Separating the fluorescence and reflectance components of coral spectra

Abstract

The optical signal leaving the surface of fluorescing corals is a combination of elastic and inelastic scatter. A new experimental method was developed to separate the fluorescence and the reflectance components that involves measurements with and without a long-pass cutoff filter that eliminates the fluorescence contribution to the signal. The required measurements were performed underwater to demonstrate the applicability of the method for in situ applications. Computations with prototype rather than individually measured fluorescence emission spectra do not significantly compromise the accuracy of the results. A model was developed for calculating the interaction of the reflectance and the fluorescence components with new incident illumination conditions. The model calculations were supported by field experiment. We show that the contribution of fluorescence to some coral's spectra in various illumination conditions justifies consideration in optical models. The results are applicable to modeling the spectra of fluorescing corals under any irradiance spectrum and interpreting remote-sensing data in the relevant wavelength range. Further research is necessary to examine the significance of fluorescence near coral reefs at various scales.