ISRD (inter-slot radiometric discrepancy) simulation based on end-to-end ray tracing for GOCI

Abstract

Geostationary Ocean Color Imager (GOCI) is the world’s first geostationary satellite for ocean color remote sensing mission. It observes coastal and ocean region around the Korean Peninsula, Japan, and East China with a spatial resolution of 500 meters. GOCI uses step-stare imaging technique by the implementation of 2D detector array (1413 x 1430) and 2-axis pointing mechanism. It enables multiple image acquisitions for the same location of FOR (Field Of Regard) at sixty-minute intervals during daytime (8 images per day in nominal operation). Because GOCI IFOV is about a sixteenth of GOCI FOR, an image acquisition and processing sequence for GOCI FOR consists 16 (4 x 4) slot image acquisitions which correspond to GOCI IFOV and image processing to combine 16 slot images into one image for GOCI FOR.Inter-Slot Radiometric Discrepancy (ISRD) of GOCI means the radiance (i.e. digital count) discrepancy in the overlapped area between adjacent slot images. This is mainly derived by the difference of solar zenith angle by the gap of acquisition time between slots with overlapped area. Due to the boustrophedonic pattern of GOCI slot image acquisition sequence, maximum difference of acquisition time is about 12 minutes. After the normalization processing in terms of solar zenith angle for the reduction of ISRD, early in GOCI on-orbit operation, systematic residual ISRD about 3% discrepancy was observed for B6 (680nm) a of 500 meters. GOCI uses step-stare imaging technique by the implementation of 2D detector array (1413 x 1430) and 2-axis pointing mechanism. It enables multiple image acquisitions for the same location of FOR (Field Of Regard) at sixty-minute intervals during daytime (8 images per day in nominal operation). Because GOCI IFOV is about a sixteenth of GOCI FOR, an image acquisition and processing sequence for GOCI FOR consists 16 (4 x 4) slot image acquisitions which correspond to GOCI IFOV and image processing to combine 16 slot images into one image for GOCI FOR.Inter-Slot Radiometric Discrepancy (ISRD) of GOCI means the radiance (i.e. digital count) discrepancy in the overlapped area between adjacent slot images. This is mainly derived by the difference of solar zenith angle by the gap of acquisition time between slots with overlapped area. Due to the boustrophedonic pattern of GOCI slot image acquisition sequence, maximum difference of acquisition time is about 12 minutes. After the normalization processing in terms of solar zenith angle for the reduction of ISRD, early in GOCI on-orbit operation, systematic residual ISRD about 3% discrepancy was observed for B6 (680nm) a