## Data
### In Situ Temperature Measurements  
We collected the SST measurements obtained by drifting and moored buoys. These data are distributed through the Global Telecommunication System (GTS) of the World Meteorological Organization (WMO), and are operationally archived by KMA. The majority of drifting buoys measure the subsurface temperature at about 20-cm depth [34], while moored buoys measure at depths of a few tens of centimeters to a few meters, depending on the type of buoy and deployment location. We used only drifting buoy SSTs for estimating the SST coefficients and validation of retrieved SSTs.  
Since in situ SST measurements obtained through GTS are occasionally suboptimal with unexpected values, quality control (QC) procedures are essential for the calibration and validation of satellite-derived SSTs [35]. In this study, a series of QC procedures developed by the KMA were applied to the individual buoy data in an effort to eliminate low-quality measurements and minimize the errors in the following process. The QC procedure was performed separately for each buoy. To begin with, if the number of observations within a day was less than 10, or the maximum difference of temperatures within a day is equal to 0 \({}^{\circ}\)C or greater than 4 \({}^{\circ}\)C due to malfunctioning of the  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Channel** & **Description** & **Wavelength (\(\upmu\)m)** & **Bandwidth (\(\upmu\)m)** & **NEDT at 300K (K)** & **Spatial Resolution (km)** \\ \hline
1 & VIS & 0.675 & 0.55–0.80 & 1 \\
2 & SWIR & 3.75 & 3.5–4.0 & \(<\)0.10 & 4 \\
3 & WV & 6.75 & 6.5–7.0 & \(<\)0.12 & 4 \\
4 & IR1 & 10.8 & 10.3–11.3 & \(<\)0.12 & 4 \\
5 & IR2 & 12.0 & 11.5–12.5 & \(<\)0.20 & 4 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Spectral channel characteristics of the Meteorological Imager (MI) on Communication, Ocean and Meteorological Satellite (COMS) (VIS: visible, SWIR: shortwave infrared, WV: water vapor, IR1: infrared 1, IR2: infrared 2).  
drifters, then the data were discarded. Next, the time-continuity test was performed by removing the data that is three standard deviations larger than the daily mean. For rigorous QC of the buoy data, the time-continuity test was repeated over 4 days of data collection. Finally, if the standard deviation of the data over 4 days was equal to zero or greater than 2 \({}^{\circ}\)C, all data for that period were eliminated. These QC procedures could significantly reduce errors in buoy measurements. The uncertainty of quality-controlled buoy SSTs estimated using the three-way error analysis between the Advanced Along Track Scanning Radiometer (AATSR), the Advanced Microwave Scanning Radiometer-EOS (AMSR-E), and buoys, was 0.23 \({}^{\circ}\)C [36].  
Figure 2 shows a comparison of time-series drifter temperatures before and after the quality-control procedures. The temporal change of the original drifter temperatures (Figure 2a,c) shows intermittent displacement with unusual spikes beyond the average water temperature range before the QC procedure. However, these abnormal data have been completely eliminated through the QC process, as shown in Figure 2b,d and eventually follow the overall pattern of time variations of SST. After evaluating the quality of the drifter temperature for 4 years, 15.4% of the total data were removed.