Four Years of TRMM/VIRS On-Orbit Calibrations and Characterization Using Lunar Models and Data fromTerra/MODIS

Abstract

Abstract Four years of on-orbit solar calibration data have been used to quantify the temporal degradation of the two reflected solar bands of the Visible and Infrared Scanner (VIRS) aboard the Tropical Rainfall Measuring Mission (TRMM) satellite. Solar calibrations, performed using an onboard solar diffuser, show no significant changes in the VIRS 1.61-μm data. The responsivity (digital counts per radiance unit) of the 0.62-μm band has changed and, as a function of days since 1998, is given by R1(day) = 69.782 − 0.0022 × day, with an annual degradation of 1.15%. Four years of on-orbit lunar measurements were also examined in an attempt to quantify any degradation in the solar diffuser. The integrated lunar reflectance with phase angles ranging from 1.6° to 106° were fit with the lunar photometric model of Hapke. A good fit was made to the 0.62-μm data, but overall, the quality of the data did not support efforts to quantify any diffuser degradation. The quality of the VIRS radiometry was also examined by...