Ultra-wideband Ground Research Articles

Characterizing heterogeneities in the subsurface with an ultra-wideband GPR: Application to WISDOM, the GPR of the Rosalind Franklin ExoMars mission

Ultra-wideband Ground Penetrating Radars (GPR) are sensitive to a large range of scatterer sizes. Considering fractal heterogeneities in the subsurface, we propose a method to retrieve their typical size L. The determination of L with this method does not require a priori knowledge of the statistical distribution of permittivity values in the investigated subsurface. The method relies on the analysis of the backscattered signal by frequency/wavelength sub-bands. It is adapted to WISDOM, the GPR onboard the rover of the Rosalind Franklin ExoMars mission (ESA), but can be applied to any ultra-wideband GPR. Based on numerical simulations, a maximum in volume backscattering is reached at the wavelength (in the subsurface) . We demonstrate that this maximum, and therefore L, can be identified even in presence of moderate electrical losses, compatible with conditions expected on the Moon or Mars. Assuming an average permittivity of 5, WISDOM (0.5-3 GHz) data products could be used to estimate L as long as it is in the range 0.9-4.2 cm The retrieval method for L is validated on experimental WISDOM data acquired in a controlled environment.

A High Signal–Noise Ratio UWB Radar for Buried Pipe Location Using Golay Complementary Sequences

A Golay-based ultra wideband ground penetrating for underground pipes location is proposed and experimentally demonstrated. Golay complementary codes with the code length of 1024 and frequency of 1 GHz are used as the probe signals. The two-dimensional image of the buried pipes is achieved by a correlation method and a back-projection algorithm. The experimental results show that both the plastic pipe and metallic pipe can be located with a range resolution of 10 cm. Furthermore, as the Golay complementary sequences are a pair of complementary sequences, the sum of their correlation function yields twice the value of the peak at the target position and zero elsewhere. Thus, compared with the stepped frequency signal radar or chaotic signal radar, the Golay-based radar can significantly improve the signal–noise ratio and has the capability of deep detection.

Integrated synchronous data acquisition subsystem for high‐speed GPR system

In this study, an integrated synchronous data acquisition subsystem for high-speed dual-channel ultra-wideband ground penetrating radar (GPR) system is designed and tested. Factors that could cause data missing and asynchronisation are analyzed. According to timing sequence, a field-programmable gate array-based onboard digital control module is integrated to synchronise the data acquisition and data storage subsystems. By applying simultaneous multi-buffer acquisition and readout mode and multi-threading configuration, as well as the critical section control and queue storage structure, the GPR data throughput is considerably improved. For the practicality of this system, a smart End-of-Job control design is performed between different threads to control data acquisition. By using different performance indexes, receiver operation characteristic curve, maximum scan rate, and the rebar detection experiment demonstrate the superiority of author's method.

Simulation and imaging using ultrawideband ground penetrating radar and finite-difference time-domain method

The whole electromagnetic field simulation model of the near-field ultrawideband ground penetrating radar imaging is established using the two-dimensional finite-difference time-domain method. According to the back-projection method, this paper focuses on the underground target imaging. The feasibility of the technology for underground target imaging is confirmed by specific examples. Some problems existing in imaging are also discussed. The result shows that the correction of electromagnetic wave propagation time is the basis of obtaining right and clear imaging. In addition, the underground target, which is close to the transmitting and receiving antenna, costs less electromagnetic wave energy, as long as the underground target is detected. The whole process can make the image more clear. (C) 2017 SPIE and IS&T

Ultra-Wideband Antenna Design for GPR Applications: A Review

This paper presents a comparative review study on ultra-wideband (UWB) antenna technology for Ground Penetrating Radar (GPR) applications. The proposed antenna designs for UWB ground penetrating radar include a bow-tie antennas, Vivaldi antennas, horn antennas, planar antennas, tapered slot antennas, dipole antennas, and spiral antennas. Furthermore a comprehensive study in terms of operating frequency range, gain and impedance bandwidth on each antenna is performed in order to select a suitable antenna structure to analyze it for GPR systems. Based on the design comparison, the antenna with a significant gain and enhanced bandwidth has been selected for future perspective to examine the penetration depth and resolution imaging, simultaneously suitable for GPR detection applications. Three different types of antennas are chosen to be more suitable from the final comparison which includes Vivaldi, horn and tapered slot antennas. On further analysis a tapered slot antenna is a promising candidate as it has the ability to address the problems such as penetration depth and resolution imaging in GPR system due to its directional property, high gain and greater bandwidth operation, both in the lower and higher frequency range.

