Multiangular and Hyperspectral Characteristics of Polarized Light Field in Case 2 Waters

The focus of this work is on the dependence of in situ hyperspectral and multiangular polarized data on the size distribution and refractive index of the suspended particles. Underwater polarization measurements were obtained using a polarimeter developed at the Optical Remote Sensing Laboratory of the City College of New York, NY. The instrument consists of three Satlantic Hyperspectral radiance sensors (recording intensity at the wavelengths 350-800nm, 8.5º field of view in water) mounted on a scanning system controlled by an underwater electric stepper motor. The degree of polarization (DOP) of the underwater light field in coastal environments was measured and the water-leaving polarized radiance was derived. In-water optical properties were also measured with an ac-9 (WET Labs). Absorption and attenuation spectra obtained with the WET Labs package are here used to derive information on the dissolved and suspend components in the water medium. Once these values are derived, they are used as input for a vector radiative transfer code, which provides the Stokes parameters for the upwelling radiance of the water body specified in the input file. The model was run while varying the real part of the refractive index of mineral particles between 1.12 and 1.26 until the modeled DOP matched the measured one. The relationship between the intensity of the maximum of the DOP and both the refractive index of the mineral particles and the shapes of their size distributions is analyzed in detail. This work highlights the potential use of underwater polarized measurements to gain information on properties of optically complex waters for remote sensing purposes, where contributions of polarized water-leaving radiances need to be accurately accounted, to take full advantage of measuring capabilities of the next generation of polarization sensitive instruments such as the Aerosol Polarimetry Sensor (APS), scheduled to be launched as part of the forthcoming NASA Glory mission.