An Estimation of Underwater Sound Velocity using 3D Hydrodinamics Modelling in Madura Strait

Abstract

Madura Strait is one of the busy straits in Indonesia due to the existence of two international ports, Tanjung Perak and Teluk Lamong ports. In order to maintain safety of navigation in this region, bathymetric surveys has to be conducted regularly. The purpose of those survey is to maintain the depth of the shipping lanes and port pools. For that purpose, depth data from the acquisition process has to be corrected properly to obtain the deliverable depth in the nautical chart. One of the corrections that has to be applied is sound velocity correction. To do that correction, the speed of the acoustic wave propagation through the water column has to be collected using Sound Velocity Profiler. This study aims to model the underwater sound speed propagation which can be utilized to correct the measure depth. The study employed the Delft-3D FLOW module to develop a hydrodynamic model in baroclinic mode so the model can produces salinity, temperature, and pressure which vary spatially and temporally. By using these parameters, a near continuous sound velocity model in water column can be estimated using the empirical formula from Chen and Millero (1977). The sound speed value is validated using the Sound Velocity Profiler measurement. The validation was performed at 4 points, and shows a small difference between sound velocity from the model and measurement using RMSE calculation and estimated depth simulation. The RMSE has value between 0.003ms⁻¹ and 0.064ms⁻¹. Based on the estimated depth simulation, the difference between the corrected depth is 0.0005 to 0.001m. This can be claimed as an evidence that the sound velocity model from the study can be applied to get the corrected depth in Madura Strait.