Abstract
Fully polarimetric synthetic aperture radar (SAR) can provide detailed information on scattering mechanisms that could enable the target or structure to be identified. This paper presents a method to detect underwater topography in coastal areas using high resolution fully polarimetric SAR data, while less prior information is required. The method is based on the shoaling and refraction of long surface gravity waves as they propagate shoreward. First, the surface scattering component is obtained by polarization decomposition. Then, wave fields are retrieved from the two-dimensional (2D) spectra by the Fast Fourier Transformation (FFT). Finally, shallow water depths are estimated from the dispersion relation. Applicability and effectiveness of the proposed methodology are tested by using C-band fine quad-polarization mode RADARSAT-2 SAR data over the near-shore area of the Hainan province, China. By comparing with the values from an official electronic navigational chart (ENC), the estimated water depths are in good agreement with them. The average relative error of the detected results from the scattering mechanisms based method and single polarization SAR data are 9.73% and 11.53% respectively. The validation results indicate that the scattering mechanisms based methodology is more effective than only using the single polarization SAR data for underwater topography detection, and will inspire further research on underwater topography detection with fully polarimetric SAR data.
Highlights
Underwater features and ocean bathymetry is an indispensable information for coastal engineering and management and coastal resources exploitation and protection [1,2]
They show single polarization Synthetic aperture radar (SAR) image can be used for shallow water depth estimation using linear dispersion relationship with some accuracy that confirm former studies on the swell patterns based method [4,7,18,19,21,22]
An underwater topography detection algorithm based on swell patterns is developed
Summary
Underwater features and ocean bathymetry is an indispensable information for coastal engineering and management and coastal resources exploitation and protection [1,2]. Safely navigating, offshore fishery and aquaculture, research on tide and biodiversity, planning for seawalls and wharf and other human activities are carried out in these areas where water depths less than 100 m. Water depth surveying are carried out by sonar measurements from dedicated vessels, which are accurate for point-measurement, but are expensive and time consuming and difficult in shallow water areas, especially in some special water areas where routine surveying cannot be achieved [2,3]. Synthetic aperture radar (SAR) is an active microwave remote sensor that has the ability to image targets on the earth in both day and night, and for almost all weather conditions [1,4]. SAR is widely applied in earth observation, especially in ocean observation. SAR polarimetry is the Remote Sens. 2017, 9, 560; doi:10.3390/rs9060560 www.mdpi.com/journal/remotesensing
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