Retrieval of chlorophyll fluorescence from reflectance spectra through polarization discrimination: modeling and...

The polarization discrimination technique we recently developed, shows that it is possible to separate the elastic scattering and the chlorophyll fluorescence signal from the water-leaving radiance by making use of the fact that the elastically scattered components are partially polarized, while the fluorescence signal is unpolarized. The technique has been shown to be applicable to a wide range of water conditions. We present an extension of experimental and analytical results, which serve to define the scope of this technique and its range of applicability. A new analysis, based on vector radiative transfer computations, and on laboratory and field measurements on eastern Long Island and in the Chesapeake Bay, shows that the technique is generally effective for both open ocean and coastal waters, but that it is limited if the ocean bottom albedo and/or multiple scattering due to very high mineral particle concentrations result in depolarizing the water-leaving radiance. In addition, we show that in contrast with the polarization-based retrieval, the traditional method of extracting fluorescence height using the baseline method can give significant errors, particularly for coastal waters where it strongly overestimates the fluorescence values.