Magnetic susceptibility 

A broad sweep method with a large variety of applications - Magnetic susceptibility is a property that can be measured in most soils. Responses are partially proportional to the amount of magnetic metal ions in the soil. It is known that areas of land subjected to human occupation exhibit enhanced magnetic characteristics. Any sites of potential identified can then be targeted using other methods. The method is also affected by varying geology.

Fluxgate gradiometer 

Normally employed on rural, open field sites and in large gardens. Occasionally works on less disturbed urban sites. 

This is a method that measures the earth’s magnetic field. It is very responsive to burning and iron objects. Also under certain conditions or circumstances it can map features such as ditches or pits that have long since silted up and been buried. It is favoured over most other methods because of the rapidity with which very large areas can be covered in a relatively short space of time.

Resistivity survey  

Can be employed on any site with vegetative or earth cover that allows electrical contact with the ground.

The method works by passing an electric current through the ground. Some objects such as stone or brick walls will resist the passage of the current, other features such as damp, silted ditches conduct the electric current more easily than the surrounding ground. The technique relies on there being a contrast in the electrical properties of materials and features across the site. As this is highly dependant on the moisture content of the ground then the success of the method may also depend on the time of year and the weather at the time of the survey, it is also very sensitive to variations in underlying geology.

Radar survey 

Commonly seen as the means by which urban landscapes can be surveyed. However, in many cases the complexity of urban disturbances and archaeological stratigraphy mean that the method can be much more efficiently employed in rural situations. Whilst it does not generally produce the resolution that resistivity does it can identify features in a similar way to resistivity survey, but with the advantage that it covers the ground much more quickly.

Aerial photographic survey 

This is commonly used as a tool when undertaking Desk-Based Studies. However, as such it only takes account of existing information available through the photographic libraries. In many cases it is possible to undertake targeted air survey using infra-red or multi-spectral film on days when ground and sky conditions allow.