Saltmarsh Mapping in the River Hamble
Saltmarshes are highly important coastal ecosystems, providing a habitat for a variety of marine and brackish species, as well acting as a natural flood defence structure for coastal communities and environments. However, they are also highly dynamic, changing seasonally and annually. Carcinus were recently contracted, in combination with SAND Geophysics, to support AQASS in a small-scale saltmarsh restoration project in the River Hamble, funded funded through a grant from The Solent Forum.
Traditional methods of surveying areas of saltmarsh are not always cost effective or detailed enough to show minute changes in habitat features, topography or morphology. Fortunately, in recent years ecologists and geomorphologists have come to realise the capability that Small Unmanned Aerial Systems (SUAS) (Drones) provide in understanding these often highly dynamic habitats. Carcinus are experts in utilising SUAS for a variety of applications, and led the development of the Joint Nature Conservation Committee (JNCC)’s Marine Monitoring Guidelines on Unmanned Aerial Vehicles (UAVs). You can read more about that project here. We are able to utilise both fixed-wing and multi-rotor aircraft to deliver high quality outputs that meet the specific accuracy and scale demanded by each application.
For this project, a Carcinus consultant flew one of our DJI Mavic 2 Pro UAVs, which is equipped with a 20-megapixel 1” CMOS Hasselblad camera sensor, in a double-gridded pattern over the study area, utilising a semi oblique camera angle.
All Carcinus drone operations are conducted in accordance with our Permission for Commercial Operations (PfCO), which is issued annually by the Civil Aviation Authority (CAA) and requires the maintenance of detailed flight records and pilot competency. Using Pix4D Photogrammetry Software and QGIS, Carcinus produced a series of highly accurate digital outputs, including an orthomosaic image with a Ground Sampling Distance (GSD) of 1 cm, a Digital Surface Model (DSM), and a hillshade that allows much more detailed visualisation of channel structure and elevation change that are not as visible from the native orthomosaic image or the DSM itself.
The positional accuracy of the outputs was further supplemented through surveying in a series of Ground Control Points (GCPs) using Post-Processed Kinematic (PPK) GNSS, giving an overall accuracy of deliverables of 0.017 m in elevation and <0.0075m in horizontal.
A Carcinus drone pilot on site in the River Hamble
Outputs from photogrammetry analysis. Our consultants are proficient at spatial and geomorphological surveying, analysis and visualisation using SUAS and software such as Pix4D and QGIS.
The data collected during this survey will be used as a baseline to monitor spatial and temporal geomorphological changes over the project lifespan (one year), to assess the efficacy of passive sediment retention in restoring this small area of saltmarsh. The project is a multidisciplinary effort, with input from consultants from a number of organisations, including Fathom Ecology, AQASS, Sand Geophysics, MarineSpace and Carcinus.