## Materials and Methods
### Study Area  
Three large wildfires that occurred in the western United States in 2016 were used to extract the sample sets for the new method. The wildfire cases included the Hot Pot Fire (Nevada), Range 12  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sensor, Satellite** & **Spectral Band** & **Bandwidth (\(\mu\)m)** & **Spectral Region** & **Spatial Resolution (m)** \\ \hline \multirow{8}{*}{MODIS, Terra/Aqua} & 1 & 0.62–0.67 & R & 250 \\  & 2 & 0.841–0.876 & NIR & 250 \\  & 3 & 0.459–0.479 & B & 500 \\  & 4 & 0.545–0.565 & G & 500 \\  & 5 & 1.23–1.25 & NIR & 500 \\  & 6 & 1.628–1.652 & SWIR & 500 \\  & 7 & 2.105–2.155 & SWIR & 500 \\  & 9 & 0.438–0.448 & B & 1000 \\  & 19 & 0.915–0.965 & NIR & 1000 \\  & 31 & 10.78–11.28 & FIR & 1000 \\  & 32 & 11.77–12.27 & FIR & 1000 \\ \hline \multirow{8}{*}{OLI, Landsat 8} & 3 & 0.53–0.59 & G & 30 \\  & 4 & 0.64–0.67 & R & 30 \\ \cline{1-1}  & 5 & 0.85–0.88 & NIR & 30 \\ \cline{1-1}  & 6 & 1.57–1.65 & SWIR & 30 \\ \cline{1-1}  & 7 & 2.11–2.29 & SWIR & 30 \\ \hline \hline \end{tabular} Abbreviations of spectral regions: B (blue), G (green), R (red), NIR (near infrared), SWIR (short wave infrared), and FIR (far infrared).  
\end{table}
Table 1: The characteristics of the spectral bands used of MODIS and OLI sensors.  
Fire (Washington) and Rey Fire (California). Three other American wildfires that occurred in 2017 were used to validate our method, including the Powerline Fire (Idaho), Tohakum 2 Fire (Nevada) and Cinder Butte Fire (Oregon). The geographic location of the six wildfire cases and their false-color composition RGB images of MODIS bands 7, 5 and 6 are shown in Figure 1. Serious wildfires frequently occur in this region due to the extreme climate, and this frequency underscores the urgent need for wildfire assessment and emergency management. The selected wildfire cases with the cloud-free MODIS data contribute to the implementation of the proposed method. All the MODIS images of the wildfires are from the Terra satellite. Through the comparison with MODIS/Terra Thermal Anomalies & Fire 5-Min L2 Swath 1 km V006 products (MOD14 version 6 products), the wildfires in the acquisition time of MODIS data were not active. Detailed information about the wildfire cases and the acquisition time of corresponding MODIS data are presented in Table 2. The information of the fuels involved was obtained from the Incident Information System (InciWeb) [37], and the detailed information of wildfire cases was obtained from the GeoMAC website (by the Geospatial Multi-Agency Coordination Group) [38; 39] and Monitoring Trends in Burn Severity (MTBS) website [40; 41].  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Wildfire Case** & **Duration** & **Acquisition Time of MODIS Data** & **Fuels Involved** \\ \hline Hot Pot Fire & 2 to 17 July 2016 & 7 July 2016 & brush, long and short grass \\ Range 12 Fire & 30 July to 29 August 2016 & 6 August 2016 & tall grass, brush and short grass \\ Rey Fire & 18 August to 15 September 2016 & 28 August 2016 & burned grass, brush, and oak canopy \\ Powerline Fire & 4 August to 25 September 2017 & 20 August 2017 & short grass, brush, dormant brush and hardwood \\ Tohakum 2 Fire & 29 August to 15 September 2017 & 5 September 2017 & slash \\ Cinder Butte Fire & 2 August to 16 October 2017 & 18 August 2017 & short grass, brownish, closed timber litter \\ \hline \hline \end{tabular}
\end{table}
Table 2: Detailed information of the wildfire cases and acquisition time of MODIS data.  
Figure 1: The geographic location and the false-color composition RGB images of MODIS bands 7, 5 and 6 of the six wildfire cases.