Ground Penetrating Radar - Case Study Example

GPR Name Class Unit Table of Contents Table of Contents 2 Introduction 2 Uses of GPR 3 GPR to detect landmines 5 GPR system components 6 Investigating faults with GPR 6 Antennae separation 7 Interference to GPR 8 Filters use in GPR 9 Significance of GPR 10 Conclusion 11 References 11 Introduction Ground Penetrating Radar (GPR) can be defined as a subsurface imaging which has the capability to come up with high resolution information on a depth from 0 to 10 m. despite this, the depths up to 40 m can be attained in some of the geological environments. The first use of GPR was in the 1970s in ice sounding in the Antarctica (Goudie, 2003). Since then GPR has gained a lot of acceptance internationally. GPR has been non-invasive and non-destructive and utilises low power non-sinusoidal electromagnetic waves where waves ranges from 10MHs to 4GHz (Yelf, 2007, p.103). The tool is effective in visualising the structure in shallow subsurface. GPR uses discrete pulses of the electromagnetic energy. Use of GPR has been used in varying environments. This article gives a literature review on GPR. This is through giving information on the uses of GPR, explaining what the GPR consists of and what affects GPR. Uses of GPR GPR uses are varied and include location of buried services, mapping of the bedrocks depths, faults and fracture areas in rock and detecting voids and cavities. GPR has also been very useful in locating existence of steel reinforcement in concrete, archaeological, investigations involving geotechnical foundation, environment and the hydrogeological surveys (Yelf, 2007). GPR has been a very important tool when carrying out subsurface inspection and quality control when engaging in construction projects. GPR has also been useful on other applications such as mapping pipes and buried objects. It has also been in use for continuous inspection of road pavements and runaways in airports. The instrument has ability to collect data at a very rapid rate hence can be used on the highways. This is especially when monitoring the changes in subgrades as well as asphalt pavements (Goudie, 2003). GPR helps a lot in monitoring the railway ballast conditions and hence can help in detecting the existence of clay zone fouling which contributes to occurrence of track instability. It has also been in use of inspecting the concrete structures. This is by locating the steel reinforcements bars and pre and post tension stress in ducts. Use of GPR in three dimensions (3D) mode has been vital in mapping multiple layers of steel in building. The process is done with an aim of eliminating chances of damages in case of drilling through such structures (Goudie, 2003). GPR is useful in inspection and quality control for the precast concrete structures. This includes concrete structures such as bridge deck beams. It is also useful in detecting the zones for honeycombing, voiding and attacks of chloride on concrete. GPR helps in mapping case of deterioration and delamination that occurs in bridge decks (Yelf, 2007). GPR have also been proved to be effective on cave detection in limestone. Despite this, there are other forms of techniques used in detecting the presence of caves and voids below the surface. Microgravity has been used in detecting caves and voids in the surface used (Abdeltawab, 2013, p.261). This is due to fact that there exists large density difference substrate and void. Despite its use, the gravity methods have several limitations since they cannot detect the shape of the void (Yelf 2007, p.102-107). This requires a surveyor to determine the actual shape of the void through simulation. The simulation results are expected to match the data observed. Resistance tomography is also used due to fact that the void has a higher resistance than the surroundings. The main disadvantage is the fact that limestone has high resistance hence the technique is less successful. Geophysical diffraction tomography has also been use (Goudie, 2003). This is through use of low frequency sound waves. The main problem with this technique is the fact that placing hydrophones and geo is time consuming and not appropriate when prospecting. This has led to the need of looking for GPR in detecting reflections caused by short bursts from the electromagnetic radiation caused by portable radar transmitter (Yelf, 2007). This is through using similar principles and methods as those used in seismic sounding. Research has shown that a 500 MHz GPR used inside a cave can help in detecting the interfaces that exists between the unconsolidated sediments and limestone bedrock. This is at a depth of 2 to 3 metres below the sediment surface. This research was able to show that selecting the best antennae frequency is the most important thing in undertaking a GPR survey (Yelf, 2007). GPR is also very important in mapping the deterioration and delamination of the bridge decks. In the timber structures and wooden beam bridges, GPR has proved to be useful in mapping the zones of termites attack (Goudie, 2003). It is also possible to map soil, rock and fill layers in the geological and geotechnical investigations as well as foundation designs. When detecting fractures in rock mass, BH-GPR has been very useful. This is especially in the detection of structural integrity of pillars and the repository of nuclear waste zones (Yelf 2007, p.102-107). It has also been approved that GPR