Dipole-dipole Configuration Research Articles

Geo-Electric Resistivity Method of Dipole-Dipole Configuration For Cavities Model 2D in Karst Area of Temurejo Village Gubug Sub-district Central Java District

<p class="Abstract">The purpose of this research is to mapping cavities in karst area in Temurejo Village, Karangrayung, Grobogan using geoelectric resistivity method and dipole-dipole configuration. Measurement consist of six lines using Multichannel S-Fields geoelectric instrument. Apparent resistivity data processing use two software, Res2DInv ver. 3.56.22 and Voxler 4.0. The result is lithology of the research location can be interpret consist of sand-silt, carbonate-silt rock, carbonate-sand rock, and carbonate rock with resistivity range 15,3-4919 Ωm. There are resistivity value anomaly in line of 1,2,3,4,5, and 6 on the carbonate rocks layer, the value is more than 4949 Ωm which can interpret as a cavity. On the first line, cavities are at depths of 20 m and 12 m, on second line are at depths of 17 m and 12 m, on third line is at depth of 19 m. Cavity continuously at depth of 18 m on fourth, fifth and sixth lines. This cavities at the depth >23 m beneath eath surface.</p>

Penyelidikan Zona Longsor dengan Metode Resistivitas dan Analisis Stabilitas Lereng untuk Mitigasi Bencana Tanah Longsor

<p>Research using geoelectric resistivity dipole-dipole configuration and slope stability analysis has been done in the area Jawar, District Dampit to find out the sliding plane landslide, landslide direction and factor of safety. Tracks Retrieval of data by the method of geoelectric resistivity as much as 5 tracks with the direction of the southeast to the northwest three tracks with a length of 100 m - 200 m and southwest to northeast as many as two passes with a length of 200-300 m. While the slope stability analysis performed topographic map data retrieval and data collection sondir and boring. Based on the analysis of the lithology of the study area using resistivity geoelectric method shows three layers of soil is clay (the top layer), tuff (middle layer) and basalt and lava (bottom layer). sliding plane landslide area is in the boundary between the layers of clay and tuff (a depth of 10.5 m). Based on the results of data processing of 3D resistivity geoelectric, landslide direction is southeast. Safety factor value of the security research area based slope stability analysis is 1.015. This value indicates that this area is prone to landslides.</p>

Seepage Zone Identification at Sutami Dam by Means of Geoelectrical Resistivity Data

A study with entitled Seepage Zone Identification At Sutami Dam By Means Of Geoelectrical Resistivity Data has been conducted. The aim of this study is to get the distribution of seepage zones in the Sutami dam body. Data acquisition has been done by using Oyo-EL McOhm Model 2119C equipment on the tracks along the side of the dam body, both downstream (exhaust) side for first and upstream (reservoir) side for second with pseudodepth section dipole-dipole configuration. Each track has a length of 400m and 380m respectively. The distance between the point electrode consists of 1 track with space (a) is 10m (n=8) and 3 tracks with a space (a) is 20m (n=8). Based on the results of data processing obtained are low resistivity values (ρ ≤ 9.57 Ωm), the moderate resistivity value (9.57 Ωm < ρ ≤ 320 Ωm), and high resistivity (ρ > 320 Ωm). The distribution of fracture zones associated with seepage zones for Sutami dam distributed over the surface to depth of 8-18 m, both upstream (reservoir) or downstream (exhaust) indicated by resistivity values 0.922 Ωm to 9.57 Ωm. The results of the 3D data processing indicates that the fracture zone is also distributed between the upstream (reservoir) and downstream (exhaust) of the Sutami dam body.

