جستجوی مقالات مرتبط با کلیدواژه « رادار نفوذی به زمین (gpr) » در نشریات گروه « زمین شناسی »

The Ground Penetrating Radar (GPR) method is high-resolution surveys with an electromagnetic pulse reflection method for shallow earth layers. This method is similar to reflection seismography, which operates on the basis of wave propagation and reflection. In a simple case, a GPR device consists of a signal generator. The signal generated by this generator is sent into the earth by the transmitter antenna. Waves travel through the earth at a high speed and when these waves hit an object or reflection surface, due to the change of electromagnetic impedance in these places, part of the waves will be reflected from the surface. The receiving antenna located in the device shows these reflections as a high peak and records the movement time and amplitudes of the reflections. The electromagnetic wave inside the earth moves downwards in the form of a three-dimensional cone, and at the same time, factors affect the speed and loss of the amplitude of these waves. In fact, the electromagnetic characteristics of the materials, which depend on the constituent materials and the amount of water in them, will have a great effect on the speed and loss of the range of the radar waves penetrating the ground. Some materials, such as polar ice, are transparent to ground-penetrating radar waves, and these waves can pass through it without much loss. Some other materials such as clays saturated with water and also sea water is cloudy to these waves and reflect or absorb these waves. Therefore, radar waves penetrating the ground are attenuated in short distances and cannot propagate in such environments.    Considering the high-resolution power of the ground penetrating radar method, as well as the high speed and ease of acquisition, it can be said that this method is useful in investigating and detecting shallow subsurface targets similar to subsurface holes, canals and other targets that have a different dielectric constant from the surrounding environment. It is an acceptable method. In addition to the effect of the frequency of the waves sent from the GPR antenna, other factors such as soil moisture, the amount of fine-grained clay materials, or the fineness of the sediments in general, reduce the depth of investigation or penetration of GPR waves. This problem is mainly caused by the higher electrical conductivity due to the presence of moisture or fine-grained sediment particles compared to coarse-grained sediments. In this study, a ground penetrating radar device with 80 MHz antenna was used and seven profiles with a total length of 662 meters were taken to investigate the intersection of Kargar Street in Tehran. The radargrams have been processed and the anomalies related to the meetings have been identified on them. These anomalies are discussed in the next step on the positioning satellite images and on the obtained results. According to the estimated results, there is a good agreement between the anomalies detected in the parallel profiles, which can be proof of the acceptable identification of possible anomalies in the study area.

This study investigates the efficiency of different geophysical methods for detecting contaminated zones as well as hidden pipes. There are a number of geophysical techniques that can be useful and beneficial for achieving these purposes. Ground penetrating radar (GPR) and electrical resistivity methods are the most useful approaches for identifying polluted areas and buried features, causing us to utilize such methods in the area. Although GPR and electrical resistivity methods are solely effective for mapping subsurface targets, the integration of these methods might provide us valuable information and valid outcomes. In this paper, electrical resistivity and GPR surveys are conducted and acquired data are modelled to investigate the pollution leakage in the ground. To achieve this aim, a polyethylene pipe with inlet and outlet valves is considered as a tank buried underground in the geophysical test site of Shahrood University of Technology. In the first step of the study, the electrical properties of the empty pipe were measured and modelled using electrical resistivity and GPR methods. In the next step, the pipe was filled by the cupric sulfate solution and electrical measurements were performed again. In addition, the electrical properties were investigated by means of electrical resistivity and GPR methods in another area, sitting on alluvial soil, after and before injecting the cupric sulfate solution. It is worth mentioning that the measurements were performed after drying the surface which was humid due to the injection of cupric sulfate to avoid false conductivity on the ground. The designed profiles include four lines on a buried reservoir and five profiles on alluvial soil. However, the 2D modeling results and interpretation of the acquired data along with two (on the buried target) and three (on alluvial soil) survey lines are just presented in this paper. After collecting and interpreting the electrical resistivity and GPR data in the study area, the results are in the form of two-dimensional models of electrical resistivity and GPR cross sections, which have been obtained by use of RES2DINV and Prism2 softwares, respectively. The obtained results revealed that the electrical resistivity method enjoys a relatively good performance in detailed detection. It is also shown that the GPR method is not able to work properly in alluvial soils with high clay and it suffers from the unsuitability of the transmitter antenna with a frequency of 150 MHz and the destructive effect of moisture on the performance. Regarding the obtained outcomes and using electrical resistivity data, ground details such as polyethylene reservoir, loose and porous soil parts and separation of different areas according to the relative humidity in them have been revealed.

