Discrimination of Sediment Type using Unmanned Aerial Vehicles (DST-UAV)

Keywords: Remote sensing; unmanned aerial vehicles; sediment; intertidal; monitoring;

This study will assess the feasibility of using unmanned aerial vehicles (UAVs) to measure sediment type such as sand and mud on beaches. Measurement of sediment type is vital to fully understand the environmental impact of coastal development. Industrial developments in the coastal zone may affect wave and tidal processes which can change the spatial coverage of sediment type. Each sediment type has varying properties which affect rates of erosion and deposition. Furthermore, different sediment types provide a diversity of ecological habitats and regulators must ensure that the coverages of different habitat do not change to an unacceptable amount.

Planned tidal lagoon schemes have caused regulators, in particular Natural Resources Wales, to question which survey tools would be suitable to monitor such changes in high tidal range regions where lagoons are likely to be constructed. High tidal range regions have wide intertidal expanses (sometimes in excess of 1km cross-shore) which means direct measurement of sediment type is difficult; both due to health and safety considerations and time constraints. Existing remote sensing techniques require manned aircraft; are expensive; and thus are not suitable for repeat surveys. Repeat surveys are needed to assess change as the natural environment responds to changes in forcing conditions over time. More cost-effective tools are therefore required to improve frequency of measurements.

UAVs represent a possible low-cost alternative. Different sensors will be tested: a standard camera, a multispectral camera and a thermal camera. Multispectral and thermal UAV based sensors have been applied to measurement of sediment properties in soil science but not to high tidal range intertidal regions. The sensors will be tested in Swansea Bay, the proposed location of the UK's first tidal lagoon. Methodologies to remotely sense intertidal sediment types using these sensors will be developed. The suitability and accuracy of the developed methodology will be evaluated. Evaluation will be made both at Swansea Bay and at a range of other test sites around the UK. The feasibility assessment will be based on the results of these trials and consideration of other limiting factors such as UAV flight regulations.

This project is important for industrial developers, environmental regulators and for the survey consultancies who conduct assessments of sediment type. This work is particularly timely since new low cost tools to monitor changes to substrate type will provide impact by feeding into the adaptive environmental monitoring plan protocols for future lagoon developments. The tools demonstrated will also be of use to identify changes caused by other natural and anthropogenic factors. More frequent and higher spatial resolution datasets will enable greater understanding of the natural variability in substrate type and hence be of great interest to the academic community. For developers, the use of UAV remote sensing will facilitate significant survey cost reduction. The techniques developed will substantially improve the safety of current operations for survey consultants who currently undertake sediment type monitoring on foot. This can be unsafe due to the presence of mud around the lower intertidal which is difficult to walk over. The methodology will extend the area that consultancies are able to measure sediment type in, providing an improved service and increasing the value of their offer to new clients. The project partner group includes: Tidal Lagoon Power, a developer; Natural Resources Wales, a regulatory body; Natural England, an advisory body; and AG Surveys, a survey consultancy. Therefore, representatives of all interested parties in the use of UAVs for the purpose of sediment mapping are included in the group.

This project will impact on multiple facets of coastal surveying by providing a feasibility assessment of a new methodology to distinguish between different sediment type. Sensors carried in unmanned aerial vehicles (UAVs) will enable low cost, high spatiotemporal resolution measurements; and the collection of measurements in previously inaccessible areas of the intertidal.

The study will provide evidence that will enable a change in regulatory guidance on the use of UAVs to measure and monitor sediment. If the results of the feasibility assessment are positive, the methodology can be specified for baseline surveys to support environmental impact assessments (EIAs) and habitat regulation assessments (HRAs); and post construction adaptive environmental monitoring plans (AEMPs). If the results of the assessment suggest the technology is not yet sufficiently advanced for the purpose, the study will provide the scientific basis to reject the use of such tools at this time. Importantly, in the case of a negative result, the study will provide a roadmap outlining the research areas and technological advances required to enable the use of this technology in future.

With the expectation of a positive result, UAVs will remove the requirement for survey personnel to approach the low tide line or travel over unconsolidated mud. This will significantly improve the safety of existing operations for survey professionals who undertake in-situ sediment sampling. The increase in area of coverage will enable consultancies to offer new data products and attract new clients. The techniques developed will facilitate a cost-reduction in operations, especially where UAVs are already used for topographical measurements. Both these aspects will increase the profitability of survey companies. A key aspect of this project is the inclusion of both regulators and consultancies in the project partner group meaning that regulators will understand the potential of the technique and hence consider its use for licencing projects. Provision of an end of project workshop will enhance uptake of results by stakeholders not in the project partner consortium. These factors will accelerate the adoption of the technology by survey companies.

For industrial developers with interests in exploitation of the coastal zone, demonstration that UAVs provide a suitable tool for monitoring of intertidal sediment type will assist with baseline data collection for EIAs and HRAs. Currently, such data collection is costly and this is often a significant barrier to the development of projects, especially novel marine renewable energy deployments. Reduction in these costs will increase the likelihood of successful projects and help maximise profitability. Similarly, the tools could be used for post-construction AEMP activities.

The high spatiotemporal resolution of data will enable greater understanding of both the natural variability in sediment type and the impact of projects. Low survey costs will promote more frequent measurements which will enable seasonal changes to be identified. Better understanding of natural change will lead to greater confidence in measurement of impact and predictions of the impact of future projects. This will facilitate the consenting of future developments in the coastal zone.

From an academic perspective, the feasibility study will extend the use of UAVs for coastal remote sensing beyond topographical measurements into sedimentological measurements. Both conference and journal publications will be produced that will engage the coastal and remote sensing communities. The tool will enable the collection of higher spatiotemporal resolution sedimentological datasets than previously obtainable and collection over previously inaccessible regions. This means new research focussing on the natural variation of sediment coverage in high tidal range regions will be feasible which will be important to coastal scientists, engineers and ecologists.