U.S. Pat. No. 5,778,114 (the “114 patent”), assigned to the same assignee as the present application and incorporated by reference herein, discloses a system that allows fiber optics to be used as a sensor and that can detect signals/activities along a cable right of way. This system operates by sending pulses of light signals down a fiber of a telecommunications plant, and detecting return signals generated along the fiber path. This will allow detection of various vibrations and frequency patterns generated in the vicinity of the fiber cable. These return signals are broken down into discrete sections along the cable and are analyzed to determine the type and location of the disturbance causing the vibration. Once a disturbance is detected the system will alert personnel to analyze the disturbance.
The '114 patent discloses a fiber sensing system that allows monitoring a fiber cable route for disturbances along its path. This device can detect personnel walking, running, digging, and vehicles, etc. along the cable right of way. This system will operate via the fiber and can look at fiber in 20 meter increments over a 25 mile span. This device operates on the same principle as an OTDR fiber test set. Disturbances along the fiber cable can be detected and analyzed by the system. Disturbances can be identified based on known patterns or frequencies generated by the disturbance. For example, a person running and a person walking can be distinguished from each other based on the pattern generated from monitoring the fibers.
Often personnel work in the area of the fiber cable. Those personnel may be authorized maintenance personnel that are aware of the underground fiber cable, or may be unauthorized personnel that present a threat to the underground plant. When a disturbance is detected, a fiber owner must investigate each disturbance. In the case of a threat being detected, a crew is sent to the site to investigate. False alarms are cost intensive and involve expensive manual overhead. What is needed is a way to distinguish non-threat disturbances from disturbances which really threaten the cable so to reduce the number of false alarms in investigating cable threats. If there is a legitimate disturbance such as scheduled maintenance near a cable route, this disturbance is a non-threat and can be ignored. When monitoring a cable route, if there are workers present in an area, there is a need to identify them as a non threat to the system.