ABOVE SURVEY CASE STUDY
Solar PV Site Topographical Surveys using UAV
PROJECT NAME: Solar PV Potential Sites
AREA: North of UK
SERVICES: Topographical Survey using UAV and ground techniques of 10 large scale potential solar PV sites
CLIENT: Above Survey
In March and April 2021 GeoAccess were asked to undertake a number of UAV topographical surveys of potential solar farm sites across the northern half of the United Kingdom. Sites ranged from 80 hectares in size up to 160 hectares.
Many sites were within FRZs which required careful planning and extra permissions before flights could be undertaken.
Contract specification was for a 3cm GSD with GCP GNSS-RTK measurement error with less than 10mm 3D RMSE in XY and Z. Final validation (check) point error on 10-20% of GCPs had to be less then 25mm XY and less then 50mm Z.
To achieve this, we decided to use a 250m grid of ground control points paying particular attention to the edges of the areas, using a combination of Propeller Aeropoints and traditional markers surveyed in using L2 GNSS RTK base station and rovers. The Propeller Aeropoints were also traditionally surveyed in to check for accuracy.
Using the DJI P4P UAV a flight height of 100m was chosen to achieve the required GSD and provide efficiency in data collection.
Flight areas were planned with numerous TOAL areas to keep the UAV in our operationally limits at all times. Key GCPs were left in place on areas overlaps to provide tie ins between areas.
Data was collected and processed in OSGB36 map projection and ODN. OSTN15 transformation and OSGM15 Geoid was used.
To complement the aerial data collection, access tracks and roadways were surveyed in using a GNSS RTK Base Station and Rover system. A known point was established using the L2 GNSS Base Station for a period of 1 hour and processed using PPK/PPP to provide a known point with +-20mm accuracy XYZ.
The RTK rover was then used to collect point data at various key locations throughout the site with total global accuracies of +-30mm.
Data was processed in Pix4D to produce 2D Orthomosaics, point clouds, textured mesh, contour plans as well as DTMs and DSMs to the contract requirements.
The combination of aerial data and ground-based data proved to be a powerful combination delivering accuracies to the client above expectations.
On a number of the sites the client required the use of LiDAR as vegetation coverage was suspected to be too dense for photogrammetry. Utilising our DJI M600Pro UAV and LiDAR USA Revolution 60 payload, flying at around 50m AGL we were able to generate point clouds with point densities of between 80-100 points per meter.
These sites were also flown with a RGB camera and the 2 data sets combined to produce a colourised 3D point cloud model. With the use of suitable GCPs the overall accuracy of this dataset far exceeded our clients’ requirements.