Stepped Frequency Continuous Wave Ground Penetrating Radar Research Articles

Directional and High-Gain Ultra-Wideband Bow-Tie Antenna for Ground-Penetrating Radar Applications

Bow-tie antennas are utilized extensively in ground-penetrating radar (GPR) systems. In order to achieve sufficient penetration depth and resolution, the bow-tie antennas for GPR applications require low operating frequency, high gain, and excellent broadband. A novel ultra-wideband (UWB) bow-tie antenna with gain enhancement for GPR applications is proposed in this paper. First, a UWB bow-tie antenna with resistive loading is designed. The metal reflector and metamaterial loading make the bow-tie antenna directional, and loading the same metamaterial on the front side of the antenna further improves directional gain. After testing, the lowest frequency of the fabricated antenna is 317 MHz, the relative bandwidth is 98.6%, the peak gain in the frequency range is 9.3 dBi, and the size is only 0.38 λ at the lowest frequency. The proposed compact antenna takes both gain and bandwidth into consideration. Finally, in order to further verify the effectiveness of the proposed antenna in the GPR system, a stepped frequency continuous wave ground-penetrating radar (SFCW-GPR) system was built. The experimental results show that the designed antenna is suitable for the GPR system of deep penetration and high-resolution detection, which is beneficial to the imaging of underground structures.

Polarimetric Chaotic Ground Penetrating Radar for Underground Pipes Detection

A polarimetric chaotic ground penetrating radar (GPR) is proposed to improve the detection accuracy of underground pipes. In this radar system, the chaotic signal is used as the probe signal and the multi-polarization detection mode is employed to gather the GPR data. Furthermore, the laplacian pyramid algorithm is applied to fuse multi-polarization components. The simulations demonstrate that by using the polarization chaotic GPR, the pipe responses are enhanced and their shape and distribution can be accurately obtained. Here, the information entropy, average gradient, spatial frequency, and standard deviation are introduced to quantitatively evaluate the imaging results. The corresponding experiment is consistent with the simulation. Additionally, to verify the performance of the polarimetric chaotic GPR, we compare the polarimetric chaotic GPR with the polarimetric stepped frequency continuous wave GPR. The experimental results show that the proposed radar improves the detection accuracy and enlarges the detection range.

Method for Compensating Signal Attenuation Using Stepped-Frequency Ground Penetrating Radar.

Ground penetrating radar (GPR) is a subsurface remote sensor that allows the user to detect, classify, and identify the buried target and structures. The radar signals are rapidly attenuated as they propagate into the ground; therefore, attenuation compensation is necessary for the visualization of the buried targets from GPR data. In this work, we developed a novel attenuation compensation approach based on the recently developed stepped-frequency continuous wave (SFCW) GPR system, which is a frequency domain sampling system with improved performance in dynamic range, sensitivity, and anti-interference ability. Because the regularly used time-varying gain function for compensating the attenuation of impulse GPR data does not make full use of the advancement of the SFCW modulation, an alternative procedure is proposed herein. The new approach is based the SFCW mechanism, and aims at improving the visualization of deeper targets by compensating the SFCW GPR signal attenuation. We first present the attenuation mode of the SFCW GPR echo, from which an inverse attenuation function is derived to compensate the amplitude loss. For the field measurement where the theoretical inverse attenuation function is difficult to achieve, we introduced a pseudo time–frequency distribution for estimating the inverse attenuation function. A procedure for amplitude attenuation has also been developed. Testing with both synthetic and experimental data return a good reconstruction of the signal amplitude, subsequently improving the ability for visualizing and detecting deeper targets.

Effect of ground undulation and mounted vehicle velocity variation on stepped frequency continuous wave GPR data

This paper describes a method to generate dataset on stepped frequency continuous wave (SFCW) ground penetrating radar (GPR) for land mine detection. Probability of target detection as well as accuracy of GPR is hindered by ground undulations and GPR mounted vehicle velocity variation. This paper proposes a novel method of filtering out ground undulation effect by ground bounce removal filter and also mitigating GPR mounted vehicle velocity variations. This work also focuses on migration of simulated B-scan and C-scan data using Kirchhoff and F-K migration algorithms. The irregular surface condition of the ground or ground undulation is modelled and a ground bounce removal filter is developed to eliminate the effects of ground undulation. Non-uniform sampling of B-scan replicates the scenario of variation in velocity of the GPR mounted vehicle. The Kirchhoff and F-K migration algorithms applied to the outcome of ground bounce removal filter dataset results in no/less error with respect to true depth and position of the landmine in all possible scenarios. An interactive graphical user interface (GUI) for generating and testing the SFCW GPR data is also discussed in this paper.

