On the Performance of Sentinel-3 Altimetry over High Mountain and Cascade Reservoirs Basins: Case of the Lancang and Nu River Basins

Satellite radar altimetry has been widely utilized in hydrological research, particularly with the advent of Sentinel-3, a Synthetic Aperture Radar (SAR) altimeter operating globally and equipped an innovative onboard tracking system referred to as open-loop command (OLTC). Utilizing pseudo-DEM (Digital Elevation Model), controlled through OLTC, holds significant promise for reliable observation inland water bodies. Nevertheless, complex geographical conditions high mountain reservoir river basins pose challenges defining appropriate targets, potentially leading reduced performance Sentinel-3. This study aims comprehensively evaluate Sentinel-3 by selecting Lancang Nu River southwest China case study. These two rivers have similar natural environment, but cascade reservoirs distinguish basin. By analyzing waveform energy from echoes virtual stations (VSs) both (27 VSs basin 39 basin), different modes OLTC versions were compared. The results indicated that detection rate Sentinel-3A increased when transitioning closed-loop mode implementation newer (36.8% 47.4%, 60.5%, 63.2% V5.0, V6.0, V6.1, respectively). Similarly, Sentinel-3B rose 64.3% (OLTC V2.0) 71.4% 75.0% V3.0 V3.1, respectively. Additionally, causing channel expansion better compared (13.0% 35.7%, considerable fluctuations surface caused impoundment led wrong pseudo-DEM, resulting poor regions before V6.0 was updated. low altitude, broad surfaces (>500 m) decreased 100% 0% mode, narrow (<500 40.9% V6.1. Although ability is improving versions, seasonal variations (usually more than 60 levels exceeded size range window (60 m), rendering complete measurement impossible.