Pola Tahanan Jenis dan Konduktivitas Batuan Mengandung Mineral Radioaktif di Botteng dan Takandeang, Mamuju, Sulawesi Barat

AbstrakKegiatan penyelidikan umum mineral radioaktif di daerah Mamuju, Sulawesi Barat merupakan tindak lanjut dari hasil pengukuran radioaktivitas lingkungan yang menunjukkan adanya nilai radioaktivitas tinggi. Kandungan mineral radioaktif yang cukup tinggi ditemukan antara lain di Desa Botteng dan Desa Takandeang yang tersusun oleh batuan berkomposisi leusit-basal tetapi karakteristik bawah permukaan daerah ini belum diketahui. Untuk mengetahui karakteristik geologi bawah permukaan, terkait dengan mineralisasi Uranium dan Thorium di daerah Botteng dan Takandeang, pengukuran geofisika menggunakan metode tahanan jenis dan polarisasi terimbas (Induced Polarization/IP) dilakukan. Pengukuran tersebut dilakukan menggunakan konfigurasi Wenner dan dipole-dipole, dimulai dengan pembuatan enam jalur pengukuran, masing-masing tiga jalur: GF/BTGY-01, GF/BTGK-02, dan GF/BTGK-04 di Botteng, dan tiga jalur lainnya: GF/TKDK-01, GF/TKDK-07, dan GF/TKDY-06 di Takandeang. Pengukuran dilakukan dengan memotong arah kemenerusan anomali radiometri permukaan. Hasil pengukuran menunjukkan keterdapatan anomali berada pada sebaran batuan autobreksia yang terlihat jelas di lokasi GF/TKDY-6, GF/TKDK-07, dan GF/BTGK-04. Beberapa indikasi mineralisasi di permukaan teridentifikasi di penampang GF/BTGK-02 dan GF/TKDK-01, dicirikan dengan anomali-anomali chargeabilitas &gt;25,14 ms di lintasan GF/BTGK-02 dan 81,4 ms di GF/TKDK-01. Anomali yang signifikan direkomendasikan sebagai lokasi pemboran. AbstractThe general investigation activities of radioactive minerals in Mamuju Area, West Sulawesi is a respon of the environmental radioactivity measurement result, which shows the existence of high radioactivity value. High radioactive mineral content found in Botteng and Takandeang Villages. From the outcrops, they composed of leucite-basalt rocks; meanwhile the subsurface characteristics of this area are unknown. To characterize the subsurface geology, related to uranium and thorium mineralization in Botteng and Takandeang area, geophysical measurement conducted using resistivity and Induced Polarization (IP) methods. The measurements carried out using Wenner and dipole-dipole configurations. The measurements started with the creation of six measurement paths where three lines: GF/BTGY-01, GF/BTGK-02, and GF/BTGK-04 are in Botteng and three other lines: GF/TKDK-01, GF/TKDK-07 and, GF/TKDY-06 are in Takandeang. Measurements conducted by crossing the surface radiometric anomaly distribution. The result showed anomaly occurences on autobreccia distribution in GF/TKDY-6, GF/TKDK-07, and GF/BTGK-04 locations. Several mineralization indication on surface identified in GF/BTGK-0, and GF/TKDK-01 sections, charaterized by chargeability anomalies more than 25.14 ms and 81.4 ms respectively. All significant anomalies are recomended as drilling location.

Soil Structure Evaluation Across Geologic Transition Zones Using 2D Electrical Resistivity Imaging Technique

This study utilizes the electrical resistivity values obtained using 2-D Electrical resistivity imaging (ERI) technique to evaluate the subsurface lithology across different geological units. The primary objective was to determine the effect of subsurface lithology on the integrity of a road pavement, which had developed cracks and potholes at various locations. The dipole-dipole configuration was utilized and a total of nine traverses were established in the study area, whose geology cuts across both the basement and sedimentary complexes. The inverted resistivity section obtained showed significant variation in resistivity along established traverses and also across the different rock units, with the resistivity value ranging from about 4 ohm-m to greater than 7000 ohm- m. The lithology as interpreted from the resistivity section revealed the presence topsoil, clay, sandy clay, sand, sand stones/basement rocks, with varying vertical and horizontal arrangements to a depth of 40m. Results suggest that the geologic sequence and structure might have contributed to the observed pavement failure. The capability of the 2D ERI as an imaging tool is observed, especially across the transition zones as depicted in this study. The study further stressed the ability of this technique if properly designed and implemented, to be capable of providing a wealth of information that could complement other traditional geotechnical and geologic techniques.

