A semianalytic Monte Carlo radiative transfer model for polarized oceanic lidar: Experiment-based comparisons and multiple scattering effects analyses

The polarization characteristic of oceanic lidar returns includes a great deal of seawater information, which plays an important role in subsurface layer detection and seawater optical property retrieval. Along with the microphysical properties of particles, the multiple scattering effect between laser light and particles in seawater is also a source of polarization, which obscures the original depolarization properties of the seawater. However, modeling multiple scattering in polarized oceanic lidar with analytical methods is a complex problem. In this paper, a semianalytic Monte Carlo (MC) polarization radiative transfer model is established to assess the impact of multiple scattering on the backscattering depolarization measurement of oceanic lidar. The MC-simulated lidar returns of both the parallel and perpendicular channels and the depolarization ratios coincide well with the experimental results from three stations in the Yellow Sea of China by shipborne polarized lidar. Further analyses show that the multiple scattering effect enhances the depolarization of seawater; specifically, the depolarization ratio of the lidar return increases with increasing penetration depth, receiver's field of view (FOV), single scattering albedo and beam attenuation coefficient of seawater. This semianalytic polarized MC model is useful for understanding the mechanism of polarized multiple scattering in seawater and for further improving the precision of optical property retrieval using oceanic polarized lidar. (C) 2019 Published by Elsevier Ltd.