Distributed Fiber Optic Sensing

Abstract

The present application relates to methods and devices for distributed fiber optic sensing, in particular distributed acoustic sensing (DAS). The sensor device (300) has a light generator (303, 305, 306) for repeatedly generating a first coded sequence of optical radiation to be emitted into a sensing optical fiber (302). The first coding sequence is coded according to the multilevel coding sequence (101) and has desired autocorrelation properties. A detector (311) detects optical radiation that has been Rayleigh backscattered from within the sensing fiber, and a processor (301c) processes the output of the detector. The processor processes the detector output in range bins and correlates, for each range bin, a detection signal derived from the detector output with the multi-level encoded sequence with a time delay corresponding to that particular range bin. This provides a measurement signal indicative of an environmental disturbance, such as an incident acoustic / seismic signal, acting on the portion of the sensing fiber corresponding to the range bin.

Description

Technical field[0001]The present application relates to distributed fiber optical sensing, and in particular to coherent Rayleigh back scatter distributed fiber optics optical sensors for detecting dynamic disturbances on sensing fibers and, specifically, for distributed acoustic sensing methods and equipment.Background technique[0002]Distributed acoustic sensing (DAS) based on Rayleigh, is known technique. The basic principle is to repeat the fiber (referred to herein as sensing fibers) using coherent lighting radiation (usually in the form of one or more optical radiation pulses).[0003]Consider the sensing fibers in consideration of a single coherent radiant pulse that is transmitted to the first end of the sensing fiber. As the pulse is propagated along the fiber, the Rayleigh scattering phenomenon of various inherent scattering points from the fiber will result in a small proportion of interrogation radiation toward the first end to scatter, and can be detected at the first end....

AI Technical Summary

Problems solved by technology

It would therefore not be possible to independently sense signals affecting the sensing portion of the fiber at lengths shorter than this

Shorter pulses would be required to provide better spatial resolution, but shorter pulses involve transmitting less optical power into the sensing fiber (the maximum intensity of the pulse is limited by the need to avoid nonlinear effects in the fiber )

Reduced energy of interrogation radiation results in reduced sensitivity

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