Brillouin shift and linewidth measurement based on double-edge detection technology in seawater
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Brillouin shift and linewidth measurement based on double‑edge detection technology in seawater K. Liang1 · R. Zhang1 · Q. Sun2 · Y. Xu1 · H. Wu3 · P. Zhang1 · B. Zhou1 Received: 27 March 2020 / Accepted: 30 August 2020 / Published online: 17 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The seawater salinity and temperature of an ocean are key parameters required for environmental evaluation, with Raman and Brillouin scattering techniques offering a potentially accurate approach. A method for Brillouin scattering spectrum measurement based on a double-edge technique is proposed, and a retrieval model for simultaneously acquiring Brillouin shifts and linewidths is built. The accuracy of the proposed retrieval model is analyzed using simulations, and the results show that this double-edge technique provides good performance in terms of Brillouin scattering spectrum reconstitution and is a feasible method for simultaneous seawater temperature and salinity inversion.
1 Introduction Raman and Brillouin scattering caused by the interaction between a laser and seawater molecules are related to both temperature and salinity, and remote sensing of these properties can be realized by detecting these two types of scattering spectrum [1, 2]. Because of the large frequency shift, wide spectrum, and relatively easy detection provided by Raman scattering, developments have been made in seawater temperature and salinity measurement using Raman scattering [3, 4]. However, from the perspective of scattering mechanisms, the Brillouin scattering cross-section is larger than that of Raman scattering, which results in a stronger echo energy intensity and deeper detection distance. In addition, the Brillouin scattering spectrum frequency shift is smaller and its distribution in the frequency domain is narrower than the Raman spectrum, while the corresponding background noise of a Brillouin scattering effective spectrum segment is lower, with a higher signal-to-noise ratio [5]. These advantages suggest that Brillouin scattering light detection and * B. Zhou [email protected] 1
School of Electronics and Information Engineering, Huazhong University of Science and Technology, Wuhan 430074, P.R. China
2
Beijing Institute of Space Mechanics and Electricity, Beijing 100076, China
3
The Third Department, China Ship Research and Development Academy, Wuhan 430074, China
ranging (lidar) is an important avenue for the development of seawater temperature and salinity measurement. As a new detection technology, Brillouin lidar has already been used for ocean remote sensing. Through the extraction of chrematistic Brillouin spectrum parameters such as Brillouin shift and linewidth (full width at half maximum), the inversion of ocean environmental parameters, such as acoustic velocity, temperature, and salinity, and underwater target detection may be realized [6, 7]. In Brillouin lidar applications, the critical step is to accurately obtain the Brillouin spectrum. In general, a scanning Fabry–Per
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