26 Nov Gavin & Doherty Geosolutions (GDG) Assist with Tidal Stream Drone Surveying
To determine the suitability of a candidate site for the development of offshore renewable energy, it is important to understand how the strength and direction of the currents vary in both time and space. The industry-standard current survey method involves the deployment of acoustic Doppler current profilers (ADCPs). Whilst these systems provide data with high temporal resolution, the spatial resolution of seabed-mounted ADCP units may be limited. Aerial drones, by contrast, allow current data to be captured over a much broader area. This is achieved by capturing video of the ocean surface and using the motion of certain surface features (foam patches, etc.) to derive estimates of the flow speed and direction. This technique, known as large-scale particle image velocimetry (LS-PIV), has been applied successfully to rivers but tidal stream sites, which are typically further from shore and have fewer surface features, represent a greater challenge.
As part of Selkie work package 7, Swansea University and partners are producing new workflows and guidance to enable the capture of surface currents from candidate tidal stream sites using existing open-source PIV software and commercially available quadcopter drones. This new approach will be designed to complement existing ADCP deployments and enable low-cost current measurements with greater spatial resolution. Used in combination, the ADCP and drone systems can provide valuable validation data for metocean models. A range of experiments has been planned to validate these drone measurements, and the findings will be shared to enable the rapid uptake of the new survey techniques by the marine energy industry. Following some initial land-based experiments, the research group at Swansea University conducted test flights at a range of candidate tidal stream sites in South Wales, and are using this data to establish best practice guidance.
To assist with the validation of the new survey techniques, Selkie partner Gavin & Doherty Geosolutions (GDG) has purchased a new drone to capture video from Irish tidal stream sites: a DJI M300 RTK model incorporating a DJI Zenmuse P1 sensor, which makes for a powerful and accurate survey system. GDG CAD Manager Eric Brennan, who is also a trained and qualified drone pilot, recently took the drone on its first test flight while working in Buncrana, on the north coast of Donegal (see the photos and map above). Eric flew the drone to a height of 120m and a maximum distance of 1.5km from shore to capture 5 test videos, each around 30s in length, of the surface of Lough Swilly. Although there are no relevant field data to compare these measurements with, he was able to use a marker buoy as a (reasonably) fixed point of reference. The GDG team is now working with the research group at Swansea University to identify opportunities for additional surveys of Irish sites in early 2022.
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