Measurements of the Sea Surface Parameters Using a New Modification of Underwater Sonar on a Marine Platform in the Black Sea

This paper presents the results of experimental measurements of the sea surface parameters during the expedition to a marine platform in the Black Sea near the Katsiveli settlement in October 2018. The measurements were carried out using underwater sonar at small angles of incidence, so the scattering mechanism remains mostly quasi-specular and is well described by tangent plane approximation (Kirchhoff approximation). The method is based on the analysis of spectral and energy characteristics of the reflected acoustic waves at underwater surface waves observation. An important feature of this method is the simultaneous use of multiple antennas with different radiation patterns. The underwater sonar antenna unit consists of one radiating antenna with a symmetrical radiation pattern and three receiving antennas of various shapes: 1 - symmetric, 2 and 3 - fan beam antennas oriented perpendicular to each other. Within the framework of this expedition, the following configuration of the antenna system was used: the width of the symmetric receiving antenna, equal to the widest axis of the fan beam antennas. The main innovation of the underwater sonar is the presence of a builtin two axial inclinometer and a compass in an external unit free from magnetic interference. In this paper, we use the original approach of calibrating the backscattering cross section based on the scattering model and the wave spectrum model. As a result of this procedure, all unknown wave parameters affecting the scattering characteristics were retrieved: the vertical orbital velocity variance, the slope variances along and across the direction of sensing, and the correlation coefficients between slopes and orbital velocity. String wave gauge and wind measurements are used in the experiments to control the effectiveness of proposed algorithms.