Abstract's details
Performance assessment of the water surface elevation of HR SWOT products based on comparisons with in-situ networks and in-flight nadir altimetry missions
Event: 2025 SWOT Science Team Meeting
Session: Hydrology: HR SWOT Data (Data Validation & Enhancement)
Presentation type: Oral
The Surface Water and Ocean Topography (SWOT) mission, conducted by CNES and NASA was successfully launched on 16 December 2022. It provides unprecedented 2D observations of the sea-surface height and mesoscale structures as well as water surface elevation over continental water surfaces. An interferometric SAR altimeter, the Ka-band Radar Interferometer (KaRIn), is designed to cover two 50-km cross-track swaths. The first seven months were dedicated to Calibration/Validation (Cal/Val) with a 1-day orbit over limited areas. The nominal phase (Science phase) follows with its 21-day repeat cycle and global spatial coverage up to 78° latitude.
This study is part of the performance assessment of the SWOT over inland water led by CNES on the French side. The High Rate (HR) mode of KaRIn, dedicated to hydrology, provides several HR SWOT products. Their performance is assessed by comparison with reference measurements. Although specific in-situ Cal/Val sites have been equipped for the validation of HR SWOT products over lakes and rivers, the existing in-situ networks are essential, especially for statistical validation that requires a significant number of comparisons. In addition, nadir altimetry measurements (Sentinel-3A/B, Sentinel-6, ICESat-2, etc.) can be used as external measurements on a large number of lakes and rivers, or to level existing gauges.
Our analysis consists of using data from the French (SCHAPI), Swiss (BAFU) and American (USGS) in situ networks to estimate the performance of SWOT HR elevation data (PIC and PID versions). In addition, we use measurements from current nadir altimetry missions (Sentinel-3A/B, Sentinel-6, ICESat-2) to assess performance over a large number of water bodies. SWOT HR data are compared with the station networks available on the Copernicus Global Land Service. ICESat-2 data (ATL13) completes the analysis of tens of thousands of lakes. We have also set up an innovative method for levelling existing gauges with ICESat-2 (ATL13), increasing the number of in situ references on which the accuracy of KaRIn can be estimated.
We will first focus on lakes and rivers, observed daily by SWOT during the Cal/Val phase, to assess the performance of HR SWOT products for monitoring short timescale variation of the water surface elevation. We will then take advantage of the global spatial coverage of the SWOT mission during the Science phase for broader statistical analysis.
Back to the list of abstractThis study is part of the performance assessment of the SWOT over inland water led by CNES on the French side. The High Rate (HR) mode of KaRIn, dedicated to hydrology, provides several HR SWOT products. Their performance is assessed by comparison with reference measurements. Although specific in-situ Cal/Val sites have been equipped for the validation of HR SWOT products over lakes and rivers, the existing in-situ networks are essential, especially for statistical validation that requires a significant number of comparisons. In addition, nadir altimetry measurements (Sentinel-3A/B, Sentinel-6, ICESat-2, etc.) can be used as external measurements on a large number of lakes and rivers, or to level existing gauges.
Our analysis consists of using data from the French (SCHAPI), Swiss (BAFU) and American (USGS) in situ networks to estimate the performance of SWOT HR elevation data (PIC and PID versions). In addition, we use measurements from current nadir altimetry missions (Sentinel-3A/B, Sentinel-6, ICESat-2) to assess performance over a large number of water bodies. SWOT HR data are compared with the station networks available on the Copernicus Global Land Service. ICESat-2 data (ATL13) completes the analysis of tens of thousands of lakes. We have also set up an innovative method for levelling existing gauges with ICESat-2 (ATL13), increasing the number of in situ references on which the accuracy of KaRIn can be estimated.
We will first focus on lakes and rivers, observed daily by SWOT during the Cal/Val phase, to assess the performance of HR SWOT products for monitoring short timescale variation of the water surface elevation. We will then take advantage of the global spatial coverage of the SWOT mission during the Science phase for broader statistical analysis.