Measurement Of Bulk Viscosity Of Seawater Based On Stimulated Brillouin Scattering

The measurement of bulk viscosity of seawater is of great significance for understanding the physical characteristics of the ocean.Lidar technology based on stimulated Brillouin scattering(SBS)has the advantages of high signal-to-noise ratio and excellent anti-jamming performance of FM measurement.It is able to quickly obtain the bulk viscosity of marine vertical space in a large area.However,in order to achieve this goal,the inversion model of bulk viscosity of seawater including seawater characteristic parameters(temperature,salinity and pressure)and stimulated Brillouin scattering spectral characteristic parameters must be established theoretically and experimentally,making the lidar measurement system to meet the requirements of realtime and accuracy in practical remote sensing.In this paper,the physical process of Brillouin scattering is analyzed,and the inversion model of bulk viscosity of seawater including seawater characteristic parameters such as temperature,salinity,pressure and the characteristic parameters of stimulated Brillouin scattering spectrum is established.On this basis,the SBS lidar system based on Fabry Perot etalon(FPE)and ICCD is used to measure the bulk viscosity of seawater;A high-precision data processing method for fast extraction of stimulated Brillouin scattering linewidth and stimulated Brillouin scattering frequency shift from SBS spectrum signal is proposed.The frequency shift and linewidth of stimulated Brillouin scattering and bulk viscosity in pure water and 32.5 ‰ simulated seawater were measured at 15 ℃ to 30 ℃.The results show that the lidar system based on FPE and ICCD proposed in this paper,combined with the inversion model of bulk viscosity of seawater,realizes the high-precision measurement of bulk viscosity.By analyzing the numerical simulation and experimental results,it is found that temperature has the greatest influence on the linewidth and frequency shift of stimulated Brillouin scattering and bulk viscosity of seawater,followed by salinity and pressure.The research results of this paper lays a theoretical and experimental foundation solidly for the future realization of remote sensing of marine environmental parameters by SBS lidar.