Archaeology has long benefited from the use of aerial photography, revealing sites that are often difficult or even impossible, to see on the ground. Interpretation and mapping of sites visible as cropmarks, soilmarks and earthworks allows a better understanding of past landscapes to inform research and management strategies. New technologies such as lidar are adding to the toolkit of the aerial surveyor.
Interpreting and mapping from aerial photographs.
Archaeological features can be identified on aerial photographs and other forms of remote-sensing in a variety of ways.
Remains may survive as earthworks, ‘lumps and bumps’, visible on the ground but often more clearly seen from the aerial perspective, especially when the sun is low in the sky. Earthworks can also be mapped using lidar, a relatively new technology that uses laser scanning to create a 3d model of the ground surface.
Hidden sites may be revealed as cropmarks, variations in vegetation growth over buried remains, and soilmarks where archaeological deposits have been brought to the surface by ploughing. Where remains are visible solely as cropmarks or soilmarks, often only a small window is seen in a given year, and it takes many years of reconnaissance to build up a picture of the whole landscape.
Aerial photographs also contain many features that may mislead the unwary and make the archaeology difficult to see. Specialist staff interpret and map the archaeological information to provide a synthesis of the data from photographs which may go back over many decades. Aerial survey projects may investigate individual sites and their immediate context or extensive landscapes covering hundreds of square kilometres.
Aerial photographs, maps and records
The English Heritage aerial reconnaissance programme continues to record several thousand archaeological sites each year. Many new discoveries are made, but photographs are also taken to monitor the condition of protected monuments and to provide illustrations for presentation and research projects.
The new photographs supplement the already extensive archive of historical aerial photographs of England held by the National Monuments Record (NMR) and made available for public research. Records resulting from aerial survey interpretation and mapping projects are also used to expand and update the information available through the NMR, and directly update online databases like those available through Heritage Gateway.
The new archaeological information provided by all aspects of aerial survey can be used as the basis for further research at a local or national level as well as helping to ensure that development work can be done with an informed view of any impact on the historic environment.