Knowledge of underwater features and ocean bathymetry plays a significant role in coastal engineering and management, resource exploitation, navigation, research on tide and biodiversity, planning for seawalls and wharves, offshore fisheries, and aquaculture. Shallow water depth surveying is essential for the protection of vessels during navigation. Conventionally, depth charts are obtained by sonar measurements carried out from dedicated vessels, which are expensive and time-consuming, and problematic in shallow water areas.
Remote sensing techniques may offer an alternative method that can be used to reduce the cost and labor needed for underwater topographic surveying and mapping. Therefore, remote sensing, due to its high ability to collect information in a short time and a wide geographical area, will be a very suitable solution for many studies and engineering projects in coastal areas. This issue is critical in Iran, which has a long coastline. In this study, an attempt was made to prepare a depth survey map of the coastal areas of the Oman Sea coast of Jask port region by implementing the swell wave spectral pattern analysis algorithm on Sentinel-1 satellite images. Synthetic Aperture Radar (SAR) is an active remote sensor that is fairly weather insensitive and has global coverage. It provides two-dimensional (2D) information on the ocean surface. Under favorable conditions, it can detect topographic seafloor features in shallow water areas.
This paper presents a practical method for shallow water depth estimation based on swell patterns in SAR images with two different data for wave period. This method is based on the refraction and wavelength changes of swell waves in coastal waters and can measure depth in medium-depth waters. The Linear Wave Theory in waters with medium depth establishes a relationship between depth, wavelength, and period of swell waves. Two-dimensional Fourier analysis was used to calculate the wavelength of swell waves, and the accuracy of calculating the wave peak was increased by applying a frequency filter. One scene of Sentinel-1 SAR image over the Jask coastal region is chosen for investigation. The estimated water depths from the SAR image using the ERA-5 wave period are compared with the Bathymetric map of Jask. The average absolute error is within 0.992 m, with root mean square error within 1.361m with the average relative error less than 6.05%. The estimated water depths from the SAR image using the estimated wave period from the deepwater image are compared with the Bathymetric map of Jask. The average absolute error is within 0.811 m, with root mean square error within 1.125 m with the average relative error less than 5.051%. This indicates that the estimated wave period from the deepwater image is better for water depth estimation than using the ERA-5 wave period. Also, Sentinel-1 SAR can detect wave shoaling and refraction in depths between 10 m and 25 m because of its high resolution. The method can be used for water depth with a 10 m detection with reasonable accuracy within the test area. Using Spectral Analysis in Deep Water Range make 17% improvement in depth derivation Accuracy Compared to the Global ERA-5 Wave Model in the Range of 0 to 25 Meters, and 30% Improvement in the Range of 20 to 25 Meters.