The importance of sound velocity determination for bathymetric survey

Abstract

Bathymetric surveys are carried out whenever there is a need to know the exact morphological trend of the seabed. For a correct operation of the echo sounder, which uses the principle of acoustic waves to scan the bottom and determine the depth, it is important to accurately determine the sound velocity in water, as it varies according to specific parameters (Density, Temperature, and Pressure). In this work, we want to analyse the role of sound velocity determination in bathymetric survey and its impact on the accuracy of depth measurement. The experiments are conducted on data set provided by “Istituto Idrografico della Marina Militare Italiana” (IIM), the official Hydrographic Office for Italy, and acquired in the Ligurian sea. In our case, the formulas of Chen & Millero (UNESCO), Medwin, and Mackenzie were applied. The introduction of errors on chemical-physical parameters of the water column (Temperature, Pressure, Salinity, Depth) simulating inaccurate measurements, produces considerable impacts on sound velocity determination and subsequently a decrease of the depth value accuracy. The results remark the need to use precise probes and accurate procedures to obtain reliable depth data.