The retrieval of scattering coefficient of marine particles from polarimetric observations

摘要

Polarized light in the oceans carries intrinsic information that can be utilized to estimate the optical and microphysical properties of the oceanic hydrosols. It is especially sensitive to the scattering coefficient, which cannot be retrieved from the unpolarized light used in current ocean color remote sensing algorithms. Through the unpolarized remote sensing reflectance (R_(rs)), these classical algorithms can only estimate backscattering coefficients b_b, but the total scattering coefficient b could be solely retrieved based on the characteristics of polarized light. The correlation is quantified in this paper. Based on extensive simulations using the vector radiative transfer program RayXP, the attenuation-to-absorption ratio (c/a), from which b is readily computed, is shown to be closely related to the degree of linear polarization (DoLP). The relationship is investigated for the upwelling polarized light for several wavelengths in the visible part of the spectrum, for a complete set of viewing geometries, and for varying concentrations of phytoplankton, non-algal particles, and color dissolved organic matter (CDOM) in the aquatic environment. It is shown that there is an excellent correlation between the DoLP and c/a for a wide range of viewing geometries. That correlation is investigated theoretically using fitting techniques, which show that it depends not only on the general composition of water but also on the particle size distribution (PSD) of the (mainly non-algal) particles. A large dataset of Stokes components for various water compositions, measured in the field with a hyper-spectral and multi-angular polarimeter, then provides the opportunity to validate the parameterized relationship between DOLP and c/a. This study opens the possibility for the retrieval of additional inherent optical properties (IOPs) from air- or space-borne DoLP measurements of the ocean.