Sea Water Intrusion in Kaligawe Semarang Based on Resistivity Data

Semarang is a city on the north coast of the island of Java, Indonesia and it is lowland areas have experienced sea water intrusion. One of interesting area is Kaligawe which located at Eastern part of Semarang. Kaligawe has big population and industrial and it need water consumption. Excessive extraction of groundwater will be resulting height difference surface ground water to the surface of the sea water due to sea water intrusion. Electric resistivity method was used to detect for salt water intrusion. Dipole-dipole configuration was applied with 3 lines to get current, potential difference, and apparent resistivity from the field. 2D model has presented using Res2Dinv to get the true resistivity and the depth of each layer. A calibration of the model was conducted based on geological information. Result showed the subsurface area has 4 layers: sandstone, sandsilt, siltstone and clay. Moreover the sea water intrusion occurs in the Northwest, East and Southern part of the study area

3D electrical resistivity tomography of karstified formations using cross-line measurements

The acquisition of a full 3D survey on a large area of investigation is difficult, and from a practitioner's point of view, very costly. In high-resolution 3D surveys, the number of electrodes increases rapidly and the total number of electrode combinations becomes very large. In this paper, we propose an innovative 3D acquisition procedure based on the roll-along technique. It makes use of 2D parallel lines with additional cross-line measurements. However, in order to increase the number of directions represented in the data, we propose to use cross-line measurements in several directions. Those cross-line measurements are based on dipole-dipole configurations as commonly used in cross-borehole surveys. We illustrate the method by investigating the subsurface geometry in a karstic environment for a future wind turbine project. We first test our methodology with a numerical benchmark using a synthetic model. Then, we validate it through a field case application to image the 3D geometry of karst features and the top of unaltered bedrock in limestone formations. We analyze the importance of cross-line measuring and analyze their capability for accurate subsurface imaging. The comparison with standard parallel 2D surveys clearly highlighted the added value of the cross-lines measurements to detect those structures. It provides crucial insight in subsurface geometry for the positioning of the future wind turbine foundation. The developed method can provide a useful tool in the design of 3D ERT survey to optimize the amount of information collected within a limited time frame.

The Effectiveness of Wenner-Schlumberger and Dipole-dipole Array of 2D Geoelectrical Survey to Detect The Occurring of Groundwater in the Gunung Kidul Karst Aquifer System, Yogyakarta, Indonesia

Until today, geoelectrical survey is the most effective method for groundwater exploration. 2D method or known as horizontal profiling is now the most appropriate method in the geoelectrical survey compare to vertical electrical sounding method. The 2D method of Wenner-Schlumberger and Dipole-dipole configuration proved to be very effective to locate conventional aquifer occurrence on volcanic terrain or sedimentary terrain. Karst aquifer system is an unconventional aquifer and acts very differ in contrast with the conventional sedimentary aquifer. Heterogeneity and discontinuity of limestones in karst terrain will reveal a wide variety of resistivities, hence it is difficult to interpret. This research has important objective to define the effectiveness of the Wenner-Schlumberger and Dipole-dipole configuration in the 2D geoelectrical survey to explore groundwater in the karst area. Field observation of geology and 2D geoelectrical survey were conducted in underground river of Kali Suci Area, Gunung Kidul. In Kali Suci where an endokarst cave was occured on the surface, line survey was placed in the top of the cave and across the geometry of the cave. Measured stratigraphy in the wall of the cave found four types of limestone which consist of packstone, wackestone, grainstone and crystalline limestone. The Wenner-Schlumberger and Dipole-dipole method can detect differentiation of limestone types and also the exposed underground river successfully. However, compared to Wenner-Schlumberger array, Dipole-dipole array reveals less vertical accuration.. Therefore, on this research, the best method to detect water saturated zone or gourndwater in the karst system is the Wenner-Schlumberger method.

