A long range optical fiber sensor such as a distributed acoustic sensor has a sensing fiber located remotely from the interrogator, with a length of transport fiber path connecting the two. Because no sensing is performed on the transport fiber then the pulse repetition rate from the interrogator can be high enough such that the pulse repetition rate and pulse power are optimised according to the sensing fiber length and hence sensing frequency response and sensitivity are also optimised according to the sensing fiber length.

The subject matter of this specification can be embodied in, among other things, a method for remotely sensing vibration includes transmitting a collection of optical pulses through an optical fiber at a predetermined frequency, detecting a collection of backscattered Rayleigh traces from the optical fiber based on a vibration of the optical fiber at a vibration frequency at a location along the optical fiber, determining a normalized differential trace based on the collection of Rayleigh traces, determining, based on the normalized differential trace, the location in the optical fiber of the vibration, and determining, based on the raw Rayleigh traces, the vibration frequency.

A method and arrangement of fibre optic distributed sensing for detection of an event at an event location within a blind region including using at least one optical fibre arranged at least partly along an object to be monitored and at least one light pattern interrogator coupled with the optical fibre; injecting light patterns at subsequent times; detecting backscatter light from the light patterns; and analyzing the backscatter light to determine the event location so that a detection range of the fiber optic distribution range of the fiber-optic distributed sensing system is extended into a blind region conventionally not accessible for detecting acoustic disturbances or acoustic events.

A method providing an increased signal-to-noise (SNR) characteristic for coherent distributed acoustic sensing (DAS) systems, the method employing fiber coils (microphones) made from sections of an optical sensing fiber that collect acoustic signals and uses multiple differential pairs of the microphones for signal averaging to improve the SNR. An analysis determines complex products (beating products) for a pair of locations that are part of a fiber microphone along the length of the optical sensing fiber that are used to determine a phase change in-between locations along the length of the optical sensing fiber.

Systems and methods for operating a distributed fiber optic sensing (DFOS)/distributed acoustic sensing (DAS) system include a length of optical sensing fiber suspended aerially by a plurality of utility poles and in optical communication with a DFOS interrogator/analyzer. The method includes operating the DFOS/DAS system while manually exciting more than one of the poles to obtain frequency response(s) of the excited poles; contrastively training a convolutional neural network (CNN) with the frequency responses obtained; classifying the utility poles using the contrastively trained CNN; and generating a profile map of the excited poles indicative of the classified utility poles.

A device may provide, to a user device, a first message instructing a technician to move fiber cables and may receive a first signal based on the technician moving the fiber cables and a rest signal based on the technician stopping movement of the fiber cables. The device may calculate a distance, an average peak signal, and a baseline signal based on the first signal and the rest signal and may calculate a data collection window based on the distance, the average peak signal, and the baseline signal. The device may provide, to the user device, a second message instructing the technician to move one fiber cable at a time and may receive second signals based on the technician moving one fiber cable at a time. The device may provide, for display to the user device, the data collection window and indications of the second signals.

Disclosed herein are embodiments of apparatuses, systems and methods configured to monitor vibrations and other signals in a pipeline to detect activities associated with theft of a substance flowing through the pipeline. To this end, such activities are determined by correlating pipeline sensor signals to anomalistic reference signals characterizing activity(ies) known to be associated with theft of a substance flowing through a pipeline—e.g., formation of a hole within a tubular member of the pipeline, a liquid being pumped into the pipeline through a wall of a tubular member thereof, a metallic article (e.g., drill) coming into contact with a tubular member of the pipeline, and the like. Advantageously, fiber optic sensors are utilized for such monitoring of vibrations and other operating conditions in elongated tubular members making up the pipeline thereby enabling activities associated with theft of a substance from the pipeline to be effectively and inexpensively detected over extended lengths of pipelines.

The present invention provides an intelligent geophysical data acquisition system and acquisition method for shale oil and gas optical fiber. A pipe string is arranged in a metal casing, and an external armored optical cable is fixed outside the metal casing; an, internal armored optical cable is fixed outside the pipe string; the external armored optical cable comprises a downhole acoustic sensing optical cable, two multi-mode optical fibers, a strain optical cable and a pressure sensor array, and further comprises horizontal ground acoustic sensing optical cables arranged in the shallow part of the ground according to an orthogonal grid, and artificial seismic source excitation points arranged on the ground according to the orthogonal grid.

A method that detects the location of undesired levels of signal loss for DAS systems. In the method, raw data is received from a DAS system with dual photodetector. Statistics are obtained from the received raw data, then processed according to the dual photodetector. The obtained statistical data are reconstructed to remove noise and the reconstructed signal is used to form the power statistics of the DAS signal in each channel. The power statistics are expected to be linearly decreasing with the distance from the sensor. A change detection algorithm is developed to detect the possible undesired levels of signal loss and to find the location of the signal loss.

A method and a system for interrogating an optical fiber includes a probe signal that has a first frequency comb at a first repetition rate (Δf) injected into the optical fiber. A backscattering signal that includes the probe signal convolved with an impulse response of the optical fiber in reflection which is sensitive to at least one parameter being measured from the optical fiber is gathered. The backscattering signal is beaten with a local oscillator signal to generate a beating signal, the local oscillator signal including a second frequency comb at a second repetition rate that is offset from the first repetition rate (Δf+δf) and being mutually coherent with the first frequency comb. The resulting beating signal is analysed to thereby determine the at least one parameter being measured from the optical fiber.