Undoubtedly, one of the evidence of tectonic activity in each region is earthquake, which has a major role in casualties and financial losses. The earthquake is usually caused by faults that sometimes extend to the depths of the earth's crust. In cases where no signs or complications of these faults are observed on the surface of the earth, it is necessary to get a better understanding of these faults and its sub branches by combining geological knowledge as well as remote sensing and geophysical instruments. The Kazar fault in the study area is a fundamental fault that has been attributed to at least six historical earthquake events. Due to quaternary activities, recognition of this fault is very important in the region. Therefore, geological and geophysical studies were carried out on the historical site of Gohartepeh in Behshahr city to reveal its hidden parts. Specific resistive methods with bipolar bipolar arrangement at 10 and 20 meters intervals are used to provide sections and maps. By examining them and considering the position and depth of the anomalies obtained in the next stages, new profiles and networks were designed. In order to obtain more accurate results, the cesium magneto metric scanning was performed on 4 profiles. Data obtained from field operations and data acquisition as well as final processing of data in specialized software have been incorporated and clearly interpreted from sub-surface structures, especially faults and discontinuities in the study area, which indicate an impressive anomalous adaptation obtained with field evidence.

Sedimentary environments are the best place to keep records of past events and evidence of fundamental events occurring on the surface of the earth within sedimentary units and their discontinuities. The identification and separation of these sedimentary units have often been the goal of many geological projects with different scientific and practical objectives. Detection of the alluvial deposit has always been of high importance when combined with their study. These hybrid studies are usually carried out in direct (sampling) and indirect methods (geophysical methods). In previous studies, in almost all researches, the necessity of carrying out sedimentology studies to better interpret the identified sequences and their adaptation to GPR studies has been emphasized by the researchers. This combination of studies, in addition to separating different units in terms of grain size, may include other factors such as the presence the quality and depth of fluid (ground water and water table), uniformity of particle size (sorting), particle size, and sedimentary structures. The main objective of this research is to identify sediments and ambient environments of alluvial soils by integrating the data from sedimentation from wells and GPR. The study area is located in Guilan province, between Kouchesfahan and Lasht-e-Nesha cities in the coastal plain of the Caspian Sea. The climate of the study area is humid and the annual rainfall is an average of 800 mm. From geomorphology point of view, the northern boundary of the Alborz is in accordance with the cluster of tertiary deposits and the coastal plain of the Caspian Sea. Under the sea terraces and alluvial plain covers, there are the Miocene-Pliocene-Quaternary marine rocks that have been displaced by the retreat of the Caspian Sea.

Firstly, GPR data (using 100 megahertz antenna, MALA) was taken to 11 km long land along the Kouchesfahan road to the Lasht-e-Nesha. Then, according to the radar profiles, they were drilling 7 sedimentary boreholes for media depth 2.7m to combine with sedimentology data. Global Positioning System is used to determine the location. the resulting data for the processing stages entered the Reflex-W software. After performing the necessary processing considering the radar facies and the depth of penetration of the waves in the radar profiles, suitable points for drilling boreholes were selected for a sampling of subsurface sediments (7 stations). The average depth of the drilled boreholes is 7.2 m. 42 Sediment samples were taken in each well based on the visible changes, including sediment type, grain size, color, moisture, and organic matter content. In the laboratory, grading experiments were carried out after the preparation of the samples (drying and separating organic matter), direct measurement of the dimensions with morphoscopy, dry sieving, and hydrometric method. In addition to the initial analysis of grain size, other statistical parameters such as the average of diameter, mean, sorting, skewness were measured.

