Geophysical Survey Systems , Inc. Research Articles

Developing a realistic numerical equivalent of a GPR antenna transducer using global optimizers

AbstractNumerical modelling of a ground‐penetrating radar (GPR) has been widely used for predicting and assessing its performance. As the transmitter and the receiver are the most essential components of a GPR system, an accurate representation of them should be included in a model. Simulating a real system is particularly challenging, especially when it comes to commercial GPR systems. A three‐dimensional model based on a 2000 MHz ‘palm’ antenna from Geophysical Survey Systems, Inc. (GSSI) is presented in this paper. The geometric features of the transducers were modelled via visual inspection, whereas their unknown dielectric properties were estimated using global optimizers in order to minimize the differences between real and synthetic measurements. In particular, the antenna was calibrated in free space and on top of a metal plate. Subsequently, the resulting model was successfully tested in various case studies to assess its performance. Models of two units of the same transducer were developed, showing that units of the same system in general are not identical. The results support the premise that global optimizers can be used to provide information on key aspects of the dielectric structure of the transducer and allow us to accurately model its behaviour in various environments.

Development of Condition Assessment Index of Ballast Track Using Ground-Penetrating Radar (GPR).

The condition of the ballast is a critical factor affecting the riding quality and the performance of a track. Fouled ballast can accelerate track irregularities, which results in frequent ballast maintenance requirements. Severe fouling of the ballast can lead to track instability, an uncomfortable ride and, in the worst case, a derailment. In this regard, maintenance engineers perform routine track inspections to assess current and future ballast conditions. GPR has been used to assess the thickness and fouling levels of ballast. However, there are no potent procedures or specifications with which to determine the level of fouling. This research aims to develop a GPR analysis method capable of evaluating ballast fouling levels. Four ballast boxes were constructed with various levels of fouling. GPR testing was conducted using a GSSI (Geophysical Survey Systems, Inc.) device (400, 900, 1600 MHz), and a KRRI (Korea Railroad Research Institute) GPR device (500 MHz), which was developed for ballast tracks. The dielectric permittivity, scattering of the depth (thickness) values, signal strength at the ballast boundary, and area of the frequency spectrum were compared against the fouling level. The results show that as the fouling level increases, the former two variables increase while the latter two decrease. On the basis of these observations, a new integrated parameter, called a ballast condition scoring index (BCSI), is suggested. The BCSI was verified using field data. The results show that the BCSI has a strong correlation with the fouling level of the ballast and can be used as a fouling-level-indicating parameter.

Ground-penetrating radar inspection of subsurface historical structures at the baptism (El-Maghtas) site, Jordan

Abstract. The baptism (El-Maghtas) site is located to the north of the Dead Sea on the eastern bank of the Jordan River. Previous archeological excavations in the surrounding area have uncovered artifacts that include the location that was home to “John the Baptist”, who lived and preached in the early 1st Century AD and is known for baptizing Jesus. Archeological excavations have revealed walls, antiquities, and ancient water systems that include conduits, pools, and ancient pottery pipes. A ground-penetrating radar (GPR) survey was carried out at select locations along parallel profiles using a subsurface interface radar system (Geophysical Survey Systems Inc. SIRvoyer-20) with 400 MHz or 900 MHz mono-static shielded antennas in order to locate archeological materials at shallow depths. The GPR profiles revealed multiple subsurface anomalies across the study area. At the John the Baptist Church site a buried wall was detected along the profiles, and at the pool site the survey delineated several buried channels. GPR data also confirmed the extension of an ancient pottery pipe at the Elijah's Hill site through the production of a clear diffraction hyperbola anomaly related to the ancient pottery pipe that could be discriminated from the 2D profiles. The GPR data were displaced using 3D imaging to define the horizontal and vertical extent of the pipe.

Ground penetrating radar (GPR) study to detect seepage pathways in the Ajanta Caves in India

The present study used the ground penetrating radar (GPR) tool to decipher the presence of fractures which may be possible pathways for seepage into the Ajanta Caves in India. GPR data were collected by 40- and 200-MHz antennas from Geophysical Survey Systems, Inc. (GSSI). The data were edited and processed using the RADAN 6.5 software. The processed data indicate the presence of fractures of varying orientation in the basaltic formations. The study shows high reflection zones indicative of fractures as well as strong absorbance zones which may be a homogeneous zone without any fractures.

Demonstration of ground-penetrating radar as a useful tool for assessing pocket gopher burrows

Ground-penetrating radar (GPR) is an innovative and non-invasive method that uses radar to penetrate the ground and develop three-dimensional digital images of the top several meters of the earth. Ground-penetrating radar has been used extensively in the fields of engineering, military science, forensic science, archaeology, and environmental remediation, but has received little attention by wildlife professionals. We demonstrated a possible application of GPR for wildlife studies for mapping burrow systems using maritime pocket gophers (Geomys personatus maritimus), a subspecies of concern as listed by the U.S. Fish and Wildlife Service. Ground-penetrating radar surveys were conducted at Naval Air Station—Corpus Christi on five 15-m × 15-m areas with >200 above-ground gopher mounds/ha during July 2007. Survey areas were scanned with a Geophysical Survey Systems Inc. SIR-3000, GPR digital control unit and a 900-MHz ground-coupled antenna. Within the 5 areas, we located 8 gophers and mapped 267 m of tunnels that had an average depth of 0.6 m. We were able to differentiate deteriorating or abandoned tunnels from active tunnels, detect an underground pipeline, and distinguish changes in soil texture using GPR. Ground-penetrating radar is a non-destructive and non-invasive method to gain knowledge of fossorial animal movements and potential destabilization of soil integrity. © 2013 The Wildlife Society.

