Ground-penetrating radar (GPR) is a Locating geophysical method that uses radar pulses to
image the subsurface. This nondestructive method uses electromagnetic rays in
the microwave band (UHF/VHF frequencies) of the radio selection range, and
registers the mirrored signals from subsurface structures. GPR can have
applications in several 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 spaces. GPR
uses high-frequency (usually polarized) radio swells, usually in the range 10
MHz to 2. 6 GHz. A GPR transmitter sends out electromagnetic energy into the
ground. When the energy encounters a buried object or a boundary between
materials having different permittivities, it may be mirrored or refracted or
tossed 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 mirrored at bounds 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
samsung s8500, and thus the puncture depth decreases. Because of
frequency-dependent attenuation components, higher frequencies do not pierce as
far as lower frequencies. However, higher frequencies may provide improved
resolution. Thus operating frequency is always a trade-off between resolution
and puncture. Optimal depth of subsurface puncture is achieved in ice where the
depth of puncture can achieve several thousand metres (to bedrock in Greenland)
at low GPR frequencies. Dry sandy garden soil or massive dry materials such as
granite, limestone, and concrete tend to be resistive rather than conductive,
and the depth of puncture could be up to 15-metre (49 ft). In wet or clay-laden
garden soil and materials with high electrical conductivity, puncture may be as
little as a few centimetres. Ground-penetrating radar antennas are generally in
contact with the garden soil for the most potent signal strength; however, GPR
air-launched antennas can be used above the garden soil. Cross borehole GPR is
rolling out within the field of hydrogeophysics to be a valuable means of
assessing the presence and amount of soil water. GPR has many applications in a
number of fields. In the Earth sciences it is used to study bedrock, garden
soil, groundwater, and ice. It is of some utility in prospecting for gold
nuggets and for diamonds in alluvial stones beds, by finding natural tiger traps
in buried stream beds that have the potential for accumulating heavier fibers.
[3] The Chinese lunar rover Yutu has a GPR on its underside to examine the soil
and crust of the Silent celestial body.
Engineering applications include nondestructive testing (NDT) of structures and pavements, locating buried structures and utility lines, and studying garden soil and bedrock. In environmental remediation, GPR is used to define landfills, contaminant plumes, and other remediation sites, whilst in archaeology it is used for mapping archaeological features and cemeteries. GPR is used in law enforcement for locating clandestine graves and buried evidence. Military uses include diagnosis of mines, unexploded ordnance, and tunnels. Borehole radars utilizing GPR are used to map the structures from a borehole in underground mining applications. Modern directional borehole radar systems are able to produce three-dimensional images from measurements available as one borehole. One of the other main applications for ground-penetrating radars is for locating underground utilities. Standard electromagnetic induction utility locating tools require utilities to be conductive. These tools are ineffective for locating plastic conduits or concrete storm and sanitary sewers. Since GPR registers variations in dielectric properties in the subsurface, it can be highly effective for locating non-conductive utilities. GPR is often applied to the Station 4 television programme Time Team which uses the technology to determine a suitable area for examination by means of excavations. In 1992 GPR was used to recover £150, 000 in cash that kidnapper Michael Sams received as a ransom for an residence agent he previously kidnapped after Sams buried the money in a field.
Engineering applications include nondestructive testing (NDT) of structures and pavements, locating buried structures and utility lines, and studying garden soil and bedrock. In environmental remediation, GPR is used to define landfills, contaminant plumes, and other remediation sites, whilst in archaeology it is used for mapping archaeological features and cemeteries. GPR is used in law enforcement for locating clandestine graves and buried evidence. Military uses include diagnosis of mines, unexploded ordnance, and tunnels. Borehole radars utilizing GPR are used to map the structures from a borehole in underground mining applications. Modern directional borehole radar systems are able to produce three-dimensional images from measurements available as one borehole. One of the other main applications for ground-penetrating radars is for locating underground utilities. Standard electromagnetic induction utility locating tools require utilities to be conductive. These tools are ineffective for locating plastic conduits or concrete storm and sanitary sewers. Since GPR registers variations in dielectric properties in the subsurface, it can be highly effective for locating non-conductive utilities. GPR is often applied to the Station 4 television programme Time Team which uses the technology to determine a suitable area for examination by means of excavations. In 1992 GPR was used to recover £150, 000 in cash that kidnapper Michael Sams received as a ransom for an residence agent he previously kidnapped after Sams buried the money in a field.
No comments:
Post a Comment