Year
2011
Abstract
Large perimeter and property edge intruder monitoring is traditionally accomplished by point sensors or ground-based radar. Point sensors provide only minimal tracking and threat information, while groundbased radar requires line of sight, is susceptible to nuisance alarms, and can be difficult to interpret. Recent advances in coherent optical time domain reflectometry excited by a multi-frequency beat signal have led to the realization of highly sensitive and reliable perimeter detection systems that use fiber optic cable as the sensing medium. Such systems support runs of 50 km per interrogator unit using low-cost communication-grade fiber optic cable. These systems measure acoustic signatures from footfalls, vehicles, or other activities as well as sensing fiber deflection from static weight above. This paper presents a concept for using such a system with fiber optic cable installed in multiple concentric loops around the perimeter of a facility. This fiber optic cable arrangement combined with novel software algorithms provides enhanced detection and basic assessment features: it calculates travel vectors and threat counts, improves threat classification, estimates time of arrival, and provides near-real-time tracking while targets are in the coverage zone. Such a system offers many advantages: it follows the terrain, operates outside line of sight, has a low nuisance alarm rate, is simple to interpret, has low failure rates, and requires no regular maintenance.