Context 168 - June 2021

C O N T E X T 1 6 8 : J U N E 2 0 2 1 23 DIGITAL TECHNOLOGY PAUL BRYAN Using drones for inspection and survey First seen in heritage surveys just over a decade ago, remotely piloted drones are now widely used for carrying cameras, thermal cameras, and laser or lidar scanners. Drones (remotely piloted aircraft systems) have their origins in military technology dating back to the 1850s, when they were used for aerial reconnaissance, and in both world wars for more destructive aerial-torpedo applications. Most commercial and consumer development of drones has occurred over the past decade, leading to them becoming a common sight in our skies, used by professionals, hobbyists and the general public. English Heritage first encountered a drone in 2008 during a demonstration of the Microdrones MD4-200 at Fountains Abbey, the world heritage site in NorthYorkshire. Although flight times were short, image resolution was low and video capture was exceedingly shaky, this demonstration showed their potential for capturing low-level aerial photography from multiple, often unique vantage points that could aid both the survey and close-range inspection of heritage buildings and structures. Modern drones, such as the DJI M300 now used by Historic England’s drone team, contain an assemblage of on-board technology to enable them to be flown safely and efficiently. This includes a global navigation satellite system to aid in-flight positioning; an inertial measure- ment unit to detect in-flight orientation and maintain stability; multiple range sensors to detect objects in their path; and artificial intel- ligence to help avoid collisions. This technology is linked through mobile phone controller apps to aid the preparation and management of the actual flights. Even with this array of on-board technology, a drone is simply a remote-controlled platform for carrying something, which in the case of heritage can be a camera, laser scanner, lidar scanner, thermal camera or a combination of such sensors. In heritage the primary sensor is usually a camera for capturing overlapping still imagery, fromwhich geospatial survey outputs can be later generated using structure-from-motion photogrammetric routines, and video sequences that aid the remote inspection of historic structures. Other application areas, such as agriculture, A view of St Mary’s Church, Kempley, taken by a drone (Photo: Historic England)