Electrical Resistivity Imaging of a Thin Clayey Aquitard Developed on Basement Rocks in Parts of Adekunle Ajasin University Campus, Akungba-Akoko, South-western Nigeria

In this study, 2-dimensional electrical resistivity surveying has been used to reveal the nature and development of a thin clayey aquitard on basement complex rocks of the Adekunle Ajasin University campus, Akungba-Akoko south-western Nigeria. The aim was to evaluate the occurrence, geometry and groundwater viability of this clayey aquitard as an alternative source of water supply on the Campus. Prior, a hand-dug well, which supplied moderate volumes of water all year round, had been abstracting water from this aquitard. Three east-west geo-electric traverses were surveyed using the dipole-dipole array configuration with an electrode separation of 5 m and a maximum dipole length of 45 m. Each of the three traverses was 60 m long. The observed field data were inverted for subsurface 2D resistivity structure using a commercially available 2.5D finite element modelling inversion software. The clayey aquitard is imaged to exist as low resistivity response patterns which have developed in elongated trough-like depressions created as a result of deep weathering of the feldspar and amphibolite-rich sections of the basement rocks of the area. This clayey layer reaches a thickness of 10 m at the southern end of the survey and in some sections is compartmentalised into segments by basement rocks which have better resisted weathering. Where the topographic slope of the ground surface is low enough as to allow the accumulation of run-off, the clayey aquitard develops into visible marshy swamps. Although, clayey aquitards of this nature supply water at low rates, their capacity to store high volumes and to be available all-year-round could prove essential to ameliorating acute water shortages experienced in the area during the dry season. DOI: http://dx.doi.org/10.5755/j01.erem.71.1.9016

2D Resistivity Imaging and Geotechnical Investigation of Structural Collapsed Lecture Theatre in Adekunle Ajasin University, Akungba-Akoko, Southwestern, Nigeria

Geotechnical and geophysical investigation involving electrical resistivity survey and laboratory test of the samples were conducted on the samples obtained at the three different locations in the area. The study is aimed at evaluating the competence of the near surface formation building construction materials. Geophysical and geotechnical methods of investigation were adopted. The Electrical Resistivity Tomography, using Dipole-Dipole configuration and soil analysis techniques were adopted. A total of four traverses and three soil samples from different location within the study area were used for the study. The geophysical results revealed that the topsoil is within the depth of 0 to 5m and it is reflective of varying resistivity which indicates materials suspected to be composed of low resistive materials such as water and underlain with a basement complex and presence of a very low resistivity in which water accumulate and percolate which makes it inimical to foundation of engineering structures. There is an evident of geological feature such as fracture within the bedrock which might aid subsidence in the area. while geotechnical results of natural moisture content, specific gravity, liquid limits, plastic limit, plasticity index, linear shrinkage, compaction and permeability ranges from 5.3-9.2%, 2.620-2.730, 23.0-41.9%, not plastic to 21.4%, from not plastic to 22.4%, 1.4-9.3,1790-2114 kg/m3, 9.1-9.9 and very low to medium respectively. Thus, the soil formation in the study area is therefore rated as relatively poor for foundation material. DOI: http://dx.doi.org/10.5755/j01.erem.69.3.5335

2D Geoelectric Imaging of the Uneme-Nekhua Fracture Zone

We have employed 2D geoelectric imaging to reveal the geometry and nature of a fracture zone in Uneme-Nekhua, southwestern Nigeria. The fracture zone is discernable from an outcropping rock scarp and appears to define the course of a seasonal stream. Data were acquired using the dipole-dipole survey array configuration with electrode separation of 6 m and a maximum dipole length of 60 m. Three traverses with lengths varying between 72 m and 120 m were laid orthogonal to the course of the seasonal stream. 2D geoelectric images of the subsurface along the profiles imaged a north-south trending fracture zone. This fracture zone appears to consist of two vertical fractures with more intense definition downstream. The eastern fracture is buried by recent sediment, while the western fracture appears to have experienced more recent tectonic activity as it appears to penetrate through the near surface. Perhaps at some point, deformation ceased on the eastern fracture and further strain was transferred to the western fracture. The fracture zone generally defines the course of the north-south seasonal stream with the exception of the downstream end where the fracture appears to have died out entirely. Two associated basement trenches lying parallel to and east of the fracture zone are also imaged.

