A SWOT-Based Approach for High-Resolution Intertidal DEM Mapping in the Elbe Estuary

Mingzhi Sun1 2, Luciana Fenoglio-Marc1, Jiaming Chen1, Jürgen Kusche1, Wei Feng2

1. Institute of Geodesy and Geoinformation, University of Bonn, Bonn 53115, Germany

2. School of Geospatial Engineering and Science, Sun Yat-sen University, Zhuhai 519082, China.

Tidal flats in the Elbe Estuary, Germany, are highly dynamic, with morphology changing rapidly due to tidal cycles, storms, and sedimentation. These changes affect water depth and tidal propagation, making high-resolution digital elevation models (DEMs) essential for hydrodynamic modeling, ecological monitoring, habitat mapping, and sediment transport studies. The Surface Water and Ocean Topography (SWOT) mission provides high-resolution elevation data, offering new potential for generating accurate DEMs of intertidal zones. This study proposes a novel approach to derive high-resolution tidal flat DEMs using only SWOT observations, by integrating backscatter intensity and water surface elevation from the wide-swath KaRIn instrument.

Exploiting the bimodal Gaussian distribution of the backscatter signal in the SWOT_L2_HR_PIXC (v2.0) product, a peak–trough thresholding algorithm is developed to segment the data and extract valid elevation observations over tidal flats during satellite overpasses. Using the backscatter coefficient as a reference, water bodies and tidal flats can be effectively distinguished. A 25-meter resolution DEM of the tidal flats in the Elbe Estuarywas generated. Observations at low tide allow to build an high-quality DEM, therefore the results depend on the repeat cycle of the satellite. The RMSE of the SWOT-derived DEM and ICESat-2 laser altimetry is 0.18 m.

By combining physical principles with data-driven characteristics, this study provides a new data source and a methodology for coastal topographic mapping.