Geostationary Ocean Color Imager (GOCI) is under development to provide a monitoring of ocean-color around the Korean Peninsula from geostationary platforms. It is planned to be loaded on Communication, Ocean, and Meteorological Satellite (COMS) of Korea. In this paper main mission of GOCI and corresponding major technical requirements are introduced. Also characteristic of the GOCI radiometric model for calibration is introduced. The GOCI is modeled as a nonlinear system in order to reflect a nonlinear characteristic of detector. Radiometric calibration concept is explained through radiometric parameter estimation method and offset correction method. For the GOCI, the offset signal depends on each spectral channel because dark current offset signal is a function of integration time which is different from channel to channel. The offset parameter estimation method using offset signal measurements for two integration time setting is described. Also error propagation for radiance estimation is examined in this paper. The error propagation for nonlinear GOCI instrument will be slightly larger than a linear instrument. The increase of error propagation induced by the nonlinear parameter depends on the integration time and the input radiance.

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<p>In ocean color remote sensing, the importance of developing and validating atmospheric correction and ocean bio-optical algorithms has been emphasized. However, if uncertainty remains in the fundamental procedure of converting the sensor signal to the top of the atmosphere (TOA) radiance, the errors will affects the overall reliability of the ocean satellite products.</p> <p>The purpose of this study is to monitor the gain parameters of two on-board GOCI-II calibration using Solar Diffuser (SD) and Diffuser Aging Monitoring Device (DAMD) and to improve the accuracy of ocean color sensors for radiometric calibration (RC) quality at the TOA level. Our results show that the SD gains parameter tends to decrease with seasonal periodicity in all bands, confirming sensor degradation and solar azimuth angle over time. In addition to the current RC model using only SD gain in the relationship between the sensor-observed digital counts and TOA radiance, we develop an azimuth angle correction model and a sensor degradation correction model. Verification will be performed by calculating the TOA radiation applied with an improved RC model around the Korean Peninsula. It will contribute to providing more stable GOCI-II ocean color products for short-term and long-term analysis.</p>