helps in detecting the presence of unmarked graves and bodies buried in snow avalanches (Yelf, 2007). GPR to detect landmines GPR research shows that it can be used in detection of the landmines. The act of detecting and clearing the landmines is an overwhelming and unsafe. This had made it vital to engage in accurate and efficient detection of landmines. The most widely used methods in landmine detection are metal detection and hand prodding (Goudie, 2003). There has also been deployment of the electromagnetic induction to detect the landmines. Despite this, the methods are not safe. This has led into investigation on the use of acoustic methods. There are also other methods being used at the moment (Abujarad, 2007). GPR has been in use to detect the buried objects which includes the landmines. The performance of the GPR depends on the subsurface conditions. Despite being a mature technology, GPR has not been highly utilised in mine detection (Yelf 2007, p.102-107). Research shows that GPR can be utilised in detecting the landmines (Abujarad, 2007). GPR system components GPR is made up of the power source which can either be internal rechargeable battery or an external battery 12 volts battery or use the alternating mains source. It has a control unit and antennae and the connecting cable. For the success of the survey, use of the correct antennae frequency is desirable (Chamberlain et al., 2000). The transmitting antenna is used to radiate the electric pulse to the ground which under ideal conditions acts as acoustic waves in its kinematics properties. The transmitted pulse which in some cases is reflected, diffracted by the features which corresponds to the changes in the earth own dielectric properties (Yelf 2007, p.102-107). Waves reflected or diffracted back is expected to be detected by the receiving antennae where it is amplified, digitized and then displayed. The results are then stored for further analysis used (Abdeltawab, 2013, p.261). The transmitter and receiver units are separate making the survey design more flexible. The data can be collected through a step or continuous mode. When using in a continuous mode, the antennae is dragged on the surface while when in the step mode, the antennae is placed on the ground (Goudie, 2003). Investigating faults with GPR Locating the characteristics of active faults is very important in the study of future regional seismic activities (Goudie, 2003). This helps in determining the potential of the earthquakes in a region. The method has been found to be useful in different situations which include looking for graveyards and imaging on the sand dune stratigraphy. Due to the nature of the faults, the area has been hard to study. A lot of fault activities happen beneath the surface making the use of GPR vital. The type of information being gained from the GPR on fault detection is based on what is being searched (Yelf, 2007). GPR is most commonly used to locate the faults. The GPR is able to transect perpendicular across a fault which makes it possible to narrow the search area. It also provides adequate information to have strong evidence on the fault location (Chamberlain et al., 2000). An increased exploration on the fault area may lead to new information. Once the fault has been located, it becomes possible to add more information. The fault strands locations are easily located from the offsets in stratigraphy (Akinpelu, 2010). A sharp vertical change in stratigraphy continuity layering is an indication of lateral displacement of a slip fault. It is possible for the heavily faulted areas to show evidence of multiple fractures when the GPR is used (Abdeltawab, 2013, p.261). Antennae separation Most of the GPR has a separate antenna which is used in transmitting and receiving in bi-static operations (Goudie, 2003). Some of the antennae have a fixed separation while others can be changed or varied. Based on the survey needs, the antennae separation should be as small as possible. This is also based on the antennae wavelengths. Also, the resolution depth decreases as the distance between the antennae increases. This impact is not very significant until the separation becomes half of the target depth. The allowed antennae separation is supposed to be 20% of the target depth (Yelf, 2007) Interference to GPR The GPR signals are masked by electromagnetic signals from the nearby sources such as radio transmitter or electricity power lines which are near the site of use. In these cases, the signals from external sources lead to saturation of the receiver sensitive electronic receiver. It is important to note that the radio receivers are a major source for the radio signals which are powerful enough to overwhelm the electronics on the receiver. At the moment, mobile phones have been acting as a major source for the ubitcous interference (Goudie, 2003). It has also been proved that the proximity to the metal objects has a negative impact on the GPR survey. If metallic reflectors are involved, the reflections from the objects at the side can be very strong. Surface features have been proved to produce sideswipe which come from the substantial radiation along the interface between the ground and air. In these situations, it is important to use shielded antennae. These antennae can be found in the range of 100 MHz and above (McGraw, 2010). The shields used are almost the same size as the antennas and has absorbing materials