PHOTOGRAMMETRY

Underwater photogrammetry

Photogrammetry is a technique for reproducing an object or landscape in three dimensions (3D) from a large number of shots taken from different angles of view. This technique has many applications, from town planning to industry to archeology, and has been integrated for a few years into the range of acquisition methods in ecology, especially in marine ecology.

Photogrammetry makes it possible to freeze the state of a marine habitat over time by reconstructing its structure in the smallest details, and to infinitely reuse this raw material in order to identify all the fixed species, and calculate structure indicators, diversity, state of health… The processing chain makes it possible to produce 3D models of incredible resolution, but also Digital Terrain Models (DTM; bathymetric models) or orthomosaics (“aerial” views) of surfaces ranging from a few tens of square meters to more than one hectare with sub-centimeter resolution. The only limit is the acquisition time and the calculation time for image processing.

Since 2016, Andromède Océanologie has made several hundred photogrammetric acquisitions, mainly of coralligenous reefs, posidonia meadows and coral reefs, but also artificial reefs (Cortiou, Sausset, Pangatalan…) or wrecks (P38, B17 …). A first methodological work on the photogrammetric acquisition and the quality of 3D models gave rise to a scientific publication within the framework of a CIFRE thesis co-supervised by Andromède Océanologie, UMR TETIS and UMR MARBEC. Several methods have since been developed to analyze 3D images and models and extract information useful for the interpretation of the ecological state of the main Mediterranean habitats, in particular an automatic mapping method for Posidonia meadows (in publication) and an algorithm for automatic recognition of the main coralligenous species (in the process of being published). The work in progress within the framework of the thesis aims to understand the relationships between the structure of coralligenous reefs and the biotic and abiotic factors that influence these complex ecosystems.

All of our 3D models produced as part of Mediterranean marine habitat monitoring campaigns are posted online on the Medtrix platform  in the MODEL project.

With its experience in photogrammetric acquisition, image processing and 3D data analysis, Andromède Océanologie has the technical and scientific skills to conduct any type of project requiring the acquisition and interpretation of photogrammetric data, including artwork.