Retrieval of sound-velocity profile in ocean by employing Brillouin scattering LiDAR

Abstract

Accurate remote sensing of the sound velocity profile of the upper-ocean mixed layers is of major important in oceanography, especially in underwater acoustic communication. However, the existing technologies cannot realize fast and real-time detection on sound velocity profile, a cost efficiency, flexibility, and real-time remote sensing technique is still highly urgent. In this paper, we propose a novel approach based on stimulated Brillouin scattering (SBS) LiDAR for retrieving the sound velocity profile. The sound velocity profiles in the upper-ocean mixed layer of South China Sea were retrieved theoretically and experimentally. We simulated the sound velocity profile of the upper-ocean mixed layer in South China Sea by using the Del Grosso algorithm and the data of temperature, salinity, depth selected from the World Ocean Atlas 2018 (WOA18). We designed a special ocean simulation system to measure the sound velocity in seawater with different temperatures, salinities, and pressures through measuring the frequency shift of SBS. Based on the measured sound velocities, we built a retrieval equation to express the sound velocity as a function of temperature, salinity, and pressure. Then, we retrieved the sound velocity profile of the upper-ocean mixed layer of South China Sea by using the retrieval equation. The results show that the retrieved sound velocity profile is good agreement with the theoretical simulation, and the difference between them is approximately 1∼2 m/s. Also, we have analyzed the differences between the theoretical simulation and experimental measurement. This work is essential to future application for remote sensing the sound velocity distribution profiles of the upper-ocean mixed layers by using the Brillouin LiDAR technique.