![]() Recently, photogrammetry, widely used for terrestrial applications, has also been used as a detailed and accurate underwater survey tool for monitoring marine benthic habitats. However, these geophysical and multispectral techniques do not have sufficient resolution to define in detail the spatial location and the number of restored plants. The Multispectral Satellite Image (MSI) technique provides data with spatial resolutions between approximately 2 m and 0.5 m. The MBES survey allows for the acquisition of higher resolution (from 0.3 m to 0.05 m resolution) bathymetry and backscatter data in shallow water (1 m to 300 m) and provides a 3D reconstruction of the seafloor and a map of acoustic response, respectively. Underwater photogrammetry, if properly applied, can provide very high-resolution and accurate models for monitoring seagrass restoration actions for ecological recovery and can be useful for other research purposes in geological and environmental monitoring. The root mean square error (RMSE) value obtained for the horizontal planimetric measurements was 0.05 m, while the RMSE value for the depth was 0.11 m. Furthermore, a 3D trilateration technique was also tested to collect Ground Control Points (GCPs) together with reference scale bars, both used to estimate the accuracy of the models and orthomosaics. ![]() ![]() A procedure for rectifying both the horizontal and vertical elevation data was developed using soundings from high-resolution multibeam bathymetry. In this study, a photogrammetry-based micro-bathymetry approach was applied to monitor Posidonia oceanica restoration actions. However, one of the most complex aspects of underwater photogrammetry is the accuracy of the 3D models for both the horizontal and vertical components used to estimate the surfaces and volumes of biomass. Underwater photogrammetric models can be used to monitor the growth and expansion of benthic communities, including the assessment of the conservation status of seagrass beds and their change over time (time lapse micro-bathymetry) with OBIA classifications (Object-Based Image Analysis). Underwater photogrammetry provides a means of generating high-resolution products such as dense point clouds, 3D models, and orthomosaics with centimetric scale resolutions.
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