DEVELOPMENT OF A CANOPY REFLECTANCE MODEL FOR CORAL REEF AREAS: INFERENCES FROM FIELD SPECTRAL MEASUREMENTS AND MODELING EFFORTS

摘要

In recent times, the observation of coral reef areas by remote sensing methods has received wide attention due to emerging worldwide environmental concerns such as coral degradation and its counteractive conservation measures. However, a vast majority of these efforts proceeded without the benefit of applying suitable geometric optics and physical radiative transfer models in resolving the reflectance behaviour of coral reef. This study focuses on the development of a directional reflectance model appropriate for analyzing coral reef areas, emphasizing the importance of shape, form and shadowing of coral canopies as main factors in influencing their appearance in images or real scenes. Here, coral canopies are treated as an assemblage of three-dimensional objects that varies with certain coral component characteristics. A combination of geometric-optical and turbid models similar to that applied commonly in plant canopies, were then modified and used to obtain a more comprehensive estimate of coral reef reflectance. These reflectance calculations are further subjected to models of radiative transfer through intervening media (object-water-atmosphere) to derive a feasible at-sensor spectral response. Results of model simulation indicate sensitivity of reflectance on viewing and illumination angles. Field spectral measurements of coral reflectance confirm this finding. The BRDF data collected and the model developed from this study can be further utilized for remote sensing data image analysis.