Detection and Localization of Subsurface Objects by Ground Penetrating Radar

1
Field evaluation of handheld landmine detection
GPR system in Croatia K. Takahashi, F. Xuan, T.
Kobayashi, Q. Lu, M. Sato Center for Northeast
Asian Studies, Tohoku University, Japan

• Handheld dual sensor system, ALIS
• (Metal detector GPR)
• Features of ALIS
• Handheld
• GPR as an add-on unit
• Similar usage of metal detectors
• Sensor tracking algorithm
• Imaging capability
• Real time MD imaging
• System configuration

Field evaluation test Benkovac, Croatia Feb.-Mar.
2006
Lane conditions

• Volumetric water content
• Mineralized soil 41, Neutral sand 32, Local
  soil 48
• Targets
• Two kinds of landmine (PMN-1A, PMA-2)
• Clutters (ITEP I0, various forms of metal
  fragments)
• Buried at depths of 5, 12.5, and 20 cm.

• GPR specifications
• Radar type Stepped-frequency
• Frequency range 500 MHz 4 GHz
• Antennas Cavity-backed spiral or Vivaldi
• Dynamic range gt70 dB
• Sampling approx. 4 sweeps/s (550 freq.
  points/s)

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Image examples PMN-1A _at_ 12.5 cm Square
shaped image can be seen in the GPR
image although the MD image is
smeared due to low metal content
and deep buried depth. PMA-2 _at_ 12.5
cm Circular shaped image can be seen
at the same location of the MD
response. An ideal MD image
for a piece of metal consists of two
semicircles colored with blue
and red.
MD image
GPR image
12 cm
6 cm
Test results PD (Probability of detection) For
lanes For targets For depths In
tough conditions for a MD (ex. mineralized soil,
high permittivity, small target, deep target),
ALIS can give better result than the MD. Since MD
cannot tell mine or fragments (i.e., all the
responses are reported as mines), no result of MD
for fragments in these figures. The results of
GPR are for only discriminated mines or
fragments, meaning that it is possible to
discriminate mines from metallic fragments by use
of GPR. ROC (Receiver Operating
Characteristic) PD vs FAR (False Alarm Rate
number of fragments detected as
mines) Ex. Effective sensor right
angle curve, Poor sensor diagonal
curve Mineralized Neutral Local soil
sand soil In relatively
homogeneous soil (mineralized soil), the
discrimination by GPR works well, resulting ALIS
has lower false alarm rate than MD at the same
PD. However, inhomogeneity gives higher false
alarm rate to GPR. Even so the curves of ALIS are
more similar to the ideal curve. It means that
ALIS (GPRMD) possesses great potential of
discrimination and it leads to high efficiency
demining operation.
ALIS Metal detector
ALIS Metal detector