The Post Hole Issue 36 March / April 2014 www.theposthole.org 8 What are non-intrusive archaeological survey techniques, and how are they used to archaeological advantages during excavation Imogen Burrell 1 1 Department of Archaeology, School of Archaeology, Geography and Environmental Sciences (SAGES), University of Reading, Reading, RG6 6AH Email: burrellimogen@hotmail.co.uk There are a variety of non-intrusive archaeological survey techniques available to archaeologists which can assist excavations before they have begun, during the excavation – bringing clarity to uncovered features, and after – to tie everything together and create a detailed excavation report. Non-intrusive techniques include field walking, sampling, aerial photography, geophysical and geochemical surveys (resistivity and magnetometer surveys) GPR, metal detecting, GIS, and LiDAR (radar acting as its underwater equivalent). The value of each method depends on different variables including the environment, climate, light, time, aim and type of excavation and budget. Non-intrusive techniques have developed over time, and while some remain fairly simple, others increase in their complexity. Field walking is normally identified as the most simplistic of non-intrusive methods to carry out. In comparison to conducting optical aerial photography, it is very straight-forward. Aerial reconnaissance requires thorough planning and must be timed precisely in order to coordinate with favourable conditions where features can be identified with ease (Balme and Paterson 2006). In addition, the equipment and materials must be used by an expert in the field of photography. Although cameras and film-types used by the masses are very adaptable, optimum equipment and materials need to be selected, as a number of colour emulsions are sensitive to colour ranges. Colour and contrast can be enhanced by computer scanning, filtering, special developing and printing processes; infrared photography or other types of non-photographic digital images may generate clearer results (Green and Moore 2010, 65). When aerial reconnaissance is conducted competently, buried sites which may not be visible at ground-level can be brought to light. The sites are captured through discolorations in the overlying soil or crops, thus creating an invaluable guide for fieldwork and mapping landscape types from certain periods over large areas (Balme and Paterson 2006). It is therefore most helpful in the initial planning process of excavation. Geophysical surveys are relatively easy to conduct as the equipment is simple to operate and, similarly to field-walking, the process requires little expertise. The simplicity of conducting a geophysical survey varies depending on which form of instrument you are using. For example, magnetic surveying does not require the insertion of probes in the ground; the instrument can be carried along a grid or linear system,