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Spaceborne photon-counting LiDAR holds significant potential for shallow-water bathymetry. However, the received photon data often contain substantial noise, complicating the extraction of elevation information. Currently, a denoising algorithm named ordering points to identify the clustering structure (OPTICS) draws people’s attention because of its strong performance under high background noise. However, this algorithm’s fixed input variables can lead to inaccurate photon distribution parameters in areas near the water bottom, which results in inadequate denoising in these areas, affecting bathymetric accuracy. To address this issue, an Adaptive Variable OPTICS (AV-OPTICS) model is proposed in this paper. Unlike the traditional OPTICS model with fixed input variables, the proposed model dynamically adjusts input variables based on point cloud distribution. This adjustment ensures accurate measurement of photon distribution parameters near the water bottom, thereby enhancing denoising effects in these areas and improving bathymetric accuracy. The findings indicate that, compared to traditional OPTICS methods, AV-OPTICS achieves higher F1-values and lower cohesions, demonstrating better denoising performance near the water bottom. Furthermore, this method achieves an average MAE of 0.28 m and RMSE of 0.31 m, indicating better bathymetric accuracy than traditional OPTICS methods. This study provides a promising solution for shallow-water bathymetry based on photon-counting LiDAR data.

This article presents a LiDAR system that utilizes a Fizeau interferometer and photomultiplier tube array to detect the water Rayleigh–Brillouin spectrum, utilized to obtain underwater temperature and salinity synchronizing measurements based on the Brillouin spectral linewidth and shift. Temperature and salinity measurements were conducted in the laboratory to verify the efficiency of the system. The results demonstrate that the LiDAR system can accurately obtain the Rayleigh–Brillouin spectral backscattering profiles of water. Following linear fitting and reconstruction, the retrieved temperature accuracy is ±0.13 °C and salinity accuracy is ±0.16‰. By effectively leveraging the multiparameter information contained in the Rayleigh–Brillouin spectrum, the system achieved precise temperature and salinity measurements. This study provides a reference for marine remote sensing applications

The Brillouin scattering spectrum has been used to investigate the properties of a liquid medium. Here, we propose an improved method based on the double-edge technique to obtain the Brillouin spectrum of a liquid. We calculated the transmission ratios and deduced the Brillouin shift and linewidth to construct the Brillouin spectrum by extracting the Brillouin edge signal through filtered double-edge data. We built a detection system to test the performance of this method and measured the Brillouin spectrum for distilled water at different temperatures and compared it with the theoretical prediction. The observed difference between the experimental and theoretical values for Brillouin shift and linewidth is less than 4.3 MHz and 3.2 MHz, respectively. Moreover, based on the double-edge technique, the accuracy of the extracted temperatures and salinity is approximately 0.1 °C and 0.5%, respectively, indicating significant potential for application in water detection and oceanography.

Optical detection methods such as Rayleigh-Brillouin scattering spectrum can be used for physical parameter measurement in solids, liquids, and gas. In this paper, a new method based on spectral characteristics is proposed to realize temperature and pressure retrieval simultaneously in gas. The characteristics of Rayleigh-Brillouin spectrum are firstly utilized to establish the retrieval model by fitting Tenti-S6 line shape with 3Voigt model at different temperatures and pressures, and then deriving the retrieval equations via regression fitting procedure. Through theoretical and measured error analyses, the characteristic retrieval model based on Rayleigh linewidth and the whole linewidth of Rayleigh-Brillouin scattering spectrum is shown to be optimal. Afterward, the retrieval model is verified using the experimental Rayleigh-Brillouin scattering spectra of N2 and air. The results indicate that, compared with the current method based on the whole linewidth or line shape of spectrum, the proposed method not only produces lower theoretical and retrieval errors but also can simultaneously retrieve the temperature and pressure of gases. The novel retrieval method provides a new idea for obtaining valuable information on gas parameters and promotes the application of Brillouin lidar remote sensing in meteorology and space science.

Brillouin spectroscopy is a powerful tool to measure the water temperature and salinity profiles of seawater. Considering the insufficiency of the current spectral measurement methods in real-time, spectral integrity, continuity, and stability, we developed a new lidar system for spectrum measurement on an airborne platform that is based on a Fizeau interferometer and multichannel photomultiplier tube. In this approach, the lidar system uses time-of-flight information to measure the depth and relies on Brillouin spectroscopy as the temperature and salinity indicator. In this study, the system parameters were first optimized and analyzed. Based on the analysis results, the performance of the system in terms of detection depth and accuracy was evaluated. The results showed that this method has strong anti-interference ability, and under a temperature measurement accuracy of 0.5 °C and a salinity measurement accuracy of 1‰, the effective detection depth exceeds 40.51 m. Therefore, the proposed method performs well and will be a good choice for achieving Brillouin lidar application in seawater remote sensing.