Measurement of inherent optical properties of water based on multiple scattering profiles using underwater off-axis single-photon lidar

Accurately measuring inherent optical properties (IOPs) in water is fundamental for characterizing light transmission in aquatic environments and advancing our understanding of biogeochemical processes. Lidar, with its capability for continuous day-and-night observations and strong water penetration, holds great potential for detecting optical parameters in water. However, ocean lidar faces challenges in addressing ill-posed equations and mitigating the effects of multiple scattering when detecting IOPs. In this study, a method for IOP detection based on multiple scattering profiles is proposed and demonstrated. First, a semi-analytic Monte Carlo approach was applied to analyze the relationship between multiple scattering profiles measured by off-axis lidar and IOPs. Next, a tank experiment was conducted to establish an analytical expression for this relationship. Subsequently, field experiments were carried out in the South China Sea using underwater single-photon lidar. Compared to <i>in-situ</i> measurements, the statistical root mean square error values were 0.007 m^-1 for the scattering coefficient, 0.012 m^-1 for the beam attenuation coefficient, and 0.014 m^-1 for the absorption coefficient, validating the feasibility of the proposed method. Overall, this new IOP measurement approach is expected to contribute to advances in ocean biogeochemical cycle research.