Investigations have led to the identification of five radar facies (Reflectors no-continuous undulating with concave-convex pattern, Reflectors continuous with concave-convex pattern, Reflectors no-continuous with different angle, Reflectors no-continuous parallel with low angle, Reflectors no-continuous with low angle and attenuation high and nine sedimentary facies; silty very fine Sand (Zs), fine Sand (s), sandy Gravel (sG), gravely fine Sand (gS), organic matter (O), silty coarse Sand (zs), coarse Sand(S), muddy slightly gravelly sand (g)Ms, which represent different parts of the river environment, including the river canal and floodplain. In this region, the amount of fine-grained particles and organic matter increases from the south to the north. The facies are likely to be part of the old channel of the Sefidrud River when the channel has been redirected to the east. Changes in the percentage of grain size in the boreholes have irregular variations, which the number of fine grain particles is increased from the upstream to downstream of the region. Grains tend to be coarser from the bottom to the top of the boreholes and finer toward the shore. Sorting are bad and very bad in most samples, which indicates the deposition of finer grain particles among coarse grains. From the upstream side, in most drilled boreholes, sediments show a finning and a coarsening upward sequence that indicates the energy fluctuations of the environment over time.

The results of this study showed that wet, fine-grained with high organic matter content environments cause the destruction of the wave and including the radar method's limitations. Also, in urban environments and through the passageways, vehicle overpasses and power rails affect radar profiles and cause the radar profile to be illegible. In the studied area, the depth of effective influence of the waves is not more than 3 meters. In this research, based on valid scientific classification, 5 radar facies and 9 sedimentary facies related to different sedimentary environments were identified. The results showed that radial facies, with respect to depth, particle size, moisture, organic matter and evaporates content limitations, can be very good for identification of various sediments, especially at low and near depths. By performing this research and matching the sedimentary and radial facies, the ability of the two methods in another interpretation was also identified and such adaptations can be applied in other areas with great confidence.

     Ground-penetrating radar (GPR) method is a pretty new, non-destructive and high-resolution geophysical method that is widely used to identify the thickness of snow and ice layers and glaciers bed, because snow and ice are transparent for electromagnetic (EM) waves. Therefore, this method has been used to determine the thickness and basement topography of Alam-kooh glacier. In this research, only the GPR acquired data using unshielded antenna with central frequency of 25 MHz along one line in Alam-kuh glacier, Kelardasht- Mazandaran, have been processed and interpreted. The GPR data acquisition has been done by using common offset method, and transmitter-receiver separation of 6 meters. The final real radargram related to one of the surveyed GPR profiles in this region has been prepared after applying various processing operations containing signal saturation correction, amplitude gain, f-k migration filtering and static (topography) correction on the raw data. After applying processing sequences on the acquired data, the EM waves reflection off the interfaces of different layers including the reflections from the glacier basement have been detected, and by assigning a suitable EM wave velocity in the ice (0.16 m/ns), the thickness of 50 m for the ice layer laid under the survey line has been estimated. Also, in present research, forward and inverse modeling of GPR data have been performed to employ for snow, ice and glaciological investigations in the AlamKooh region of Mazandaran. To achieve this goal, GPR response of synthetic model corresponding to the real radargram was simulated first, by 2-D finite-difference time domain (FDTD) method. Afterward the inversion method by solving an optimization problem was employed to validate the interpretation of real GPR data. Based on the nature, physical and geometric properties of the subsurface target in the field data, their synthetic model have been built and their two-dimensional GPR responses forward modeling using ReflexW software and finite difference algorithms improved in the frequency domain, have been obtained. Also, it has been used an effective algorithm, coded in GUI environment of MATLAB programming software and as a result, a reliable and accurate inverse modeling has been carried out. In the present study, to simulate the behavior of the propagation of EM waves in GPR method, two-dimensional finite difference method has been used. The main advantage of this method is its comparative simplicity of the concept, high accuracy and simple implementation for complex and arbitrary models as well as easily adjusting the antenna when applied. In this study, acquisition of GPR field data and synthetic data modeling have been carried out in TM mode. The radargrams of the GPR data have been demonstrated using ReflexW software after performing necessary processing sequences.      The obtained results reveal that moraine materials covering the surface of the area are mainly fine-grained granite. The bed-rock or basement in the area is also granite. The polarity representing ice-bed rock is clearly seen on the GPR profiles. The topography of the glacier basement has successfully been detectable using just by GPR method. The electrical resistive nature of the glacier has caused large penetration depth of GPR pulses in this research. Furthermore, the results of the research for presented profiles on the basis of forward and inverse modeling output of GPR data in comparison with real GPR radargrams in the region validated the accuracy of GPR investigations in the area. Although with a quick glance, the error obtained by the inverse modeling for real GPR data seems unexpected and unacceptable, absolutely the high rate of error depends on many factors influencing on the real earth models containing various limitations existing in all forward modeling algorithms and software packages, impossibility of making forward modeling exactly according to the real models (due to the complex nature of the ground), taking into account the homogeneity and uniform host environment and targets in the modeling process unlike the diversity, the presence of different types of noises and so on. Therefore, making a controlled geophysical test site and trying performance of inverse modeling algorithm for field GPR data in this site, as well as determining the important physical parameters such as dielectric permittivity and electrical conductivity by experimental method through sampling from different depths for complex geological environments are suggested.

