PHOTOGRAMMETRY

Sub-marine photogrammetry

Photogrammetry is a technique that is used to reproduce an object or landscape in three dimensions (3D) using a high number of shots taken from different angles. There are many application for this technique, from city planning, to industry, to archaeology, and over the past few years it has been built into the range of ecological acquisition methods, in particular in marine ecology.
Photogrammetry makes it possible to freeze the state of a marine habitat in time by rebuilding its structure in the smallest details, and then using this raw material over and over again to identify all the species and calculate structure, diversity and health indicators… The processing makes it possible to produce 3D models with unbelievable resolution, but also Digital Elevation Models (DEM; bathymetric models) or orthomosaics (aerial” views) of surfaces from a few dozen square metres to over a hectare with sub-centimetre resolution. The only limit is the acquisition time and the calculation time needed to process the images.
Since 2016, Andromède Océanologie has carried out several hundred photogrammetry acquisitions, mainly of coralligenous reefs, Posidonia meadows, and coral reefs, but also of artificial reefs (Cortiou, Sausset, Pangatalan, etc.) or of shipwrecks (P38, B17, etc.). A first work on photogrammetry acquisition methodology and 3D model quality resulted in a scientific publication as part of a CIFRE thesis co-supervised by Andromède Océanologie, the TETIS UMR and the MARBEC UMR. Since then, several methods have been developed to analyse the images and 3D models and extract the information useful to interpret the ecological state of the main Mediterranean habitats, in particular an automatic Posidonia meadow cartography method (publication in progress) and an automatic algorithm to recognise the main coralligenous species (publication in progress). The ongoing work as part of the thesis aims to understand the relationship between coralligenous reef structure and the biotic and abiotic factors that influence these complex ecosystems.
All the 3D models created as part of the Mediterranean marine habitat monitoring campaigns are put on line and can be accessed from the Medtrix platform.
Thanks to its photogrammetry acquisition, image processing and 3D data analysis experience, Andromède Océanologie has the technical and scientific know-how to carry out any project requiring the acquisition and interpretation of photogrammetry data, including on engineering structures.

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