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Use of Fiber Optic Communication Lines with a Phase-Sensitive Reflectometer for Recording Seismic Signals

Authors
  • Ilinskiy, D. A.1, 2
  • Alekseev, A. E.3, 4
  • Ganzha, O. Yu.2
  • Semikin, D. E.3, 4
  • Ojha, M.5
  • 1 Moscow Institute of Physics and Technology (State University), Dolgoprudny, Moscow oblast, 141701, Russia , Dolgoprudny (Russia)
  • 2 Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, 117997, Russia , Moscow (Russia)
  • 3 PetroFiber Ltd., Moscow, 105082, Russia , Moscow (Russia)
  • 4 Fryazino Branch, Kotelnikov Institute of Radio Engineering and Electronics, Russian Academy of Sciences, Fryazino, 141190, Russia , Fryazino (Russia)
  • 5 CSIR—National Geophysical Research Institute, Hyderabad, 500007, India , Hyderabad (India)
Type
Published Article
Journal
Seismic Instruments
Publisher
Pleiades Publishing
Publication Date
May 25, 2021
Volume
57
Issue
3
Pages
231–248
Identifiers
DOI: 10.3103/S0747923921030051
Source
Springer Nature
Keywords
License
Yellow

Abstract

AbstractDistributed acoustic or vibration measurements on a fiber optic communication line (FOCL) began rapid development in 2005. One of the effects used for this purpose is the Rayleigh scattering effect. Rayleigh scattering is an elastic process caused by local inhomogeneities of the refractive index of a FOCL. Optical pulses with a certain time interval are launched into the optic fiber, and a small part of the backscattered light is recorded by the detector. Small deformations of the optic fiber associated with vibration (or seismic) events change the intensity of backscattered light. Analysis of the interference pattern for each section of the fiber makes it possible to identify the characteristics of the vibration effect on a specific section of the fiber. A key feature of the phase-sensitive reflectometer used in the experiment is the use of a two-pulse phase-modulated optical packet as a probing signal. An experiment was conducted to compare the records of seismic excitations recorded by standard seismic equipment and with reflectometer records. The experiment was carried out on a 200 m straight-line single-mode FOCL buried 30 cm below ground. A 5 kg hammer was used as the seismic vibration source. The blows were delivered to a metal substrate lying on the ground. Time synchronization of the seismic data with the reflectometer data was performed based on the detected first shock intakes. The experience of simultaneous recording of low-power seismic excitations has shown that direct comparison of the response of a fiber optic system and geophones is impossible. The recorded data must be converted to the same physical values. In a specific experiment, the acceleration values measured by the seismic system were converted into displacements. Analysis of the converted data and reflectometer data showed that for small deformations of less than one strain, the optical channels show good signal repeatable accuracy. Optical channel data obtained even with large deformations show that they can be used for seismic engineering purposes make it possible to obtain reliable seismic sections, despite some discrepancies in signal shape. Channel density can compensate for this disadvantage.

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