Compensating for Irradiance Fluxes When Measuring the Spectral Reflectance of Corals In Situ

This study employed an ensemble of instruments to monitor irradiance fluxes during measurement of the spectral reflectance of one coral in situ at Roatan Island, Honduras. The underwater light field (400-700 nm) was considerably more variable under sunny or partially cloudy sky conditions than the above-water light field. Measurements under overcast conditions had low variability both above and at the coral target. Correlations between simultaneously collected above water and underwater downwelling fluxes had R-2 values of 0.02%, 63.0%, and 96.3% under sunny, variable, and overcast sky conditions, respectively. Simultaneous measurements of both upwelling radiance and downwelling irradiance using a dual-fiber hyperspectral sensor significantly reduced the variance in the spectral reflectance of a coral target, regardless of sky conditions, especially as compared with a single-fiber configuration.