Graham Lee – Archaeological Officer
We recently commissioned additional high resolution LiDAR data (Light Detection and Ranging) for several areas of the North York Moors in partnership with Durham University who are currently involved in a long term research project on the coast. The data is collected by scanning the ground with beams of laser light. LiDAR data sees through vegetation and tree canopies which otherwise can obscure the view of the ground level to conventional air photography. For this commission we were particularly interested in areas of heather moorland.
Most publically available georeferenced LiDAR data in England comes from the Environment Agency. It is relatively low resolution, with data points collected at 1 metre or 50 centimetre intervals. The collected points enable the ground surface to be accurately mapped – the more points that are collected, the greater amount of detail that is recorded and revealed through 3-D representation. The newly collected data we now have is at 10 centimetre resolution which equates to about 90 data points per square metre. The amount of data means the ground topography can be perceived through relatively dense stands of vegetation, such as gorse. For large expanses of the North York Moors which are covered in thick protective heather the idea is that this new data will help us to artificially see the archaeological earthworks beneath. It was this upland moorland plateau where prehistoric people lived and farmed and buried their dead.
As an archaeologist I am looking for human-made patterns in the landscape which represent different forms of earthworks created by human activity – either upstanding banks or ditches/hollows –which are visible in the data. Once noted, experience with data collected from aerial photographic survey allows these features to be interpreted. The interpretation is not necessarily conclusive – some more complex features will require a ground visit to collect further information before an interpretation can be firmed up. The features identified can then be incorporated within the National Park Authority’s Historic Environment Record (HER) which is the catalogue of our current archaeological knowledge. New and enhanced information which increases our understanding of archaeological landscapes is also very important for the protection and future management of archaeological sites.
Initial examination of the LiDAR data for Levisham Moor has greatly increased our knowledge of the complexity and extent of the prehistoric and medieval field systems as well as other sites that survive here. This means that individual sites – such as possible prehistoric hut circles, as well as the extent of field system remains – can be precisely located and mapped rather than just using a general area. This is a considerable advance in our knowledge which greatly simplifies the locating of sites on the ground within extensive areas of what can seem like featureless heather moorland.
Fig 1: Dundale Rigg, Levisham Moor – The LiDAR imagery shows up the subtle remains of earthwork banks of an earlier (?Prehistoric or ?Medieval) field system overlain by later ridge and furrow cultivation. Also visible is a Bronze Age round barrow (mapped as a tumulus) with a central disturbance from the 1930s and a trial excavation from 1962, and the faint curvilinear traces of what is thought to be a prehistoric hut circle towards the top left of the photo.
Fig 2: Horness Rigg, Levisham Moor – Remains of a probable Prehistoric field system. The enclosed platform at the southern end, which sits within rather than being overlain by the fields, has been dated by excavation to the Late Iron Age or Roman periods.
In the future new information supplied by the LiDAR survey will be used to aid and stimulate research into the history and development of Levisham Moor and other areas in the North York Moors, as well as informing management, presentation and interpretation. LiDAR does not remove the need to confirm details on the ground and there is always work to do to look for associated features that may not be visible on the LiDAR, but it is enormously helpful in the quest for increased archaeological knowledge.