Calibration for the solar channel using MODIS-derived BRDF parameters over Australian desert targets

Communication Ocean Meteorological Satellite (COMS) is the first Korean geostationary satellite. The Meteorological Imager (MI) aboard the COMS will measure the reflected solar radiation within a spectral band (550 ~ 800 nm) as well as emitted infrared radiation at 4 spectral bands. As no in-flight calibration device will be available for solar channel, a development of vicarious calibration is required for producing level 1.5 data.

In this study we develop a method utilizing satellite-derived BRDF for the calculation of TOA radiance which then will be used for the COMS solar channel calibration. We chose bright desert targets that are assumed to be less influenced by clear-sky atmospheric conditions because of larger surface reflection. Spatial and temporal variations of MODIS-derived BRDF were examined over the Australian Simpson desert and then targets showing smallest variations were selected as test targets. At the selected targets, seasonally varying BRDFs were used as inputs to a radiative transfer model (6S) to simulate MODIS visible channel radiances. Computed radiances were then compared with MODIS-observed radiances to evaluate the degree of uncertainties of this approach. Results indicate that the relative bias between simulation and observation appears to be within ±5% calibration uncertainly level.