Underground optical fiber cable localization including DFOS and TDOA methods
A method for the non-destructive localization of underground optical fiber cables that utilizes distributed fiber optic sensing (DFOS) and time difference of arrival (TDOA) data associated with received signals of impulsive surface vibrations to localize the underground optical fiber cable by solving non-linear least square optimization problem(s). The method utilizes only TDOA information of received signals of impulsive surface vibrations to determine such localizations and does not require synchronization between a vibration source and DFOS receiver. The method may employ man-made impulsive vibrations to determine the localization. In operation the method involves 1) impulse-like vibration excitation and signal collection; 2) TDOA estimation of the received signals from DFOS; and 3) non-linear least square optimization applied to the TDOA information for underground optical fiber localization.
1. A method for the non-destructive localization of underground fiber optic cable using distributed fiber optic sensing (DFOS) and time difference of arrival (TDOA), the method comprising:
providing vibration excitation to fiber optic cable and receiving Rayleigh backscattered signals from the fiber optic cable;
performing a time difference of arrival (TDOA) analysis on the received signals such that TDOA information is generated;
determining the localization of the underground fiber optic cable from the TDOA information via non-linear least square optimization;
an optical interrogator unit that generates optical pulses, introduces them into the optical fiber, and receives Rayleigh backscattered signals from the fiber; and
a data processor unit that is configured to:
determine from the backscattered signals, mechanical vibrations experienced by the optical fiber along its length resulting from a vehicle operating on the highway; and
determine characteristics of the vehicle that produced the determined mechanical vibrations.
2. The method of claim 1 wherein the exact location of the underground fiber optic cable is unknown at the time of excitation.
3. The method of claim 2 wherein the vibration excitation is provided at different geographic locations such that the excitation is performed at multiple points on the fiber optic cable.
4. The method of claim 3 wherein the vibration excitation is performed at multiple points on fiber segments having fixed consecutive spacing along the fiber.
5. The method of claim 4 wherein for each vibration excitation impulse, the TDOA information of the received signals is determined by comparing estimated first signal arrival timestamps.
6. The method of claim 5 wherein the excitation is performed by a vibration source X s 1 , and coordinates of 3 consecutive points X r 1 , X r 2 , X r 3 , where X s 1 is known and X r 1 , X r 2 , X r 3 are unknowns that determine a 2D location of the fiber optic cable segment, and the locations are determined according to the following relationships:
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7. A non-destructive localization method for underground fiber optic cable comprising:
generating optical pulses and introducing them into the fiber optic cable;
providing vibration excitation to one or more segments of the fiber optic cable in a cross-fiber scanning pattern;
receiving Rayleigh backscattered signals from the fiber optic cable;
performing a time difference of arrival (TDOA) analysis on the received signals such that TDOA information is generated;
determining the localization of the underground fiber optic cable segment(s) from the TDOA information.
8. The method of claim 7 wherein the vibration excitation are performed according to a plurality of scan lines at a fixed spacing, said scan lines originating from one side of the fiber optic cable segment(s) geographic location to another side of the fiber optic cable segment(s) geographic location such that the scan is performed across the fiber optic.
9. The method of claim 8 wherein said scan lines are not parallel to one another.
10. The method of claim 8 wherein scan lines are not perpendicular to the fiber optic cable.