Development of a New High Speed Dual-Channel Impulse Ground Penetrating Radar

This paper presents the development of a dual channel, air coupled Ultra-Wideband (UWB) Ground Penetrating Radar (GPR) targeting highway pavements and bridge deck inspections. Compared to most existing GPRs with a single channel and low survey speeds, our GPR possesses competitive features, including wide area coverage, high spatial resolution and operating capability at normal highway driving speed (up to 60 mph). The system has a two-channel microwave front end, a high speed (8 Gsps) real time data acquisition unit, a high throughput multithread data transmission and storage module, and a customized low-cost control element developed in a field-programmable gate array (FPGA). Experiments with different steel reinforcing bars establish GPR system performance.

Comparison of antenna dispersion and digital signal processing effects in ultrawideband Ground Penetrating Radar systems

Abstract In Ground Penetrating Radar it is of great interest to have a pulse width as narrow as possible to achieve best resolution capability. However, ultrawideband antennas may cause distortion to the radar signal due to dispersion, which is dependent on the frequency and bandwidth, as well as the direction of radiation. As dispersion causes an increase of the peak's width, the resolution capability is degraded. When frequency-based radar systems are utilized, such as stepped-frequency radar, a transformation of the recorded frequency-domain data to time domain is often required. There are different means of transformation at hand, the most popular being inverse Fourier Transform. Generally, such a transformation involves certain degrees of freedom in the processing of the data, which affect the appearance or even distort the resulting signal in time domain. In the same way, distortion may also be introduced to signals obtained by pulse radar, which is operating in time domain, when digital signal processing filters are applied to the time-domain data, modifying their frequency content. In contrast to dispersion these effects can be controlled — but not avoided. As an example, the typical sinc-shaped distortion of the time-domain signal after inverse Fourier Transform may be avoided by windowing of the frequency-domain data, a well-known basic technique in the digital signal processing domain. As dispersion, also windowing causes a broadening of the peak's width. However, this leads to the important question, to which degree both, dispersion and windowing, affect the time domain signal and which of them has more severe impact. In this paper we investigate both effects. We compare dispersion of different ultrawideband Vivaldi, Bowtie and Loaded Bowtie antennas with the ideal (theoretical) non-dispersive one. And we compare these results with the distortion effects introduced to the radar signal by windowing frequency-domain data prior to inverse Fourier Transform.

A three dimensional approach for tracking cracks in bridges using GPR

Abstract Corrosion associated with reinforcing bars is the most significant contributor to bridge deficiencies. The corrosion is usually caused by moisture and chloride ion exposure. The reinforcing bars are attacked by corrosion and yield expansive corrosion products. These oxidation products occupy a larger volume than the original intact steel and internal expansive stresses lead to cracking and debonding. There are some conventional inspection methods for the detection of the reinforcing bar's corrosion but they can be invasive and destructive, often laborious, and lane closure is required and it is difficult or unreliable for any quantification of corrosion. For these reasons, bridge engineers always prefer more to use the ground penetrating radar (GPR) technique. In this work a novel numerical approach for three dimensional tracking and mapping of cracks in the bridge is proposed. The work starts from some interesting results based on the use of the 3D imaging technique in order to improve the potentiality of the GPR to detect voids, cracks or buried objects. The numerical approach has been tested on data acquired on a bridge by using a pulse GPR system specifically designed for bridge deck and pavement inspection. The equipment integrates two arrays of Ultra Wide Band ground coupled antennas, having a main working frequency of 2 GHz. The two arrays are using antennas arranged with a different polarization. The cracks, associated often to moisture increase and higher values of the dielectric constant, produce a not negligible increase of the signal amplitude. Following this, the algorithm, organized in preprocessing, processing and postprocessing stages, analyzes the signal by comparing the value of the amplitude all over the domain of the radar scan.

Buried Object Characterization Using Ultra-Wideband Ground Penetrating Radar

In this paper, a method to characterize buried nonmagnetic objects in ground using ultra-wideband (UWB) ground penetrating radar (GPR) is proposed. In this method, UWB pulses are radiated by the radar, while scattered signals from the ground with the buried object are received. The received signals are then post-processed to estimate the depth, thickness, and electrical properties of the buried object. A constant depth and thickness is enforced at all frequencies while the signals are processed to extract the buried object characteristics, resulting in more accurate estimations and reduced processing time. In addition, path loss due to the close proximity of the radar to the ground is compensated analytically. The applicability of the proposed method is validated with several planar objects and a boulder that we typically encounter in the construction industry. The proposed method can achieve sufficient reliability in estimating the permittivity of buried objects for the purpose of material identification. Incorporating the proposed method into the GPRs enhances their existing imaging ability by adding material identification capability.

EBG Structures with Fractal Topologies for Ultra-Wideband Ground Bounce Noise Suppression

Electromagnetic bandgap (EBG) structures consisting of fractal high impedance topologies and effective bridges are proposed and employed for ultra-wideband (UWB) ground bounce noise (GBN) suppression in power and ground plane pairs. These structures have shown good performance. For the first design utilizing fractal high impedance topology with one iteration and meander lines, it provides −49 dB noise suppression from 202 MHz to 20 GHz. Both simulated and measured results are presented to verify the performance. Furthermore, the GBN suppression behaviors of topologies with different iterations have been studied, and the impact of the power plane with the first design on the signal integrity has also been investigated.

