Manhole position specification method and manhole position specification system

Patent metadata

Field	Value
Publication number	US-11644347-B2
Application number	US-201917275327-A
Country	US
Kind code	B2
Filing date	Sep 12, 2019
Priority date	Sep 20, 2018
Publication date	May 9, 2023
Grant date	May 9, 2023

Abstract

A manhole position identification method of the present invention includes: measuring, from an end of an optical fiber, a temporal variation in scattering light from the optical fiber when an impact blow is applied to a cover of a manhole located on a path of the optical fiber, so as to obtain temporal variations in a scattering light intensity distribution in a longitudinal direction of the optical fiber; determining an occurrence of vibration due to the impact blow based on the temporal variations at positions in the scattering light intensity distribution, so as to identify an impact blow position on the optical fiber; and associating the impact blow position on the optical fiber with a map position of the manhole whose cover has received the impact blow, so as to identify a position of the manhole expressed in terms of optical fiber length from the end.

First claim

The invention claimed is:

1. A manhole position identification method comprising:
a first step of measuring, from an end of an optical fiber, a temporal variation in scattering light from the optical fiber when an impact blow is applied to a cover of a manhole located on a path of the optical fiber, so as to obtain temporal variations in a scattering light intensity distribution in a longitudinal direction of the optical fiber;
a second step of determining an occurrence of vibration due to the impact blow based on the temporal variations at positions in the scattering light intensity distribution, so as to identify an impact blow position on the optical fiber; and
a third step of associating the impact blow position on the optical fiber with a map position of the manhole whose cover has received the impact blow, so as to identify a position of the manhole expressed in terms of optical fiber length from the end,
wherein in the first step, redetermined vibration due to a designated frequency is applied as the impact blow to the cover, and in the second step, the vibration due to the impact blow is detected by calculating a spectrum of an envelope curve with respect to a temporal variation signal at each of the positions in the scattering light intensity distribution, and performing filtering processing for extracting a peak of the designated frequency on the spectrum.

2. The manhole position identification method according to claim 1 , wherein in the first step, applying the impact blow and measuring the temporal variations in the scattering light are synchronized with each other using a communication interface.

3. The manhole position identification method according to claim 1 , wherein in the first step, for the measurement of the temporal variations in the scattering light, optical time domain reflectometory is used that measures back scattering light generated by an incident light pulse, and the frequency of the impact blow is set to a frequency having a period that is longer than a time period in which the light pulse makes a round trip through the optical fiber.

4. The manhole position identification method according to claim 1 , wherein the first step employs a method in which an optical interferometer is used to measure, from two ends of the optical fiber, a temporal variation in the scattering light.

5. A manhole position identification system to be connected to an end of an optical fiber, and configured to identify the position of a manhole located on a path of the optical fiber, comprising:
an optical meter configured to measure, from the end, temporal variations in scattering light from the optical fiber when an impact blow is applied to a cover of the manhole, so as to obtain temporal variations in a scattering light intensity distribution in a longitudinal direction of the optical fiber;
a vibration mechanism configured to apply predetermined vibration due to a designated frequency as the impact blow to the cover; and
a signal processing unit configured to determine an occurrence of vibration due to the impact blow based on the temporal variations at positions in the scattering light intensity distribution, so as to identify an impact blow position on the optical fiber, and to associate the impact blow position on the optical fiber with a map position of the manhole whose cover has received the impact blow, so as to identify a position of the manhole expressed in terms of optical fiber length from the end,
wherein the signal processing unit is configured to detect the vibration due to the impact blow by calculating a spectrum of an envelope curve with respect to a temporal variation signal at each of the positions in the scattering light intensity distribution, and performing filtering processing for extracting a peak of the designated frequency on the spectrum.

Assignees

• Nippon Telegraph & Telephone

Inventors

• Okamoto Tatsuya
• Iida Daisuke
• Oshida Hiroyuki
• Manabe Tetsuya

Classifications

• G01D5/35306 Primary

  using an interferometer arrangement · CPC title

• G01H9/004

  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

• G01D5/35358

  using backscattering to detect the measured quantity · CPC title

• E02D29/14 Primary

  Covers for manholes or the like; Frames for covers {(gully gratings E03F5/06)} · CPC title