Dimension stones market is considered as an important and profitable sector of mineral deposit business due to their share in national economic performance. There exist a number of technical reports highlighting a lack of rock quality control in the sequence of quarrying and dimension stones production procedures, which has lowered the production efficiency and consequently the profitability of this strategic mineral industry in Iran. The quality of dimension stones depends on several factors which fractures, joints, voids and fine beddings are the most important factors that down-grade the quality. Therefore, foremost the quality and desirability of the building stone must be precisely determined by sampling, compressive strength testing and preparing microscopic sections. All of the mentioned evaluation methods are destructive. Moreover, sampling and performing multiple tests on all parts of a quarry or on all quarried stone blocks, is not possible. Detection of fractures hidden into the dimension stone blocks is achievable using fast, low-cost, accurate and non-destructive ground-penetrating radar (GPR) method. GPR is a high-resolution geophysical method which uses electromagnetic waves with high-frequency in order to map structures and detect buried objects in subsurface without coring or any destruction of the medium.

In current research, GPR method has been applied to evaluate the quality of quarried travertine blocks at Haji-Abad quarry complex in Mahallat district, Markazi province, before starting any processing operation. To achieve this goal, the 2-D GPR responses of synthetic models resembling cubic dimension stone blocks containing fine layering and discontinuities, were primarily simulated using a modified 2-D finite-difference forward modeling program in the frequency-domain coded in MATLAB. Among the variety of available numerical methods, the finite-difference time-domain (FDTD) method has paid more attention due to having the simple understanding of the concepts, flexibility, simulation and modeling of complex environments and the acceptability of its responses in the applied cases. In this research, the simulation has been implemented for both calcareous and dolomitic rocks (including travertine and marbles) and granites. In the study area, the GPR data acquisition was carried out using a GPR system equipped with shielded 250 MHz central frequency antenna, 0.5 m antenna distance and 2 cm sampling intervals by monostatic common-offset reflection profiling method. In order to process, analyze and interpretation of data, Ground Vision and Radexplorer software were employed. The most important pre-processing and processing operations applied to the data to provide the final sections, comprising time-zero correction, dewowing (removing very low frequency components from the data), DC shift removal, Butterworth filtering, running average, background removal and types of amplitude gain.
Results and The results of the forward modeling show that the GPR response of fine beddings interfaces and major discontinuities hidden in the volume of dimension stone blocks are clearly detectable. Interpretation of the actual radargrams taken from a real GPR case study (Haji-Abad quarry complex) after employing various B-scan pre-processing and filtering procedures, indicates that GPR method is highly capable to detect fine beddings and discontinuities in order to evaluate the quality of dimension stone before starting any quarrying process. Validation of the obtained results of the present research was carried out on one of the blocks with a predicted large oblique joint while the existence of the large joint was proven under the cutting saw in the stone processing plant. However, it should be noted that due to the existence of inherent heterogeneity encompassing fine beddings, in addition to noises from different sources and their associated multiple reflections in real radargrams, the response of shallow major discontinuities may mask the response of minor ones located underneath or deeper, so as a result may not be detectable with routing GPR radargrams.

