Ocean lidar remote sensing technology based on

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image: Fig.2| Schematic diagram of Brillouin’s experimental underwater lidar system for temperature and salinity measurement based on multiwire technology.
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Credit: OAS

A new post from Optoelectronic advances; DOI 10.29026/oea.2023.220016 discusses ocean lidar remote sensing technology based on Brillouin scattering spectrum.

The monitoring of marine environmental information is of great importance for the development of marine science, the maintenance 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 marine environmental monitoring due to its advantages of water penetration, strong energy, and high vertical profile resolution.

Ocean laser remote sensing primarily measures environmental information by analyzing backscattered echo energy or spectral information. In the energy dimension, the backscattered echo contains a variety of scattered signals and noise, and the signal-to-noise ratio of the echo is low, which limits the measurement accuracy. Furthermore, the echo energy characteristic information is limited and is only used for single parameter inversion. While the different dispersions have their own spectral distribution characteristics in the spectral dimension, and the spectrum is not easy to be polluted by noise, leading to a high signal-to-noise ratio. At the same time, the spectrum contains rich information, and measurement of multiple environmental elements can be performed through a variety of spectral features. Therefore, lidar using spectral 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 independently distinguished, and the spectrum is stable and has a large amount of information. Simultaneous inversion of the temperature and salinity of seawater can be performed using the Brillouin spectrum. In addition, the Brillouin scattering cross section is large, which makes the Brillouin detection have a strong scattering signal and detection depth. Therefore, lidar based on Brillouin spectrum measurement has great potential in marine multiparameter remote sensing.

At present, Brillouin lidar has fully demonstrated its ability in high-precision measurement of seawater temperature and vertical salinity profile in theory, simulation, and laboratory experiments. However, the existing Brillouin spectral measurement technology has the application requirements of real-time spectral detection integrity and rapid and continuous measurement in the real-time synchronous measurement application of seawater subsurface temperature and profile. salinity vertical. Therefore, overcoming the technical bottleneck of real-time and continuous measurement of the entire Brillouin scattering spectrum is an important research topic to promote the application of Brillouin lidar.

According to the actual measurement needs of Brillouin lidar, the research group of Prof. Kun Liang of Huazhong University of Science and Technology, together with the Beijing Space Electromechanical Research Institute and the University of Electronic Science and Technology, carried out the research work of the use of the Brillouin spectrum. for performing high-precision profile measurements of temperature and salinity underwater.

The team proposed the double-edged Brillouin spectrum measurement method combined with PMT. Based on the idea of ​​sparse reconstruction, the energies of two or more narrowband local spectra are measured by a multi-edge filter. Then, with the help of the Brillouin scattering spectrum function, the full Brillouin scattering spectrum with ultra-high resolution is obtained by using the energies. Finally, the spectral characteristic parameters of the scattering spectrum are extracted and used for the synchronous inversion of seawater temperature and salinity.

The measurement technique adopts a wideband multi-channel edge filter to ensure that each channel can transmit large spectral energy, which theoretically guarantees the bathymetric capacity of the system. The full super-resolution spectrum is reconstructed according to the sparse low-resolution narrowband filter and the high-precision measurement of the Brillouin spectrum is performed. Therefore, this technique considers the depth of detection and the measurement accuracy of the system. In addition, the photoelectric conversion module with high sensitivity and short response time, and the high sampling rate data acquisition module are also used in the system to ensure fast and continuous measurement of the temperature and salinity profile of the seawater.

According to the Brillouin detection technology principle, the team developed a lidar test system. This system adopts a coaxial transceiver design, and the laser is incident on the water through the telescope system to generate the Brillouin scattering signal. The backscattered signal received by the telescope system is first passed through the iodine pool to filter out Rayleigh scattering and meter scattering background noise. The remaining Brillouin scattering light is then split into two parts. PMT picks up a part as reference signal (signal Igram), and the other part after the double edge filter composed of two Fabry Perot etalon is picked up by two PMTs (signals I1 and metwo). Finally, based on the two relative edge energies obtained I1 / MEgram and metwo / MEgramthe corresponding Brillouin scattering spectra are obtained with the idea of ​​sparse reconstruction.

After obtaining the spectrum using the above system, with the data feature analysis, spectral feature extraction data correction, and temperature and salinity inversion model operations, the system performs the measurement with a temperature accuracy of 0, 5℃ and a salinity accuracy of 1psu, which has reached the highest level in the world. Overall, the measurement results show the potential of the Brillouin spectrum detection method in the measurement of environmental elements of seawater and oceanographic research and provide theoretical and technical support to promote the practical application of scatter-based lidar. of Brillouin.

Item reference: Wang YQ, Zhang JH, Zheng YC, Xu YR, Xu JQ et al. Brillouin scattering spectrum for liquid detection and applications in oceanography. advanced optoelectronics 6, 220016 (2023). doi: 10.29026/oea.2023.220016

Keywords: Brillouin scattering spectrum / double edge technique / temperature / salinity / oceanography

Professor Kun Liang’s team, School of Electronic Information and Communication, Huazhong University of Science and Technology, began to focus on the research of Rayleigh Brillouin lidar and scattering remote sensing applications in 2003. In recent years, relying On platforms such as Huazhong University of Science and Technology and Wuhan National Photoelectric Research Center, the research group has made influential research achievements in remote sensing of atmosphere and seawater with Rayleigh Brillouin scattering lidar. . Currently, the team’s lab has two sets of atmospheric lidar systems for measuring wind, temperature, and pressure, and two sets of seawater lidar systems for measuring temperature, salt, and target detection. Professor Kun Liang has successively chaired many national projects such as the National Natural Science Foundation of China and the National 863 program. He won 2 first prizes of scientific and technological progress in Hubei Province and applied for 17 invention patents. Currently more than 40 articles have been published, of which more than 30 are included in SCI.

The Yun Su research group at the Beijing Space Electromechanical Research Institute is subordinate to the Central Space Laser Information Detection Technology Professional Laboratory of the Chinese Academy of Space 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 chaired many domestic research projects, such as the 863 program, completed the optical design of the domestic multi-type space optical remote sensing charging system. He won 2 provincial and ministerial awards, published more than 30 articles in the research field, and more than 80 patents.

The research team led by Professor Hai-Feng Lü from the University of Electronic Science and Technology is mainly engaged in researching the physics of condensed matter and the interaction mechanism between laser and matter. In recent years, he has chaired and participated in major state projects, foundational natural science projects, and national key laboratory opening projects. The main research fields of the team include laser irradiation damage mechanism and pretreatment, Brillouin laser scattering spectrum analysis, high-power intrinsic vortex electromagnetic field generation and transmission technology, etc. The research group has published more than 50 articles in international journals such as Phys. Rev. Lett., Phys. Rev. B, App. physics lett., opt. let., appl. Browse. science

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