## 2 Materials and Methods
### Data and Study Area  
Feng Yun-2G is the fifth operational satellite of the first generation of geostationary meteorological satellites launched by China on 31 December 2014, which can observe the parameters of the earth's surface and atmosphere widely and continuously. The main remote sensor is the visible and infrared spin scanning radiometer with 5 channels, including one visible channel (VIS), one medium-wave infrared channel (IR4), one water vapor channel (IR3) and two long-wave infrared channels (IR1 and IR2). The detailed parameters of each channel are shown in Table 1.  
In this paper, the original data are the images from four infrared channels of the Feng Yun-2G satellite, which are provided by the National Satellite Meteorological Center. ([[http://satellite.nsmc.org.cn/PortalSite/Data/Satellite.aspx](http://satellite.nsmc.org.cn/PortalSite/Data/Satellite.aspx)]([http://satellite.nsmc.org.cn/PortalSite/Data/Satellite.aspx](http://satellite.nsmc.org.cn/PortalSite/Data/Satellite.aspx)), accessed on 25 June 2022). One full-disk data file is generated every half hour or one hour. The file structure is shown in Figure 2, including file attributes and scientific datasets. Every file includes the geographic location of the image center, cloud classification, five-channel images and calibration tables and is saved as the hierarchical data format (HDF). The red digits are the number of the datasets, while the white digits are the size of one dataset. Moreover, the center also provides a lookup table so that the users could calculate the longitude and latitude of every pixel in the image. Due to the high transmittance of the earth's atmosphere in the atmospheric windows, the radiation value from two long wave channels and one middle wave channel mainly depends on the temperature and the emissivity of the earth's surface. The emissivity of the same target is usually constant. The peak wavelength of most objects on the earth's surface is in the long-wave infrared channel, so the brightness temperature data from the long-wave infrared channel could show the temperature change trend of most objects on the earth's surface [32]. The data from the medium-wave infrared channel show the temperature change of the high-temperature targets and are affected by the reflection of solar radiation in the daytime, so data at night are selected in this paper. The water vapor channel is in the strong absorption band of water vapor, which is one of the main infrared absorption gases in the earth's atmosphere [33]. \begin{table}
\begin{tabular}{c c c} \hline
**Channel** & **Spectral Interval** & **Spatial Resolution** \\ \hline VIS & 0.55–0.75 μm & 1.25 km (5 km) \\ IR1 & 10.3–11.3 μm & 5 km \\ IR2 & 11.5–12.5 μm & 5 km \\ IR3 & 6.3–7.6 μm & 5 km \\ IR4 & 3.5–4.0 μm & 5 km \\ \hline \end{tabular}
\end{table} 
Table 1: The specific information of each channel. Figure 1: The flow of the research method. China is located between the Pacific seismic zone and Euro-Asia seismic zone, so earthquakes happen frequently there, especially in Qinghai-Tibet Plateau, Yunnan-Guizhou Plateau and Taiwan. In China, the terrain is high in the west and low in the east, as shown in Figure 3. The lines in different colors are the different types of plate boundaries. The topography data are provided by the University of California San Diego. ([[http://topex.ucsd.edu/marine_topo/mar_topo.html](http://topex.ucsd.edu/marine_topo/mar_topo.html)]([http://topex.ucsd.edu/marine_topo/mar_topo.html](http://topex.ucsd.edu/marine_topo/mar_topo.html)), accessed on 23 July 2022). China has a wide territory and rich soil resources, mainly including 15 types of soil. The variation of water content in the soil during the earthquake preparation period may also lead to anomalies in infrared remote sensing images [3]. The study area of this paper is between 0\({}^{\circ}\) N to 60\({}^{\circ}\) N and 70\({}^{\circ}\) E to 140\({}^{\circ}\) E, including China and the surrounding area.