Ground-penetrating radar
Ground-penetrating radar (GPR) is a
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
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.
History
The first patent for a system designed to use continuous-wave radar to locate buried objects was submitted by Gotthelf Leimbach and Heinrich Löwy in 1910, six years after the first patent for radar itself (patent DE 237 944). A patent for a system using radar pulses rather than a continuous wave was filed in 1926 by Dr. Hülsenbeck (DE 489 434), leading to improved depth resolution. A glacier's depth was measured using ground penetrating radar in 1929 by W. Stern.[4]
Further developments in the field remained sparse until the 1970s, when military applications began driving research. Commercial applications followed and the first affordable consumer equipment was sold in 1975.[4]
In 1972, the Apollo 17 mission carried a ground penetrating radar called ALSE (Apollo Lunar Sounder Experiment) in orbit around the Moon. It was able to record depth information up to 1.3 km and recorded the results on film due to the lack of suitable computer storage at the time.[5][6]
Applications
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 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.[7] The Chinese lunar rover Yutu has a GPR on its underside to investigate the soil and crust of the Moon.
Engineering applications include
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 in a single borehole.[8]
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. GPR was also used to recover £150,000 in cash ransom that Michael Sams had buried in a field, following his 1992 kidnapping of an estate agent.[9]
Military
Military applications of ground-penetrating radar include detection of unexploded ordnance and detecting tunnels. In military applications and other common GPR applications, practitioners often use GPR in conjunction with other available geophysical techniques such as
In May 2020, the U.S. military ordered ground-penetrating radar system from Chemring Sensors and Electronics Systems (CSES), to detect
Vehicle localization
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 100 km/h (60 mph) have been demonstrated.[11] Closed-loop operation was first demonstrated in 2012 for autonomous vehicle steering and fielded for military operation in 2013.[11] Highway speed centimeter-level localization during a night-time snow-storm was demonstrated in 2016.[12][13] This technology was exclusively licensed and commercialized for vehicle safety in ADAS and Autonomous Vehicle positioning and lane-keeping systems by GPR Inc. and marketed as Ground Positioning Radar(tm).
Archaeology
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.[14]
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 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.[15]
Burial sites
GPR is used by criminologists, historians, and archaeologists to search burial sites.
Advancements in GPR technology integrated with various 3D software modelling platforms, generate three-dimensional reconstructions of subsurface "shapes and their spatial relationships". By 2021, this has been "emerging as the new standard".[25]
Glaciology
adding images to it so that it can be better illustrated. (May 2023) |
Radioglaciology is the study of glaciers, ice sheets, ice caps and icy moons using ice penetrating radar. It employs a geophysical method similar to ground-penetrating radar and typically operates at frequencies in the MF, HF, VHF and UHF portions of the radio spectrum.[26][27][28][29] This technique is also commonly referred to as "Ice Penetrating Radar (IPR)" or "Radio Echo Sounding (RES)".
Glaciers are particularly well suited to investigation by radar because theThree-dimensional imaging
Individual lines of GPR data represent a sectional (profile) view of the subsurface. Multiple lines of data systematically collected over an area may be used to construct three-dimensional or
Limitations
The most significant performance limitation of GPR is in high-conductivity materials such as clay soils and soils that are salt contaminated. Performance is also limited by signal scattering in heterogeneous conditions (e.g. rocky soils).
Other disadvantages of currently available GPR systems include:
- Interpretation of radar-grams is generally non-intuitive to the novice.
- Considerable expertise is necessary to effectively design, conduct, and interpret GPR surveys.
- Relatively high energy consumption can be problematic for extensive field surveys.
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.[46]
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 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.
Power regulation
In 2005, the
Similar technologies
Ground-penetrating radar uses a variety of technologies to generate the radar signal: these are impulse,
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 devices, or other hidden objects in walls, floors, and structural elements.[49][50]
GPR is used on vehicles for close-in high-speed road survey and landmine detection as well as in stand-off mode.[definition needed]
In Pipe-Penetrating Radar (IPPR) and In Sewer GPR (ISGPR) are applications of GPR technologies applied in non-metallic-pipes where the signals are directed through pipe and conduit walls to detect pipe wall thickness and voids behind the pipe walls.[51][52][53]
Wall-penetrating radar can read through non-metallic structures as demonstrated for the first time by
SewerVUE Technology, an advanced pipe condition assessment company utilizes Pipe Penetrating Radar (PPR) as an in pipe GPR application to see remaining wall thickness, rebar cover, delamination, and detect the presence of voids developing outside the pipe.
