Contemporary ocean colour radiometers and inversion algorithms to derive optical properties and oceanic constituents rely only on the scalar treatment of water-leaving radiance (Lw).

However, Lw polarization components, which contain embedded hydrosol information, have been largely neglected.

Here, a research team led by Dr. HU Bingliang from Xi'an Institute of Optics and Precision Mechanics (XIOPM) of the Chinese Academy of Sciences (CAS) examines Lw polarization characteristics, based on vector radiative transfer (RT) simulation, for determining suspended particulate matter in highly turbid waters.

 Angular distributions of ρp (%) at the TOA under different wavelengths simulated by PCOART with solar zenith angles of 0°, 30°, and 60°, respectively. The three rows correspond to 490 nm, 555 nm, and 670 nm, respectively. (Image by XIOPM)

The RT simulations show that parallel polarization radiance (PPR) can improve the retrieval of Lw, with a higher relative fraction of ocean colour signal to total radiance (Ioc/It) than the total intensity (I).

Moreover, the reflectance for PPR (ρp), compared with that for I, is more sensitive to inorganic particle concentration (IPC) variations, particularly those in the red and NIR bands. Additionally, ρp displays significant directional, and spectral variations with respect to geometrical conditions, and the maximum ρp (~10%) is highly peaked at 555 nm in the solar plane.

Furthermore, the superiority of PPR to retrieve IPCs, based on the back propagation neural network, was discussed with a very high determination coefficient.

Significant improvements in inversion accuracy were observed for PPR with a lower relative deviation (0.901%) than I (3.740%). This study high-lights that PPR might be used as an alternative approach to retrieve Lw and thus to derive biogeochemical parameters, particularly in turbid coastal waters.

(Original research article “International Journal of Remote Sensing” (2020) https://doi.org/10.1080/01431161.2020.1727059)