o .-based ocean lidar remote sensing technology

Photo: Figure 2 | Schematic diagram of Brillouin’s experimental underwater lidar system for temperature and salinity measurements based on multi-edge technology.
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New post from optoelectronic advance; DOI 10.29026 / or any .2023.220016 Discusses ocean lidar remote sensing technology based on Brillouin scattering spectrometry.

The monitoring of marine environmental information is of great importance in the development of marine science, the preservation of marine rights and interests, the development of marine resources and the establishment of the marine industry. Laser remote sensing has become one of the important means of monitoring the marine environment due to its water penetration, strong energy and high vertical resolution.

Ocean laser remote sensing mainly measures environmental information by analyzing scattered echo energy or spectral information. In the power dimension, the return echo contains a variety of scattered signals and noise, and the echo signal-to-noise ratio is low, which limits the measurement accuracy. Besides, the characteristic information of the echo energy is limited which is only used for single parameter inversion. While different scattering has its own spectral distribution characteristics in the spectral dimension, and the spectrum is not easy to pollute with noise, resulting in a high signal-to-noise ratio. At the same time, the spectrum contains rich information, and multiple environmental elements can be measured by a variety of spectral features. Therefore, the use of lidar spectroscopic detection is an important direction for the development of marine monitoring in the future.

Compared with other scattering spectra, the Brillouin scattering spectrum can be distinguished independently, and the spectrum is stable and has rich information. Simultaneous reversal of sea water temperature and salinity can be achieved by Brillouin spectrum. In addition, the cross-section of Brillouin scattering is large which makes Brillouin detection with strong scattering signal and depth of detection. Therefore, Brillouin spectrometry-based lidar has great potential in marine multiparameter remote sensing.

At present, Brillouin lidar has fully demonstrated its ability to high-resolution measurement of sea water temperature and vertical salinity from theory, simulation and laboratory experiments. However, the current Brillouin spectrophotometric technology has requirements for real-time application, safety of spectroscopic detection, rapid and continuous measurement in the application of simultaneous real-time measurement of subsurface seawater temperature and salinity vertical profile. Therefore, breaking through the technical bottleneck of real-time measurement and continuous measurement of the full Brillouin scattering spectrum is an important research topic for enhancing Brillouin lidar application.

According to the actual measurement needs of Brillouin lidar, the research team of Professor Kun Liang of Huazhong University of Science and Technology, together with Beijing Institute of Space Electromechanical Research and University of Electronic Science and Technology, conducted research work using Brillouin spectrum to achieve high-accuracy lateral measurement of underwater temperature and salinity.

The team proposed Brillouin’s method for double-edge spectrometry along with PMT. Based on the notion of scattered reconstruction, the energies of two or more local spectra are measured by means of a multi-edge filter. Then, with the help of the Brillouin scattering spectrum function, the complete Brillouin scattering spectrum is obtained at very high resolution using energies. Finally, the characteristic spectral parameters of the scattering spectrum are extracted and used for the simultaneous reflection of sea water temperature and salinity.

The measurement technology is based on a wide-band multi-channel edge filter to ensure that each channel can transmit large spectral power, which theoretically ensures the ability of the system to measure bathymetry. The entire hyper-resolution spectrum is reconstructed according to the scattering low-resolution narrowband filter, and the high-resolution measurement of the Brillouin spectrum is achieved. Therefore, this technique takes into account the detection depth and measurement accuracy of the system. In addition, a high-sensitivity, short response time photovoltaic conversion module and a high sampling rate data acquisition module are also used in the system to ensure continuous rapid measurement of seawater temperature and salinity.

According to the principle of Brillouin detection technology, the team developed a lidar test system. This system adopts transceiver coaxial design, and drops the laser into the water through the telescope system to generate Brillouin scattering signal. The backscattered signal received by the telescope system is first passed through an iodine pool to filter out Rayleigh scattering background noise and counter scattering. Then, the remaining Brillouin scattering light is divided into two parts. One part is collected by PMT as a reference signal (I . signalg), and the other part after the double edge filter composed of two Fabry Perot etalon collected by two PMTs (signals I1 and me2). Finally, based on the obtained relative edge energies1 / Ig and me2 / Igthe corresponding Brillouin scattering spectra are obtained with the notion of scattered reconstruction.

After obtaining the spectrum using the above system, with the processes of data characteristic analysis, spectral feature extraction data correction, temperature and salinity inversion model, the system achieves the measurement with a temperature accuracy of 0.5 °C and a salinity accuracy of 1psu, which has reached the highest level in the world. Overall, the measurement results demonstrate the potential of the Brillouin spectrum detection method in seawater ecological measurement and oceanographic research and provide theoretical and technical support to enhance the practical application of lidar based on Brillouin dispersion.

Article reference: Wang YQ, Zhang JH, Zheng YC, Xu YR, Xu JQ et al. Brillouin scattering spectrometry for fluid detection and applications in oceanography. Opto-Electron Adv 6, 220016 (2023). dui: 10.29026 / or any .2023.220016

Key words: Brillouin scattering spectrum / double edge technology / temperature / salinity / oceanography

Professor Kun Liang’s team, College of Electronic Information and Communication, Huazhong University of Science and Technology, began to focus on the research of Rayleigh Brillouin scattering and remote sensing lidar applications in 2003. In recent years, relying on platforms such as Huazhong University of Science and Technology and the National Photoelectric Research Center in Wuhan , the research group has made impressive research achievements in Rayleigh-Brilloin for remote lidar sensing of atmosphere and seawater. Currently, the team’s laboratory contains two sets of atmospheric lidar systems for measuring wind, temperature and pressure, and two sets of seawater lidar systems for temperature and salt measurement and target detection. Professor Kun Liang has successively presided over many national projects such as the National Natural Science Foundation of China and the National 863 Program. He won two first prizes for scientific and technological progress in Hubei Province and applied for 17 patents. At present, more than 40 papers have been published, of which more than 30 are included by SCI.

Researcher Yun Su’s group of the Beijing Aerospace Electromechanical Research Institute is affiliated with the Core Professional Laboratory of Space Laser Information Sensing Technology of the Chinese Academy of Aerospace Technology. They are mainly engaged in research work in the fields of space optical remote sensing, ocean remote sensing, space optical system design, computational optics, etc. Researcher Su Yun has led several national research projects such as the 863 program, and completed the optical design of a local multi-species optical remote sensing loading system. She has won two provincial and ministerial level awards, and has published more than 30 research articles and more than 80 patents.

The research team led by Professor Hai Feng Lu of the University of Electronic Science and Technology is mainly engaged in research into condensed matter physics and the laser-matter interaction mechanism. In recent years, he has chaired and participated in major state projects, projects of the Natural Science Foundation and projects of opening key national laboratories. The team’s main research areas include laser radiation damage mechanism and pretreatment, Brillouin laser scattering spectrum analysis, high-power internal electromagnetic field generation technology, transmission technology, etc. The research group has published more than 50 papers in international journals such as Phys. Reverend Litt. , Phys. Rev. B, AP. Phys. Lett. , Opt. I wish. , Application. browse. Sciences.

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