Statistical characterization of the diffuse attenuation coefficient over tropical corals

Remote-sensing of submerged features can help to monitor coral reef ecosystems by monitoring spectral signatures within the visible spectrum. A satellite or airborne image could be used to delineate those areas of coral stress requiring immediate attention. One limitation, however, to the accuracy of this technique is that the water column over a submerged coral reef modifies the signal received by the sensor. The authors report on a study in Fiji were measured profiles of the diffuse attenuation coefficient are used to better understand the properties of the water column over various substrates. Downwelling irradiance and upwelling radiance in SeaWiFS channels were collected over coral reefs, debris surface, sand channels, and blue water with depths far beyond the range of the 70 metre cable. Principal components analysis of vertical water column profiles reveals that irradiance values can be used to distinguish between different bottom types based on the magnitude of component loadings. The technique provides consistent output when discriminating between bottom types at various depths. These results may be used to better define algorithms and are encouraging with respect to water column correction for image interpretation