Betul Yilmaz

A Review on Migration Methods in B-Scan Ground Penetrating Radar Imaging

Even though ground penetrating radar has been well studied and applied by many researchers for the last couple of decades, the focusing problem in the measured GPR images is still a challenging task. Although there are many methods offered by different scientists, there is not any complete migration/focusing method that works perfectly for all scenarios. This paper reviews the popular migration methods of the B-scan GPR imaging that have been widely accepted and applied by various researchers. The brief formulation and the algorithm steps for the hyperbolic summation, the Kirchhoff migration, the back-projection focusing, the phase-shift migration, and the - migration are presented. The main aim of the paper is to evaluate and compare the migration algorithms over different focusing methods such that the reader can decide which algorithm to use for a particular application of GPR. Both the simulated and the measured examples that are used for the performance comparison of the presented algorithms are provided. Other emerging migration methods are also pointed out.

A new and practical formulation of bistatic Inverse Synthetic Aperture Radar imaging and verification of the formulation using numerical examples

A compact formulation of bistatic inverse synthetic aperture radar (ISAR) imaging is provided and presented thru numerical simulation of various perfect scatterers. The imaging formulation is derived for small-angle and small-bandwidth conventions. After completing the formulation, its relationship to monostatic set-up is examined and discussed. To validate the algorithm, the images of point target models are then simulated and presented for different bistatic geometries. It is shown that for a range of bistatic angle, the imaging algorithm successfully works and has the advantage of reduced bandwidth over the monostatic case at the cost of worse resolution.

Ultra Wide Band horn antenna design for Ground Penetrating Radar: A feeder practice

Ultra-Wide Band (UWB) technology in Ground Penetrating Radar (GPR) imaging has been an interested research topic for the last couple of decades. Although there have been a lot of work and research conducted on this subject, there c still interested research matters that has to be studied. UWB directional antennas are one of the critical components for UWB-GPR applications. The parameters of the antennas that are used within the system affect the performance of the application. The horn antenna; for example, can give the focusing ability needed in some applications thanks to its high directivity feature. Although there are many parameters that affect the design of a Horn antenna, aperture size and the feeder type are commonly used parameters to obtain wider frequency operation. In this study, the effect of different feeding structures on frequency bandwidth for a fixed waveguide dimensions are investigated and the results are shared. For this purpose, various feeding structures that are straight wire feeder, spherical feeder, cylindrical feeder and conical feeder are examined and the simulated and the measured bandwidth results are presented. Furthermore, we propose a new feeder type that provides better simulation results in terms of bandwidth is introduced. With this new structure, the horn antenna is optimized using an antenna simulation software; CST-Microwave Studio and the corresponding produced antenna is measured to complete the design.

Through-the-wall imaging radar experiments based on 8-element vivaldi radar sensor

In this work, we present the experimental results and the formed radar images of Through-the-Wall Imaging Radar (TWIR) experiments that were conducted by our recently developed radar sensor. Experiments towards to detection and imaging of both the stationary and the moving targets were conducted. A back-projection type focusing algorithm was applied to focus the raw radar images. The resultant measured TWIR images with good resolution features in both depth and cross-range domain have demonstrated the notable performance of our radar sensor.

Sub-aperture method for the wide-bandwidth wide-angle inverse synthetic aperture radar imaging

In this paper, a method for obtaining focused inverse synthetic aperture radar (ISAR) images of targets based on the radar backscattering measurements taken over wide bands and wide angles. The proposed method divides wide angle and wide frequency band into small aperture bands in the spatial frequency or Fourier domain. This set-up makes it possible to use fast calculation of ISAR images for every sub-aperture data set as in the case of standard ISAR case of small-bandwidth and small-angle. The details of the method are presented and numerical examples are given for the validation the method. The electromagnetic scattering estimation from the target is calculated via a hybrid simulator that uses both the physical optics and the shooting & bouncing ray concepts.

An Experimental Study and Concept Evaluation on Tree-Interior Imaging Radar Using Sinusoidal Template-Based Focusing Algorithm

An algorithm for detecting cavities inside a tree-body is presented with simulation and measured examples. The details of the imaging algorithm that is based on sinusoidal template focusing routine are given. First, the algorithm is tested with the simulation scenario for which perfect reconstruction of the simulated cavity structure together with tree-body is successfully formed in MATLAB programming environment. Then, the algorithm is applied to the measurement data that have been collected from a laboratory set-up. Collected backscattered measurements from the tree-body (with cavity) structure are used to generate the image of the scene by the help of our proposed algorithm. The resultant radar images of the measured data collected from the laboratory arrangement have shown the applicability of the developed algorithm for the detection of cavity structures inside tree-bodies.

A focusing algorithm for tree-penetrating radar imaging: An experimental study and concept evaluation

In this work, we have presented a focusing algorithm for tree-penetrating radar applications. The details of our imaging and focusing algorithm to detect cavities inside a tree-body were given. First, the algorithm has been tested with the simulation data that were generated by the help of perfect point scatterers. Then, the algorithm was applied to the measurement data that have been collected from a laboratory set-up. The resultant radargram of the measured data has demonstrated the effectiveness and the success of the proposed algorithm.

Design and prototype of radar sensor with Vivaldi linear array for through-wall radar imaging: an experimental study

Abstract. We present a radar sensor that was designed to detect and image moving objects/targets on the other side of a wall. The radar sensor was composed of a linear array of Vivaldi antenna elements, an radio frequency (RF) switch, a microcontroller unit, and an RF transceiver. For the linear array, a total of eight antenna elements were used as sensors in synthetic aperture radar (SAR) configuration in the cross-range axis to improve the resolution in this dimension. Design steps of Vivaldi antenna elements and the entire linear array were presented. After the design, the prototyping procedure and the details of the radar sensor were given. Through-the-wall radar (TWR) imaging experiments were performed for stationary and moving targets using the assembled sensor. The resultant TWR images after these experiments were presented. During the image formation, a back-projection type image focusing algorithm was implemented and applied to increase the signal-to-noise ratio of the raw images. The constructed radar images demonstrated that our radar sensor could successfully detect and image both stationary and moving targets on the other side of the wall.

A radar sensor design and prototype for through-the-wall imaging radar applications

In this work, we present the complete design and prototype processes for a radar sensor that can be used for Through-The-Wall Imaging Radar applications. The simulation and optimization of the antenna element were done using CST Electromagnetic simulator software. The full array that was composed of 8-Vivaldi antenna elements aere also simulated and optimized using CST. The radar sensor was configured by the 8-element Vivaldi array, RF transceiver, RF switch, microcontroller and computer set-up. The final production of the radar sensor was presented and the integration steps of the sub units were shared. The good agreement between the simulated and the measured results for the antenna parameters demonstrate the success of the design and prototyping process.