Experimental Analysis of an Ultrawideband Hybrid EBG/Ferrite Ground Plane

This paper presents an experimental analysis of the previously presented ultrawideband and low-profile hybrid electromagnetic-band-gap (EBG)/ferrite ground plane. The method implemented to fabricate the hybrid ground plane, the experimental measurement procedure, and the experimental results will be described. Measurements were performed in a transverse electromagnetic (TEM) cell that was specifically designed and characterized for these measurements. As will be shown, the experimental results of the reflectivity and phase analyses of the ultrawideband hybrid ground plane show good correlation with the simulated results.

Numerical Modeling of Ultrawide-Band Dielectric Horn Antennas Using FDTD

A detailed characterization of the input impedance of ultrawide-band (UWB) dielectric horn antennas is presented using the finite-difference time-domain (FDTD) technique. The FDTD model is first validated by computing the characteristic impedance of two conical plate transmission lines (including planar bow-tie antennas) and comparing the results to analytical solutions. The FDTD model is next used to calculate the surge impedance of dielectric horn antennas using the conical plates as launchers. Design curves of the surge impedance for different choices of geometries and dielectric loadings are provided. The modeled antennas are particularly attractive for applications such as UWB ground penetrating radars (GPR) applications.

Moderately rough surface underground imaging via short-pulse quasi-ray Gaussian beams

An adaptive framework is presented for ultra-wideband ground penetrating radar imaging of shallow-buried low-contrast dielectric objects in the presence of a moderately rough air-soil interface. The proposed approach works with sparse data and relies on recently developed Gabor-based narrow-waisted quasi-ray Gaussian beam algorithms as fast forward scattering predictive models. First, a nonlinear inverse scattering problem is solved to estimate the unknown coarse-scale roughness profile. This sets the stage for adaptive compensation of clutter-induced distortion in the underground imaging problem, which is linearized via Born approximation and subsequently solved via various pixel-based and object-based techniques. Numerical simulations are presented to assess accuracy, robustness and computational efficiency for various calibrated ranges of problem parameters. The proposed approach has potential applications to antipersonnel land mine remediation.

Moderately rough dielectric interface profile reconstruction via short-pulse quasi-ray gaussian beams

A new technique for estimating the coarse-scale profile of a moderately rough interface between air and a homogeneous dielectric halfspace is presented. The proposed approach is based on space-time sparsely sampled reflected field observations and uses a quasi-ray Gaussian beam fast-forward model, coupled with a compact parameterization of the surface profile in terms of B-splines, from which the profile estimation problem is posed as a nonlinear optimization problem. Numerical experiments are presented to assess accuracy, reliability, and computational efficiency. The proposed approach finds applications in adaptive schemes for rough surface underground imaging of shallowly buried targets via ultra wide-band ground penetrating radars.

Time-domain sensing of targets buried under a Gaussian, exponential, or fractal rough interface

The authors numerically examine subsurface sensing via an ultrawideband ground penetrating radar (GPR) system. The target is assumed to reside under a randomly rough air-ground interface and is illuminated by a pulsed plane wave. The underlying wave physics is addressed through application of the multiresolution time-domain (MRTD) algorithm. The scattered time-domain fields are parametrized as a random process and an optimal detection scheme is formulated, accounting for the clutter and target signature statistics. Detector performance is evaluated via receiver operating characteristics (ROCs) for variable sensor parameters (polarization and incident angle) and for several rough-surface statistical models.

Sensor Fusion for the Detection of Landmines

The detection of buried anti-personnel mines (APMs) is widely considered as a problem which may only be solved with a combination of two or more complementary sensors. We present processing and fusion results obtained from a multisensor data set, acquired with a pulse induction metal detector (MD), a pulsed ultra wide band ground penetrating radar (GPR) and a 3–5μ thermal infra-red (IR) camera. Various types of soils, clutter objects and burial conditions were recorded. Anti-personnel mines included minimum metal mines as well as mines with a significant metal content. We use a special projection to map a 3D GPR data cube, with time or depth as vertical co-ordinate, into a horizontal plane view 2D image. Object contours are then derived, based on an edge extraction method, followed by an automatic detection of circular shapes with a Hough-transform. In the association step, the stand-off IR image, the metal detector and GPR images and related detections are mapped onto a common cartesian grid on the ground surface. Detection results are fused on a decision level, using a Bayesian approach. Our results indicate that the GPR performance approximately matches that of the metal detector. With both sensors all metallic mines and around 60% of the minimum metal mines were detected. In the case of two false alarms per square meter combined detection probability clearly exceeds single sensor performance.