## Materials and Methods
### Remote Sensing Data and Preprocessing
#### 2.2.2 Remote Sensing Data Preprocessing  
Preprocessing of the remote sensing data included radiometric calibration, geometric correction, and atmospheric correction. First, radiometric calibration converted the digital number value of the raw image to radiance based on Equation (1) [55]. \[L_{e}(\lambda_{e})=Gain\cdot DN+Offset \tag{1}\]  
where \(L_{e}(\lambda_{e})\) is the radiance, and Gain and Offset are the calibration coefficients. The unit is \(\mathrm{W}\ \times\mathrm{m}^{-2}\ \times\ \mathrm{sr}^{-1}\ \times\mathrm{\upmu m}^{-1}\) The Gain and Offset values for ZY-3 MUX, GF-1 WFV, and HJ-1 CCD were obtained from the CRESDA and are shown in Table 3[55]. However, due to the unstable radiation performance of HJ-1 CCD data, a cross-radiometric calibration was conducted using a method that considers the characteristics of the surface bidirectional reflectance distribution function (BRDF) [47; 57]. The calibration accuracy of the four spectral bands of the HJ-1 CCD sensor was 5%, which meets the requirements for absolute radiometric calibration accuracy [58]. The radiance was then converted to top of atmosphere (TOA) reflectance based on Equation (2) [16]. \[\rho=\frac{\pi\cdot L\cdot d^{2}}{ESUN_{\lambda}\cdot\cos\theta_{s}} \tag{2}\] \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Sensor** & \multicolumn{2}{c}{**ZY-3 MUX**} & \multicolumn{2}{c}{**GF-1 WFV**} & \multicolumn{2}{c}{**HJ-1 CCD**} \\ \hline  & \multicolumn{2}{c}{Wavelength} & \multicolumn{1}{c}{Bands} & \multicolumn{1}{c}{Wavelength} & \multicolumn{1}{c}{Bands} & \multicolumn{1}{c}{Wavelength} \\  & \multicolumn{1}{c}{(\(\upmu\)m)} & \multicolumn{1}{c}{Bands} & \multicolumn{1}{c}{(\(\upmu\)m)} & \multicolumn{1}{c}{Bands} & \multicolumn{1}{c}{(\(\upmu\)m)} \\  & 1 & 0.45–0.52 & 1 & 0.45–0.52 & 1 & 0.43–0.52 \\ Spectral characteristics & 2 & 0.52–0.59 & 2 & 0.52–0.59 & 2 & 0.52–0.60 \\  & 3 & 0.63–0.69 & 3 & 0.63–0.69 & 3 & 0.63–0.69 \\  & 4 & 0.77–0.89 & 4 & 0.77–0.89 & 4 & 0.76–0.90 \\ Spatial resolution (m) & 5.8 & & 16 & & 30 \\ Radiometric resolution (Bit) & 10 & & 10 & 8 \\ Swath width (km) & 51 & & 200 (single); 800 (4 cameras) & 360 (single); 700 (two) \\ Revisit time (days) & 5 & & 4 & 4 & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Technical specification of the ZY-3 MUX, GF-1 WFV, and HJ-1 CCD cameras. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Sensor** & **Date** & \begin{tabular}{c} **Local** \\ **Time** \\ \end{tabular} & \begin{tabular}{c} **Solar Zenith** \\ **Angle** \\ \end{tabular} & \begin{tabular}{c} **Solar Azimuth** \\ **Angle** \\ \end{tabular} & \
\begin{tabular}{c} **View Zenith** \\ **Angle (Mean)** \\ \end{tabular} &
\begin{tabular}{c} **View Azimuth** \\ **Angle (Mean)** \\ \end{tabular} \\ \hline ZY-3 MUX & 20140727 & 11:15:23 & 25.28\({}^{\circ}\) & 216.38\({}^{\circ}\) & 0\({}^{\circ}\) & 216.38\({}^{\circ}\) \\ GF-1 WFV & 20140727 & 11:50:19 & 22.08\({}^{\circ}\) & 201.62\({}^{\circ}\) & 29.97\({}^{\circ}\) & 74.57\({}^{\circ}\) \\ HJ-1 CCD & 20140728 & 10:00:09 & 34.97\({}^{\circ}\) & 295.49\({}^{\circ}\) & 25\({}^{\circ}\) & 53.59\({}^{\circ}\) \\ Landsat-8 OLI & 20140725 & 10:59:34 & 27.67\({}^{\circ}\) & 131.88\({}^{\circ}\) & 0\({}^{\circ}\) & 95.31\({}^{\circ}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Satellite data acquisition information for ZY-3 MUX, GF-1 WFV, HJ-1 CCD and Landsat-8 OLI. where \(\rho\) is TOA reflectance, \(\pi\) is 3.1415, \(L\) is the sensor spectral radiance, \(d\) is the earth-sun distance in astronomical units, \(ESU\lambda_{\lambda}\) is the extraterrestrial solar irradiance, and \(\theta_{\rm s}\) is the solar zenith angle. The \(ESU\lambda_{\lambda}\) values for ZY-3 MUX, GF-1 WFV, and HJ-1 CCD are shown in Table 3[55]. Because of the high quality of the raw ZY-3 MUX and GF-1 WFV data on clear days, the atmospheric correction of these images was conducted using FLAASH in Environment and Visualizing Images (ENVI) software.