2.1.1. GK2A Data

In this study, we used GK2A/AMI data provided by the Korea Meteorological Administration (KMA)/National Meteorological Satellite Center (NMSC). GK2A is located at 128.2◦E and started operational services for 16 channels of AMI on 25 July 2019 [58]. To retrieve LST, level-1B of GK2A/AMI, level-2 of GK2A/AMI, auxiliary data of solar zenith angle (SZA), and satellite VZA data were used. The characteristics of the GK2A data used in this study are shown in Table 1. The brightness temperatures of channel 13 (10.35 µm) and channel 15 (12.36 µm) were used for adapting the split-window method. These infrared channels have a spatial resolution of 2 km at the nadir point and a temporal resolution of 10 min. Because LST is retrieved only for clear sky and land pixels, cloud mask and land/sea mask data are necessary. In this algorithm, we used GK2A cloud mask data as developed by NMSC/KMA [62]. In addition, we used the LSE of the two split-window channels derived by the vegetation cover method (VCM) using the land cover map, GK2A VI, and the look-up table of spectral emissivity [63]. The LSE data were produced from the GK2A LSE algorithm, and these data have a spectral resolution of 2 km and a temporal resolution of 1 day. In this study, GK2A LSTs were retrieved for 4 months from July to October 2019.


**Table 1.** The characteristics of GK2A/AMI data used in this study.

### 2.1.2. Validation data

To validate the retrieved LST, the ground measured upward longwave radiation data were used. The Tateno station of the Baseline Surface Radiation Network (BSRN) at 140.126◦E and 36.058◦N is a ground station in Japan and has been measuring upward longwave radiation every 1 min using the Kipp and Zonen CGR4 pyrgeometer [64–67]. Another type of validation data is high-quality LST data derived from another satellite. The MODIS LST (MOD11\_L2, MYD11\_L2 swath Collection 6) datasets were used for comparison with GK2A LSTs [32]. The spatial resolution of the MODIS LST was 1 km at nadir. The MODIS LST data are provided every 5 min for the swath region according to the orbit of Terra/Aqua satellites. In this study, GK2A LSTs were validated using the BSRN and MODIS LST data for 4 months, from July to October 2019.
