Woodhenge and Aerial Survey in the Stonehenge Landscape

On the first day of the MPhil field trip to Wessex, we stopped at Woodhenge. While the space is only marked by knee-high concrete pillars, this stop on the trip gave us an opportunity to discuss many of the choices involved in heritage preservation and management. The concrete posts are minimal, they represent the position and estimated size of the original posts, but make no suggestion of their height or whether they had a purpose such as supporting a roof. A plaque on the site illustrated the various suggestion for the original appearance of Woodhenge. While building a more elaborate structure on the site might be more visually appealing, it also might be misleading, as much is unknown about what Woodhenge actually looked like.

Woodhenge was originally detected in aerial photographs of the Stonehenge landscape in 1925. Aerial photography has been an invaluable tool for the remote sensing of archaeological sites for nearly a century, aiding in excavation planning and identifying traces of sub-surface archaeological features. 

Aerial photographs are particularly useful in detecting buried structures that may subtly effect the topography, growth of vegetation, coloration, and deposition of snow. Often these differences are occur on too large of a scale to be recognized as a feature to a surveyor on foot.

A second type of aerial remote sensing now commonly used in archaeology, LIDAR, or Light Detection And Ranging, is an active remote sensing technique that has a variety of applications from atmospheric observation to ocean floor mapping to environmental monitoring. A laser pulse is emitted from a scanner on an airplane and the time it takes the laser to bounce off an object below and come back is recorded. From this, the distance between the object and the plane is determined.

   

Aerial Survey of the Stonehenge Landscape, UK

An aerial study of the Stonehenge area, using both aerial photographs and LIDAR, was completed as a joint project between the UK government’s Environment Agency and English Heritage. The results of this study were published in 2005 by R.H. Bewley, S.P. Crutchley, and C.A. Shell in Antiquity in an article entitled ‘New Light on an Ancient Landscape: Lidar Survey in the Stonehenge World Heritage Site.'

English Heritage hoped that the LIDAR survey could provide information about which features of the landscape were still visible above the surface and which had been leveled to the extent that no visible trace remained. It was believed that all features that had not been completely leveled by ploughing had been identified, since the Stonehenge area is one of the most studied archaeological landscapes in Europe. The authors did not expect the LIDAR survey to find new sites. The survey did however identify new features and sites in the landscape and demonstrated that some sites, which had been categorized as having ‘no visible surface expression,’ were indeed still expressed above the surface.

Field systems near the Winterbourne Stoke Barrow group at Stonehenge with underlying lidar data illuminated from the north. From Bewley et al, 2005. © English Heritage - Original data from The Environment Agency

Such sites include new field system enclosures through illumination of LIDAR images from the North (seen in blue in both pictures). These had not been identified in aerial photographs because the banks are oriented parallel to the sun’s path, so that they rarely produce shadows. Additionally, the LIDAR survey found features obscured by the vegetation of the Fargo Plantation at the west end of the Cursus (pictured below), including some field system boundaries and the course of a WWII rail line not preserved outside the wooded area. The images here show previously identified features in orange and new ones in blue.

 

In addition to exceeding expectations and identifying new features in the Stonehenge landscape, the information gathered from this survey had practical applications for the management of the Stonehenge area. The survey was taken into account for plans to build a new visitors center. The LIDAR survey informed the decision on where to put the new center so as to avoid areas where archaeological features are expressed. 

LIDAR image of the west end of the Cursus and the wooded Fargo Plantation, illuminated from the northeast. From Bewley et al, 2005 © English Heritage - Original data from The Environment Agency