Ground penetrating radar (GPR) method is a non-destructive geophysical method that is used to detect subsurface heterogeneities, and also, to recognize various shallow targets. In the present research, forward and inverse modeling of GPR data was carried out to detect subsurface buried pipes. In Shahrood University of Technology campus, GPR data along several survey lines were acquired using 250 MHz shielded antenna to detect hydrocarbon transfer pipes. To achieve the goal, the real radargram along the survey lines in the area was obtained after applying different processing operations including signal saturation correction, static correction and amplitude gain on the GPR data using ReflexW software. Then, the synthetic radargram corresponding to the real radargrams was simulated using finite-different time domain (FDTD) method. In this study, acquisition of field GPR data and synthetic models were carried out in TM mode. Afterward, the inversion method with solution of an optimization problem was employed for validation of the interpretation of GPR radargram in order to detect buried targets. The results of this study on the basis of conformity of real GPR data with GPR response of their respective synthetic models validated the accuracy of GPR investigations in detection of buried pipes in the area.

Today, it is indispensable to transmit and retain fuels, water and other energy resources by buried pipes, tanks and cables in urban and non-urban areas. Thus, the generation of huge and costly underground networks for this purpose is inevitable. Following the creation of such networks, their maintenance, and prevention from possible destructions are needed. Otherwise, considerable financial losses and irreparable environmental contaminations may occur. Often, a sufficient physical contrast between these installations and their surrounding media exists, and as a result, these installations are considered as suitable targets for detection by ground penetrating radar (GPR) method. In this paper, GPR data, acquired from a GPR survey on buried pipes including metallic pipes for gas transmission, have been processed and interpreted to detect the buried metallic pipes and other subsurface anomalies. To investigate the advantages or efficiency and drawbacks of the GPR method in this application, we have compared the results of the GPR method with the results of the magnetic method performed on the same targets. The results of this comparison are given in the following.
The GPR method provides a higher resolution in comparison to the magnetic method. However, GPR waves in subsurface highly conductive media are intensively attenuated. Hence, the depth of penetration in the latter method is limited. As can be seen from the GPR depth sections obtained from the GPR survey in the study area, the depth of penetration is even less than two meters. The magnetic method, despite its weak resolution, can more successfully detect the targets in highly conductive media provided that there is a good magnetic susceptibility contrast between the target and the surrounding medium. In urban areas, where high noise levels exist magnetic surveys unlike GPR methods via shielded antenna cannot be successfully performed. In this research, first, both the GPR and magnetic surveys have been carried out along survey lines passing the buried gas pipelines and other shallow subsurface targets in Qaleh-Showkat area that is approximately located 10 km to the west of Shahrood city to detect the targets. Then, the results of the GPR and magnetic surveys have been compared. As a result, we have found that the GPR method provided higher resolution in the detection of small anomalies located at shallow depths and near each other. However, in the locations having high electrical conductivities, the GPR method, unlike the magnetic method, could detect very shallow subsurface targets or anomalies even high attenuation of the GPR waves happen in these situations.

