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Ground Penetrating Radar Detector of Buried Mines

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Development of Microwave Imaging Techniques for Ground Penetrating Radar Detector of Buried Mines

Tech Area / Field

  • INF-SIG/Sensors and Signal Processing/Information and Communications

Status
8 Project completed

Registration date
10.09.2002

Completion date
28.01.2009

Senior Project Manager
Genisaretskaya S V

Leading Institute
National Academy of Sciences of the Republic of Belarus / Institute of Applied Physics, Belarus, Minsk

Collaborators

  • Helsinki University of Technology, Finland, Helsinki\nRST Raumfahrt Systemtechnik GmbH, Germany, Salem

Project summary

Purpose of the project.

Development of robust inverse scattering methods, algorithms and software for signal processing in mine detection system based on step-frequency ground penetrating radar.

State of the art.

About 100 millions of mines are spread out over dozens of countries throughout the world creating permanent danger for population and retarding their development. Thus humanitarian demining is important social and economic problem for those countries. There exist a number of technologies of mine detection/removal, in most of which different non-contact sensors such as metal detectors, ground penetrating radar (GPR), infrared cameras and nuclear quadrupole resonance technique are employed.

In the last decade, GPR became one of the most promising tools for detection and recognition of buried mines and unexploded ordnance (UXO). Notable number of researchers are involved in the development of corresponding methods and devices. Special sessions had been devoted to the topic at all recent conferences on microwaves or nondestructive testing (31th European Microwave Conference, London, 25-27 September 2001 – “Focused session on multi sensor systems for landmine detection”, 9th International Conference on Ground Penetrating Radar, Santa Barbara, 29 April-2 May 2002 – session “UXO/Mine detection”, 8th European Conference on Nondestructive Testing, Barcelona, 17-21 June 2002 – session “Landmines detection”), to name a few.

Detection of mines especially buried at shallow depths is a very challenging task for GPR due to the strong clutter caused by soil inhomogeneity and crosstalk between antennas and ground surface. The analysis of existing publications on GPR shows that they group mostly around two topics: design of the antenna systems for work in the proximity of ground surface, and signal processing techniques. Huge amount of work has been done in GPR data processing. Numerous methods had been applied for reducing clutter and detecting/discriminating underground targets in real soil: different super-resolution algorithms with matched filtering (A. van der Merwe and I.J. Gupta, “A novel signal processing technique for clutter reduction in GPR measurements of small, shallow land mines,” IEEE Trans., vol. GRS-38, no. 6, 2000, pp. 2627-2637), hidden Markov models, wavelet transforms, genetic and neural network approaches, Kalman filtering, synthetic aperture focusing (Y. Dong et al., “Multi-aspect detection of surface and shallow-buried unexploded ordnance via ultra-wideband synthetic aperture radar,” IEEE Trans., vol. GRS-39, no.6, 2001, pp. 1259-1270) etc. As a result, characteristics of mine detection GPR systems are nowadays in general comparable with those of metal detector.

Further improvement of performance of the GPR mine detectors requires utilization of more adequate data processing and visualization algorithms like tomographic imaging. So far, inverse scattering methods had been applied to the problem using mostly synthetic input data (e.g. T.J. Cui, W.C. Chew, A.A. Aydiner, and S. Chen, “Inverse scattering of two-dimensional dielectric objects buried in a lossy earth using the distorted Born iterative method,” IEEE Trans., vol. GRS-39, no. 2, 2001, pp. 339-346). Design of improved GPR antenna system as well as careful accounting for the near field effects would help to suppress clutter and enhance detection characteristics, too.

Impact of the proposed project on the progress in the field.

The project is intended to reconstruct positions and shapes of underground objects and obtain reliable data about their dielectric properties. Comparisons of the obtained information and parameters of real minelike targets help to discriminate objects and thus enhance probability and reliability of mine detection. The signal processing algorithms and corresponding software developed in the project can be used in existing and future step-frequency GPR and hybrid systems for detection of buried anti-tank and anti-personnel mines.

Results of the project will contribute to the solution of important humanitarian problem such as demining of large areas in different countries and saving lives and health of people.

Project team.

The team includes researchers from the Laboratory of Microwave Methods for Nondestructive Testing, Institute of Applied Physics, formerly involved in development of different testing devices for missiles and rocket fuel. All the researchers had been engaged in microwave imaging problems and study of GPR antennas for more than 10 years. Three national basic research projects concerning solution of inverse problems, detection and recognition of buried objects had been completed since 1991. Results of this work have been published in several papers in top-level scientific journals such as IEEE Transactions on Antennas and Propagation and presented at major European and World conferences.

The project can help to integrate researchers of the laboratory into European scientific community. Therefore, research activities will be redirected from the testing of weapon materials to peaceful applications.

Expected results.

In the project, the following results will be obtained:

– robust frequency domain imaging methods and algorithms for reconstruction of shallow subsurface objects such as landmines using real step-frequency GPR data;


– GPR signal preprocessing methods and algorithms accounting for unwanted crosstalk between GPR antenna and ground surface and reducing clutter;
– modified GPR antennas with lower level of clutter caused by the near field effects;
– mobile step-frequency mine detection system for the field tests;
– PC software implementing above methods and algorithms and software for visualization of the shallow layer of soil;
– results of comparative tests of the developed techniques and software with those provided by foreign collaborators.

