Hyperspectral polarimetric imaging of the water surface and retrieval of water optical parameters from multi-angular...

Total and polarized radiances from above the ocean surface are measured by a state-of-the-art snapshot hyperspectral imager. A computer-controlled filter wheel is installed in front of the imager allowing for recording of division-of-time Stokes vector images from the ocean surface. This system, to the best of our knowledge, for the first time provided a capability of hyperspectral polarimetric multi-angular measurements of radiances from above the water surface. Several sets of measurements used in the analysis were acquired from ocean platforms and from shipborne observations. Measurements made by the imager are compared with simulations using a vector radiative transfer (VRT) code showing reasonable agreement. Analysis of pixel-to-pixel variability of the total and polarized above-water radiance for the viewing angles of 20°-60° in different wind conditions enable the estimation of uncertainties in measurements of these radiances in the polarized mode for the spectral range of 450-750 nm, thus setting requirements for the quality of polarized measurements. It is shown that there is a noticeable increase of above-water degree of linear polarization (DoLP) as a function of the viewing angle, which is due both to the larger DoLP of the light from the water body and the light reflected from the ocean surface. Results of measurements and VRT simulations are applied for the multi-angular retrieval of the ratio of beam attenuation coefficient (c_tot) to absorption coefficient (a_tot) in addition to the other parameters such as absorption and backscattering coefficients retrieved from traditional unpolarized methods.