Summary Geophysical methods can effectively be used for delineation and maintenance of man-made subsurface installations. These installations are suitable targets for detection by ground penetrating radar (GPR) method. In this non-invasive method, high frequency electromagnetic (EM) waves in the frequency range 10 to 1000 MHz are used for detection, demonstration and investigation of shallow subsurface structures. The most important advantage of this method over other geophysical methods its high resolution, high speed of survey and nondestructiveness. In urban areas where the ground surface is covered by asphalt and also noise level is high, it not possible to use other geophysical methods while obtain high resolution data without destruction of the asphalt. However, the GPR method with shielded antenna acts well in urban areas. This method can present a three-dimensional (3-D) picture from the subsurface in which an accurate estimation of the subsurface structures can be made. In this method, EM waves, generated by the GPR transmitter, are sent into the ground and the reflections from the subsurface structures are received by the GPR receiver. The GPR waves are intensively attenuated in high conductive subsurface media and hence, the depth of penetration of GPR waves in this method is limited. In this research work, the depth of penetration of the GPR waves in the study area decreases to less than 2 meters. In this research, an urban survey area where various metallic and non-metallic pipes have been buried is selected, and then, GPR survey is performed on a grid in the area. As a result of processing and interpretation of the acquired GPR data, the subsurface targets at different depths are detected with relatively good accuracy and resolution.
Introduction Nowadays, transmission of fuels, water and other energy resources by buried pipes, tanks and cables in urban areas is a substantial necessity for human beings. This leads to creation of huge and costly underground networks. Following creation of such networks, a very important matter is the maintenance of these man-made installations to prevent them from possible destructions. These destructions to the installations are not normally observable at the ground surface as the installations are located in the subsurface areas. These destructions that can occur due to different reasons can cause considerable financial losses and also irreparable environmental contaminations. In this regard, geophysical methods can be used for delineation and maintenance of these installations. Often there is a sufficient physical contrast between these installations and their surrounding media. Thus, these installations are suitable targets for detection by GPR method. In this method, high frequency EM waves in the frequency range 10 to 1000 MHz are used for detection, demonstration and investigation of shallow subsurface structures.
Methodology and Approaches In this research work, GPR method has been used in an urban survey area where various metallic and non-metallic pipes have been buried. The GPR survey has been performed on a grid in the area, and then, the GPR data have been acquired using 250 MHz Noggin Plus GPR system with shielded antenna. Following processing and interpretation of the GPR acquired data, two-dimensional (2-D) and 3-D maps and depth cross-sections are obtained. As a result of this GPR survey, the subsurface targets at different depths in the 3-D maps have been detected with relatively good accuracy and resolution. These 3-D maps can considerably help the interpreter to interpret the GPR data reliably and accurately. Moreover, significant and relatively comprehensive information from these 3-D maps is obtained. 3-D presentation of the GPR data is very useful in the 3-D visualization of the subsurface, and thus, can indicate the targets more precisely.
Results and Conclusions In this research work, the depth of penetration of the GPR waves in the study area was less than 2 meters. 2-D and 3-D GPR maps and depth cross-sections were obtained as a result of processing and interpretation of the GPR acquired data. Moreover, the subsurface targets at different depths in the 3-D maps were well detected with relatively good accuracy and resolution. 3-D presentation of the GPR data is very useful in the 3-D visualization of the subsurface, and thus, can indicate the targets more precisely. The results of this research indicate that non-invasive, fast and cheap GPR method has considerable advantages over other geophysical methods in civil engineering applications.

The method of ground penetrating radar (GPR) has increasingly been used for investigation of surface and internal structures of glaciers within the last few decades. This geophysical method distinguishes different structures of glaciers considering the existence of electrical permittivity contrast between ice, air, sediment debris and water in the glaciers. In this research, the GPR acquired data using unshielded antenna with central frequency of 25 MHz along 3 lines in Alam kuh glacier, Kelardasht, Mazandaran, in June 2012, have been processed and interpreted. In order to remove the effect of low-frequency unwanted reflections overlain on high-frequency reflections from all GPR sections, we have used dewow filter. Moreover, we have used gain function for signal enhancement, especially in late times of the GPR data acquisition. Considering the coarse topography of the study area, we have also applied topography correction on the data, and then, the obtained results have been compared with the obtained results without topography correction to demonstrate the importance of topography correction on GPR data. Moraine materials, covered the surface of the area, are mainly fine-grained granite. The bed rock or basement in the area is also granite. The polarity representing ice-bed rock is clearly seen on the GPR profiles. Furthermore, the results of this research indicate that recognition of moderate and cold ice areas in the glacier, type of the glacier (Multi-thermal), holes and topography of the glacier basement has successfully been possible using only the GPR method. The electrical resistive nature of the glacier has caused large depth of penetration of GPR waves in this research work.

