, Solar radiation, Sensors, Sun, Bolometers
From October 1984 until September 30, 1999, on-orbit, the Earth Radiation Budget Satellite (ERBS)/Earth Radiation Budget Experiment (ERBE) nonscanning, active cavity radiometers (ACR) were calibrated using observations of the incoming total solar irradiance, and of reference irradiances from an on-board tungsten lamp and blackbodies in order to determine drifts and shifts in the ACR responses. On October 7, 1999, the ERBE elevation drive system failed near the earth nadir viewing configuration. Thereafter, the elevation failure prevented observations of the on-board, built-in calibration systems. On July 23, August 8, and December 10, 2002, the ERBS was pitched 180 degrees to observe cold space, representative of a 3 Kelvin blackbody, in order to determine the ACR's zero-irradiance offsets. On December 4, 2002, the ERBS was pitched 180 degrees away from the earth in order to observe the sun, and to determine the ACR's gains. In this paper, the 2002, 180-degree pitch calibrations are compared with the earlier 1984-1999, calibrations which were obtained using the on-orbit, built-in calibration systems. In addition, the 2002 calibrations are compared with earlier scheduled November 21, 1984, and October 20, 1985, 180-degree pitch calibrations, as well as with deep space calibrations from unscheduled July 2, 1987, January 16, 1999, and November 16, 2000, ERBS spacecraft tumbles. The 2002 ACR offsets were found to be consistent with 1984-2000 offsets at the 1.0 Wm-2. 1984-1999, ERBE top-of-the-atmosphere (TOA), and satellite altitude (SA) earth irradiances are presented. Analyses of the TOA ERBE earth irradiances indicate that the TOA irradiance time series exhibited a 1.7 Wm-2 increase as a result of 1988-1992, and 1998-2002 satellite altitudinal decreases during periods of maximum solar magnetic activity.
