Low frequency electromagnetic induction methods for detection of landmines

1. Low frequency electromagnetic induction methods for detection of landmines ACROSS Colloquia Davorin Ambruš University of Zagreb, Faculty of Electrical Engineering and Computing Department of Electronic Systems and Information Processing Research Centre for Advanced Cooperative Systems (ACROSS) November, 2012.

2. 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..

3. Landmine problem • Mine infestation • World level: • 50-100 millions landmines worldwide • 5.000 – 20.000 casualties per year • Croatia: • 716 km2of 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 detectionmethods ?

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

5. Antipersonnel landmines • Classification: Blast and fragmentation mines • Standard demining procedure using metal detectors and mechanical prodders • Specific problem: minimum metal mines (MM) • 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

6. Humanitarian demining procedure Vegetation removal, formation of a test lane Mine detection Mine removal 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

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

8. 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 • Prodders

9. 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 HSTAMIDS (Handheld Standoff Mine Detection System)

10. 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 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

11. Advanced EMI methods • 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 REF: F. Shubitidzeet al., “Application if NSMS model to multi-axis time domain EMI data”, Proc. of SPIE Vol. 6953 , 2008. 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.

12. Induced dipole model • Metal target approximated by the magnetic dipole 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

13. Ground balancing • 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

14. Inversion of target and soil properites 1st approach: subtract soil response from observed data, then invert for target parameters 2nd approach: simultaneous inversion of target and soil properties

15. Advanced model-based UXO detectors MPV-II sensor, G&G Sciences MPV (Man Portable Vector) sensor, G&G Sciences GEM-3D+, Geophex, USA.

16. 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 (?)