Georeferenced underwater photogrammetry to map marine habitats and submerged artificial structures

Over the past decade, underwater photogrammetry has been experiencing an increased interest due to the enhancement of camera performance and computing power. This study describes the test of two new methods to perform georeferenced underwater photogrammetry. The first one uses the coupling between photogrammetry by scuba diving and positioning with acoustic data from a multibeam echo sounder; the second one utilises direct positioning technology with a surface floating device (photogrammetric platform). When compared with one another, the platform had a higher mapping efficiency, while being limited by depth and underwater visibility. Georeferenced underwater photogrammetry is expected to have a wide range of applications in the field of marine habitats' conservation such as seagrass meadows and the survey of submerged man-made structures such as artificial reefs and port infrastructure.