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13-01-2009, 02:23 PM
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Fiber Optic Cables Can Detect Underground Tunnels
These are the same cables used in telecommunications
By Tudor Vieru, Science Editor
Softpedia


http://news.softpedia.com/images/news2/Fiber-Optic-Cables-Can-Detect-Underground-Tunnels-2.jpg

Technion-Israel Institute of Technology researchers have recently announced that they have devised a way of using telecommunications-grade fiber optic cables to detect war-time underground tunnels, like those used by Hamas in the Gaza strip to smuggle in weapons across the Israeli border. Their finds are to be presented in Orlando, Florida, in April 2009, at the Defense, Security and Sensing Conference of SPIE. The Society of Photographic Instrumentation Engineers is a group seeking to further scientific advancements in areas related to optics and photonics, and was founded in 1955 in California.

“Tunnel excavation is accompanied by the release of stresses that cause permanent – though very tiny – displacements and strains in the ground. If you can measure these strains in the soil with sensitive equipment, you can find the tunnel's location,” Dr. Assaf Klar, one of the two main researchers and a member of the Technion Faculty of Civil and Environmental Engineering (FCEE), explains.

He adds that the disturbances generated by underground excavations are quite different from those generated by other causes, which would undoubtedly make their system work. Alongside Klar, Dr. Raphael Linker has also played a major role in the new research. He is, likewise, a member of FCEE.

Using high-tech computer simulations, the two have “trained” a computer to recognize various soil profiles, which are to be recognized by a device known as Brillouin optical time domain reflectometry (BOTDR). The signal that the fiber optic ensemble transmits propagates through the ground, where a natural process known as “wavelet decomposition” breaks it into smaller patterns.

These patterns are then filtered and analyzed, and any irregularities are matched against the existing databases, featuring the profiles of tens of thousands of tunnels discovered worldwide. The researchers say that if there's an artificial structure below the ground, the system will locate it, allowing the army to get a tactical advantage over the combat zone.

If the supply routes are localized, patrols could be set at tunnel entrances, and capture militants who supply extremists with weapons. Their contact people could also be found, which would virtually put an end to the Hamas weapon supplies. Needless to say, that would almost surely mean victory for Israel. The only thing that is standing in the way of this happening is time.




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Nader 3:16
13-01-2009, 04:27 PM
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13-01-2009, 06:34 PM
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14-01-2009, 02:19 AM
ÇáÝßÑÉÈÊÚÊãÏ Ú effet brillouin íáí ÚäÏæ ÍÓÇÓíå ßÈíÑÉ ÚÇáÍÑÇÑÉ æÇáÖÛØ íáí ããßä íÊÚÑÖáÇ fibre.
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La diffusion Brillouin stimulée (DBS) se manifeste par la génération d’une onde optique rétrodiffusée, appelée onde Stokes, suite à l’interaction entre la lumière et les ondes acoustiques présentes dans le milieu diffusant. A partir d’un certain niveau d’intensité lumineuse, toute la puissance supplémentaire injectée est transférée dans l’onde Stokes. La DBS apparaît, de ce fait, comme une limitation majeure pour les télécommunications à fibres optiques, dans le sens où elle limite la puissance maximale que peut transmettre une fibre optique. Lors de sa génération, l’onde Stokes subit un décalage de fréquence, appelé par extension décalage Brillouin, qui est directement proportionnel à la vitesse de propagation des ondes acoustiques dans le milieu diffusant. Le décalage de Brillouin dépend en outre des propriétés optiques de la fibre et de la lumière incidente et, s’élève à environ 13 GHz dans les fibres optiques à base de silice et à une longueur d’onde de 1.3 μm. Il présente, par ailleurs, une grande sensibilité, à tous les effets modifiant la vitesse acoustique, en particulier aux variations de températures et aux contraintes appliquées à la fibre. Les caractéristiques spectrales de la lumière diffusée véhiculent ainsi des informations sur les grandeurs ambiantes, telles que température et présence de contraintes. Cette propriété confère à la DBS une potentialité élevée pour la réalisation de capteurs à fibres optiques.

Nader 3:16
14-01-2009, 02:46 AM
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