which damps any undesired signals. When being used in lower frequencies, the size of the antennae and portability makes it hard to make shielding. The practical limitations in portability lead to the need for use of shielded GPR systems where the transmitter and the receiver are placed in a single housing. This makes it hard to use bi-static antennae especially for the midpoint surveys. Another issue is the outcrop accessibility when using the GPR equipment. It is bulky to haul the survey equipment to the top of the outcrop (Akinpelu, 2010). It is almost impossible to carry the bulky GPR and the survey equipment required to the top of the outcrop being targeted. There is use of short hikes and all-terrain vehicles or helicopters (Chamberlain et al., 2000). Filters use in GPR Human induced noise and improvement of the visual quality of the GPR data has been carried out using filters. There is use of different filters such as band pass and the sophiscated filters. It has been proved that use of simple filers is vital in removing low frequency noise. For specific problems, high frequency filters are used. When the noise frequencies are higher than the main GPR signal, temporal filters are used (Akinpelu, 2010). They act as the clean-up filters to ensure that GPR has a better visibility. High pass filters has been used to allow the high frequency components to pass while the low frequency components are removed while low pass filters does the opposite. High pass and low pass filters are combined in a GPR system to ensure frequencies on both sides of the system are let through (Goudie, 2003). Significance of GPR GPR is a low cost and convenient method for research. It is a tool which has a capability to increase the quality, quantity and improve the relative of ease in research when compared to other methods of research (McGraw, 2010). For example, use of GPR is very important than trenching and digging. By simply using the GPR, it is possible to determine the depth of bedrock instead of digging multiple small pits. GPR has been proved to save time and money in the process. It is important to note that funding is a very vital part in research (McGraw, 2010). The saving of money through this process makes it possible to save the funding money which can be used on other areas. More research is done using less money when GPR is utilised. The GPR systems have proved to be major tools in reducing the costs of research. It is important to note that GPR systems are fully mobile hence can be taken to remote areas where it is impossible to use other methods (Yelf, 2007). GPR has proved to be useful as complements to other methods making the research more effective. GPR is coupled with the traditional methods to make the research more efficient. It is important to note that digging trenches is highly costly and leads to disturbing of the area. Use of GPR makes it possible to narrow the area of search (Akinpelu, 2010). The GPR reduces the costs of digging new trenches in areas which are less suitable. GPR data has also been vital in enhancing the information which has been gained from digging of trenches. It is also important to note that GPR can travel to deeper depths and lead to a more comprehensive model in the faulted area (Yelf, 2007). Conclusion GPR is a technology that has proved to be non-invasive when used on the subsurface stratigraphy and underground phenomena. It provides a very vital and effective method in exploration. The advantages of the GPR have made it a very important technology. There are new discoveries on the use of GPR technology. The advances in the GPR technology make it more appealing for use. Despite its useful, the technology has several shortcomings. The technology also suffers from interference problems which can influence the data collection in a negative way. Use of filters helps in reducing the interference problems. There is also use of antennae shielding. The GPR is a tool that can find use in fault detection and landmine detection among others. GPR has also been used in investigating the structures in limestone within a depth of 20m. GPR has the capability to prove that they are a useful method in evaluating the limestone outcrops before mining or quarry development. The significance of GPR shows that it is a technology that will be useful more in future as more research is carried out. References Abdeltawab, Samir. "Karst Limestone Geohazards in Egypt and Saudi Arabia." International Journal of Geoengineering Case histories 2.4 (2013): 261. Abujarad, Fawzy. Ground penetrating radar signal processing for landmine detection. Diss. Otto-von-Guericke-Universität Magdeburg, Universitätsbibliothek, 2007. Akinpelu, Oluwatosin Caleb. Ground penetrating radar imaging of ancient clastic deposits: a tool for three-dimensional outcrop studies. Diss. University of Toronto, 2010. Chamberlain, Andrew T., et al. "Cave detection in limestone using ground penetrating radar." Journal of Archaeological Science 27.10 (2000): 957-964. Goudie, A. ed., 2003. Geomorphological techniques. Routledge. McGraw, Timothy Joseph. Assessment of Ground-Penetrating Radar and Comparison with Resistivity for Detecting Subsurface Cavities within Karst Topography in North-Central Ohio. Diss. Bowling Green State University, 2010. Yelf, Richard J. "Application of ground penetrating radar to civil and geotechnical engineering." Electromagnetic Phenomena 7.1 (2007): 102-117. Read More

