page_title: Ground-penetrating radar
hierarchical_section_title: Ground-penetrating radar
caption_attribution_description: Ground-penetrating radar depth section (profile) collected on an historic cemetery in Alabama, USA. Yellow arrows indicate very distinct reflections, probably associated with human burials. "hyperbolic" reflections, appearing as an inverted U, are typically associated with discrete objects. Less distinct hyperbolic reflections are indicated by red arrows. dashed blue lines indicate horizontal and sloping reflectors, probably bedrock. The many smaller reflections near the surface are likely to be caused by tree roots. Because of the nature of the site, subsurface testing was not conducted, but these interpretations are supported by surface indications (grave markers and depressions) and with line-to-line patterning within the GPR data.
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 (GPR) is a geophysical method that uses radar pulses to image the subsurface.  This nondestructive method uses electromagnetic radiation in the microwave band (UHF/VHF frequencies) 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 (usually polarized) 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. The principles involved are similar to seismology, except GPR methods implement electromagnetic energy rather than acoustic energy, and energy may be reflected at boundaries where subsurface electrical properties change rather than subsurface mechanical properties as is the case with seismic energy.
  The electrical conductivity of the ground, the transmitted center frequency, and the radiated power all may limit the effective depth range of GPR investigation. Increases in electrical conductivity attenuate the introduced electromagnetic wave, and thus the penetration depth decreases. Because of frequency-dependent attenuation mechanisms, higher frequencies do not penetrate as far as lower frequencies. However, higher frequencies may provide improved resolution. Thus operating frequency is always a trade-off between resolution and penetration. Optimal depth of subsurface penetration is achieved in ice where the depth of penetration can achieve several thousand metres (to bedrock in Greenland) at low GPR frequencies. Dry sandy soils or massive dry materials such as granite, limestone, and concrete tend to be resistive rather than conductive, and the depth of penetration could be up to 15 metres (49 ft). However, in moist or clay-laden soils and materials with high electrical conductivity, penetration may be as little as a few centimetres.
  Ground-penetrating radar antennas are generally in contact with the ground for the strongest signal strength; however, GPR air-launched antennas can be used above the ground.
  Cross borehole GPR has developed within the field of hydrogeophysics to be a valuable means of assessing the presence and amount of soil water.
caption: A ground-penetrating radargram collected on a historic cemetery in Alabama, US Hyperbolic arrivals (arrows) indicate the presence of diffractors buried beneath the surface, possibly associated with human burials. Reflections from soil layering are also present (dashed lines).
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