## 3 Coherence Detection and Inland Water Body Monitoring
### Retrieval of Inland Water Body (Or Lake Water Body) Surface Height  
Studying the height measurement of inland water bodies (lake water bodies) plays an important role in water resource management, climate research, ecological environment monitoring, and other fields. The height of inland water bodies (or lake water bodies) can be obtained through missions such as satellite height measurement and radar altimetry [96]. However, the radar altimetry constellation limits the spatiotemporal sampling required for the systematic and periodic mapping of lakes [97]. In GNSS-R, height measurement is based on the differential propagation delay between the direct signal and the reflected signal (known as the bistatic delay), which can be obtained from the ranging code (known as the group delay) or carrier phase (known as the phase delay). The principle of the retrieval of inland water body height is shown in Figure 5. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Reference** & **Satellite Data** & **Detection Area** & **Method** & **Result (Accuracy)** \\ \hline
[91] & CYGNSS L1/L0 & Amazon basin, & Entural wetlands & Entropy detector & Small water bodies can be detected and imaged under heavy vegetation (i.e., 400 tons/hectare). \\ \hline
[42] & CYGNSS L0 & Qinghai Lake & \
\begin{tabular}{c} Fusion method of \\ signal–power ratio and \\ effective area delay \\ distance (D\({}_{\text{L8}}\)) \\ \end{tabular} &
\begin{tabular}{c} Can achieve higher spatial resolution \\ (0.7 km), with retrieval result error of \\ about 0.5 km. \\ \end{tabular} \\ \hline
[92] & CYGNSS L0 & Mississippi River & Coherent Coefficient & Proves the feasibility of using the \\  & & & & \\ \hline
[53] & \begin{tabular}{c} Spire, \\ CYGNSS L0 \\ \end{tabular} & \begin{tabular}{c} North America, north \\ Eursais, and near the Gulf \\ of Mexico (Spire data). \\ Southeast USA, Amazon \\ River basin, and \\ Qinghai–Tibet Plateau \\ (CYGNSS data). \\ \end{tabular} & \begin{tabular}{c} North America, north \\ Eursais, and near the Gulf \\ of Mexico (Spire data). \\ \end{tabular} & \
\begin{tabular}{c} Jointly uses carrier phases \\ and signal strength \\ \end{tabular} &
\begin{tabular}{c} As for CYGNSS, the difference is \\ mainly less than 0.43 km, with an \\ average of 0.18 km and a standard \\ deviation of 0.16 km. \\ \end{tabular} \\ \hline
[21] & CYGNSS FM02 L0 & Rousseau Lake, Florida & Coherent Coefficient & An overlay of the mean coherent \\  & & & & coefficient in a Google Earth historical \\  & & & & image, which clearly shows the \\  & & & & consistency between high coherent \\  & & & & coefficient pixels and the presence of \\  & & & & inland water bodies. \\ \hline
[93] & CYGNSS L0 & Amazon River & \
\begin{tabular}{c} The threshold, normalized \\ variance, 2-score, variance, \\ and circular correlation \\ (Cir Cor) discriminations \\ \end{tabular} &
\begin{tabular}{c} This multi-feature method achieves a \\ high discrimination accuracy (\(\sim\)90\%) \\ and provides a high temporal \\ resolution (20 Hz). \\ \end{tabular} \\ \hline
[94] & CYGNSS L0 & Orinoco River & \
\begin{tabular}{c} OL tracking of the \\ reflection signal phase [71] \\ and a novel error \\ correction approach \\ \end{tabular} &
\begin{tabular}{c} The retrieved river surface slope \\ ranges from 3.9 to 5.1 cm/km. \\ \end{tabular} \\ \hline
[95] & Spire & Mississippi River & OL tracking &
\begin{tabular}{c} The retrieved river surface slopes \\ range from 2.2 to 16.6 cm/km, with \\ lower sections being flatter. \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Key content summary of the literature related to inland water body detection. In order to perform inland water surface height retrieval, [PERSON] and [PERSON] [98] used CYGNSS's coherent DDMs from 2020 to 2022 to retrieve the surface height of inland water bodies. They detailed the algorithms and techniques for detecting water surface height using these data, providing a new method for retrieving the height of inland water bodies.