Hu, Chuanmin, Kenneth J. Voss

Limnol. Oceanogr., 43(6), 1998, 1198-1206 | DOI: 10.4319/lo.1998.43.6.1198

ABSTRACT: The oceanic Fraunhofer line discriminator (OFLD), designed to measure the solar-stimulated inelastic scattering in the ocean, has been deployed in various types of water in Florida Bay and the Dry Tortugas to measure Fraunhofer lines and oxygen-absorption lines near 689 nm in the solar spectrum. The line-filling principle and previous work enable us to partition the measured light into elastic, Raman scattering, and fluorescence components. We show that in optically deep, oligotrophic water, where chlorophyll a (Chl a) concentration is as low as 0.1 mg m-3, fluorescence near 689 nm was still measurable by the OFLD. In moderately eutrophic shallow waters, where Chl a concentration ranges from 0.2 to 0.8 mg m-3, the fluorescence from either Chl a or dissolved organic matter in the water column was found to be a negligible component of the total light field due to the additional light reflected from the bottom. We also include measurements of the solar-stimulated fluorescence for benthic surfaces, such as brain coral, and have found these to be saturated under normal solar illumination.

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