Underwater Photogrammetry as an Environmental Assessment Tool to Monitor Coral Reefs and Artificial Structures

Abstract

Over the past decade, photogrammetry has grown considerably thanks to technical advances in digital cameras and computing performance. Popular in terrestrial applications with the development of UAV acquisition, photogrammetry provides access to accurate scene reconstruction, high-resolution measurements, and temporal comparisons with a wide range of geolocated and scaled 2D and 3D supports. Nowadays, photogrammetry represents a particular challenge in the underwater field such as environmental monitoring, marine construction, technical inspection, and archaeology. Our study aims to develop underwater acquisition protocols and new tools for marine resources surveys and management to understand the role of 3D characteristics in both coral reefs and artificial structures. Two specific protocols were designed and optimized to reconstruct from coral colonies to coral reefs and artificial structures (up to 500m²) with a mean resolution of 0.05cm/pixel. Here several quantitative descriptors based on 2D and 3D metrics (such as slope, length, surface, volume, rugosity) were calculated for morphological studies and temporal comparisons. The photogrammetric technique now offers higher quality and accuracy tools compared to traditional survey methods. These advantages make possible to access to new scientific surveys of underwater ecosystems and as environmental management tools may prove to be valuable for future.