This means our aircraft set-up is ideal for extensive monuments, such as those along the ridge of the Malvern Hills or where there are continuous archaeological features. The latter includes the settlements and field systems that extend across large parts of areas such as Dartmoor in Devon or the Yorkshire Dales. Therefore, we aim to use the aeroplane or the drone for different circumstances and sometimes for work on the same site or area. So far, our trials suggest that the light aircraft photography can achieve about the same Ground Sampling Distance (a measure of scale and accuracy) as drone footage, depending on the height flown and lens used. The GSD for the Malvern Hills examples is 5 centimetres, an acceptable level of tolerance for most archaeological purposes.
By taking our own vertical photographs, we can ensure we have the right conditions and resolution for archaeological illustration and survey. We will use them to create digital 3-D visualisations to help illustrate sites and landscapes but their main application is in monitoring the condition of large archaeological monuments.
We have two different vertical automatic-camera set-ups attached to each of the Cessna-172’s that we lease.
Emma Trevarthen from our York team covers the north of England from Sherburn-in-Elmet. The aircraft there uses a camera placed over a hole in the floor of the plane.
Damian Grady from our Swindon team covers the south from Oxford Airport (Kidlington) and uses a camera pod fixed to the wing strut of the aircraft. We use a Digital SLR camera (Nikon D850) linked to an Inertial Measurement Unit (IMU) and a Global Positioning System (GPS). During a vertical survey, the aircraft flies a proscribed straight course with constant height and direction and the camera automatically takes pictures at set intervals to create overlapping images.