Aerial Archaeology in Wales
The flying programme
The Royal Commission’s flying programme has three main aspects: exploratory work, the photography of sites and landscapes of national importance, and recording of industrial or architectural subjects. Exploratory reconnaissance is used to discover and record ‘new’ sites, some of which may only be seen from the air. In late spring or summer the buried ditches of plough-levelled sites may cause patterns of lush growth or ‘cropmarks’ in ripening arable fields or pasture; at the same time, buried stonework of walls and roads can cause crops to whither and parch out leaving lighter lines. In both these ways, cropmarks can show the position and layout of otherwise invisible archaeological sites. Very faint earthwork remains, often found in upland regions, can be equally difficult to see on the ground. When these sites are photographed in low winter or spring sunlight the effects of light and shadow, at times combined with a dusting of frost or wind-blown snow, can help to pick out indistinct outlines with striking clarity. In very dry summers, when conditions are exceptional, many hundreds of ‘new’ cropmark sites can be discovered in the space of just a few months, showing the fundamental contribution aerial photography can make to our understanding of the archaeology of Wales.
In liaison with Cadw, the Royal Commission also overflies Scheduled Ancient Monuments (SAMs) to monitor and photograph their condition. The flying programme continues to respond to changing research and conservation priorities and in recent years aerial photography has been employed to record for posterity the rapidly-changing urban and industrial landscapes of Wales. The Royal Commission actively co-ordinates and funds the work of aerial reconnaissance and air photo mapping by other bodies in Wales.
Toby Driver, Air Survey Officer.
Air Photo Mapping and Record Creation programme
Air photography of archaeological sites in Wales can only be a first step towards fully identifying, recording and eventually managing the archaeological heritage of Wales. Many parts of Wales, particularly in the upland zone, still await basic archaeological survey to identify and record their archaeological heritage. In recent years, field projects such as the Royal Commission’s Uplands Initiative, begun in 1991, have sought to redress this balance. However, since 1995 a programme of digital air photo mapping and record creation in Wales has also begun to make a significant impact on the study of upland and plough-levelled lowland archaeological landscapes in the country. By the year 2000, air photo mapping had been completed for 551.75 sq kms of Wales or 2.67% of the total landmass, while mapping of cropmark evidence alone has been completed for a further 1,118 sq kms or 5.41% of Wales.
The air photo mapping programme in Wales has a remit to rapidly record all redundant features of the built landscape from earliest times until the end of the Second World War, mapping and recording all sites for a 25 sq. km area in about 10 days. Crucially, the programme in Wales has always been computer-based and provides a digital plan of each and every site for use in research and management work.
Since 1995 our programme of air photo mapping has developed enormously in terms of technology and technique, from the days of FastCAD and FastMAP GIS between 1995 and 1998, to the change over to ArcView GIS in 1999. The Bradford Aerial 5 programme and AutoCAD are used for rectification in the flat plane (for scanned images and vector plots respectively) which, with careful checking, gives us the accuracy levels we require for 1:10,000 first-level mapping; to within 5m on level terrain and between 5-15m in undulating or hilly terrain. Sites plots are drawn up in ArcView GIS. Records are created on-screen writing to a FoxPro database. Once incorporated into a GIS and viewed against other datasets, such as site databases and priority areas for Upland Survey, the air photo map becomes a powerful tool for managing the archaeological heritage over wide areas.
David Thomas, Air Photo Mapping Officer.