A distributed fiber optic sensor with the ability of detecting and locating intruders
on foot and vehicles over long perimeters (>10 km) was studied. The response
of the sensor to people walking over or near it and to vehicles driving nearby was observed
and analyzed. The sensor works on the principle of phase sensitive optical time
domain re
ectometry, making use of interferometric effects of Rayleigh backscattered
light along a single mode fiber. Light pulses from a highly stable Er:doped fiber laser
emitting single longitudinal mode light and exhibiting low frequency drift are passed
through one end of the buried fiber. The backscattered light emerging from the same
fiber end was monitored using a photodetector. The phase changes produced in the
light pulse due to the pressure of the intruder walking directly above or near the
sensor or from the seismic disturbances created by vehicles moving in the vicinity of
the sensor are detected using the phase sensitive Optical Time Domain Re
ectometer (OTDR).
Field tests were conducted with the sensing element as a single mode fiber in a
3-mm diameter cable buried at depths ranging from 8 to 18 inches in clay soil. It was
observed that the sensor could detect intruders walking transverse to the cable line at
a distance of 40 ft from it. A car moving at a speed of 30 mph on a rough road could
be consistently detected up to a distance of 480 ft from the sensor, while a car driven
on a smooth road 200 ft from the sensor could be detected only when passing through
rough patches on the road. Tests were also performed with an intruder walking near the sensor while a car was driven at a speed of 30 mph on a rough road. The effect
on the signal due to the intruder on foot could be distinguished clearly only when the
car was at least 200 ft away from the sensor.
The results in this thesis represent the first quantitative study of the sensitivity
of the sensor under varied test conditions. It is expected that these findings will be
helpful in the practical implementation of the long perimeter intrusion sensor along
high security domains like national borders, military bases and government buildings.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/3087 |
| Date | 12 April 2006 |
| Creators | Kuppuswamy, Harini |
| Contributors | Taylor, Henry F. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | 1805734 bytes, electronic, application/pdf, born digital |
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