Shangguan Mingjia, Liao Zhuoyang, Guo Yirui
Opt Express. 2024 Feb 26;32(5):8189-8204. doi: 10.1364/OE.509596.
Lidar has emerged as a promising technique for vertically profiling optical parameters in water. The application of single-photon technology has enabled the development of compact oceanic lidar systems, facilitating their deployment underwater. This is crucial for conducting ocean observations that are free from interference at the air-sea interface. However, simultaneous inversion of the volume scattering function at 180° at 532 nm (βm) and the lidar attenuation coefficient at 532 nm ( ) from the elastic backscattered signals remains challenging, especially in the case of near-field signals affected by the geometric overlap factor (GOF). To address this challenge, this work proposes adding a Raman channel, obtaining Raman backscattered profiles using single-photon detection. By normalizing the elastic backscattered signals with the Raman signals, the sensitivity of the normalized signal to variations in the lidar attenuation coefficient is significantly reduced. This allows for the application of a perturbation method to invert βm and subsequently obtain the . Moreover, the influence of GOF and fluctuations in laser power on the inversion can be reduced. To further improve the accuracy of the inversion algorithm for stratified water bodies, an iterative algorithm is proposed. Additionally, since the optical telescope of the lidar adopts a small aperture and narrow field of view design, tends to the beam attenuation coefficient at 532 nm (cm). Using Monte Carlo simulation, a relationship between cm and is established, allowing cm derivation from . Finally, the feasibility of the algorithm is verified through inversion error analysis. The robustness of the lidar system and the effectiveness of the algorithm are validated through a preliminary experiment conducted in a water tank. These results demonstrate that the lidar can accurately profile optical parameters of water, contributing to the study of particulate organic carbon (POC) in the ocean.
激光雷达已成为一种用于垂直测量水中光学参数的有前景的技术。单光子技术的应用推动了紧凑型海洋激光雷达系统的发展，便于其在水下部署。这对于进行不受海 - 气界面干扰的海洋观测至关重要。然而，从弹性后向散射信号中同时反演532 nm处180°的体积散射函数（βm）和532 nm处的激光雷达衰减系数（ ）仍然具有挑战性，特别是在受几何重叠因子（GOF）影响的近场信号情况下。为应对这一挑战，本研究提出增加一个拉曼通道，利用单光子探测获取拉曼后向散射剖面。通过用拉曼信号对弹性后向散射信号进行归一化，归一化信号对激光雷达衰减系数变化的敏感度显著降低。这使得可以应用微扰方法反演βm并随后获得 。此外，还可以减少GOF和激光功率波动对反演的影响。为进一步提高分层水体反演算法的精度，提出了一种迭代算法。另外，由于激光雷达的光学望远镜采用小孔径和窄视场设计， 趋向于532 nm处的光束衰减系数（cm）。利用蒙特卡罗模拟，建立了cm与 的关系，从而可以从 推导出cm。最后，通过反演误差分析验证了算法的可行性。通过在水箱中进行的初步实验验证了激光雷达系统的稳健性和算法的有效性。这些结果表明，激光雷达能够准确测量水体的光学参数，有助于海洋中颗粒有机碳（POC）的研究。
