Magnetometry represents one of a number of geophysical techniques employed in archaeological prospection to inform on archaeological impacts ahead of proposed development and to advise archaeological test trenching and excavation. Frequently used to determine the often non-visible boundaries of archaeological remains, magnetometer surveys enable archaeologists to examine the location, form and extent of a diverse array of archaeological features no longer evident at the surface, including
- Enclosure remains & expansive walled settlements
- Hillforts & promontory forts
- Henges, tumuli & ancient burial grounds (enclosed)
- Military encampments
- Roman villa & castle foundations
- Ecclesiastical enclosures & deserted medieval villages
The basis for use of magnetometry in archaeological prospection derives from the abundance of natural iron oxides in most soils, and our ability to measure subtle variations in the magnetic properties of these iron oxides caused by human activity. Discrete variations in soil magnetism associated with buried archaeological remains derive typically from in situ burning and organic enrichment of the soil, through activities such as cooking and heating; pottery manufacture and metal working; as well as use of fired construction materials such as ceramic tiles and brick. These burnt, fired and organic rich deposits create subtle magnetic contrasts visible as discrete magnetic anomalies superimposed on the earth’s geomagnetic field.
TARGET’s magnetometer instrumentation comprises of an array of highly stable fluxgate gradiometer sensors combined with cm precision GPS. This advanced survey instrumentation enables high resolution mapping of buried archaeological remains, for both large and small-scale projects, and it can be used on foot or with the aid of a quad bike. Typically, completion of 1ha high resolution magnetometer survey per hour is estimated for most sites, although in exceptional conditions daily completion of 15 hectares or more is feasible.