At the recent African Aerospace and Defence (AAD) 2024 exhibition, Denel Integrated Systems Solutions (Denel ISS) demonstrated the capabilities of a distributed acoustic sensing system. The live demonstration featured a DAS interrogator unit housed in a shelter, connected to a fibre optic (f/o) cable. This cable, buried along a fence and service road, acted as the sensing medium. Movements of people and vehicles were detected in real-time and displayed on a map inside the shelter.

The events were relayed to a security incident management system, which utilized additional sensors like CCTV cameras and Thermal Radar (thermal imaging) to confirm and classify perceived threats during all-weather day and night conditions. This system integration showcased how multiple sensors in a layered defence system work together to improve overall situational awareness in a threat rich environment like national key points, borders and other military/commercial installations.

DAS technology, first described by Professor Xiaoyi Bao of the University of Ottawa in 2010, utilises a single strand of fibre optic cable to transmit laser pulses. By analysing the back-scattered light from these pulses, the system can accurately pinpoint the location and type of an event. When calibrated, DAS can achieve positional accuracy within 10 meters over a cable length of circa 200 km and classify events with over 95% accuracy. The system can measure strain and temperature changes along the cable, enhancing its detection capabilities and thus applications.

DAS is particularly effective in detecting a wide range of activities, such as walking, digging, drilling, tunnelling, or shooting, near the buried fibre optic cable. This covert, non-line-of-sight monitoring system can detect events with a vibration or acoustic signature. As f/o cable is used as a sensing medium, the system acts as a string of “passive” microphones along the length of the cable, requiring no electrical power and is immune to electromagnetic (EM) interference such as lightning. Vehicles traveling along or crossing the cable’s route can be tracked, with sensing distances extending up to 100 kilometres along a perimeter and even further with specialized cables.

Rapid advancements in DAS technology have led to its widespread adoption in various industries. In the oil and gas sector, it is used for seismic monitoring of drill holes and detecting pipeline leaks or tampering. The transportation industry employs DAS to monitor road traffic and infrastructure conditions, while railways use it to track train movements and prevent illegal activities. DAS is crucial for monitoring telecommunication, electrical, and copper cable infrastructure, enabling proactive responses to vandalism. In security applications, DAS helps protect sensitive perimeters, such as those around airports, military/commercial installations, and borders.

Border management is a key area where DAS technology shines, allowing up to 200 kilometres of border to be covertly monitored between two interrogators. This technology minimizes the need for costly and often ineffective patrols using drones and personnel only. Now drones and other sensors can be used to verify events reported by a DAS system. Once an event has been confirmed, border guards can be dispatched directly to the affected area, enabling rapid interdiction of illegal activities. DAS acts as a force multiplier when integrated with other systems integrated by Denel ISS, enhancing the overall effectiveness of border security, Dr Dawie Roos from Denel ISS explained.

DAS technology has been effectively deployed between borders in North America, Europe and Southeast Asia, to name a few. By deploying DAS along these borders, nations can eliminate dependency on third-party technologies, such as satellite imagery, that could compromise national security, he concluded.

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