The impact of algal fluorescence on the underwater polarized light field

Multiangular, hyperspectral measurements of the underwater polarization light field, as well as comprehensive measurements of IOPs were collected in several cruise campaigns in the Chesapeake/Virginia area and New York Harbor/Hudson River areas. The waters examined were mostly eutropic water with Chlorophyll a concentration up to approximately 57 μg/L. It is found that Chlorophyll a fluorescence markedly impacts (reduces) the underwater degree of polarization (DOP) in the 650 - 700 nm spectral region. By taking note of the unpolarized nature of algal fluorescence and the partially polarized properties of elastic scattering, particularly by non-algal particles, we were able to separate the Chlorophyll a fluorescence signal from the total radiance. The analysis is based on comparisons of the underwater multiangular, hyperspectral polarization measurements which include fluorescence, compared with adding - doubling polarized radiative transfer simulations of elastic scattering which use measured IOPs as input, and which do not include fluorescence. The difference between the two shows the impact of fluorescence. These relationships are examined in detail, and the efficacy of using DOP measurements for underwater fluorescence retrieval is evaluated for different scattering geometries and water conditions.

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