During the past 80 years, ground-penetrating radar (GPR) has evolved from a skeptically received glacier sounder to a full multicomponent 3D volume-imaging and characterization device. The tool can be calibrated to allow for quantitative estimates of physical properties such as water content. Because of its high resolution, GPR is a valuable tool for quantifying subsurface heterogeneity, and its ability to see nonmetallic and metallic objects makes it a useful mapping tool to detect, localize, and characterize buried objects. No tool solves all problems; so to determine whether GPR is appropriate for a given problem, studying the reasons for failure can provide an understanding of the basics, which in turn can help determine whether GPR is appropriate for a given problem. We discuss the specific aspects of borehole radar and describe recent developments to become more sensitiveto orientation and to exploit the supplementary information in different components in polarimetric uses of radar data. Multicomponent GPR data contain more diverse geometric information than single-channel data, and this is exploited in developed dedicated imaging algorithms. The evolution of these imaging schemes is discussed for ground-coupled and air-coupled antennas. For air-coupled antennas, the measured radiated wavefield can be used as the basis for the wavefield extrapolator in linear-inversion schemes with an imaging condition, which eliminates the source-time function and corrects for the measured radiation pattern. A handheld GPR system coupled with a metal detector is ready for routine use in mine fields. Recent advances in modeling, tomography, and full-waveform inversion, as well as Green's function extraction through correlation and deconvolution, show much promise in this field.

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Surface and borehole ground-penetrating-radar developments

This paper describes the further engineering development and performance of the MINEHOUND affordable humanitarian mine detector, sponsored by the UK Department for International Development and developed by ERA Technology. Using a radically different patented approach from conventional ground penetrating radar (GPR) designs, in terms of the man machine interface, MINEHOUND offers simplicity of use and affordability, both key factors in humanitarian demining operations. Trials were carried out during the period 2002-2004 and have been reported at SPIE 2002 and SPIE 2004. MINEHOUND has the capability of detecting completely non-metallic mines and offers an affordable solution to hand held mine detection. The GPR is a time-domain radar transmitting 1ns duration impulses at a repetition frequency of 1MHz. The GPR transmitter- receiver and associated control and signal processing is mounted on a compact purpose designed printed circuit board 220mm by 100mm. A dedicated state of the art “Blackfin” DSP processor is used to provide all control and signal processing functions. Trials of batches of MINEHOUND are planned for 2005 in the Cambodia and Angola as well as the Balkans.

MINEHOUND production development

The magnetic dipole polarizability tensor is an object-specific property possessing information about the size, shape, and material. This information could be used by electromagnetic induction sensors typically used for demining operations to discriminate between buried mines and clutter, reducing false alarm rates, and improving demining throughput and safety. This paper presents a methodology capable of obtaining the spectroscopic tensors of small metallic objects and low metal anti-personnel mine surrogates. The experimental results are validated against simulated and analytical solutions to ensure that the obtained tensor truly represents the absolute object tensor. Absolute tensors for a number of typical clutter items and mine surrogates are presented, with significant variance observed between those of mine and clutter.

Magnetic Polarizability Tensor Spectroscopy for Low Metal Anti-Personnel Mine Surrogates

7. Ground-Penetrating Radar

GPR has been thought a useful sensor for detection of buried land mines, but no GPR has been practically deployed in humanitarian demining. Since 2002, we have developed a new hand-held land mine detection dual-sensor ALIS. ALIS is equipped with a metal detector and a GPR, and it has a sensor tracking system, which can record the GPR and Metal detector signal with its location. It makes possible to process the data afterwards, including migration. The migration processing drastically increases the quality of the image of the buried objects. ALIS uses two different GPR systems, namely VNA (Vector Network Analyzer) based GPR and an Impulse GPR. VNA based GPR can provide better quality GPR images, although the impulse GPR is faster and light weight. ALIS evaluation tests have been held in mine affected courtiers including Afghanistan, Croatia, Egypt and Cambodia. In the two-month evaluation test in Cambodia, ALIS worked without any problem. After some demonstrations and evaluation, we got many useful suggestions. Using these advises, we have modified the ALIS and it is now more easy to use. ALIS will be commercialized in 2007.

Development of the Hand held dual sensor ALIS and its evaluation

This paper describes the further development of the MINETECT affordable humanitarian mine detector produced by ERA Technology with sponsorship from the UK Department for International Development. Using a radically different patented approach from conventional ground penetrating radar (GPR) designs in terms of the man machine interface, MINETECT offers simplicity of use and affordability, both key factors in humanitarian demining operations. Following trials in 2002 and reported at SPIE 2002, further development work including research on classifying mines, based on data from planned trials in the United Kingdom, is presented. MINETECT has the capability of detecting completely non-metallic mines and offers a considerable improvement in hand-held mine detection.

An affordable humanitarian mine detector

This paper describes a polarised Short Wavelength Infra-Red (SWIR) system using Commercial Off-The-Shelf (COTS) technology, which was assessed against a variety of tripwires and backgrounds during night and day trials as part of a DSTL (UK) programme. The system comprises a polarised SWIR illuminator and cameras fitted with SWIR filters and polarisers. Various image-processing techniques were developed and evaluated including Stoke's S1 parameter, the Radon Transform and a novel and robust feature detector. Within the limits of the optical system, a tripwire recognition capability in vegetation was achieved that approached that of a human.

Rajan Amin

Papers

MINEHOUND production development

An affordable humanitarian mine detector

Use of COTS technology in tripwire detection