Laser Focused: Interpreting Landscapes with Drone Lidar
- DATE WRITTEN:
- READING TIME: 3 minutes
- AUTHORS: Tom Weavill (Geomatics Officer) and Zoe Arkley (Senior Heritage Consultant)
Archaeology has long benefitted from a view from above, whether that is aerial photography from manned aircraft, satellite imagery or just a camera on a stick. This view is even more vital when trying to understand historic landscapes, where the interplay of topography, archaeology, modern development and conservation requirements need to be understood.
Over the past 15 years or so, uncrewed aerial vehicles (UAVs), aka drones, have provided archaeologists with an affordable and rapidly deployable method for capturing high quality aerial data on a landscape-wide scale. The variety of sensors now on offer mean that archaeologists can gather many different types of data for analysis. These include high-resolution photographs, airborne laser scanning (ALS) or multispectral imaging.
These methods provide not only some of the most informative and visually impressive outputs, but also some of the most accessible, which can be beneficial for non-specialist audiences. In particular, ALS from drones allows a high-level understanding of historic landscapes to be made in relatively short timeframes, prior to targeting smaller areas for more detailed study.
This kind of work is becoming increasingly important, especially with national schemes like Higher Tier Countryside Stewardship grants, which support landowners who are taking positive steps to care for the environment on their land. These landscapes often contain important heritage assets, so it’s essential to understand how to enhance the natural environment without harming the historic setting and to spot opportunities to protect and improve those heritage assets at the same time.
Behind the data
Today, UAVs have gone far beyond just being used to take ‘report cover’ images for projects and we are now far more likely to employ them as semi-autonomous survey tools to collect metrically and spatially accurate data.
When UAVs are used in a survey role, they are still subject to the checks and controls of a more traditional terrestrial survey. As such, all of our survey flights are undertaken using positioning correction, either via a GPS on-board the UAV or through a GPS receiver at an accurately known location on the ground. This means our datasets can be integrated with other mapping data.
From a single flight of an area, we can gather enough data to create digital elevation models , digital terrain models, photogrammetric models, orthophotos and more!
The journey
First, our team carries out a flight‑planning phase. In this stage we gather the necessary permissions, check for any potential airspace or site restrictions, and plan the flight route.
Once everything is approved, we can move on to the survey itself. Typically, we can cover an area of around four hectares in about 20 minutes, with the only real limiting factor being the number of available batteries. Flights are usually conducted autonomously at an altitude of around 60 m above ground level and a speed of 5 m/s. This allows us to capture high‑quality data and create a point cloud of the terrain at a resolution of roughly 1–3 cm, including features such as trees and building roofs.
After processing, the point cloud is classified into ground and non‑ground points. More detailed classification can be added if required, for example, identifying structures, roads, or specific monuments. The ground points are then used to generate a 0.25 m resolution raster digital terrain model. Additionally, digital surface models can also be created, which include both ground and non‑ground features.
