Airborne Lidar and Historic Environment Records

Article excerpt

The authors assess the potential contribution of lidar surveys to national inventories of archaeological resources ('Historic Environment Records), and compare the relative costs and sensitivity of lidar and aerial photography.

Keywords: England, aerial survey, lidar, aerial photography

Introduction

The new technique of lidar survey (Light Detection and Ranging) has already been applied to landscape mapping (Barnes 2003; Bewley et al. 2005; Bofinger et al. 2006; Harmon et al. 2006; Powlesland et al. 2006), geoarchaeological prospection and evaluation (Brunning & Far-Cox 2005; Challis 2005; 2006; Challis et al. 2006; Carey et al. 2006; Jones et al. 2007) and the detection of upstanding archaeological remains beneath the vegetation canopy (Devereux et al. 2005; Doneus & Briese 2006; Risbol et al. 2006; Sittler & Schellberg 2006; Crow et al. 2007). Lidar only detects features that rise above ground level (however slightly), so cropmark and soilmark sites are generally beyond its reach, although variations in crop height--one aspect of the cropmark phenomenon--may be detectable (Challis et al. 2006). The utility of lidar for finding new sites and defining historic environments has been broadly recognised (Holden et al. 2002; Bewley 2003; Crutchley 2006) but systematic application and evaluation is still in its infancy. It will be important to keep under review its growing utility within the armoury of prospection procedures applied in the research and management of archaeological resources.

This paper assesses the potential of lidar to enhance existing records of the historic environment, using a case study from a river valley in the agricultural midlands of England. Lidar elevation data at a spatial resolution of 2m was collected over a 25km stretch of the valley of the River Dove on the Derbyshire/Staffordshire border. These data were compared with the existing inventory of sites for the study area and with a selected sample of vertical aerial photography. While this assessment is based on a British example, we feel that the results have implications for cultural resource management internationally.

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Study area

The study area comprised a 25km segment of the valley floor of the River Dove between Rocester and its confluence with the River Trent at Newton Solney, a total land area of 10 703ha (Figure 1). The study area is dominated by pasture, with limited arable cultivation and woodland. The landscape is a patchwork of fields and farmsteads of post-medieval origin, with extensive areas of earthwork ridge and furrow betraying traces of an earlier, medieval, agricultural regime. Other upstanding earthworks relate to water meadows, deer parks, a moat and a miscellany of others, also largely of medieval and post-medieval origin. Belowground archaeology includes infrequent prehistoric round barrows, and occasional surface finds of prehistoric and Romano-British origin. The relative scarcity of arable agricultural land means that sites which depend for their detection on cropmarks or artefacts from the plough zone are poorly represented (8 per cent in Staffordshire and 18 per cent in Derbyshire). Sites evidenced by earthworks, and so visible to airborne lidar, dominate the existing record of the study area (18 per cent in Staffordshire and 38 per cent in Derbyshire).

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Method

Lidar data collected by the UK Environment Agency currently covers approximately 16 million hectares, 66 per cent of the land surface of the United Kingdom (Brown et al. 2003). Although the usual resolution (2m) is low, the broad coverage means that its assessment for archaeological usage is imperative. The present study used data from the survey covering 107km2 of the Dove valley. The data were imported into a geographical information system (GIS) developed using ESRI ArcGIS 9. …