Ground-penetrating radar – wikipedia f gas regulations 2015


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 gas nozzle stuck in car 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. [1]

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 gas 10 ethanol 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.

GPR has many applications in a number of fields. In the Earth sciences it is used to study bedrock, soils, groundwater, and ice. It is of some utility in prospecting electricity problem in up for gold nuggets and for diamonds in alluvial gravel beds, by finding natural traps in buried stream beds that have the potential for accumulating heavier particles. [3] The Chinese lunar rover Yutu has a GPR on its underside electricity quiz and answers to investigate the soil and crust of the Moon.

Engineering applications include nondestructive testing (NDT) of structures and pavements, locating buried structures and utility lines, and studying soils and bedrock. In environmental remediation, GPR is used to define landfills, contaminant plumes, and other remediation sites, while 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 detection of mines, unexploded ordnance, and tunnels.

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 detects variations in dielectric properties in the subsurface, it can be highly effective for locating non-conductive utilities.

GPR was often used on the Channel 4 television programme Time Team which used 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 estate agent he had kidnapped after Sams buried the money in a field. [5] Archaeology [ edit ]

The concept of radar is familiar to most people. With ground penetrating radar, the radar signal – an electromagnetic pulse – is directed into the ground. Subsurface objects and stratigraphy (layering) will cause reflections that are picked up by a receiver. The travel electricity inside human body 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 electricity song billy elliot 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.

A recent novel approach to vehicle localization using prior map based images from ground penetrating radar has been demonstrated. Termed Localizing Ground Penetrating Radar (LGPR), centimeter level accuracies at speeds up to 60 mph have been demonstrated. [8] Closed-loop operation was first demonstrated in 2012 for autonomous vehicle steering and fielded for military operation in 2013. [8] Highway speed centimeter-level localization during a night-time snow-storm was demonstrated in 2016. [9] [10] Three-dimensional imaging [ edit ]

Individual lines of GPR data represent a sectional (profile) view of the subsurface. Multiple lines of data systematically collected over an area electricity usage by country may be used to construct three-dimensional or tomographic images. Data may be presented as three-dimensional blocks, or as horizontal or vertical slices. Horizontal slices (known as depth slices or time slices) are essentially planview maps isolating specific depths. Time-slicing has become standard practice in archaeological applications, because horizontal patterning is often the most important indicator gas 1981 of cultural activities. [11] Limitations [ edit ]

Radar is sensitive to changes in material composition, detecting changes requires movement. When looking through stationary items using surface-penetrating or ground-penetrating radar, the equipment needs to be moved in order for the radar to examine the specified area by looking for differences in material composition. While it can identify items such as pipes, voids, and soil, it cannot identify the specific materials, such as gold and precious gems. It can however, be useful in providing subsurface mapping of potential gem-bearing pockets, or vugs. The readings can be confused by moisture in the ground, and they can’t separate gem-bearing pockets from the non-gem-bearing ones. [12]

When determining depth capabilities, the frequency range of the antenna dictates the size of the antenna and the depth capability. The grid spacing which is scanned is based on the size of the targets that need to be identified and the results required. Typical grid spacings can be 1 meter, 3 ft, 5 ft, 10 ft, 20 ft for ground surveys, and for walls and floors 1 inch–1 ft.

The speed at which gas natural inc a radar signal travels is dependent upon the composition of the material being penetrated. The depth to a target is determined based on the amount of time it takes for the radar signal to reflect back to the unit’s antenna. Radar signals travel at different velocities through different types of materials. It is possible to use the depth to a known object to determine a specific velocity and then calibrate the depth calculations.

A special kind of GPR uses unmodulated continuous-wave signals. This holographic subsurface radar differs from other GPR types in that it records plan-view subsurface holograms. Depth penetration of this kind of radar is rather small (20–30 cm), but lateral resolution is enough to discriminate different types of landmines in the soil, or cavities, defects, bugging gas bubble disease devices, or other hidden objects in walls, floors, and structural elements. [15] [16]

Wall-penetrating radar can read through non-metallic structures as demonstrated to ASIO and Australian Police in 1984 while surveying an ex Russian Embassy in Canberra. Showed police how to watch people up to two rooms away laterally and through floors vertically, could see metal lumps that might be weapons; GPR can even act as a motion sensor for military guards and police, Project carried out first in 1984 Canberra Australia.(Also used for detecting Ghosts on TV show.{air disturbance in a locked room})