Reassessing System Parameter Optimization in Enhancing Oceanic Lidar Penetration Depth Under Multiple Scattering

Abstract

Lidar is a key technique for 3-D ocean observation, and improving its penetration depth has long been a central objective in system design and optimization. However, multiple scattering induces lateral photon redistribution, causing time-of-flight-based penetration-depth estimates to be overestimated due to misinterpretation of delayed photons as deeper signals. Therefore, the actual contribution of improvements in key lidar system parameters—including laser pulse energy, receiver aperture ( $D$ ), receiver field of view (FOV), and transmitted wavelength—to penetration-depth enhancement should be critically reassessed. Here, a semianalytical Monte Carlo (MC) model is developed to simulate lidar backscattering signals in typical Case-1 waters, assuming a vertically homogeneous water column and neglecting surface wave effects. Simulations are performed across a broad range of chlorophyll-a concentrations (Chl- $a$ ) and for multiple observational configurations, including spaceborne, airborne, shipborne, and underwater platforms. Photon step lengths and corresponding physical depths are simultaneously tracked to quantify effective penetration depth. The results demonstrate that system lidar parameter optimization markedly improves effective penetration depth under weak multiple-scattering conditions, whereas its impact becomes marginal when multiple scattering is strong. Notably, in coastal waters, the conventionally assumed benefits of enlarging the FOV or shifting the transmitted wavelength toward the green band are generally ineffective in enhancing effective penetration depth. Sensitivity analyses using different scattering phase functions (SPFs) yield consistent conclusions. This study provides a quantitative reassessment of lidar system parameter optimization under multiple-scattering conditions, refines the understanding of penetration-depth enhancement in optically complex waters, and offers theoretical guidance for the design and performance evaluation of oceanic lidar systems.