# COMS Visible Channel Calibration Using Moon Observation Data  
[PERSON] and [PERSON]  
1 National Meteorological Satellite Center, Korea Meteorological Administration, 64-18 Guam-gil,  
Gwanghyewon-myeon, Jincheon-gun 27803, Chungcheongbuk-do, Korea; [EMAIL_ADDRESS]  
1  
Footnote 1: email: [EMAIL_ADDRESS]; tae-hyeong@korea. as an on-board radiometric calibration device. However, the calibration system used by the Albedo Monitor of COMS cannot be implemented for monitoring long-term degradation of the visible channel as it has a larger uncertainty than the signal. Therefore, the use of other calibration methods is necessary for long-term monitoring of sensor degradation. To monitor and analyze visible channel degradation and stability, a variety of post-launch calibration techniques have been developed by the satellite operation community. Vicarious calibration, which uses a not-in-orbit stable object as the calibration reference target, is employed to examine the sensor in-orbit degradation patterns or to provide post-launch calibration coefficients. To reduce the risk of erroneous degradation trending, multiple calibration methods are often used to verify results. In this respect, several vicarious calibration methods, which use different stable targets, have been studied for use with COMS visible channels; KMA has implemented inter-calibration methods for geostationary meteorological imagers within the framework of GSICS, with calibration targets of the DCC (Deep Convective Cloud) and the Moon. Vicarious calibration methods using a radiative transfer simulation have also been developed in collaboration with Seoul National University [6]. These calibration methods use invariant Earth surface targets such as deserts [7], DCC [8; 9], Rayleigh scattering, and sun-glint over a clear ocean surface [10; 11], and assume that the time-series of stable reference target observations (either direct satellite measurements or ratios of satellite measurements to modeled simulations of the reference) are scattered along a trend that can be used to describe the instrument degradation pattern. However, the performance of reference targets needs to be well understood and characterized to estimate and understand calibration uncertainty; when short-term variations in reference targets are well understood and characterized, they can be removed or simulated to improve calibration accuracy [12]. On the basis of these reference targets, vicarious calibration methods can provide either relative or absolute calibration correction coefficients. The Sonoran Desert is one of the largest deserts in North America and can be observed by both GOES (Geostationary Operational Environmental Satellite)-East and GOES-West satellites. It has long-term stability and can thus be used as a reference target for the development of long-term GOES visible climate data with calibration accuracy traceable to MODIS Collection 6 data at about 3-4% [13]. However, as a result of the impacts of a strong BRDF (Bidirectional Reflectance Distribution Function) effect and occasional climate variations such as ENSO (El Nino-Southern Oscillation) events, it is not an appropriate reference target for use with operational or near real-time data calibration. The DCC has high reflectance and relatively flat spectra in the visible wavelength range; as such, it can be used as a stable reference target to provide an absolute calibration accuracy of less than 3% for the GEO (Geostationary Satellite) visible channels and that of less than 1% for the LEO (Low Earth Orbit satellite) [14]. The DCC is available to all the Earth observation satellites and has been selected by the GSICS community (an international collaboration to enhance calibration and validation of satellite observations) as a common reference for inter-calibrating visible channels for different satellite instruments [15]. The Moon can be used as an invariant reference target, and its use was suggested nearly 20 years ago as a component in addressing in-flight calibration [16; 17].