Stepped Frequency Continuous Wave Ground Research Articles

Step-Frequency Ground Penetrating Radar for Agricultural Soil Morphology Characterisation

Soil morphology plays a fundamental role in the vertical and lateral movements of solutes and water transport, providing knowledge regarding spatial distribution of its textural properties and subsurface dynamics. In this framework, the measured values of electrical conductivity are able to reveal the heterogeneity of soil that is present in a particular agricultural field and they are affected by more than one important physical characteristic: soil texture, organic matter, moisture content, and the depth of the clay pan. In the microwave region, these dynamics are known to exhibit a frequency dependent behaviour. This study explores the application of a Step Frequency Continuous Wave Ground Penetrating Radar (SFCW GPR) to shed light on the practical impact that these dependencies have on the imaging results, not only regarding the electrical characterisation of the subsurface morphology, but also in its correct interpretation. This information is of notable importance for determining water-use efficiency and planning precision-agriculture programs. The results clearly show visible and significant fluctuations of the amplitude levels, depending on the considered central frequency, demonstrating that the frequency dependence of electromagnetic properties of heterogeneous soil are significant and cannot be ignored if the aim is to properly define the subsurface attributes. The measurements also suggest that correlating the delineated variations might help in the identification of extended features and the classification of areas that possess similar properties in order to increase the confidence in monitoring soil resources.

An Improved Modified Universal Ultra-Wideband Antenna Designed for Step Frequency Continuous Wave Ground Penetrating Radar System.

Step Frequency Continuous Wave Ground Penetrating Radar (SFCW-GPR), as a tool for nondestructive testing of shallow soil surface targets, the realization of the function of SFCW-GPR is mainly based on the theory of refraction, reflection and scattering of electromagnetic wave in the discontinuity of dielectric constant. So, the UWB antenna system, an important part of SFCW-GPR, becomes more indispensable. In this paper, an improved modified universal antenna is designed, simulated and fabricated. Based on a typical Bow-tie antenna, it is modified by the methods of lumped loads, cavity-backed loading and structure loading. The simulated and measured results show that the UWB antenna has 1.36 GHz bandwidth from 0.64 to 2.0 GHz with three resonant wavelength peaks, and having been modified and improved, the UWB antenna performances including voltage standing-wave ratio (VSWR), input impedance, the boresight gain and current distribution, are much better than the typical Bow-tie antenna. In addition, the results of verification experiment of Step Frequency Continuous Wave (SFCW) show that the antenna can be applied to the working scenarios of SFCW-GPR.

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.

Signal processing for coal layer thickness estimation using high‐resolution time delay estimation methods

The coal mining research technology is gaining popularity in terms of thickness measurement of coal mining horizon. The main challenge is to improve a robust sensing method for estimating the coal layer thickness left on mine-haulage way roofs for mine safety. This study addresses this challenge by step frequency continuous wave ground penetrating radar (GPR), whose resolution is dependent on bandwidth. To improve the time resolution of GPR signal, this study adopted four high-resolution algorithms, which are also known as subspace methods, namely, estimation of signal parameter via rotational invariance techniques, multiple-signal classification (MUSIC) algorithm, polynomial version of MUSIC, i.e. root-MUSIC and root-Min-Norm. The performance of all these algorithms is compared with synthetic data generated by the plane wave model and full wave model. The results are presented in terms of resolution power as well as relative root-mean-square error on the estimated thickness.

Stepped Frequency Continuous Wave Ground Penetrating Radar Imaging Algorithm Based on Multi-task Bayesian Compressive Sensing

Aiming at the joint sparsity of target imaging space of SFCW-GPR, the idea of multi-task learning is introduced into the Bayesian compressive sensing reconstruction algorithm, multi-task Bayesian compressive sensing(MT-BCS) algorithm is proposed in the paper. A common prior hierarchical Bayesian model is used for different tasks, MT-BCS algorithm can fully exploit the statistical characteristics and structural information of radar echo data and recover original signals from far fewer random samples. The simulation results show that the reconstruction accuracy of MT-BCS algorithm is better than BCS algorithm under the same conditions.

Sparsity‐based SFCW‐GPR autofocusing imaging method under EM wave velocity uncertainty

To tackle the problem of the uncertainty of EM wave propagation velocity in the subsurface medium, a novel sparsity-based autofocusing imaging method for stepped frequency continuous wave ground penetrating radar system is proposed. On the basis of the parametric sparse recovery method, the proposed imaging method exploits the sequential L 0 and L 2 norms minimisation strategy to simultaneously retrieve the EM wave propagation velocity information and the high-quality focused image. Experimental results demonstrate the validity and effectiveness of the proposed imaging method.

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.

Investigation of Air/Ground Reflection and Antenna Beamwidth for Compressive Sensing SFCW GPR Migration Imaging

For stepped frequency continuous wave ground penetrating radar (SFCW GPR), the image of buried targets is usually reconstructed by a combination of point-like scatters whose number is much smaller than that of pixels of target space image. The intrinsic sparseness of target space offers a migration imaging method to make the high-quality image of underground region based on compressive sensing (CS) theory. In this paper, the effects of air/ground interface and antenna beamwidth on CS-based SFCW GPR migration imaging are presented and analyzed. It is shown that the presence of the strong air/ground interface reflection and finite antenna beamwidth usually challenges the robust CS migration imaging algorithm in practice. To overcome this problem in the context of CS migration imaging, an improved CS migration imaging method for SFCW GPR system is proposed in this paper. Experimental results show that the approach is robust to deliver a high-quality image of underground region.

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.

Hexagonal Monopole Strip Antenna with Rectangular Slot for 100–1000 MHz SFCW GPR Applications

A printed ultra wideband (UWB) monopole antenna is proposed for applications on stepped frequency continuous wave (SFCW) ground penetrating radar (GPR) within a frequency range of 100–1000 MHz. The proposed antenna consists of a hexagonal strip line with resistive loading and a rectangular slot that is added to the ground plane side of the printed antenna implemented on FR4 epoxy materials. The resistive loading at the hexagonal monopole is effective to increase bandwidth in the higher frequency region, while the rectangular slot is used to improve bandwidth characteristic in the lower frequency region. This paper investigates the characteristic improvement in the lower frequency region by applying a parametric study on the rectangular slot that is added at the ground plane side of the UWB monopole antenna. Computer simulation was conducted and measurements were carried out to validate the result.