An In-Orbit Radiometric Calibration Method of the Geostationary Ocean Color Imager

The Geostationary Ocean Color Imager (GOCI) has been developed for the first time to provide multispectral data which is useful to detect, monitor, and predict short-term changes of coastal ocean environment around the Korean Peninsula from a geostationary platform. In this paper, an in-orbit solar calibration method for GOCI is introduced. Based on the radiometric model of GOCI, solar calibration method using onboard calibration devices has been constructed. A nonlinear radiometric model has been validated using test results obtained during ground tests. The gain parameters of the GOCI radiometric model will be continually updated by the in-orbit solar calibration. The GOCI is equipped with two onboard calibration devices: Solar Diffuser (SD) and Diffuser Aging Monitoring Device (DAMD). The SD, which is located in front of a pointing mirror covering full aperture of the GOCI, is used for calibrating end-to-end radiometric response. The DAMD, which covers partial aperture, detects a potential degradation of the SD.

I Introduction

Space-Based observations of ocean color began with the Coastal Zone Color Scanner, which was launched in 1978. Since then, many missions have been launched by many countries with increasing sophistication for ocean-color monitoring: Sea Viewing Wide Field-of-View Sensor, ocean color and temperature scanner, Ocean Color Monitor, Moderate Resolution Imaging Spectro-Radiometer, and Medium Resolution Imaging Spectro-Radiometer. The relatively low revisit frequency of these sensors on low Earth-orbiting satellites, further reduced in the presence of clouds, is inadequate to resolve processes operating at shorter time scales [1]. High-frequency observation using geostationary platform has been required in order to remove effects of tidal aliasing and to validate tidal mixing terms in coastal ecosystem models. Unfortunately, there is no geostationary platform providing measurement data of ocean color [2]. The Korea Aerospace Research Institute (KARI) has a plan to launch Communication, Ocean, and Meteorological Satellite (COMS), which is a geostationary platform carrying three different mission payloads. The Geostationary Ocean Color Imager (GOCI), which is manufactured by Astrium SAS, is one of the main payloads for the COMS and will be the first instrument to provide consistent monitoring of ocean color from geostationary platforms. The COMS contract to develop the satellite and to provide support for system activities has been awarded by KARI to ASTRIUM France. After completing environmental tests at a payload level, the GOCI has been integrated on the COMS, and it completed environmental testing at the satellite level in January 2010.