The Hyper-Spectral Characteristics of Coral Species and Habitats in Hong Kong

This study explores the feasibility of coral remote sensing in local waters. The spectra of coral species and coral habitats (sand and rock) were collected in the field and the laboratory. The pure spectra of the local coral species and habitats had distinctive characteristics in the visible range of 470-650 nm, with distinctive spectral shoulders restricted to 580-650 nm. The pure target spectra were tested statistically and were discriminative, although the coral species were similar to rock. A semi-analytical model was used to simulate the target spectra under the water column effect. The simulated spectra failed to distinguish between the distinctive spectral features due to the acute water attenuation at 580-600 nm and the continued attenuation from 600 nm onwards. They were less separable as the water depth increased at 3-5 m. The hyper-spectral, simulated spectra were then applied to multi-spectral Landsat 7 and SPOT 5 for mapping. The obtained results were poor. The spectral properties of the satellite imagery were the important factors, and needed more visible bands prior to the wavelength range of water attenuation. Thus, at present, the feasibility of using remote sensing to map local corals is not high. It is hoped that this feasibility can be raised by enhancing the target spectral signals and selecting the appropriate satellite imagery.