# Inversion of Chlorophyll-a Concentration in Wuliangsu Lake Based on OGolden-DBO-XGBoost
## 2 Materials and Methods
### Data Sets
#### 2.2.2 Remote-Sensing Data  
Remote-sensing satellite data from the Sentinel-2A and Sentinel-2B satellites of the Sentinel series of satellites of the European Space Agency are mainly used for detecting information on various aspects such as agriculture, forestry cultivation, and pollution of lakes and offshore waters [23]. The same multispectral imager, which covers visible light, near-infrared, and short-wave infrared wavelengths, is carried by every Sentinel-2 satellite. Table 3 lists the bands that are available for imaging collection. The Sentinel-2 series of satellites can systematically photograph land and coastal waters from latitudes 56\({}^{\circ}\)S to 84\({}^{\circ}\)N. The two satellites have a complementary repeat cycle of five days, which has a high access frequency and improves the accuracy and efficiency of experimental data acquisition [24].  
Remote-sensing satellite data were selected from remote-sensing images that were synchronous or quasi-synchronous with the sampling dates of measured Chl-a concentration and with less than 20% cloud cover over the study area. Remote-sensing image data  
\begin{table}
\begin{tabular}{c c c} \hline
**Standard Grade** & **Chl-a (ug/L)** & **Nutritional Level** \\ \hline I & \(<\)1.6 & Light nutrition \\ II & 1.6–10 & Middle nutrition \\ III & 10.0–26 & Light eutrophication \\ IV & 26.0–64 & Middle eutrophication \\ V & 64.0–160 & Severe eutrophication \\ ShoddyV & \(>\)160 & Extreme eutrophication \\ \hline \end{tabular}
\end{table}
Table 1: Chl-a concentration hierarchy.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Measured Data**} & \multicolumn{2}{c}{**Sentinel-2A**} & \multicolumn{2}{c}{**Sentinel-2B**} \\ \cline{2-5}  & \begin{tabular}{c} **Central** \\ **Wavelength** \\ **(nm)** \\ \end{tabular} & \begin{tabular}{c} **Bandwidth** \\ **(nm)** \\ \end{tabular} & \begin{tabular}{c} **Central** \\ **Wavelength** \\ **(nm)** \\ \end{tabular} & \
\begin{tabular}{c} **Bandwidth \\ **(nm)** \\ \end{tabular} &
\begin{tabular}{c} **Spatial Resolution** \\ **(m)** \\ \end{tabular} \\ \hline Band 1 & 433.9 & 27 & 442.3 & 45 & 60 \\ Band 2 & 496.6 & 98 & 492.1 & 98 & 10 \\ Band 3 & 560.0 & 45 & 559.0 & 46 & 10 \\ Band 4 & 664.5 & 38 & 665.0 & 39 & 10 \\ Band 5 & 703.9 & 19 & 703.8 & 20 & 20 \\ Band 6 & 740.2 & 18 & 739.1 & 18 & 20 \\ Band 7 & 782.5 & 28 & 779.7 & 28 & 20 \\ Band 8 & 835.1 & 145 & 833.0 & 133 & 10 \\ Band 8A & 864.8 & 33 & 864.0 & 32 & 20 \\ Band 9 & 945.0 & 26 & 943.2 & 27 & 60 \\ Band 10 & 1373.5 & 75 & 1376.9 & 76 & 60 \\ Band 11 & 1613.7 & 143 & 1610.4 & 141 & 20 \\ Band 12 & 2202.4 & 242 & 2185.7 & 238 & 20 \\ \hline \end{tabular}
\end{table}
Table 3: Sentinel-2 sensor spectral characteristic information.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{1}{c}{**Standard Grade**} & \multicolumn{1}{c}{**Chl-a (ug/L)**} & \multicolumn{1}{c}{**Nutritional Level**} \\ \hline I & \(<\)1.6 & Light nutrition \\ II & 1.6–10 & Middle nutrition \\ III & 10.0–26 & Light eutrophication \\ IV & 26.0–64 & Middle eutrophication \\ V & 64.0–160 & Severe eutrophication \\ ShoddyV & \(>\)160 & Extreme eutrophication \\ \hline \end{tabular}
\end{table}
Table 1: Chl-a concentration hierarchy.  
were downloaded from the ESA Copernicus Data Centre ([[https://scihub.copernicus.eu/dhus/#/home](https://scihub.copernicus.eu/dhus/#/home)]([https://scihub.copernicus.eu/dhus/#/home](https://scihub.copernicus.eu/dhus/#/home)), accessed on 30 July 2021).