EU Detect Force Technology, an advanced soil research company, design utilizes X6 Plus Grounding Radar (XGR) as an hybrid GPR application for military mine detection and also police bomb detection.
The "Mineseeker Project" seeks to design a system to determine whether
References
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- ^ a b "History of Ground Penetrating Radar Technology". Ingenieurbüro obonic. Archived from the original on 2 February 2017. Retrieved 13 February 2016.
- ^ "The Apollo Lunar Sounder Radar System" - Proceedings of the IEEE, June 1974
- ^ "Lunar Sounder Experiment". Lunar and Planetary Institute (LPI). Apollo 17 Experiments. Retrieved 24 June 2021.
- (PDF) from the original on 5 July 2013. Retrieved 9 December 2012.
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- ^ Birmingham Mail
- ^ "Army orders ground-penetrating radar system from CSES for detecting hidden IEDs in $200.2 million deal". Military & Aerospace Electronics. 13 May 2020.
- ^ ISSN 1556-4967.
- ^ Enabling autonomous vehicles to drive in the snow with localizing ground penetrating radar (video). MIT Lincoln Laboratory. 24 June 2016. Archived from the original on 19 January 2017. Retrieved 31 May 2017 – via YouTube.
- ^ "MIT Lincoln Laboratory: News: Lincoln Laboratory demonstrates highly accurate vehicle localization under adverse weather conditions". www.ll.mit.edu. Archived from the original on 31 May 2017. Retrieved 31 May 2017.
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- ^ a b Wadsworth, William T. D. (22 July 2020). "Geophysics and Unmarked Graves: a Short Introduction for Communities". ArcGIS StoryMaps. Retrieved 24 June 2021.
- ^ "Remains of 215 children found at former residential school in B.C." The Canadian Press via APTN News. 28 May 2021. Retrieved 4 June 2021.
- ^ "Saskatchewan First Nation discovers hundreds of unmarked graves at former residential school site". CTV News. 23 June 2021. Retrieved 24 June 2021.
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- ^ Stern, W (1930). Principles, methods and results of electrodynamic thickness measurement of glacier ice. Zeitschrift für Gletscherkunde 18, 24.
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- ^ "Gems and Technology – Vision Underground". The Ganoksin Project. Archived from the original on 22 February 2014. Retrieved 5 February 2014.
- European Telecommunications Standards Institute. September 2009. ETSI EG 202 730 V1.1.1.
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- Jaufer, Rakeeb M., Amine Ihamouten, Yann Goyat, Shreedhar S. Todkar, David Guilbert, Ali Assaf, and Xavier Dérobert. 2022. "A Preliminary Numerical Study to Compare the Physical Method and Machine Learning Methods Applied to GPR Data for Underground Utility Network Characterization" Remote Sensing 14, no. 4: 1047. https://doi.org/10.3390/rs14041047
Further reading
An overview of scientific and engineering applications can be found in:
- Jol, H. M., ed. (2008). Ground Penetrating Radar Theory and Applications. Elsevier.
- Persico, Raffaele (2014). Introduction to ground penetrating radar: inverse scattering and data processing. John Wiley & Sons.
A general overview of geophysical methods in archaeology can be found in the following works:
- Clark, Anthony J. (1996). Seeing Beneath the Soil. Prospecting Methods in Archaeology. London, United Kingdom: B.T. Batsford Ltd.
- Conyers, Lawrence B; Goodman, Dean (1997). Ground-penetrating radar: an introduction for archaeologists. Walnut Creek, CA: AltaMira Press. OCLC 36817059.
- Gaffney, Chris; John Gater (2003). Revealing the Buried Past: Geophysics for Archaeologists. Stroud, United Kingdom: Tempus.
External links
- "EUROGPR – The European GPR regulatory body".
- "GprMax – GPR numerical simulator based on the FDTD method".
- "Short movie showing acquisition, processing and accuracy of GPR readings". Archived from the original on 22 December 2021 – via YouTube.
- "FDTD Animation of sample GPR propagation". Archived from the original on 22 December 2021 – via YouTube.
- "GPR Electromagnetic Emissions Safety Information". 17 May 2016. Archived from the original on 13 September 2018. Retrieved 15 February 2017.
- "Utility mapping with 3D GPR".