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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