SYNTHETIC APERTURE RADAR FOR BATHYMETRIC MAPPING IN NEARSHORE COASTAL WATER

Bathymetric measurements are critical for understanding underwater topography, particularly in nearshore regions where accurate data are essential for navigation, coastal development, and marine resource management. Traditional methods, such as sonar and LiDAR, while accurate, are often

expensive and limited in spatial coverage. Satellite-Derived Bathymetry (SDB) offers an alternative, leveraging remote sensing technologies to infer water depths. Synthetic Aperture Radar (SAR) is a powerful tool for SDB due to its all-weather, day-night imaging capabilities and its ability to capture surface wave patterns influenced by underwater features. This study focuses on applying SAR for bathymetry in the coastal waters near the Onne Port Complex, located in Nigeria's Niger Delta. Initially, Sentinel-1 SAR data were preprocessed for radiometric calibration, speckle filtering, terrain

flattening, and geometric correction. The preprocessed images were then analyzed for wave characteristics using Fast Fourier Transform (FFT), enabling the extraction of dominant wavelengths associated with underwater features. These wave parameters were integrated with Linear Wave Theory to estimate depths. Ultimately, SAR data were compared with NASADEM and the General Bathymetric Charts of the Oceans (GEBCO) datasets to validate and refine depth estimations. Raster calculations and masking techniques were used to extract and visualize bathymetric details. Gridded datasets, such as GEBCO, were used as reference models due to the unavailability of buoy data in the study area. The study highlights SAR's capacity to map shallow water bathymetry, addressing challenges such as limited optical penetration in turbid waters and the lack of in-situ data. While SAR-based bathymetry offers significant advantages, including cost-effectiveness and large-area coverage, it also has limitations. These include the reliance on robust models, sensitivity to environmental factors, and the need for ground-truth calibration. The findings demonstrate the potential of SAR to complement traditional methods, especially in regions with limited accessibility.

Keywords: Satellite-Derived Bathymetry (SDB), Synthetic Aperture Radar (SAR), coastal management, wave pattern analysis