###### Abstract
Operating in high-resolution SAR mode [10], the ground track separation of Sentinel-3 at the equator is approximately 104 km. In contrast, the CryoSat-2 ground track separation at the equator reaches 7.7 km at the expense of its temporal resolution, at 369 days. Sentinel-3 exhibits the best along-track resolution at 300 m, close to the resolution of CryoSat-2 in SAR and interferometric SAR (SARIn) modes. However, CryoSat-2 has a focus on the cryosphere, and as a result covers most continental surfaces in LRM. Therefore, Sentinel-3 constitutes the first altimetry mission that covers the globe completely in SAR mode, and is thus the most ideal tool for inland water level monitoring thanks to its good global coverage and sufficient temporal and spatial resolutions. The majority of previous studies [12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27] focus on relatively large water bodies with a scale of several kilometers. One of the first studies employing satellite altimetry for inland water level extraction was performed by [PERSON] et al. [12], who processed Geodetic Satellite (Geosat) waveforms to estimate the water levels at four sites in the Amazon basin. A root-mean-square \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Satellite Mission** & **Mission Period** & **Inclination** & **Revisit Time** & **Along-Track** & **Ground Track** \\  & & **(deg)** & **(Days)** & **Resolution (km)** & **Separation at** \\ \hline Geosat 1 & 1985–1990 & 108 & 17 & 1.7 & 16 \\ ERS 2 1 and 2 & 1991–2011 & 98.5 & 35 & 1.7 (ocean mode) & 80 \\ TOPEX/Poseidon 3 & 1992–2006 & 66 & 10 & 2.2 & 315 \\ GFO 4  & 1998–2008 & 108 & 17 & 1.7 km & 164 \\ Jason 1, 2, and 3 & 2001–present & 66 & 10 & 2.2 & 315 \\ Envisat 5 & 2002–2012 & 98.55 & 30-35 & 1.7 & 80 \\ CryoSat-2 6  & 2010–present & 92 & 369 & SARIN & 7.7 \\  & & & 1.6 (LRM) & \\ HY-2 7 & 2011–present & 99.3 &
\begin{tabular}{c} Two phases (14 \\ and 168) \\ \end{tabular} & 1.9 & 100 \\ SARAL 8 & 2013–present & 98.55 & 35 & 1.4 & 75 \\ Sentinel-3 & 2016–present & 98.6 & 27 & 0.3 & 104 \\ SWOT 9 & Planned on 2021 & 77.6 & 21 & 0.1 & 0 \\ JASON-CS 10  & Planned on 2022 & 66 & 10 & 0.3 & 315 \\ SENTINEL-6 & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & & & \\ \hline \hline \end{tabular}  
* Geodetic Satellite. 2 European remote sensing satellite. 3 Topography Experiment/Poseidon. 4 GEOSAT Follow-On satellite. 5 Environmental Satellite. 6 Earth Explorer Opportunity Mission. 7 Haiyang-2/Ocean-2. 8 Satellite with Argos (Data Collection System) and ALiKa (Altimeter in Ka-band). 9 Surface Water Ocean Topography Mission.  
Footnote 10: footnotemark: [ENDFOOTNOTE]  
Jason Continuity of Service Mission.  
\end{table} 
Table 1: Satellite radar altimetry missions. error (RMSE) of 70 cm was estimated between the satellite and in situ measurements. Since then, with new generations of satellites, the spatial resolution and the accuracy of the orbit determination have both improved, thereby increasing the accuracies of the estimation results. Accordingly, several studies have since focused on lakes and large rivers with scales, ranging from 1000 km\({}^{2}\) to 80,000 km\({}^{2}\), and demonstrated good results [12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27]. For example, [PERSON] et al. [17] used Environmental Satellite (Envisat) and CryoSat-2 SAR data to retrieve the water levels over Vaenern (Sweden, 5650 km\({}^{2}\)) and Lake Okeechobee (Florida, 1900 km\({}^{2}\)), and obtained good accuracies with RMSEs, varying from 4 cm to 9 cm between the satellite-retrieved water levels and in situ measurements.