Acoustic sensors to protect borders, critical infrastructure

Published 29 November 2007

Two British companies offer an intriguing border, perimeter, and critical infrastructure protection solution: Sensors, using optical time domain reflectometry (OTDR), continuously monitor the length of existing or installed cable to detect, locate, and categorize security breaches every 10 meters over a 40 km length of optical fiber

There is a near-unanimity in the United States over the need to bolster security along the U.S.-Mexico border (and, as we wrote the other day, along the twice-as-long U.S.-Canada border). The debate centers on how much money should be spent on these projects, and what technologies should be used. Here is an intriguing technology which is relevant to this debate — but which is also suitable for perimeter defense of critical infrastructure assets and other high-value and sensitive facilities. Dorchester, Dorset-based Qinetiq has teamed up with Bristol-based Sensoptics to develop and distribute technology aiming to provide enhanced security around perimeter fences and along borders and oil and gas pipelines. OptaSense is a platform which is attached to one end of a single-mode fiber-optic cable (which carries a single lightwave with a large bandwidth) turning the cable into an array of acoustic sensors. Distributed sensor arrays are not unique, but this technology differs in that it does not require additional sensors such as strain gauges attached along the length of the cable. The sensor uses optical time domain reflectometry (OTDR) continuously to monitor the length of existing or installed cable to detect, locate, and categorize security breaches every 10 meters over a 40 km length of optical fiber. Signal processing software then analyzes the acoustic signals picked up along the cable to determine whether there has been a security breach. The signal is extracted from each 10 meter section of fiber, so it is unaffected by the acoustic disturbance on any other section. When a security breach is recognized, its location is relayed to an operator on a map, plan, or aerial photograph.

According to Sensoptics, a length of cable buried in 30 cm of damp clay can detect a man running from 10 meters away and a car travelling on an uneven surface at 30 mph from 50 meter away. The system is thus particularly well suited to long-line security applications such as border and perimeter security as well as cable and pipeline protection. For border security, anybody climbing, cutting, digging, or tunnelling near the fence will generate small vibrations in the ground, which disturb the fibre and cause an alarm to be raised. OptaSense has its origins in a similar system called Cobalt, which was developed by Andrew Lewis and his colleagues at Sensoptics. Cobalt itself was born out of a project undertaken by Sensoptics to detect nearby excavation equipment to protect telecommunications giant AT&T’s fiber-optic cables from accidental damage. Sensoptics realized that excavation vehicles have a unique acoustic signature and that acoustic signatures could be applied to anything which makes contact with the ground. The system is now called OptaSense, and Qinetiq has supplied the device with technology to improve the categorization of alarms. Previously, Cobalt’s level of classification fell into three categories: human, vehicle, and unknown. “Imagine converting a fiber-optic cable into a microphone every 10m,” said Magnus McEwen-King, Qinetiq Ventures investment director. He said that microphone picks up a lot of noise and as a result the user ends up with enormous amounts of acoustic data which needs to be analyzed. “We’re enhancing the product by adding our advanced detection classification and localization capabilities that have been born out of decades of looking at acoustic signatures and pattern recognition in maritime environments.” He added: “We’re marrying a technology that gives us an acoustic signature with Qinetiq’s signature pattern recognition capabilities. This means that OptaSense can tell if an animal or a person, a large or small vehicle or even a tracked vehicle, triggers the signal. This level of discrimination makes the product attractive to a host of industries with particular security requirements.”

Qinetiq and Sensoptics signed an exclusive distribution and joint development agreement, with Qinetiq marketing and promoting the technology. The company will also act as the distribution channel for the product. The agreement does not cover U.S. government applications, which is subject to separate arrangements Sensoptics has with AT&T. According to McEwen-King, there has so far been an enormous amount of interest in the technology. “We’ve had rail, telecoms, security and pipeline companies showing an interest. They all have two things in common: distributed infrastructure which is prohibitively expensive, plus most of them have some sort of fiber in the ground already. One of OptaSense’s unique features is its ability to use existing fiber, which means the minimal installation disruption for the customer.”

The Israeli company Magal offers a product — PipeGuard — which also relies on categorization of acoustic information collected by sensors (the company calls them :geophones”) to detect intrusion.