Underwater photogrammetry, whilst generally accepted to be at an experimental phase of development, shows promise as an alternative or complementary dataset to hydroacoustic survey in very shallow-water environments, particularly for applications such as characterizing habitats including spawning grounds for rare fish species.
HydroSurv has been investigating the development of 3D models of underwater environments using photographic data collected using a small USV (mREAV) as the collection platform.
The company internally developed an underwater camera system for installation within the host USV moonpool, controlled by the vessel’s embedded control system – using distance or time intervals to trigger the camera shutter achieving sufficient overlap in the photographs to reconstruct the seafloor. This system was developed using commercially available off-the-shelf equipment running custom firmware to integrate the sensor to the vehicle, enabling high-optical quality photographs to be obtained at a sensible cost.
A series of pre-programmed trials were conducted from a beach with a wide variety of bottom compositions – including shingle, boulders and reefs, using the USV as the sole means of data collection without personnel working afloat, or safety vessel intervention. Data was post-processed using proprietary software to create initial 3D models from the ‘calibration’ surveys, resulting in the successful development of several models showing the various survey areas. This work has been of considerable interest to hydrologists and ecologists who can apply this process to their existing studies. Initial study has also formed the basis of further research focusing on similar applications above water – including asset inspection for dry-stone quay walls in ports and harbours and splash-zone inspection of monopile / jacket foundations for renewable energy assets using hybrid LiDAR / photogrammetry techniques.