Low frequency electromagnetic induction methods for detection of landminesACROSS Colloquia

Davorin Ambruš

University of Zagreb, Faculty of Electrical Engineering and ComputingDepartment of Electronic Systems and Information ProcessingResearch Centre for Advanced Cooperative Systems (ACROSS) November, 2012.

Summary• Landmine problem• Existing detection methods• Current trends in R&D of mine detectors• Metal detectors in humanitarian demining• Research on novel EMI methods and

approaches• Work in progress..

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Landmine problem• Mine infestation

– World level:• 50-100 millions landmines worldwide• 5.000 – 20.000 casualties per year

– Croatia:• 716 km2 of mine suspected area (1,3 % of territory)• 90.000 landmines• > 230 mine incidents, > 100 persons killed (1998-2012)

• Current state of demining technology + estimated cost (~ 30 billions $) 450-500 years for removal of all mines

• Novel or improved existing detection methods ?

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Landmine problem

4REF: Croatian Mine Action Centre, http://www.hcr.hr

Antipersonnel landmines• Classification: Blast and fragmentation mines• Standard demining procedure using metal

detectors and mechanical prodders• Specific problem: minimum metal mines (MM)

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Sensitivity• Probability of

detection > 0,996 (UN norm ?)

• MM mines very high sensitivity needed

Specificity• Discrimination

between metal parts of a mine and metallic clutter

• False alarm rate (FAR) – up to 1.000 per mine (!)

• Mine detector’s qualitiy determined by ROC curves

Humanitarian demining procedure

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Vegetation removal, formation of a test lane

Photos: “Test and Evaluation of Japanese GPR-EMI Dual Sensor Systems at Benkovac Test Site in Croatia”, The Croatian Mine Action Center Center for testing, development and training Ltd., http://www.ctro.hr

Mine detection

Mine removal

Minimum metal mines and clutter

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Photos: C. Bruschini, A Multidisciplinary Analysis of Frequency Domain Metal Detectors for Humanitarian Demining, PhD Thesis, Vrije Universiteit Brussel, Belgium, 2006.

Existing detection methods• Low frequency electromagnetic methods

– Metal detectors - inductive (EMI) and magnetometric (MAG)– Electrical impedance tomography (EIT)– Capacitive detectors

• Ground penetrating radar (GPR)• Other electromagnetic methods

– Electro-optic detectors (IR and hyperspectral)– X-ray and Gamma-ray backscatter

• Acoustic methods• Explosive detectors

– Nuclear quadrupole resonance (NQR)– Explosive vapor detectors

• Prodders8

Current R&D trends• New detection methods

– R&D limited due to relatively small and specific market– Focused mainly on explosive detection

• Improvement of existing methods– EMI, GPR, NQR, acoustic detectors

• Multi-sensor and multi-modal systems– Data fusion algorithms– Commercial multi-sensor systems:

• EMI+GPR (ALIS (Tohoku University),Vallon…)• EMI+GPR+MAG• EMI+GPR+NQR (HSTAMIDS, US Army)• EMI+GPR+IR

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HSTAMIDS(Handheld Standoff Mine Detection System)

Conventional metal detectors in HD• Two-coil configurations

(transmit and receive)• Continuous wave (frequency

domain) detectors vs. pulse induction (time domain)

• Typical frequency spectrum 30 Hz – 100 kHz

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a) “OO” coils b) “DD” coils c) “4B” coils

d) coaxial coils, gradiometer conf. RX

e) concentric coils, gradiometer conf. TX

f) concentric coils, gradiometer conf. RX

REF: C. Bruschini, A Multidisciplinary Analysis of Frequency Domain Metal Detectors for Humanitarian Demining, PhD Thesis, Vrije Universiteit Brussel, Belgium, 2006.

Inductive balancing – using proper coil configurations and/or pulse excitation

• In order to reduce the false alarm rate, additional information on target properties is needed:– Shape (is the target spherical, elongated or plate-like ?)– Principal dimensions– Orientation– Position (burial depth)– Material properties (conductivity, permeability)

• Mine discrimination / classification:• Pattern recognition approach• Model-based approach

Advanced EMI methods

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REF: H. Krueger et al., “Advanced Signal Processing for Reduction of False Alarm Rate of Metal Detectors for Humanitarian Mine Clearance”, IEEE International Instrumentation and Measurement Technology Conference, IMTC 2006, pp. 1452-1456, Sorento, Italy, April 2006.

REF: F. Shubitidze et al., “Application if NSMS model to multi-axis time domain EMI data”, Proc. of SPIE Vol. 6953 , 2008.

Induced dipole model• Metal target approximated by the magnetic

dipole

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Magnetic field of a dipole at observation point

Interaction of the primary field and a target

Diagonalized magnetic polarizability tensor

Inversion procedure when the target location is known

Inversion procedure when the target location is unknown

Ground balancing

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• Compensation of electromagnetic properties (electrical conductivity/magnetic permeability) of soil

• Major problem – highly mineralized (magnetic) soils

• Simple compensation based on highpass filtering and frequency differencing schemes

• Model-based compensation methods based on frequency-dependant magn. susceptibility models and smooth spatial distribution of soil EM properties

Assumption of linearity for a detector response

Inversion of target and soil properites

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1st approach: subtract soil response from observed data, then invert for target parameters

2nd approach: simultaneous inversion of target and soil properties

Advanced model-based UXO detectors

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MPV (Man Portable Vector) sensor, G&G Sciences

MPV-II sensor, G&G Sciences

GEM-3D+, Geophex, USA.

Work in progress.. / research plans..• Design of a prototype stage EMI detector

sensor head (3-coil, transmitter-bucked design)

• Design of a complete laboratory set-up and test bed filled with soil

• Application of the induced dipole model and related inversion algorithms to prototype detector for simple test targets

• Development of the soil model and related inversion algorithms for recovering spatial distribution of EM properties

• Development of inductive positioning system for dynamic tracking of the sensor head position (?)

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