12-10-2012, 05:51 PM
LANDMINE DETECTION USING IMPULSE GROUND PENETRATING RADAR
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INTRODUCTION
Landmines and unexploded ordnance (UXO) are a legacy of war,
insurrection, and guerilla activity. Landmines kill and maim approximately
26,000 people annually. In Cambodia, whole areas of arable land cannot be
farmed due to the threat of landmines. United Nations relief operations are
made more difficult and dangerous due to the mining of roads. Current
demining techniques are heavily reliant on metal detectors and prodders.
Technologies are used for landmine detection are:
Metal detectors--- capable of finding even low-metal content mines in
mineralized soils.
Nuclear magnetic resonance, fast neutron activation and thermal
neutron activation.
Thermal imaging and electro-optical sensors--- detect evidence of
buried objects.
Biological sensors such as dogs, pigs, bees and birds.
Chemical sensors such as thermal fluorescence--- detect airborne and
waterborne presence of explosive vapors.
In this discussion, we will concentrate on Ground Penetrating
Radar (GPR). This ultra wide band radar provides centimeter resolution to
locate even small targets. There are two distinct types of GPR, time-domain
and frequency domain. Time domain or impulse GPR transmites discrete
pulses of nanosecond duration and digitizes the returns at GHz sample
rates. Frequency domain GPR systems transmit single frequencies either
uniquely, as a series of frequency steps, or as a chirp. The amplitude and
phase of the return signal is measured. The resulting data is converted to the
time domain. GPR operates by detecting the dielectric contrasts in the soils,
which allows it to locate even non metallic mines.
In this discussion we deal with buried anti-tank (AT) and antipersonnel
(AP) landmines which require close approach or contact to
activate. AT mines range from about 15 to 35 cm in size. They are typically
buried up to 40cm deep, but they can also be deployed on the surface of a
road to block a column of machinery. AP mines range from about 5 to
15cm in size. AT mines which are designed to impede the progress of
destroy vehicles and AP mines which are designed to kill and maim people.
HARDWARE DESCRIPTION
The impulse GPR system developed in the International Research
Centre for Telecommunications-transmission and Radar (IRCTR). Impulse
GPR system comprises a Impulse generator, Transmitter, Receiver, Pulse
extender, A/D converter, Processor and Visual display.
IMPULSE GENERATOR
The pulse generator delivered by SATIS Co. produces 0.8 ns
monocycle pulses. The unique feature of this generator is its small trailing
oscillations, which are below 2.4% of maximum amplitude during the first
2 ns and below 0.5% afterwards. The advantage of a monocycle in
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comparison with a mono pulse is that the frequency spectrum of the first
one decreases to zero at low frequencies, which cannot be efficiently
transmitted via the antenna system, while the frequency spectrum of the
second one has a global maximum there. As a result, the magnitude of the
field radiated by an antenna system fed by a monocycle is considerably
larger than the magnitude of the field radiated by the antenna system fed by
a monopulse with the same magnitude.