In brief

PAGE 524 Researchers from South Korea have developed a walking speed estimation and treadmill control algorithm for a user-driven treadmill. Data is gathered as the user walks on the treadmill wearing insole pressure sensors. The correlation between walking speed and centre of pressure was investigated to develop a feedforward scheme, ensuring speed control of the treadmill. The user-driven treadmill has applications in training, rehabilitation, sports and entertainment. PAGE 520 A microstrip antenna array (MAA) with metasurface has been designed and fabricated for ultra-wideband radar cross-section (RCS) reduction, whilst preserving its radiation characteristics. The research from China uses size-adjustable unit cells to achieve different reflection phase distributions. The proposed MAA can reduce the RCS in the ultra-wide frequency band 6.2–27.3 GHz for both x and y polarisations. Estimation of walking speed and treadmill control using data from insole pressure sensors. PAGE 538 Researchers from China mounted a dielectric lens on the topside of a silicon imaging chip to improve radiation patterns of an on-chip patch antenna. The integrated lens causes the main beam of radiation patterns to become narrower, thus achieving a finer spatial resolution for imaging applications. The technology can be applied in THz imaging. Microstrip antenna array with metasurface designed for ultra-wideband RCS. PAGE 546 A sixteenth-mode substrate integrated waveguide (SMSIW) bandpass filter loaded with complementary split-ring resonator (CSRR) is proposed by researchers from India. The SMSIW filter operates at 2.45 GHz and has a bandwidth of 8.2%. It is compact, occupying 6.25% of a conventional integrated waveguide. It is also simple, has low-loss and is easy to fabricate. Lens placed on topside of imaging chip improves radiation patterns of antenna. PAGE 568 An autofocusing imaging method for stepped frequency continuous wave ground penetrating radar (SFCW-GPR) is presented in this Letter from China. The method overcomes the uncertainty of electromagnetic wave propagation velocity in the subsurface medium, by using the sequential L0 and L2 norms minimisation technique. Compact, simple, low-loss and easy to fabricate bandpass filter. Autofocusing imaging method for SFCW-GPR.

Nonuniform fast Fourier transform-based fast back-projection algorithm for stepped frequency continuous wave ground penetrating radar imaging

Stepped frequency continuous wave ground penetrating radar (SFCW-GPR) systems are becoming increasingly popular in the GPR community due to the wider dynamic range and higher immunity to radio interference. The traditional back-projection (BP) algorithm is preferable for SFCW-GPR imaging in layered mediums scenarios for its convenience and robustness. However, the existing BP imaging algorithms are usually very computationally intensive, which limits their practical applications to SFCW-GPR imaging. To solve the above problem, a fast SFCW-GPR BP imaging algorithm based on nonuniform fast Fourier transform (NUFFT) technique is proposed in this paper. By reformulating the traditional BP imaging algorithm into the evaluations of NUFFT, the computational efficiency of NUFFT is exploited to reduce the computational complexity of the imaging reconstruction. Both simulation and experimental results have verified the effectiveness and improvement of computational efficiency of the proposed imaging method.

GPR MODELING FOR RAPID CHARACTERIZATION OF LAYERED MEDIA

The success of a ground penetrating radar (GPR) signal modeling scheme largely depends on its accuracy and computational efficiency. Most of the modeling schemes suffer from inaccuracy because of unrealistic assumptions of complex GPR environment. In this respect full wave model (FWM) of GPR signal is a promising approach for accurate characterization of multi-layered media. However, large computation time of FWM compared to other simplified models makes the approach inefficient for real time application. In this work an FWM scheme is developed based on electric field equivalent magnetic current density at antenna phase center. The compact analytical expression of Green's function representing response due to layered media is derived. Then a plane wave model (PWM) is proposed by introducing a spreading factor based on simplified expression of the FWM. The model inversion is successfuly carried out by a gradient based algorithm. A stepped frequency continuous wave GPR in off-ground monostatic configuration is implemented in laboratory environment to verify performances of the models. Experimental analysis proves that the proposed PWM is as accurate as FWM, and its computation efficiency is enormous to detect layered media parameters.

