08-16-2017, 10:59 PM
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ABSTRACT
Ground penetrating radar is a non destructive technique for evaluation of subsurface structures in earth, or concrete. To sum that up, it lets us locate rebar, conduits, voids, and other features under the surface of the concrete. It does this by broadcasting low wattage radio waves into the ground, and timing the reflections.
It is very similar to the way that fish finders work, except that it uses radio, where fish finders use sound. In both cases, the return signal is timed very accurately, and the echoes are translated, and displayed visually, in a form that trained users can then interpret.
Radio waves travel around us constantly. They are in the air, in the earth, in electrical systems. They can penetrate surfaces that light(visible) can not. That is why you can use your cellular phone in a room with no windows.
l. INTRODUCTION
Landmines and unexploded ordinance (UXO) are a legacy of war, insurrection, and guerilla activity. Landmines kill and main approximately 26,000 people annually. In Cambodia, whole areas of arabie 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 used for Landmines detection are metal detectors which are capable of finding even low metal content mines in mineralized solids, Nuclear magnetic resonance, fast neutron activation and thermal neutron activation, Thermal imaging and electro-optical sensors, Biological sensors such as dogs, pigs, bees and birds, chemical sensors such as thermal florescence- detect airborne and water borne prescience of explosive vapors.
Because of the difficulty detecting the tiny amounts of metal in a plastic Landniines with a metal detector, technology development as been funded in other variety of geophysical surface imaging application including utility mapping and hazardous waste container location and has been actively applied to the problem of landmines detection for nearly 20 years. When parameters such as frequency range, antenna size, antenna separation, and system timing are optimized for detection of mine sized object in the near subsurface. GROUNDING PENITRA TING RADAR is quite effective in detective both metal and plastic Landmines in a variety of soils. In this discussion, we will concentrate on GPR.
2 BLOCK DIAGRAM
There are two distinct types of GPR system, time domain and frequency domain. Time domain or impulses GPR transmits 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 nonmetallic mines.
In this discussion we deal with buried anti-tank (A T) and antipersonnel (AP) Landmines which require close approach or contact to activate. AT mines ranges from about 15 to 35 cm in size. They are typically buried up to 40 cm deep. But they can also be deployed on the surface of a road to block a column of machinery. AP mines ranges from about 5 to 15cm in size. AT which are designed to kill the maim people.
GPR is quite effective in detecting both metal and plastic Landmines in a variety of soils. The depth of penetration is a function of both the frequency range produced and the soil at attenuation. Lower frequency components penetrate further, but it is a higher frequency component that is necessary to image and resolve smaller targets. Both impulses based and swept frequency GPR system have been employed in Army sponsored research program. Generally a system with a bandwidth of roughly 1 to 4 GHz is effective for detection of landmines.
Ultimately, GPR images the dielectric property of the soils and any discontinues appear as signal, if s011 were perfectly homogenous; a discontinuity caused by a landmine would stand out as an anomaly against the background. Unfortunately, even under near-ideal test track conditions, soil itself is a remarkably inhomogeneous medium, and false alarms are easily generated from the background itself.
Because of this, automatic target recognition (ATR) algorithms employed by impulses - based GPR systems typically calculate and remove background and try to detect the hyperbolic signatures that are characteristic in size and shape of landmine targets in GEO - Centers 400 series energy in focusing ground penetration radar (EFGPR) we employ a fuzzy logic- based algorithm that use protypes or feature sets, for landmines and protypes than to clutter. At each location in data set, we lock in side a neighborhood of adjacent points, extract a feature set and calculate if the feature set is closer to the mine prototypes. The output is a plan view, outputting targets reports when a blob is of an appropriate size and shape.