## 4 Atmospheric Correction Results and Analysis
### Comparison and Validation with Sentinel-2 Surface Reflectance Products  
Sentinel-2 is part of the \"Global Environment and Security Monitoring\" program, carrying a multispectral imager with 13 bands at spatial resolutions of 10 m, 20 m, and 60 m and a swath width of 290 m. Among these, bands 2, 3, 4, 5, and 8 have central wavelengths \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Imaging** & **Imaging Time** & \begin{tabular}{c} **AOD** \\ **CWW (g/cm\({}^{2}\))** \\ \end{tabular} & **Band** & \
\begin{tabular}{c} **Measured** \\ **Reflectance** \\ \end{tabular} & **ACSR** &
\begin{tabular}{c} **Absolute** \\ **Error** \\ \end{tabular} \\ \hline \multirow{4}{*}{Dunhuang site} & 25 January & & & B1 & 0.2095 & 0.1952 & 0.0143 \\  & 2021 & AOD = 0.247 & B2 & 0.2498 & 0.2301 & 0.0197 \\  & 2021 & CWV = 0.33 & B3 & 0.2708 & 0.2556 & 0.0152 \\  & (HJ-2B) & & B4 & 0.2707 & 0.2536 & 0.0171 \\  & & & B5 & 0.2796 & 0.2679 & 0.0117 \\ \hline \multirow{4}{*}{Dunhuang site} & 27 January & & & B1 & 0.2143 & 0.1902 & 0.0241 \\  & 2021 & AOD = 0.273 & B2 & 0.2428 & 0.2446 & 0.0018 \\  & (HJ-2A) & CWV = 0.28 & B3 & 0.2687 & 0.2722 & 0.0035 \\  & & & B4 & 0.2677 & 0.2605 & 0.0072 \\  & & & B5 & 0.2746 & 0.2788 & 0.0042 \\ \hline \multirow{4}{*}{High- reflectance site} & 25 January & & & B1 & 0.2615 & 0.2634 & 0.0019 \\  & 2021 & AOD = 0.225 & B2 & 0.3261 & 0.3176 & 0.0085 \\  & 2021 & CWV = 0.29 & B3 & 0.3747 & 0.3667 & 0.008 \\  & (HJ-2B) & & B4 & 0.3815 & 0.3664 & 0.0151 \\  & & & B5 & 0.4005 & 0.3911 & 0.0094 \\ \hline \multirow{4}{*}{High- reflectance site} & 27 January & & & B1 & 0.2683 & 0.2631 & 0.0052 \\  & 2021 & AOD = 0.228 & B3 & 0.3261 & 0.3354 & 0.0199 \\  & (HJ-2A) & CWV = 0.25 & B3 & 0.375 & 0.3954 & 0.0204 \\  & & & B4 & 0.383 & 0.3826 & 0.0004 \\  & & & B5 & 0.3982 & 0.415 & 0.0168 \\ \hline \multirow{4}{*}{Wheat field} & \multirow{4}{*}{23 March 2021 field} & \multirow{4}{*}{ADD = 0.628 CWV = 2.35} & B1 & 0.0423 & 0.0539 & 0.0116 \\  & & & B2 & 0.0612 & 0.0746 & 0.0134 \\  & (HJ-2B) & & B3 & 0.0339 & 0.0499 & 0.0161 \\  & & & B4 & 0.1667 & 0.1597 & 0.0070 \\  & & & B5 & 0.4349 & 0.4053 & 0.0296 \\ \hline \multirow{4}{*}{Wheat field} & \multirow{4}{*}{25 March 2021 field} & \multirow{4}{*}{ADD = 0.453 CWV = 1.53} & B1 & 0.0424 & 0.0533 & 0.0109 \\  & & & B2 & 0.0582 & 0.0694 & 0.0112 \\  & & & B3 & 0.0331 & 0.0429 & 0.0098 \\  & & & B4 & 0.1627 & 0.1521 & 0.0106 \\  & & & B5 & 0.4301 & 0.4129 & 0.0172 \\ \hline \multirow{4}{*}{River water} & \multirow{4}{*}{23 March 2021 field} & \multirow{4}{*}{ADD = 0.599 CWV = 2.14} & B1 & 0.0612 & 0.0793 & 0.0181 \\  & & & B2 & 0.0909 & 0.1085 & 0.0176 \\  & & & B3 & 0.0927 & 0.1015 & 0.0088 \\  & & & B4 & 0.0820 & 0.0943 & 0.0123 \\  & & & B5 & 0.0414 & 0.0541 & 0.0127 \\ \hline \multirow{4}{*}{River water} & \multirow{4}{*}{25 March 2021 field} & \multirow{4}{*}{ADD = 0.439 CWV = 1.40} & B1 & 0.0623 & 0.0792 & 0.0169 \\  & & & B2 & 0.0890 & 0.1038 & 0.0148 \\ \cline{1-1}  & & & B3 & 0.0910 & 0.0927 & 0.0017 \\ \cline{1-1}  & & & B4 & 0.0841 & 0.0756 & 0.0085 \\ \cline{1-1}  & & & B5 & 0.0422 & 0.0485 & 0.0063 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison table of measured SR and atmospheric corrected SR.  
and spatial resolutions similar to those of the HJ-2A/B satellite's MSC. The specifics are detailed in Table 4.  
The Sentinel-2 L2A product provides atmospheric-corrected surface reflectance images, which are the surface reflectance products. The accuracy of Sentinel-2's surface reflectance products has undergone extensive comparative validation, and a quality assessment report has been released, making it a reliable product for surface reflectance accuracy verification [29; 30; 31]. To overcome the limitation of ground-based in situ measurements, which cannot encompass a wide variety of land cover types, this study utilizes Sentinel-2 surface reflectance products to compare and validate the atmospheric-corrected surface reflectance of the HJ-2A/B.