T.G. Savelyev

UWB Array-Based Sensor for Near-Field Imaging

In this paper, the development of an ultra-wideband (UWB) array-based time-domain radar sensor for near-field imaging is described. The radar sensor is designed to be used within a vehicle-mounted multisensor system for humanitarian demining. The main novelty of the radar lies in the system design with a single transmitter and multichannel receiver. Design of the UWB antenna array is also novel. The radar produces 3D images of subsurface by 1D mechanical scanning. The imaging capability of the radar is realized via electronic steering of the receive antenna footprint in a cross-scan direction and synthetic aperture processing in an along-scan direction. Imaging via footprint steering allows for a drastic increase in the scanning speed.

Investigation of Time–Frequency Features for GPR Landmine Discrimination

Ground-penetrating radar (GPR) is capable to detect plastic antipersonnel landmines as well as other subsurface targets. In order to reduce false alarms, an option of automatic landmine discrimination from neutral minelike targets would be very useful. This paper presents a possibility for such discrimination and analyzes it experimentally. The authors investigate time-frequency features of an ultrawideband (UWB) target response for the discrimination between buried landmines and other objects. The discrimination method includes the extraction of an early-time target impulse response, its time-frequency transformation, and the extraction of time-frequency features based on a singular value decomposition of the transformed image. In order to take into account the changes in the UWB target signals, the experimental conditions are completely controlled to focus on the behavior of the targets response with respect to its depth and the horizontal position of the GPR above it. The dependence of the features on the GPR bandwidth is analyzed as well. The Mahalanobis distance is used as a criterion for optimal discrimination. The obtained results define the best features and conditions when the landmine discrimination is successful. For comparison, the discriminant power of the proposed features has been tested on a dataset, acquired during a field campaign in Angola

Modified Kirchhoff Migration for UWB MIMO Array-Based Radar Imaging

In this paper, the formulation of Kirchhoff migration is modified for multiple-input-multiple-output (MIMO) array-based radar imaging in both free-space and subsurface scenarios. By applying the Kirchhoff integral to the multistatic data acquisition, the integral expression for the MIMO imaging is explicitly derived. Inclusion of the Snells law and the Fresnels equations into the integral formulation further expends the migration technique to subsurface imaging. A modification of the technique for strongly offset targets is proposed as well. The developed migration techniques are able to perform imaging with arbitrary MIMO configurations, which allow further exploration of the benefits of various array topologies. The proposed algorithms are compared with conventional diffraction stack migration on free-space synthetic data and experimentally validated by ground-penetrating radar experiments in subsurface scenarios. The results show that the modified Kirchhoff migration is superior over the conventional diffraction stack migration in the aspects of resolution, side-lobe level, clutter rejection ratio, and the ability to reconstruct shapes of distributed targets.

UWB array-based radar imaging using modified Kirchhoff migration

This paper presents a new modification of Kirchhoff migration algorithm for ultra-wideband (UWB) array-based radar imaging. The developed algorithm is evolved from traditional Kirchhoff migration which is based on the classical integral theorem of Helmholtz and Kirchhoff. The new algorithm is designed for array-based radar imaging with arbitrary multiple input multiple output (MIMO) configuration. The developed algorithm is compared with conventional diffraction stack migration using both synthetic data from numerical simulation and measurement data from landmine detection. The results have shown promising improvements in the aspects of beamwidth, side-lobe rejection ratio and the ability to reconstruct shapes of distributed targets.

Comparison of UWB technologies for human being detection with radar

UWB radar for detection and positioning of human beings in complex environment can be developed based on different technologies such as video impulse, quasi-random noise, stepped-frequency continuous wave and frequency-modulated continuous wave. These technologies are compared on the basis of meeting functional requirements to such a radar. Relative advantages and disadvantages of these technologies for such an application as human being detection and positioning are pointed out. Recommendations for selection of an optimal technology are given.

Assessment of Electromagnetic Requirements for UWB Through-Wall Radar

This paper investigates electromagnetic requirements for ultra-wideband (UWB) through-wall radar. It includes the evaluation of propagation loss, dynamic range and radar resolution for typical through-wall scenarios. The evaluation results in analysis and comparison of different transmission schemes.

Revised range point migration method for rapid 3-D imaging with UWB radar

Surveillance UWB imaging radar systems require rapid radar imaging methods. One such method, called SEABED, has been demonstrated to work well for simple-shaped targets, but not for complex-shaped targets. To resolve the difficulties, the RPM method was developed to generate better images even for complex-shaped targets, albeit at the cost of processing speeds. This paper proposes an alternative method which is a hybrid of the SEABED and RPM methods that can quickly generate high-quality images for complex-shaped targets. To show its effectiveness, the performances of the three imaging methods are compared using simulations and experiments.

Weighted near-field focusing in an array-based GPR

This paper presents a 3-D imaging technique for an ultra-wideband (UWB) ground penetrating radar (GPR) with a single transmit antenna and a linear receive array. The video impulse GPR working in the frequency band of 0.3–3 GHz has been designed in IRCTR for landmine detection, i.e., for a near-field application. Installed on a vehicle it can image in one mechanical scan a strip of 84 cm width due to the length of array aperture. The imaging is done by software means only. The developed imaging technique combines a real aperture focusing in the array plane with a synthetic aperture focusing in the mechanical scan direction. To compensate for parasitic time delays in the array channels, a calibration procedure is also described. Owing to directional properties of transmit antenna, the distribution of signal strength over the array is nonuniform that requires an amplitude correction when focusing the real aperture. The authors analyzed how this affects the footprint of the focused array, its cross-range resolution capability and the image quality of antipersonnel plastic landmines which were buried under different array channels. The analysis bases on experimental data sets acquired in the facilities of IRCTR and TNO-DSS. As a result, the authors propose a weighted array focusing that improves the cross-range resolution and provides proper imaging of typical buried landmines.

Array-Based GPR for Shallow Subsurface Imaging

Recently we have reported development of an UWB array-based time-domain Ground Penetrating Radar for landmine detection. The radar is designed to be used within a vehicle-mounted multi-sensor system for humanitarian demining and produces 3D images of subsurface by ID mechanical scanning. In this paper, we demonstrate imaging capabilities of the developed system. The imaging capability of the radar is realized via electronic steering of the receive antenna footprint in cross-scan direction and synthetic aperture processing in along-scan direction. Imaging via footprint steering allows for drastic increase of the scanning speed.

Subsurface Imaging with UWB Linear Array: Evaluation of Antenna Step and Array Aperture

This paper presents the investigation of antenna step and aperture size for an ultra-wideband (UWB) ground penetrating radar (GPR) with a linear array. The procedure includes the optimization of receiving array, verification of optimization results by EM simulation and experimental measurement for both surface and subsurface imaging. The imaging algorithm used for the evaluation combines the focusing of the array and the synthetic aperture radar technique in the mechanical scan direction.