The design and processing algorithm of oceanic LIDAR requires an effective lidar simulator. Currently, most simulation methods for lidar signal propagation in seawater use elastic scattering. In this study, a new semi-analytical Monte Carlo (MC) model for oceanic lidar inelastic signals is developed to investigate chlorophyll fluorescence and Raman scattering in seawater. We also used this model to simulate the echo signal of high spectral resolution lidar (HSRL) in the particulate and water molecular channels. Using this model, the effects of chlorophyll concentration, multiple scattering, receiving field of view (FOV), scattering phase function (SPF), receiver full width at half maximum (FWHM) and inhomogeneous seawater were investigated. The feasibility and effectiveness of the model were verified by the lidar equation under small and large FOVs. The results showed that chlorophyll concentration and vertical structure and multiple scattering have considerable and integrated effects on echo signals, which could provide a reference for the design of oceanic fluorescence and HSRL lidar systems and contribute to the development of processing algorithms.

The next-generation FengYun-3H satellite carrying a greenhouse gas absorption spectrometer (GAS) is planned for launch by 2024 with a strengthened ability to help researchers understand the global carbon cycle. However, assessments of the atmospheric CO₂-detection capabilities of GAS are still incomplete, mainly in the following aspects: previous studies on the spectral range of GAS instruments often used the weak absorption band of CO₂ molecules (1.61 μm); research on the measurement accuracies of different atmospheric environments above oceans is lacking; and most studies considered land surfaces as the bottom boundaries. Here, we simulated high spectral CO₂ absorption spectra in both the strong and weak bands (2.06 and 1.61 μm) while considering the effects of different instrumental (spectral resolution and sampling rate) and environmental (wind speed, visibility, and rough sea surface) parameters. This is the first atmospheric CO₂ absorption spectrum study to consider rough-sea-surface effects. The preliminary results show that the root mean squared error (RMSE) and mean absolute difference (MAD) values of the atmospheric CO₂ transmittance spectra of GAS are 0.031 and 0.011, respectively, in the 1.61 μm band and 0.05 and 0.033 in the 2.06 μm band, revealing that GAS is competitive among similar CO₂ instruments. This study provides a design reference for next-generation GAS instruments and contributes to spectral data CO₂ processing in the above-sea atmosphere.

Ocean LiDAR technology is of high interest and particularly promising for ocean applications. However, its application in complex oceanic environments is often limited by traditional elastic scattering mechanisms. Most existing ocean LiDAR simulation techniques focus primarily on elastic scattering, with limited attention given to inelastic scattering. This paper presents a novel semi-analytical Monte Carlo (MC) simulation method that integrates photon tracking algorithms with polarization state simulation, incorporating non-elastic scattering processes—such as Raman scattering, Brillouin scattering, and fluorescence—and polarization effects. By combining analytical solutions with numerical lidar simulations, the proposed semi-analytical method improves both the precision and efficiency of simulations. Additionally, the method constructs models for fluorescence, Raman scattering, Brillouin scattering, and polarization scattering. These models were used to conduct a detailed analysis of non-elastic scattering and polarization scattering echo signals in stratified water, as well as the effects of chlorophyll concentration on these signals. Compared to traditional MC methods, the semi-analytical approach offers obvious advantages in computational efficiency and accuracy. The study also investigates the impact of multiple scattering, stratified water, particle size distribution, field of view, and spectral bandwidth on non-elastic and polarization scattering echo signals. It highlights the significant influence of multiple scattering on signal detection accuracy and the critical role of changes in optical properties within stratified water. Non-elastic and polarization scattering signals play a crucial role in ocean LiDAR research, and the semi-analytical MC model developed in this paper offers new insights and tools for the understanding and simulation of these signals.

This paper presents a novel Semi-Analytical Monte Carlo (SAMC) method developed for simulating the radiative transfer of full-polarization marine LiDAR signals within complex marine environments. Traditional marine LiDAR techniques, which predominantly rely on the intensity and linear polarization of backscattered signals, encounter limitations in complex settings. To acquire more detailed particulate morphological information, full-polarization LiDAR was introduced by incorporating circular polarization observation capabilities in recent years. However, the comprehensive calculation of full Stokes vectors brings about several inherent drawbacks, such as computational inefficiency and slow convergence. To address these issues, the SAMC method combines photon tracing with semi-analytical full polarization state tracking. It innovatively introduces polarization direction and phase difference variables into the radiative transfer process, thereby enabling the simulation and modeling of circular polarization echo signals. Based on the SAMC model, this study carried out simulation experiments regarding the transmission of lasers with different initial polarization states in water bodies. The impacts of LiDAR parameters, chlorophyll concentration, particle size range, and solar background light on full-polarization backscattered signals were analyzed. The results indicate that changes in polarization states are closely related to chlorophyll concentration and particle size, and multiple scattering effects have a significant influence on full-polarization signals. Moreover, the study explored the influence of the receiver field of view on signal quality and the discrimination ability of full - polarization channels for particles of different sizes. The unique advantages of circular polarized light in resisting solar background interference were also analyzed. This research not only conducts an in-depth analysis of the underwater full-polarization light transmission mechanism but also provides scientific support for the calibration of full - polarization LiDAR backscattered signals. The capacity to distinguish between different particle sizes using full-polarized channels offers a promising approach for the optical remote sensing of marine particle size distributions. The circular polarization's resistance to solar interference and its ability to maintain signal integrity under bright sunlight conditions represent significant advantages for marine remote sensing applications.