Vibration Detection
3-D Seismic Sensors Form Web Against Intruders
By barbara opall-rome
Published: 28 September 2009 Print | Email
NETANYA, Israel - A small, 5-year-old Israeli company appears to have breached the technological barrier that, until now, has limited the ability of microphones, geophones and other off-the-shelf seismic sensors to reliably detect, classify and locate subterranean and surface infiltrations.

Now undergoing prototype testing by Spider Technologies Security (SpiderTech), the new seismic-based perimeter protection system - called Tarantula - creates an underground web of small, self-processing, three-dimensional sensors to detect digging, walking or motorized movement at about twice the ranges of existing systems.

Field tests in Israel and elsewhere have detected human targets at distances of about 30 meters, developers here said. Ranges are significantly longer - a minimum of 100 meters - for light vehicles, whereas heavy vehicles can be detected at a minimum of 300 meters, they say.

Like its namesake, SpiderTech's Tarantula uses its web as a tripwire alert against approaching intruders. And like the invertebrate, the high-tech Tarantula relies not on sight, but on sensitive hairlike extensions to feel out potential danger. In this case, individual sensors act as the creature's vibration-sensitive hairy legs, separating out environmental noise, classifying targets by seismic signature and pinpointing - within five meters - the location of approaching threats both on the surface and underground.

Under the preliminary deployment concept, sensors are buried about 50 centimeters underground at 40-meter intervals, forming a weblike array that is controlled by a single exchange unit, or SpiderTech Web (STW). Each STW can control up to 200 such sensors, while the envisioned system architecture allows for stacking of up to another 200 STWs, all of which are to be linked to a centralized PC-based command-and-control system.

What distinguishes Tarantula from other stealthy, seismic-based sensors, developers said, is its patented SpiderTech Sensor (STS), which includes three pairs of acceleration transducers - one pair for each axis, enabling full three-dimensional detection. These powerful accelerometers combine differential signals culled from each of the three axes into a virtual, single-point 3-D measurement.

Data processors integrated into each STS initiate detection, reduce environmental clutter, calculate the direction and estimated time of arrival and autonomously classify approaching threats. Because raw data is processed internally in each STS, the system does not suffer bottlenecks that occur in legacy systems, where several sensors are connected via main processing units, said Sever Mican, SpiderTech's chief technical officer.

"Until today, seismic-based systems offered limited strategic value due to a number of factors, including very high false-alarm levels, bottlenecks between sensors and processing units, and their inability to detect and classify targets in all environments at meaningful ranges," Mican said.

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