Rayleigh fading mitigation via short pulse coherent distributed acoustic sensing with multi-location beating-term combination

Patent metadata

Field	Value
Publication number	US-11566937-B2
Application number	US-202016879505-A
Country	US
Kind code	B2
Filing date	May 20, 2020
Priority date	May 22, 2019
Publication date	Jan 31, 2023
Grant date	Jan 31, 2023

Abstract

Aspects of the present disclosure describe Rayleigh fading mitigation via short pulse coherent distributed acoustic sensing with multi-location beating-term combination. In illustrative configurations, systems, methods, and structures according to the present disclosure employ a two stage modulation arrangement providing short interrogator pulses resulting in a greater number of sensing data points and reduced effective sectional length. The increased number of data points are used to mitigate Rayleigh fading via a spatial combining process, multi-location-beating combining (MLBC) which uses weighted complex-valued DAS beating results from neighboring locations and aligns phase signals of each of the locations, before combining them to produce a final DAS phase measurement. Since Rayleigh scattering is a random statistic, the MLBC process allows capture of different statics from neighboring locations with correlated vibration/acoustic signal. The combined DAS results minimize a total Rayleigh fade, in both dynamic fading and static fading scenarios.

First claim

The invention claimed is:

1. An improved optical fiber distributed acoustic sensing system comprising:
a length of optical fiber; and
an optical interrogator that generates optical pulses, introduces them into the optical fiber and receives Rayleigh reflected signals from the fiber;
the improved optical fiber sensing system CHARACTERIZED BY:
a coherent receiver configured to extract information from the Rayleigh reflected signals wherein said short-pulse interrogation optical pulses having a pulse-width <=4 ns;
a two stage, cascaded pulse modulator;
the system configured to perform a multi-polarization-state (MPSC) combining process wherein
the MPSC process includes four beating products ζ xx , ζ yy , ζ xy , ζ yx that are computed at once in a digital signal processor (DSP), and all of them are used for fiber strain computation.

2. An improved optical fiber distributed acoustic sensing system comprising:
a length of optical fiber; and
an optical interrogator that generates optical pulses, introduces them into the optical fiber and receives Rayleigh reflected signals from the fiber;
the improved optical fiber sensing system CHARACTERIZED BY:
a coherent receiver configured to extract information from the Rayleigh reflected signals wherein said short-pulse interrogation optical pulses having a pulse-width <=4 ns;
a two stage, cascaded pulse modulator;
the system configured to perform a multi-polarization-state (MPSC) combining process wherein
the MPSC process includes four beating products ζ xx , ζ yy , ζ xy , ζ yx that are computed at once in a digital signal processor (DSP), and all of them are used for fiber strain computation; and
the four beating products ζ xx , ζ yy , ζ xy , ζ yx are weighted and combined into a single combined beat product result, ζ[n].

Assignees

• Nec Lab America Inc
• Nec Corp

Inventors

• Ip Ezra
• Huang Yue-Kai
• Hu Junqiang
• Murakami Shuji

Classifications

• G01H9/004 Primary

  using fibre optic sensors (light guides per se G02B6/00, acousto-optical devices specially adapted for gating or modulating in optical wave guides G02F1/125) · CPC title

• G01B9/02092

  Self-mixing interferometers, i.e. feedback of light from object into laser cavity · CPC title

• G01B9/02015

  characterised by the beam path configuration · CPC title

• G01D5/35361

  using elastic backscattering to detect the measured quantity, e.g. using Rayleigh backscattering · CPC title

• G01V1/181

  Geophones · CPC title