Estimation of Coastal Bathymetry Using Wavelets

Diogo Santos,Tiago Abreu,Paulo A Silva,Paulo Baptista

doi:10.3390/jmse8100772

Diogo Santos, Tiago Abreu + Show 2 more

Open Access

https://doi.org/10.3390/jmse8100772

Copy DOI

Abstract

When waves propagate in coastal areas at depths lower than one half the wavelength, they exhibit a different signature at the sea surface and the observed wavelength pattern enables inferring bathymetries. Commonly, a spectral analysis using the fast Fourier transform (FFT) is employed to derive wavelength and wave direction of swell waves, in nearshore regions. Nevertheless, it is recognized that this method presents limitations, particularly regarding depth inversion limits that do not allow obtaining bathymetric data close to the shoreline. This work explores a wavelet spectral analysis to obtain bathymetric data. This new imaging methodology is applied over different seafloors with 2D and 3D features such as longshore bars or headlands. The synthetic images of the water surface are generated from a numerical Boussinesq-type model that simulates the propagation of both regular and irregular waves. The spectral analysis is carried to estimate the water depths, which are validated with the model’s bathymetry. Wavelet image processing methodology shows very positive results, revealing the capabilities of this new methodology to map shallow marine environments.

Highlights

The nearshore area is an extremely dynamic system, with variations in its morphology over short periods of time
These methods, presenting a very high precision, are relatively expensive and difficult to operate in shallow waters, and their use depends on favorable weather and wave conditions [1], so monitoring is not done regularly
Regardless of the cutoff filter, the results revealed a systematic undesirable behavior, that is, good results were only felt in parts of the domain, depending on the adopted values to filter the wavelengths

Summary

Introduction

The nearshore area is an extremely dynamic system, with variations in its morphology over short periods of time Due to these rapid variations, constantly monitoring the morphology of the seafloor, especially in coastal and harbor areas, is relevant for navigation safety and in terms of coastal erosion management. The most used methods for monitoring the seafloor are based on acoustic systems (e.g., single and multibeam echosounder). These methods, presenting a very high precision, are relatively expensive and difficult to operate in shallow waters, and their use depends on favorable weather and wave conditions [1], so monitoring is not done regularly. Satellite images allow monitoring the water depth, covering large and remote areas, where the seafloor topography can change relatively fast due to storms [2,3,4]

Methods

Results

Discussion

Conclusion