Extending the ERBE Nonscanner Shortwave Data Record through August 2005

The current Earth Radiation Budget Experiment (ERBE) nonscanner data set from the Earth Radiation Budget Satellite (ERBS) spans 15 years, from November 1984 through September 1999. During this period, semi-monthly internal and solar calibrations of the radiometers were performed by rotating the detectors to an internal calibration source and to a solar port for viewing the Sun as a calibration source. At the end of a calibration performed on October 6, 1999, the radiometers failed to return to the nadir earth-viewing position and were stuck at a titled angle. Since then, an additional five years of radiometric data has been collected by the ERBE nonscanner instrument. These data are currently not usable for climate studies because of the artifacts introduced by the off-nadir tilt of the instrument and the loss of instrument calibration after the October 6, 1999 instrument anomaly event.

This paper describes our work to extend the current ERBE nonscanner shortwave data set through August 2005. This includes (1) re-establishing instrument calibration after the October 6, 1999 instrument anomaly event using data collected during special spacecraft pitch-over maneuvers, (2) determining the instrument off-nadir tilt angle with solar irradiance data, (3) removing the off-nadir instrument tilt artifact from the nonscanner shortwave data record using new inversion algorithms, and (4) validating the extended nonscanner shortwave data record using nonscanner shortwave data before and after the instrument anomaly event, as well as other available shortwave and shortwave proxy data sets. The ultimate goal of this work is to recover a sufficient amount of ERBS nonscanner shortwave data between October 1999 and August 2005 to tie the ERBE and CERES shortwave data record together. Such a long term multi-decadal (25 plus years) shortwave data record is essential for understanding our climate system and its variability.