Theoretical and experimental examinations of the capacitively coupled resistivity (line antenna) method

The capacitively coupled (CC) resistivity method is an emerging geophysical technique for near-surface investigations. However, there are two major problems associated with using the CC resistivity (line antenna) system in ground investigations. These two problems are (1) the geometrical factor and (2) measurement biases. We first derive the geometric factor for the line-antenna array in a dipole-dipole configuration. The new expression of the geometric factor considers the separation between the two current (and the two potential) line antennas, thereby improving the accuracy of the measured apparent resistivity. Second, from the electroquasistatic point of view, a quadruline model that can describe the characteristics of the CC resistivity (line antenna) system is derived based on the previously published quadrupole model. The validity of the quadruline model is verified experimentally. Based on the quadruline model, it is found that the dielectric properties of the line-to-ground capacitor and the ground permittivity produce measurement bias at low and high current frequencies, respectively. If the operating current frequency is around the kHz range and the ground resistivity is relatively high, such as in permafrost areas, the ground permittivity can also create measurement bias to cause the actual value to be underestimated. The experimental results and the predictions by the quadruline model suggest that the measurement bias induced by the gap between the line antenna and the ground surface becomes significant and cannot be ignored as the gap height is large and the associated ground resistivity is low. In general, the CC resistivity (line antenna) measurements are not biased by the gap effect when the gap height is less than 0.01 m, which can easily be achieved for tests on flat ground.

Pendugaan Struktur Bawah Permukaan Peninggalan Purbakala Situs Candi Jabung, Probolinggo, Indonesia Menggunakan Metode Geolistrik Resistivitas

The sounding of geoelectrical resistivity distribution using dipole-dipole configuration around the Jabung temple site located in the Jabung Candi village, Paiton, Probolinggo District, East Java province, Indonesia has been done by using Resistivitymeter OYO MacOhm. The aim of the research was to determine the distribution and depth of rock below the Jabung temple area also as an information for investigation and discovery efforts of ancient objects which are still burried. Aquisition are taken by ten lines and ±20.042 m 2 of coverage area. Line 1, 2, 3, 4, 5, 6 located around in Menara Sudut temple at length of measurement line12 m and at a distance of electrode spacing are 1 m, where lines 1 and 4 located in outcrop of Menara Sudut tample. While lines 7, 8, 9, and 10 located in all area of Jabung temple. Lines 7 and 8 have length of measurement lines 150 m with spacing 10 m, while lines 9 and 10 have length of measurement lines 200 m with spacing 4 m, where line 8 located pass to main Jabung tample. The processing of data was using RES2DINV software. Resistivity values that are used to determine the temple rock is the resistivity value of sandy clay. Base on geoelectrical investigation and interpretation shows the sandy clay as temple rock with resistivity value 33 Ω.m to 92.6 Ω.m on average depth of 1.79 m and the others remain of tample rock around the main Jabung tample. This research shows geoelectrical method is good idea to subsurface sounding especially for archeology case, it caused this method is simple and more cheap than ekskavation method.

Characterization and Delineation of Potential Evaporite Geohazards Using Electrical Resistivity Methods along FM 2185, Culberson County, Texas

Extensive karst development within the Delaware Basin of West Texas and southeastern New Mexico poses a significant threat to infrastructure. Dissolution of regional evaporite strata have led to karst geohazards including sinkholes, subsidence features, and caves. The study area is located within the Gypsum Plain in Culberson County, Texas, and includes outcrops of Permian Castile and Rustler strata that host gypsum karst. Land reconnaissance surveys conducted during summer of 2019 documented numerous surface karst features proximal to Farm to Market Road 2185 (FM 2185). In combination with traditional survey techniques, electrical resistivity methods were used to delineate karst features along a 48 km segment of FM 2185. Capacitively-coupled resistivity (CCR) and direct-current resistivity (DCR) methods were used to characterize evaporite karst features that do not manifest surficially but pose potential geohazard concerns. CCR data were acquired using the Geometrics OhmMapper G–858 resistivity system, which uses a dipole-dipole configuration composed of five receivers connected by 2.5 m coaxial cables and a transmitter offset of 2.5 m. In combination with the medium analyzed, this geometric configuration enabled resistivity soundings up to 2.5 m deep. DCR data was collected with a SuperSting (R8/IP) multi-electrode earth resistivity meter using 112 electrodes with 2 m spacing and a dipole-dipole array configuration. This enabled a depth of investigation of up to 25 m. Data were processed using Advanced Geosciences Inc.’s (AGI’s) EarthImager 2D software and used to delineate and characterize karst-related geohazards in the shallow subsurface within the study area. Five sites are presented to demonstrate karst variability and electrical resistivity method effectiveness in geohazard detection in gypsum strata.

