Polarimetric Imaging of the Ocean Surface

Above water polarized radiance from the ocean surface contains important information about the air-water interface. A novel polarization camera (Teledyne DALSA), which is based on a Sony polarization imaging sensor, providing a high-resolution image where each pixel contains four subpixels. These four subpixels are a built-in linear polarizer that are oriented in the 0,45,90 and -45 degrees. The attached lens allows for a field of view (FOV) of about 40° degrees for the center of the image. The camera is equipped with a filter wheel containing five spectral band-pass filters, thus providing multi-spectral, multi-angular, polarimetric data with high spatial resolution in the 400–900nm spectrum. The camera has undergone radiometric calibration and was used in various illumination conditions. These conditions of different viewing geometries and water environments in field campaigns in the NYC area are along the US East Coast. This allowed for characterization of the spatial and temporal Stokes vector distributions of the water surface, their estimations of related uncertainties, and the evaluation of sun glint’s impact. We further assessed the dependence of the degree of linear polarization on water constituent concentrations. Results are compared to concurrent measurements of total and polarized radiances with a state-of-the-art snapshot hyperspectral imager.

The acquired polarization information was then used to retrieve wave slopes parameters in sunny conditions. Expanding the scope of a methodology for polarization slope sensing was originally applicable only for measurements in overcast conditions.

The combination of hyperspectral imager and polarization camera allows to observe spectral and polarization properties of the wind-roughed ocean at high spatial and temporal resolution, with the goal of advancing our understanding of the air-water interface and in-water light propagation.