Directional variations in parallel polarized water-leaving radiance for suspended particulate matters in coastal waters based on radiative transfer simulation

Abstract

The inversion of total suspended particulate matter (TSM) from ocean color remote sensing data in coastal waters is still highly inaccurate due to contributions of various oceanic constituents and non-linear independently variation of each other. Since the absorption and scattering by molecules, aerosols, and hydrosols and reflection, transmission over the sea surface, the initially completely unpolarized sunlight becomes partially polarized after transmitting in the coupled atmosphere-ocean system (AOS). Hence, the polarization of the sunlight, which contains embedded information on atmospheric and water optical properties, has largely been neglected. In addition, the parallel polarization radiance (PPR) has two significant advantages in effectively diminishing the sun-glint contamination and enhancing the ocean color signal at the top-of-atmosphere (TOA). In this study, the directional variations in parallel polarized water-leaving radiance of suspended particulate matters in coastal waters, based on the vector radiative transfer simulations (RT), were examined. The simulations reveal that the traditional radiation intensity (I) and parallel polarization radiance (PPR) display significant multidirectional and spectral variations with respect to the observation geometries, and TSM concentrations. Moreover, the water-leaving (Lw) radiance for I and PPR have the same angular distribution pattern and magnitude under different bands. In addition, the relative fraction of Lw to Lt for PPR is large than I, indicating that the PPR can improve to retrieve the Lw radiance at the TOA. Furthermore, an exponent relationship between the Rrs_p and the TSM concentration has been established with low corresponding AD (1.258%) and RMSE (0.202). It demonstrates that the polarization of the Lw radiance is closely related to oceanic constituents, and has great potential for the retrieval of TSM concentrations.