William Megarry

Posterior Probability Modeling and Image Classification for Archaeological Site Prospection: Building a Survey Efficacy Model for Identifying Neolithic Felsite Workshops in the Shetland Islands

The application of custom classification techniques and posterior probability modeling (PPM) using Worldview-2 multispectral imagery to archaeological field survey is presented in this paper. Research is focused on the identification of Neolithic felsite stone tool workshops in the North Mavine region of the Shetland Islands in Northern Scotland. Sample data from known workshops surveyed using differential GPS are used alongside known non-sites to train a linear discriminant analysis (LDA) classifier based on a combination of datasets including Worldview-2 bands, band difference ratios (BDR) and topographical derivatives. Principal components analysis is further used to test and reduce dimensionality caused by redundant datasets. Probability models were generated by LDA using principal components and tested with sites identified through geological field survey. Testing shows the prospective ability of this technique and significance between 0.05 and 0.01, and gain statistics between 0.90 and 0.94, higher than those obtained using maximum likelihood and random forest classifiers. Results suggest that this approach is best suited to relatively homogenous site types, and performs better with correlated data sources. Finally, by combining posterior probability models and least-cost analysis, a survey least-cost efficacy model is generated showing the utility of such approaches to archaeological field survey.

The Influence of Viewshed on Prehistoric Archaeological Site Patterning at San Clemente Island as Suggested by Analysis of Synthetic Aperture Radar Images

The use of synthetic aperture radar (SAR) imagery collected by the NASA AirSAR platform to detect archaeological site location on San Clemente Island, one of the Southern Channel Islands, has been described in several publications. Here we provide a concise review of the use of SAR for that purpose, as well as a description of how a precise surface model also generated by SAR data was used to examine the spatial distribution of sites by means of viewshed modeling. Results of the direct detection model are evaluated using gain statistics that make use of a recently completed 100% survey of all accessible areas on San Clemente Island. Viewshed analyses generated by use of the surface model suggest a number of economic and ideological factors that might have influenced the distribution of archaeological sites on the island. Among these are intervisibility among locations on both San Clemente Island and nearby Santa Catalina Island that provided the means by which to coordinate crucial substance activities, such as hunting sea mammals, and reinforced the social relationships that were essential to such activities.

Beyond the Bend: Remotely Sensed Data and Archaeological Site Prospection in the Boyne Valley, Ireland

The UNESCO World Heritage Site of the Archaeological Ensemble of the Bend in the Boyne (‘Bru na Boinne’) is one of the most important archaeological landscapes in Europe. This paper reviews results from an ongoing project which is using high-resolution elevation (LiDAR) data and Worldview2 multispectral imagery to identify and catalogue new sites in and around the World Heritage Site. It stresses the importance of using a range of methodologies when remotely exploring landscapes, and illustrates how even within one of the most studied landscapes in Europe remote sensing technologies can identify new and exciting information.

Emerging Applications of LiDAR / Airborne Laser Scanning in the Management of World Heritage Sites

Remotely sensed data and imagery have revolutionized the way we understand archaeological sites and landscapes. LiDAR / airborne laser scanning (ALS) has been used to capture the often subtle topographic remnants of previously undiscovered sites even in intensely studied landscapes, and is rapidly becoming a key technology in survey projects with large extents and/or difficult terrain. This paper examines the practical application of this technology to archaeological heritage management, with special attention given to how ALS can support the World Heritage List nomination process and management of WHS archaeological sites and landscapes. It presents a number of examples from published ALS studies alongside case studies from projects undertaken by the authors at Cultural Site Research and Management and the Cultural Site Research and Management Foundation, Baltimore, Maryland, USA. The paper opens with a review of how ALS has been used at established World Heritage Sites, focusing on the Archaeological Ensemble of the Bend in the Boyne, Ireland, and the Angkor Archaeological Site in Cambodia. ALS applications for site prospection and demarcation, and viewshed analysis is explored in this section. Following this, we explore how ALS has been used to support two recent applications: the successfully nominated Monumental Earthworks at Poverty Point, USA and the recently nominated Orheiul Vechi Archaeological Landscape in Moldova. We propose that the detail offered by ALS data greatly strengthens nomination dossiers by emphasizing the outstanding universal value of sites, highlighting significant features and providing greater context to wider landscapes, and is particularly efficacious in delineating site boundaries for legal protection and long-term management. Finally, we conclude with a look at some of the practical considerations involved in the use of ALS, including access and training.