On-orbit Radiometric Calibration of GOCI-II Solar Diffuser with Improved Bidirectional Transmittance Distribution Function

Abstract

n-orbit radiometric calibration is a crucial process to ensure the accuracy of satellite data and acquire reliability for various ocean color products. This study will present the update of GOCI-II radiative correction algorithm to ensure the continuous quality and accuracy of the Geostationary Ocean Color Imager-II (GOCI-II) products. The GOCI-II has utilized an on-board calibration device monitoring system using a Solar Diffuser (SD) and Diffuser Aging Monitoring Devices (DAMD) to continuously produce the absolute radiometric gain parameters derived from the Sun. The time series of the SD gain data (K1) exhibits an increasing tendency to possible sensor degradation as well as seasonal variability. To remove the sensor degradation effects on ocean color products, we improved the radiative correction algorithm to consider the SD/DAMD measurements. The improved radiative correction algorithm includes Bidirectional Transmittance Distribution Function (BTDF) correction and sensor degradation model, which collectively operate to compensate for the observed seasonal fluctuation and estimate degradation trend in radiometric gain values. The results demonstrate the impact of BTDF correction and sensor degradation model on the spectrum of Top of Atmosphere (TOA) radiance, confirming the capability for improving the long-term stability of GOCI-II data.