The resistivity image of the Muráň fault zone (Central Western Carpathians) obtained by electrical resistivity tomography

The resistivity image of the Muráň fault zone (Central Western Carpathians) obtained by electrical resistivity tomographyThe paper describes the application of geophysical prospecting techniques for estimation of the fault's inclination. The field survey was carried out across the Muráň fault structure in the Slovenské rudohorie Mts (central Slovakia). Three different geophysical methods were used to map the fault zone: Electrical Resistivity Tomography (ERT), induced polarization (IP) and radon emanometry. All these methods have been used to locate the fault zone area, but the principal aims of this research are to test the efficiency of the 2D ERT technique to recognize the geometrical characterization of the fault and to improve our tectonic knowledge of the investigated area. For the synthetic cases, three geometric contexts were modelled at 60, 90 and 120 degrees and computed with the l2norm inversion method, the l1norm with standard horizontal and vertical roughness filter and the l1norm with diagonal roughness filter. In the second phase this geophysical methodology was applied to fieldwork data. Our results confirm that the ERT technique is a valuable tool to image the fault zone and to characterize the general geometry, but also the importance of setting up the right inversion parameters. The main contribution of the geophysical investigations in this case was the determination of the location and confirmation of the inclination of the Muráň fault. The result of this study is the ability to make a visual estimation of the direction and dip of the fault. Pursuant to this work the dipole-dipole electrode configuration produces the best resolution, particularly for the location of vertical and dipping structures. The advantage of this array is that it shows the ability to assess the trend of the dip and therefore it can be strongly recommended. The result is also a case study of a small scale tectonic survey involving geophysical methods.

Analisis Potensi Longsoran Menggunakan Metode Reistivity dan Metode USLE pada Daerah Ranu Pani, Kecamatan Senduro Kabupaten Lumajang

Has done research in the Ranu Pani area is one of the area where landslides have its potentiality, due to its location on the edge of the mountains where the soil is clay, slightly, sandy and has a very high fertility rates. One of the methods used to analyze landslide potential is using USLE (Universal Soil Loss Equation). In addition, the resistivity method with dipole-dipole configuration is also used to determine the structure of the soil and slip areas in the hills in the area Ranu Pani. Debris flow obtained from calculations using the USLE method in the second trajectory is equal to 796.5 tons/year, and the third trajectory is equal to 291.506 tons/year. According to the classification level of erosion, Ranu Pani area is an area with very dangerous level of erosion hazard, because the value of debris flow is more than 180 tons/year. With the high value of debris flow erosion, causing higher sedimentation of the lake, because the Ranu Pani lake accommodate most of the debris flow erosion of the hills around it.

Application of ERT Survey for Addressing the Issues of Urban Rain Storm Water Logging in the Qassim Province of Saudi Arabia

The Qassim province is one of the most arid regions of Saudi Arabia, however heavy rainfall events have led to water logging problems in the populated centers like Buraidah mainly as a consequence of construction in low lying areas and valleys. Urban rain storm water logging problem were reported at 4 localities in the Buraidah Municipal area after heavy rainfall in November 2008 and March 2009. The logged water from these sites were directed to 4 manmade lakes however the stagnant water in these lakes posed a serious environmental threat mainly in the form of water borne disease. Keeping this problem in mind, a detailed geophysical investigation in the form of Electrical Resistivity Tomography was carried out using the SYSCAL Pro Unit at these 4 locations with a dipole-dipole configuration. The survey was helpful in delineating the wet zones from the dry ones and based on the interpretations the optimum depth and sites of 4 injections bore-wells were determined at each locality. These injection bore-well would serve the dual propose of getting rid of the stagnant water in these lakes and also recharging the underlying aquifers.

