State of the art radiometer standards for NASA´s Earth Observing System

The multi-angle imaging spectro-radiometer (MISR), to be launched in 1998, is one of five instruments on NASA´s first Earth Observing System (EOS) platform. The 3% (1σ) absolute radiometric calibration requirement is considered challenging, particularly since it must be maintained through the five-year mission life. The instrument requirements have led to the development of an on-board calibrator (OBC) consisting of diffuse panels and photodiode-based radiometric standards. Although used extensively in national standard laboratories, MISR will be the first in-orbit instrument to utilize Spectralon calibration targets, and the first instrument to establish a radiometric scale in orbit using detector-based standards. The team has adopted the nomenclature high quantum efficiency (HQE) technology to refer to the implementation of 100% internal quantum efficient photodiodes in a trapped configuration. Filtered HQE radiometers are being utilized in the preflight calibration phase to calibrate the flat-field source, they will also be used to characterize solar-reflected light from the diffuse calibration targets during the mission. In addition, radiation-resistant photodiodes will be utilized as part of the OBC