Characterization of the Total and Polarized Radiance from the Ocean Surface through Hyperspectral Polarimetric Imaging
Abstract
Multi-angular, polarized radiance measured above the ocean surface can be used for the retrieval of water parameters in addition to the ones retrieved from traditional un-polarized methods. However, several challenges need to be overcome in such procedures, which includes accurate correction of measured Stokes vectors for polarized skylight reflection and relatively small signal to noise ratio due to the small degree of linear polarization of the water-leaving light radiation. We present results of measurements by a state-of-the-art snapshot hyperspectral imager, which simultaneously acquires spectra with 4nm spectral resolution in the wavelength range of 450-950nm with a 40° field-of-view for 20°-60° viewing angles. The imager does not require any along track movement and allows the continuous collection of data from stationary structures or slow moving platforms such as ships or helicopters. In addition, a computer controlled filter wheel is installed in front of the imager allowing division-of-time Stokes vector images from the ocean surface.
Several sets of measurements used in the analysis were acquired from ocean platforms in the NYC area, Duck, NC and from shipborne observations in the Gulf of Mexico and along the Florida coast. Measurements made by the imager are compared with simulations using a vector radiative transfer codes showing good agreement. Analysis of pixel-to-pixel variability of the total and polarized above water radiance, sky radiance and derived water-leaving radiance for the viewing angles of 20°-60° in different wind conditions led to the estimation of possible uncertainties in measurements of these radiances in un-polarized and polarized modes for the whole spectral range, thus setting requirements for the quality of polarized measurements. Impacts of aerosols on and spectral variations of the sea surface reflectance coefficient are specifically studied for both the radiance and the polarized terms of the Stokes vector.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMOS11D1437G
- Keywords:
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- 3311 Clouds and aerosols;
- ATMOSPHERIC PROCESSESDE: 3339 Ocean/atmosphere interactions;
- ATMOSPHERIC PROCESSESDE: 4264 Ocean optics;
- OCEANOGRAPHY: GENERALDE: 4275 Remote sensing and electromagnetic processes;
- OCEANOGRAPHY: GENERAL