The behaviour of Ground Penetrating Radar (GPR) electromagnetic field can be simulated using Maxwell’s equations and associated boundary conditions. So far a number of numerical methods for modeling GPR data have been proposed including the popular Time Domain Finite Difference (TDFD) technique. The popularity of TDFD is mainly due to being relatively simple to implement، its high flexibility and capability to simulate complex subsurface geology. Also، the TDFD approach is not only conceptually accurate for complex geological models but also enables us to design realistic antenna and to study physical electromagnetic phenomena such as dispersion in electrical properties. Despite having these advantages، the finite difference method has pitfalls such as becoming very time consuming in simulating the most common media especially with high dielectric permittivity causing the forward modeling process to become very time consuming even by modern high-speed computers. Synthetic GPR responses are useful for predicting expected GPR data over known geometries such as horizontal cylinders and prisms. The GPR data and subsurface lithological and hydrogeological properties are related through a numerical forward modeling engine. Therefore، the GPR forward modeling engine can transform the subsurface electrical properties into expected GPR responses which in turn can be used for optimizing data acquisition procedures on pre-defined subsurface targets. Since any efficient inversion routine requires a fast forward modeling engine، this study aimed the development of a fast forward modeling algorithm capable of being implemented in any inversion routine. To have efficient numerical forward modeling algorithm، we have adapted a leap-frog، staggered-grid approach introduced by Yee، which incorporates offsetting the electric and magnetic field components in both space and time in such a way that the finite difference approximations of the governing partial derivatives in each equation are centered on the same spatiotemporal location. Obviously 2-D modeling is limited and cannot fully account for antenna behaviour and out-of-plane variations in material properties; however، many important features common to most GPR responses can be identified via employing a computationally cost effective 2D algorithm. In the current study، the patterns of GPR responses that are well known to be hyperbola in shape are used as leading models in order to reduce the execution time. A GPR system collects the reflected pulses coming from different depths in the form of traces which when gathered along with a profile، they make a GPR section called radargram. In general، the simulated GPR traces of common reflected objects are time shifted like the Normal MoveOut (NMO) traces encountered in seismic reflection responses. This property suggests the application of Fourier transform to the GPR traces and the use of time shifting property of such transformation to interpolate traces between the adjusted traces in frequency domain. Therefore، the lateral resolution of GPR traces computed along with any profile is enhanced using a linear interpolation in the Fourier domain resulting in an increased speed of the forward modeling algorithm. Selecting the minimum lateral trace to trace interval with the appropriate sampling frequency of the signal، prevent any aliasing to occur. It is shown that such methodology can significantly decrease the computing time by more than 12. 5 times.

Every geophysical method has its own advantages and disadvantages. The integration of the results obtained surveys using various geophysical methods causes the weaknesses of a particular geophysical method to be covered by the other geophysical methods. For this, different exploration, engineering, environmental and other investigations using various geophysical methods usually provide more reliable results. In this research work, it is attempted to integrate the results of electrical resistivity tomography (ERT) and ground-penetrating radar (GPR) surveys in order to examine the advantages and weaknesses of each of the two methods, and finally, to present more accurate and more reliable interpretation as a result of this integration. The ERT method that is, in fact, one of optimal resistivity survey methods, renders acceptable results in complex geology areas. The GPR method as a high resolution non-destructive geophysical method, which is based on transmission of electromagnetic waves in the ground and recording the reflected waves the interfaces of the subsurface layers, is used for shallow subsurface investigations. In this research work, a water qanat was ed as a suitable target for detection by these two geophysical methods, and the, ERT and GPR surveys were carried out in an area enclosing the target. The results obtained processing, modeling and interpretation of the acquired data indicated that the GPR method, compared to the ERT method, had higher resolution than the ERT method. However, the ERT method, compared to the GPR method, had higher depth of penetration. The results of both methods were mainly in good agreement with each other in depicting features such as subsurface cavities, variation of the grain sizes of the subsurface sediments and water percolation the qanat to its surroundings. Furthermore, following the integration of the results of these two methods, it was found that the accuracy and reliability of the interpretation were considerably enhanced.

