However, higher frequencies may provide improved resolution. Because of frequency-dependent attenuation mechanisms, higher frequencies do not penetrate as far as lower frequencies. Increases in electrical conductivity attenuate the introduced electromagnetic wave, and thus the penetration depth decreases. The electrical conductivity of the ground, the transmitted center frequency, and the radiated power all may limit the effective depth range of GPR investigation. 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. A receiving antenna can then record the variations in the return signal. 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 GPR transmitter and antenna emits electromagnetic energy into the ground. GPR uses high-frequency (usually polarized) radio waves, usually in the range 10В MHz to 2.6В GHz. In the right conditions, practitioners can use GPR to detect subsurface objects, changes in material properties, and voids and cracks. GPR can have applications in a variety of media, including rock, soil, ice, fresh water, pavements and structures. 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.

It is a non-intrusive method of surveying the sub-surface to investigate underground utilities such as concrete, asphalt, metals, pipes, cables or masonry. Ground-penetrating radar ( GPR) is a geophysical method that uses radar pulses to image the subsurface. Reflections from soil layering are also present (dashed lines). Hyperbolic arrivals (arrows) indicate the presence of diffractors buried beneath the surface, possibly associated with human burials. A ground-penetrating radargram collected on a historic cemetery in Alabama, US.

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