Creating finite-difference time-domain models of commercial ground-penetrating radar antennas using Taguchi’s optimization method

Very few researchers have developed numerical models of ground-penetrating radar (GPR) that include realistic descriptions of both the antennas and the subsurface. This is essential to be able to accurately predict responses from near-surface, near-field targets. We have developed a detailed 3D finite-difference time-domain models of two commercial GPR antennas — a Geophysical Survey Systems, Inc. (GSSI) 1.5-GHz antenna and a MALÅ Geoscience 1.2-GHz antenna — using simple analyses of the geometries and the main components of the antennas. Values for unknown parameters in the antenna models (due to commercial sensitivity) were estimated by using Taguchi’s optimization method, resulting in a good match between the real and modeled crosstalk responses in free space. Validation using a series of oil-in-water emulsions to simulate the electrical properties of real materials demonstrated that it was essential to accurately model the permittivity and dispersive conductivity. When accurate descriptions of the emulsions were combined with the antenna models, the simulated responses showed very good agreement with real data. This provides confidence for use of the antenna models in more advanced studies.

Design and field experiments of a ground‐penetrating radar for Mars exploration

We developed a wideband, low‐power, lightweight, prototype ground‐penetrating radar (GPR) for subsurface exploration for Mars. The transmitter and receiver subsystems were constructed using a commercially available radio frequency (RF) and digital integrated circuits, connectorized components, and evaluation boards. The transmit/receive system, antennas, laptop controller, and batteries are all accommodated on a 2.5‐m sled. Field experiments were conducted in Kansas and Alaska. The experiments in Kansas tested the operation of the system. The primary objective of the Alaska experiments was to investigate the ability of a GPR to detect and distinguish between subsurface deposits of ice and ice‐cemented soils. The investigation depths of these experiments ranged from 1 m to 30 m, and the subsurface geology included near‐surface thaw, discontinuous permafrost, water‐saturated soils, and lenses of pure ice. Dielectric contrasts within the ground were detected with near‐meter resolution; however, identifying the geologic context of an interface was difficult due to ambiguities associated with reflection data. These investigations demonstrate some of the difficulties associated with inverting reflection data to obtain dielectric properties of the subsurface. Fortunately, previous geophysical investigations such as drilled cores and seismic surveys helped to constrain the geology, and numerical simulations provided an additional resource for the interpretations. On Mars, additional geological context will be limited and numerical simulations will become extremely important for data interpretation. Due to these difficulties, we demonstrate in one experiment how dielectric information can be obtained directly from bistatic measurements with a fixed transmitter and mobile receiver. Finally, a comparison with a commercially available Geophysical Survey Systems, Inc. (GSSI) radar system is presented, and we discuss how the system can be modified and improved for future exploration on Mars.

Ground‐penetrating radar and magnetic survey to the west of Al‐Zayyan Temple, Kharga Oasis, Al‐Wadi Al‐Jadeed (New Valley), Egypt

AbstractAl‐Zayyan Temple or Qasr Al‐Zayyan might be regarded as one in a chain of several fortresses that the Romans built to secure the salver's trade caravan route between Asyut and Sudan, known as Darb Al‐Arbain. Al‐Zayyan temple lies about 25 km south of Al‐Kharga city, the capital of the New Valley, and deviates to the east of Al‐Kharga‐Paris main road some 2 km along the Al‐Zayyan‐Aarif minor road. The background information about the temple is very scarce, and even what is known is neither clear nor accurate. Some indications have ascribed it to Amenebis and that it was restored during the reign of Emperor Antoninus (AD 138–161). An integrated ground‐penetrating radar (GPR)survey using the SIR 2000 Geophysical Survey Systems, Inc. (GSSI) together with magnetic survey using FM36 (GeoScan) and the three component fluxgate gradiometer TRM‐70D (Tokin) have been applied to the western side of the temple. The results show relatively large‐scale buried structures in a direction intersecting that of the present temple at about 45°. Some particular features within the structure have been speculatively ascribed on the basis of comprehending their signatures in the GPR sections. The magnetic results have improved the identification of some objects revealed by the GPR and provided ideas about some of the other features. Copyright © 2002 John Wiley & Sons, Ltd.

Initial appraisal of ground probing radar for site investigation in Britain : Darracott, B W; Lake, M I Ground Engng, V14, N3, April 1981, P14–18

This article describes the equipment and the use of the method on a number of typical site investigations. The results of the tests are given and some of the problems and limitations of UK are discussed. The system used was that manufactured by Geophysical Survey Systems Inc (GSSI) of New Hampshire, USA, and is designed primarily as a shallow sub-surface exploration tool for engineering applications. The radiated signal is in the form of an electromagnetic 3 nano second transient in the low vhf range. Reflected waves can be displaced on a chart recorder calibrated in terms of depth. The resolution depends upon the pulse length and the frequency of the signals. Soil conductivity places the greatest limitations on the use of radar, but in favourable conditions penetration of up to 30 metres can be obtained. Results from the nine tests in various conditions described show that the technique appears to work well in sandy soils where ground water is fresh and in rocks. It is best used where known targets such as pipes, sewers or old foundations are being searched for. The system does not work at all well in areas where there are near-surface clays. (TRRL)