The Stokes vector components and the degree of linear polarization of light reflected from the air-water interface contain information about the roughness of the ocean surface, which is correlated with the wave slope statistics and may be used to retrieve it using the Polarization Slope Sensing (PSS) method (Zappa et al., 2008). This statistic is a part of the radiative transfer simulations in the atmospheric correction of the ocean color satellites and other applications. A modification of the method, which minimizes the impact of upwelling light on polarimetric measurements of the reflected light was applied by using Teledyne DALSA camera equipped with a Sony sensor, where each of 1232x1028 pixels had four subpixels with 0-, 90-, 45- and 135-degrees orientation of polarization. In addition, a filter wheel with several color filters was installed in front of the camera, allowing to measure wave slope characteristics at several spectral bands. Shipborne measurements during VIIRS Cal/Val cruises in the Gulf of Mexico and in Hawaii and from a helicopter at several heights during the CCNY cruise in the Chesapeake Bay showed the advantage of the proposed modified polarimetric slope sensing technique. Measured variances of the wave slopes were mostly in the range predicted by Cox-Munk relationships with corresponding standard deviations.
The degree of linear polarization of above-water radiance contains information on the attenuation-to-absorption ratio in the surface layer of the ocean. With additional inversion algorithms to retrieve size distribution, backscattering ratio and bulk refractive index of marine particle populations, polarization is thus an important component in the retrieval of optical and microphysical properties in the ocean. Accordingly, in preparation of the upcoming PACE mission, we used an artificial dataset of water IOPs and atmospheric properties in conjunction with radiative transfer simulations to explore the potential of a neural network approach for systematic conversion of top-of-atmosphere polarization values first into above-water polarization, then finally into an estimation of local optical and microphysical properties. Additionally, we used polarization images acquired in situ during a cruise in the Gulf of Mexico to study wave slope statistics as derived from a modified polarimetric slope sensing technique and found them to compare well with the classic wave slope variances of Cox and Munk.
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