MODIS reflective solar bands (RSB) calibration is provided by an on-board solar diffuser (SD). On-orbit changes in the
SD bi-directional reflectance factor (BRF) are tracked by a solar diffuser stability monitor (SDSM). The SDSM consists
of a solar integration sphere (SIS) with nine detectors covering wavelengths from 0.41 to 0.94 μm. It functions as a
ratioing radiometer, making alternate observations of the sunlight through a fixed attenuation screen and the sunlight
diffusely reflected from the SD during each scheduled SD/SDSM calibration event. Since launch, Terra and Aqua
MODIS SD/SDSM systems have been operated regularly to support the RSB on-orbit calibration. This paper provides an
overview of MODIS SDSM design functions, its operation and calibration strategies, and on-orbit performance. Changes
in SDSM detector responses over time and their potential impact on tracking SD on-orbit degradation are examined.
Also presented in this paper are lessons learned from MODIS SD/SDSM calibration system and improvements made to
the VIIRS SD/SDSM system, including preliminary comparisons of MODIS and VIIRS SDSM on-orbit performance.
|