Inversion of quasi-3D DC resistivity imaging data using artificial neural networks

The objective of this paper is to investigate the applicability of artificial neural networks in inverting quasi-3D DC resistivity imaging data. An electrical resistivity imaging survey was carried out along seven parallel lines using a dipole-dipole array to confirm the validation of the results of an inversion using an artificial neural network technique. The model used to produce synthetic data to train the artificial neural network was a homogeneous medium of 100Ωm resistivity with an embedded anomalous body of 1000Ωm resistivity. The network was trained using 21 datasets (comprising 12159 data points) and tested on another 11 synthetic datasets (comprising 6369 data points) and on real field data. Another 24 test datasets (comprising 13896 data points) consisting of different resistivities for the background and the anomalous bodies were used in order to test the interpolation and extrapolation of network properties. Different learning paradigms were tried in the training process of the neural network, with the resilient propagation paradigm being the most efficient. The number of nodes, hidden layers, and efficient values for learning rate and momentum coefficient have been studied. Although a significant correlation between results of the neural network and the conventional robust inversion technique was found, the ANN results show more details of the subsurface structure, and the RMS misfits for the results of the neural network are less than seen with conventional methods. The interpreted results show that the trained network was able to invert quasi-3D electrical resistivity imaging data obtained by dipole-dipole configuration both rapidly and accurately.

Comparison of Wenner and dipole–dipole arrays in the study of an underground three-dimensional cavity

The objective of this paper was to compare Wenner and dipole-dipole configurations in delineating an underground cavity at a site near the University of Malaya, Malaysia. A three-dimensional electrical resistivity imaging survey was carried out along seven parallel lines using Wenner and dipole-dipole arrays. A three-dimensional least-squares algorithm, based on the robust inversion method, was used in the inversion of the apparent resistivity data. In the inverted model, both the horizontal and vertical extents of the anomalous zones were displayed. Results indicate the superiority of the Wenner array over the dipole-dipole array for determining the vertical distribution of the subsurface resistivity, although the dipole-dipole array produced a better lateral extent of the subsurface features. The results show that the three-dimensional electrical resistivity imaging survey using both the Wenner and dipole-dipole arrays, in combination with an appropriate three-dimensional inversion method and synthetic model analysis, can be highly useful for engineering and environmental applications, especially for underground three-dimensional cavity detection.

Sensitivity functions of frequency-domain magnetic dipole-dipole systems

The resolution capabilities of airborne electromagnetic (AEM) frequency-domain systems are traditionally analyzed in terms of the footprint, which provides a simple measure of the lateral extent of the earth volume involved in a given measurement. However, considerably more detailed insight into the system resolution capabilities can be obtained by studying the 3D sensitivity distribution as defined by the Fréchet derivatives. A qualitative analysis of the 3D sensitivity distributions for six typical magnetic dipole-dipole configurations demonstrates that the spatial resolution characteristics differ widely and that the optimal coil configuration for practical investigations depends on the expected target characteristics. For all six coil configurations, the 3D sensitivity distributions reveal significant sign changesdownwards and outwards from the center, stressing the necessity of reliable starting models for successful inversion of frequency-domain AEM data. Likewise, the central zone of sensitivity for the in-phase component is always larger than for the quadrature, indicating an inferior lateral resolution of the former. A new sensitivity footprint is defined, based on the at-surface behavior of the sensitivity distribution, simply as the area where the sensitivity is at least 10% of its maximum value. For the vertical coaxial (VCA) coil configuration, the size of the sensitivity footprint in the [Formula: see text]-direction (perpendicular to the flight path) is approximately a factor of two larger than in the [Formula: see text]-direction (along the flight path), while there is virtually no difference for the horizontal coplanar (HCP) coil configuration. The ratio of the HCP to VCA sensitivity footprint exceeds one in both [Formula: see text]- and [Formula: see text]-directions, suggesting that the VCA coil configuration has the best lateral resolution.