Coral threat levels from climate change have increased around the globe. Coral reefs are nature’s best coastal protection device [MS48]. They dissipate portions of the wave energy through a system of multi-scalar tunnels to gradually reduce the power of large swells. As complex and permeable underwater structures, reefs refract waves instead of reflecting them which results in sand deposition instead of erosion [GP17]. Currently, reefs are threatened around the globe because of rising sea temperatures due to global warming, elevated levels of CO2 from pollution acidifying the oceans and radical practices such as dynamite fishing. Architects study their geometry to develop artificial coral reef systems to regrow premorse parts of corals and coastal protection devices [Vo18]. To understand the reef geometry detailed surface configurations and textures of a natural coral reef, a workflow was developed for close-range underwater coral reef monitoring that outputs high precision 3-D point cloud models. Utilizing the case study site of Gili Trawangan, Indonesia, underwater data from high- resolution still image and video data were collected of a natural coral reef and 3-D reconstructed precise point cloud models from both datasets.

In this paper both reconstructed point cloud models are presented and result from underwater photo- and videogrammetry are compared followed by discussing the potential of both methods for a close-range underwater survey. The accuracy and reliability of both techniques by measuring objects of known size is demonstrated.