Improvement of Stepped-Frequency Continuous Wave Ground-Penetrating Radar Cross-Range Resolution

This paper presents some experimental results obtained with newly developed stepped-frequency continuous wave (SFCW) ground-penetrating radar in a frequency range from 400 to 4845 MHz. This paper describes the procedures to remove the delays within the transmitter, the receiver, and the antenna system and analyzes the experimental results obtained after processing the measured data. The measured system footprint and the experimental results show that using an ultrawideband (UWB) Archimedean spiral antenna decreases the coupling signal but does not provide the needed cross-range resolution. Based on the measured dimensions of the footprint, a synthetic aperture procedure is used to improve the radar cross-range resolution from around 60 cm to about 6 cm. This paper shows the ability of the radar to detect dielectric objects and to exhibit their shape as it works with circularly polarized waves. What makes this paper different from prior work, which presents some experiments using a vector network analyzer set up to work as an SFCW radar, is that the data were acquired with a real system working with circular polarization and using two UWB Archimedean spirals. The calibration procedures as well as the synthetic aperture procedure were developed and validated based on measured data with the SFCW radar.

Performances of a stepped-frequency continuous-wave ground penetrating radar

Abstract Ground penetrating radars (GPRs) are used to detect surface laid or shallowly buried objects. They can work either in the time or frequency domains. This paper presents the performances of newly developed stepped frequency continuous wave ground penetrating radar operating from 400 MHz to 4845 MHz, to provide good penetration and high resolution, which works with parallel and sequential transmission. We show the advantage of using circularly polarized waves for reproducing the shape of the target. The paper regards system calibration, antenna footprint, and range and cross-range resolution. The experimental results refer to surface laid as well as shallowly buried metallic and dielectric objects and show the ability of the radar not only to detect but to exhibit the shape of the targets.

3D IMAGING METHOD FOR STEPPED FREQUENCY GROUND PENETRATING RADAR BASED ON COMPRESSIVE SENSING

Long data collecting time is one of the bottlenecks of the stepped-frequency continuous-wave ground penetrating radar (SFCW- GPR). We discuss the applicability of the Compressive Sensing (CS) method to three dimensional buried point-like targets imaging for SFCW-GPR. It is shown that the image of the sparse targets can be reconstructed by solving a constrained convex optimization problem based on l1-norm minimization with only a small number of data from randomly selected frequencies and antenna scan positions, which will reduce the data collecting time. Target localization ability, performance in noise, the efiect of frequency bandwidth, and the efiect of the wave travel velocity in the soil are demonstrated by simulated data. Numerical results show that the presented CS method can reconstruct the point-like targets in the right position even with 10% additive Gaussian white noise and some wave travel velocity estimation error.

Processing stepped frequency continuous wave GPR systems to obtain maximum value from archaeological data sets

ABSTRACTStepped frequency continuous wave ground penetrating radar (GPR) systems allow highly detailed data sets to be collected across a wide bandwidth using a multi‐element array antenna, such as the 3D‐radar GeoScope system. Although the final presentation of the results is similar to time‐domain systems, the correct processing of the initial frequency domain data acquired in the field is essential to obtain the maximum information from the site. Processing begins with the identification of a suitable frequency window for conversion to the time‐domain using an inverse Fourier transform and demonstrates how the use of a varying frequency window with depth can improve the final results. Various methods for background subtraction to minimize the loss of data quality and cope with the strong surface reflection experienced by an air‐launched antenna are also explored. The geometry of the air‐launched antenna is also considered with specific regard to developing a three‐dimensional migration model that accounts for the variation in a signal response expected from such a system. This paper explores these themes with relation to data from archaeological sites and also considers the data processing challenges presented by high density (e.g., 0.075 m x 0.075 m) multi‐hectare surveys.

Compressive Stepped-Frequency Continuous-Wave Ground-Penetrating Radar

Data acquisition speed is an inherent problem of stepped-frequency continuous-wave (SFCW) radars, which may discourage further usage and development of this technology. We propose an emerging paradigm called compressed sensing (CS) to overcome this problem. In CS, a signal can be reconstructed exactly based on only a few samples below the Nyquist rate. Accordingly, the data acquisition speed can be increased significantly. A novel design of an SFCW ground-penetrating radar (GPR) with high acquisition speed is proposed and evaluated. Simulation by a monocycle waveform and actual measurement by a vector network analyzer at a GPR test range indicate the applicability of the proposed system.