page_title: Ground-penetrating radar
section_title: Archaeology
hierarchical_section_title: Ground-penetrating radar / Applications / Archaeology
caption_attribution_description: English: Ground Penetrating radar depth slices of an underground structure. Plaview maps isolating specific depth are constructed from many lines of data collected at close intervals. The structure depicted is a crypt at an historic cemetery in Saint Paul, Minnesota, USA.
context_page_description: Ground-penetrating radar is a geophysical method that uses radar pulses to image the subsurface. This nondestructive method uses electromagnetic radiation in the microwave band of the radio spectrum, and detects the reflected signals from subsurface structures. GPR can have applications in a variety of media, including rock, soil, ice, fresh water, pavements and structures. In the right conditions, practitioners can use GPR to detect subsurface objects, changes in material properties, and voids and cracks.
  GPR uses high-frequency radio waves, usually in the range 10 MHz to 2.6 GHz. A GPR transmitter and antenna emits electromagnetic energy into the ground. When the energy encounters a buried object or a boundary between materials having different permittivities, it may be reflected or refracted or scattered back to the surface. A receiving antenna can then record the variations in the return signal.
context_section_description: Ground penetrating radar survey is one method used in archaeological geophysics. GPR can be used to detect and map subsurface archaeological artifacts, features, and patterning.
  The concept of radar is familiar to most people. With ground penetrating radar, the radar signal – an electromagnetic pulse – is directed into the ground (it is important to not get GPR surveys confused with electromagnetic surveys, a recent survey of an Iron Age hillfort in Hampshire recently revealed the discrepancies between Magnetometry, EM and GPR surveys over the same area). Subsurface objects and stratigraphy (layering) will cause reflections that are picked up by a receiver. The travel time of the reflected signal indicates the depth. Data may be plotted as profiles, as planview maps isolating specific depths, or as three-dimensional models.
  GPR can be a powerful tool in favorable conditions (uniform sandy soils are ideal). Like other geophysical methods used in archaeology (and unlike excavation) it can locate artifacts and map features without any risk of damaging them. Among methods used in archaeological geophysics, it is unique both in its ability to detect some small objects at relatively great depths, and in its ability to distinguish the depth of anomaly sources.
  The principal disadvantage of GPR is that it is severely limited by less-than-ideal environmental conditions. Fine-grained sediments (clays and silts) are often problematic because their high electrical conductivity causes loss of signal strength; rocky or heterogeneous sediments scatter the GPR signal, weakening the useful signal while increasing extraneous noise.
  In the field of cultural heritage GPR with high frequency antenna is also used for investigating historical masonry structures, detecting cracks and decay patterns of columns and detachment of frescoes.
caption: GPR depth slices showing a crypt in a historic cemetery. These planview maps show subsurface structures at different depths. Sixty lines of data – individually representing vertical profiles – were collected and assembled as a 3-dimensional data array that can be horizontally "sliced" at different depths.)
exif: {}