Detection of subsurface installations and knowing their characteristics and accurate burial places are some challenges that the engineers involved always face with. Urban development, and thus, the necessity for the development of new and convenient installation networks and also the need for maintenance of old installation networks indicate the significance of accurate placement of the subsurface installations. In this regard, non-destructive methods have been considered to be used by many engineers in this field in order to save time and costs and also to reduce the disturbances due to unnecessary drillings in urban areas. In general, geophysical methods are among the most important non-destructive methods. One of shallow subsurface geophysical methods which has obtained some degree of success in this regard is the ground penetrating radar (GPR) method. In this research work, the GPR method is applied in several case studies having different subsurface conditions, and thus, the capability of the GPR method is investigated for accurate placement of subsurface installations in these case studies. Furthermore, we use a different procedure in data interpretation and analysis to analyze the characteristics of amplitude, phase and frequencies of GPR pulses in order to derive maximum information from GPR sections. Three-dimensional (3D) data survey in one of case studies carried out in this research work had made it possible to process, interpret, and visualize subsurface structures in 3D form. Besides, resistivity surveys in the study area had provided us with the possibility of investigation and correlation of the GPR data results with the resistivity findings. Considering that a survey line had been carried out on the subsurface media containing high electrical conductivities, the unfavorable influence of the conductivities of survey media on the GPR measurements made along the survey line was indicated. Since the resistivities (or conductivities) of the subsurface media play an important role in the penetration of GPR waves, we can estimate the resistivities of the subsurface media by analyzing the frequency spectrum of the GPR pulses propagated in the media. Furthermore, the systematic noise affecting the GPR measurements is recognized by this frequency–spectrum analysis as this noise has frequencies different from those of signals. This study also considers GPR and resistivity investigations along a survey line crossing subsurface metallic and non-metallic installations, and thus, detailed investigations made on these subsurface targets. In this area, an estimation of the diameter of the non metallic pipe installed for transferring of water in the subsurface has been made with a good accuracy from the acquired GPR time section along the survey line. Moreover, the analysis of amplitude and phase characteristics of the GPR pulses from some parts of the survey line has made it possible to distinguish or separate GPR responses of metallic installations from non-metallic ones. Finally, by considering GPR measurements along a survey line passing a subsurface non-metallic pipe, we investigated the effect of the fluid inside the pipe.

Ground water, cavities, and isolate buried structures embedded at shallow depths are well detectable by resistivity and GPR methods because of distinct contrast in their electric and electromagnetic properties in comparison with their surrounding media. In this research work, 3 different profiles on such targets have been chosen, and their responses have been investigated. Using both resistivity and GPR methods together, it has also been possible to investigate capabilities and limitations of the methods in practice. The results obtained from this research work indicate that the GPR method, in addition to its speed and simplicity in data acquisition, is very successful in detection of interfaces or boundaries between different media in which electromagnetic properties at the boundaries change rapidly. The resistivity surveys, which have been carried out using Wenner array in this study, indicate low resistivity of the media under investigation. The low resistivity of the subsurface media caused the depth of penetration of the GPR method to be low, and as a result, made it impossible to investigate the targets buried at depths greater than 2 meters. Unlike the GPR method, the resistivity method has not been very successful in detection of multiple targets with high resistivity contrasts. Lower resolution of the resistivity method in comparison with GPR method has caused this problem. In this study, considerable information has been obtained by selecting two different processing algorithms and applying them on a series of raw GPR dataset. The obtained information from the resistivities of the subsurface structures as a result of the resistivity surveys has made it possible to choose and apply these processing algorithms. This research work well indicates that high conductive areas in resistivity sections coincide with the areas in the GPR sections having intensive attenuation. This characteristic can be used well in the interpretation of the GPR sections. Finally the resistivity method can be introduced as a suitable supplementary geophysical method to the GPR method.