Three-dimensional morphometric measurements of reef corals using underwater photogrammetry techniques
We describe a novel technical approach to accurately measure surface area and other morphological characteristics of corals and similar irregular objects from underwater photography. A standard Nikonos camera system was used with a slide-scanner to produce multiple overlapping images of the object. PhotoModeler software was used to process the images and build a 3-D model of the object, which was subsequently analyzed using 3-D computer-aided design (CAD) packages. The accuracy of the technique was tested on irregularly shaped polystyrene models of known dimensions and on preserved coral skeletons. The technique was applied to the quantitative assessment of partial mortality in corals, but many applications are possible, including surface area measurements to standardize ecophysiological studies in the field and morphometric analyses. It represents the only noninvasive technique we are aware of for determining surface areas of large corals in the field. The most serious limitation of the technique is the time-consuming nature of the process, which increases with the complexity of the object and precludes many routine applications.