This is through using similar principles and methods as those used in seismic sounding. Research has shown that a 500 MHz GPR used inside a cave can help in detecting the interfaces that exists between the unconsolidated sediments and limestone bedrock. This is at a depth of 2 to 3 metres below the sediment surface. This research was able to show that selecting the best antennae frequency is the most important thing in undertaking a GPR survey (Yelf, 2007). GPR is also very important in mapping the deterioration and delamination of the bridge decks.

In the timber structures and wooden beam bridges, GPR has proved to be useful in mapping the zones of termites attack (Goudie, 2003). It is also possible to map soil, rock and fill layers in the geological and geotechnical investigations as well as foundation designs. When detecting fractures in rock mass, BH-GPR has been very useful. This is especially in the detection of structural integrity of pillars and the repository of nuclear waste zones (Yelf 2007, p.102-107). It has also been approved that GPR helps in detecting the presence of unmarked graves and bodies buried in snow avalanches (Yelf, 2007).

GPR to detect landmines GPR research shows that it can be used in detection of the landmines. The act of detecting and clearing the landmines is an overwhelming and unsafe. This had made it vital to engage in accurate and efficient detection of landmines. The most widely used methods in landmine detection are metal detection and hand prodding (Goudie, 2003). There has also been deployment of the electromagnetic induction to detect the landmines. Despite this, the methods are not safe. This has led into investigation on the use of acoustic methods.

There are also other methods being used at the moment (Abujarad, 2007). GPR has been in use to detect the buried objects which includes the landmines. The performance of the GPR depends on the subsurface conditions. Despite being a mature technology, GPR has not been highly utilised in mine detection (Yelf 2007, p.102-107). Research shows that GPR can be utilised in detecting the landmines (Abujarad, 2007). GPR system components GPR is made up of the power source which can either be internal rechargeable battery or an external battery 12 volts battery or use the alternating mains source.

It has a control unit and antennae and the connecting cable. For the success of the survey, use of the correct antennae frequency is desirable (Chamberlain et al., 2000). The transmitting antenna is used to radiate the electric pulse to the ground which under ideal conditions acts as acoustic waves in its kinematics properties. The transmitted pulse which in some cases is reflected, diffracted by the features which corresponds to the changes in the earth own dielectric properties (Yelf 2007, p.102-107). Waves reflected or diffracted back is expected to be detected by the receiving antennae where it is amplified, digitized and then displayed.

The results are then stored for further analysis used (Abdeltawab, 2013, p.261). The transmitter and receiver units are separate making the survey design more flexible. The data can be collected through a step or continuous mode. When using in a continuous mode, the antennae is dragged on the surface while when in the step mode, the antennae is placed on the ground (Goudie, 2003). Investigating faults with GPR Locating the characteristics of active faults is very important in the study of future regional seismic activities (Goudie, 2003).

This helps in determining the potential of the earthquakes in a region. The method has been found to be useful in different situations which include looking for graveyards and imaging on the sand dune stratigraphy. Due to the nature of the faults, the area has been hard to study. A lot of fault activities happen beneath the surface making the use of GPR vital. The type of information being gained from the GPR on fault detection is based on what is being searched (Yelf, 2007). GPR is most commonly used to locate the faults.

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