Assessing Seagrass Restoration Actions through a Micro-Bathymetry Survey Approach (Italy, Mediterranean Sea)

Abstract

Underwater photogrammetry provides a means of generating high-resolution products such as dense point clouds, 3D models, and orthomosaics with centimetric scale resolutions. 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). 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. In this study, a photogrammetry-based micro-bathymetry approach was applied to monitor Posidonia oceanica restoration actions. A procedure for rectifying both the horizontal and vertical elevation data was developed using soundings from high-resolution multibeam bathymetry. 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. 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. 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.

Seasonality strongly affects short‐term C‐storage in coastal macrophyte communities

“…Several techniques exist to upscale C content from multiple samples to a unit of land, a commonly used technique is the back‐of‐envelope calculation, where the C content of collected samples is multiplied by habitat extent (Ladd et al 2022). The habitat extent of vegetated seascapes is frequently quantified through photographic characterization of aquatic vegetation (e.g., Rodil et al 2019; Rende et al 2022). Overall, our results suggest that photographic characterization of aquatic vegetation is influenced by the timing of data collection.…”

Multitemporal Seagrass Mapping and Monitoring of Posidonia Meadows and Banquettes for Blue Carbon Conservation: The Poseidon Project

“…In this regard, multi/hyperspectral satellite sensors (i.e., Sentinel 2 MSI and PRISMA) have been successfully tested to monitor the stress level of PO (Borfecchia et al, 2021): time-series imagery exploits high-resolution data, while up-to-date sensors and techniques would allow to achieve even ultra-high resolution also for the time-series. More recently, photogrammetry is also increasingly being used to monitor the state of PO and the outcome of restoration projects, to derive finer-scale measurements with respect to the other geomatics techniques (Rende et al, 2022). In particular, monitoring protocols with underwater photogrammetry entail the integration of GNSS-RTK positioning performed with a small boat, depth measurements and a diver-operated underwater propulsion vehicle for image collection.…”

3D-Reconstruction of a Giant Posidonia oceanica Beach Wrack (Banquette): Sizing Biomass, Carbon and Nutrient Stocks by Combining Field Data With High-Resolution UAV Photogrammetry

“…The availability of high-resolution orthomosaics and DEMs in a georeferenced environment using OBIA (Object-Based Image Analysis) classification techniques allows rapid and effective mapping of natural and physical habitats. Mapping and comparison of validated thematic maps (2D) (Rende et al, 2022) and volume estimates (3D) obtained from OBIA classification are also essential tools for environmental monitoring of medium and large-scale areas such as those of the Capo Feto area. This first high-resolution classification (Figures 4, 5) compared with future surveys (time-lapse), will allow us to estimate the quantity of biomass and carbon accumulated or exported.…”