A Spatial-Domain Crest-Line Tracking Method for Swell-Based Shallow-Water Bathymetry Retrieval from Sentinel-1 SAR Imagery

Shallow-water bathymetry is essential for coastal dynamics, navigation, engineering, and marine-resource management, especially where in situ observations are sparse. This study proposes a wave-stripe-based method for shallow-water bathymetric retrieval from Sentinel-1A VV-polarized SAR imagery. After texture-preserving denoising, multidirectional Gabor enhancement, K-means segmentation, and skeleton tracking, wave-crest centerlines are extracted and local wavelengths are measured as the normal spacing between adjacent crest lines. The dominant wave period is estimated from deep-water wavelengths, and water depth is retrieved using the linear wave dispersion relation. The method was evaluated using five Sentinel-1 acquisitions, with SAR-derived representative wave periods ranging from 12.45 to 14.96 s. Based on the mean retrieval performance across the five acquisitions, the 0–20 m depth range yielded an RMSE of 3.87 m, an MAE of 3.56 m, and r = 0.95, while the corresponding values for 0–50 m were 6.06 m, 5.02 m, and 0.97, respectively. The most stable performance occurred within the 5–20 m depth range. The method reduces fixed-window spectral averaging and improves the representation of local wavelength variability, supporting rapid bathymetric mapping along open-coast environments with clear swell-induced wave stripes, relatively gentle bathymetric slopes, and limited field observations.