## 6 Summary and Conclusions  
The COMS/MI has observed sea-surface radiances that can be used for the estimation of SST in extensive regions including the western Pacific Ocean and the eastern Indian Ocean. Its areal coverage contains most of the countries with the highest population in the world. So, the spatial and temporal variations of SSTs in the seas within the COMS coverage are of significance in many aspects. Many international institutions have been producing daily, weekly, or monthly SST products. However, the contribution of geostationary satellites in this region has been very low, except for the recent Japanese geostationary satellite, Himawari-8, with unprecedented spatial and temporal resolution. The COMS/MI data can also contribute to the composite SST product. To do so, there is a strong need for the SST coefficients to be optimized to COMS/MI observations. Unfortunately, the SST coefficients of COMS/MI over the full disk area that satisfy a certain level of accuracy have not been available. Thus, this study tried to suggest optimized algorithms and coefficients which are able to estimate the SSTs for the past years covering the entire period of COMS' operation. Prior to the derivation of the SST coefficients of COMS/MI, a procedure of quality control was applied to surface drifting buoy data for the period of April 2011 to March 2015. In addition, a series of the threshold methods were also applied to satellite observations to remove cloud-contaminated and problematic pixels. The thresholds of each step were determined by being optimized for COMS/MI. Then, the matchup database between the COMS/MI-observed radiance data and in situ measurements were generated to estimate the coefficients for SST retrieval and to validate the accuracy of COMS/MI-derived SSTs. The number of matchup points generated through the quality-control procedure was ultimately 284,175 for the four years. The RMSEs and bias errors were slightly higher than the other representative algorithm suggested by OSI SAF, addressing the effect of the satellite zenith angle in the formulation. However, the present algorithms revealed better performance at low SST range, i.e., less than 10 \({}^{\circ}\)C. The low SST range is of importance in the regional seas around the Korean Peninsula for which SSTs tends to decrease below 0 \({}^{\circ}\)C in winter, especially along the Russian coast in the East Sea (called Sea of Japan) and at a part of the Bohai Sea and coastal region of the North Korea. These regions are also very important for weather forecasts, as well as for oceanographic applications. Although the present algorithms do not eliminate the SZA effects on SST errors, especially at the edge of the full-disk region, the estimated SSTs seem to have advantages in terms of the non-existence of extreme overestimation or underestimation. The errors of COMS/MI-derived SSTs exhibited underestimation in coastal regions with a distance of less than 10 km from the coastline, regardless of MCSST or NLSST. This might be related to diverse causes from coastal topography, small-scale oceanic features, land contamination, and so on. It is recommended that the present coefficients should be taken into account for the determination of SSTs at particular coastal regions. SST errors did not reveal any characteristics with regard to both wind speed and latitude. For the validation of the estimates of SST coefficients, the COMS/MI SSTs derived from April 2014 to March 2015 were compared with in situ temperatures. The validation results confirmed the possibility of the continuous use of the SST coefficients. Thus, it is expected that the COMS/MI SST data of more than 7 years, which is retrieved using the coefficients suggested in this study, can be used to understand ocean phenomena and to produce the SST climatology fields for the Asia-Pacific region. Conceptualization, K.-A.P. ; Methodology, K.-A.P. and H.-J.W. ; Data Processing and Validation, H.-J.W. and E.-Y.L. ; Writing-Original Draft Preparation, H.-J.W.