Application of the results.

Scientific and practical significance of the obtained results rely on the development of robust inverse scattering methods and software usable for real GPR data. Such methods allow to derive more information about the underground objects, and therefore alleviate their detection and discrimination. However, inverse scattering methods are very sensitive to the accuracy of the input information. That is why despite of large amount of proposed inversion methods, most of them work well only with synthetic data. This is the reason why in the proposed project research of microwave inverse scattering is accompanied by clutter reduction algorithms and antenna design, that aim to remove partially from the input data components, not accounted in the mathematical formulation of the inverse problem.

Results of the project will lead to enhanced performance of the mine detection systems that include GPR sensors. Thus the project possesses valuable humanitarian and social significance like the whole problem of humanitarian demining. Keeping in mind that detection of shallow subsurface targets is general visualization problem encountered elsewhere, the methods and algorithms developed in the project after some adaptation can be utilized e.g. in civil engineering – for non-destructive testing of walls, bridge decks etc., and in biomedicine – for early detection of breast tumors of women being nowadays even more important humanitarian problem than demining.

Compliance of project activity with ISTC goals.

The project meets ISTC goals as follows:

– gives to the scientists and engineers participating in the project, an opportunity to redirect their knowledge from the testing of missile materials and rocket fuel to humanitarian demining;


– encourages integration of the researchers involved in the project, into the international scientific community via collaborative research, comparative tests of imaging algorithms, participation in conferences, scientific information exchange;
– supports applied research in the field of microwave imaging for the purpose of environmental protection in many countries by minefield clearance;
– supports transition to market economy as the research team participating in the project can form in the future a scientific and technical company producing software and apparatus for radar visualization of non-transparent media in different practical applications such as civil engineering, industrial non-destructive testing and biomedicine.

Scope of activities.

The project duration is of 30 months. 6 tasks will be fulfilled in the project. The scope of activities includes the following tasks:

– investigation of robust 2D inverse scattering methods for reconstruction of minelike objects buried at shallow depths in inhomogeneous lossy media;


– development of broadband traveling wave GPR antenna exhibiting low level of clutter caused by the parasitic near-field effects;
– development of calibration techniques and signal preprocessing algorithms taking into account non-ideality of GPR antennas and suppressing clutter;
– development of mobile battery-supplied step-frequency GPR system for raw data collecting and verification of the performance of the data processing and imaging algorithms;
– development of the algorithms and software implementing data processing and inverse scattering methods;
– experimental verification of developed imaging techniques using fabricated antenna systems and data processing algorithms using indoor and outdoor test facilities. Comparative tests of the developed data processing and inverse scattering algorithms with those provided by collaborators, including field tests.

Role of foreign collaborators.

The cooperation with the collaborators of the project will promote exchange of scientific information concerning the project research, cross-check of the obtained results and their practical application. Foreign collaborators will participate in technical monitoring of the project activities, experimental verification and comparative tests of the developed techniques and software. Results of work will be discussed in joint seminars and international conferences. In particular, the following forms of collaboration are provided:

– P. Vainikainen, Professor, Dept. of Electrical and Communication Engineering, Radio Laboratory, Helsinki University of Technology. Planned participation forms: providing the project researchers with measurement equipment, work stations, high frequency simulation software; discussion of objectives, methods and results;


– M. Sato, Professor, Tohoku University, Center for Northeast Asian Studies. Planned participation forms: discussion of the project objectives, technical approaches and obtained results; cross-checks of the imaging methods and data processing algorithms; evaluation of the system by simulation and laboratory test;
– H.M. Braun, RST Raumfahrt Systemtechnik GmbH. Planned participation forms: technical monitoring of the project activities; comparative tests of the imaging algorithms and software developed for the mine detection with those available at RST Raumfahrt Systemtechnik GmbH.

Technical approach and methodology.

In the project, modern technical approaches and methodology will be employed. Solution of inverse scattering problems will be based on iterative optimization techniques such as Newton-Kantorovitch procedure. This procedure had been successfully used by the project team for robust solution of one-dimensional inverse problem using frequency domain input data. Besides, applicability of nonlinear optimization approach and local shape function method will be tested and discussed. Regularization techniques will be used to enhance stability and convergence of solutions of inverse problems.

Antenna analysis should be based essentially on computer simulations with the use of modern software like Ansoft HFSS 6.0, Remcom FDTD 5.0, IE3D etc. The project team has designed and fabricated several GPR antennas like tapered slot antennas and hybrids. Their comparison will be carried out using technique proposed recently by the project team.

Calibration methods for step-frequency GPR will be based on study of near field behavior of radiated wave. Recently, the researchers of IAP NASB developed simple calibration method for step-frequency radar that accounts to some extent for antenna dispersion and unwanted multiple reflections. This method will be improved.

Further clutter reduction can be achieved after calibration by the parametric modeling of received signals utilizing adaptive basis functions. Consequently, the clutter response will be discriminated and subtracted.


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