5:15 PM - 6:30 PM
[STT35-P01] DAS test observations using Optical Fibers laid by various methods
Keywords:DAS, optical fibers
In recent years, many results of seismic observation using the technology of Distributed Acoustic Sensing (DAS) have been published. The main features of DAS are as follows.
(1) One-dimensional distribution measurement over the entire optical fiber is possible with one measurement.
(2) The distance resolution is determined by the light pulse width incident on the optical fiber, and changes in a range narrower than the light pulse width are observed as averaged values, so it is difficult to measure physical values at points.
(3) The scattered light generated by impurities and defects in the optical fiber is weak, and processing such as averaging is performed to reduce noise.
(4) There is a distance resolution determined by the sampling frequency.
(5) Due to the transmission loss of the optical fiber, the signal strength of the scattered light at a farther distance becomes weaker than that near the device. The maximum measurable distance exists.
However, the physical quantity of the data observed by the DAS is a strain rate, different from the physical quantity obtained by the seismometer and is an averaged value in a certain section.
We are investigating whether the vibration intensity is linear with respect to seismic motion. A single-mode 4-core 1km optical fiber is laid in a tunnel in the Funagira district of Tenryu-ku, Hamamatsu City, Shizuoka Prefecture, and DAS test observations are being conducted. We observed natural earthquakes with DAS and confirmed seismic waves corresponding to P and S waves at each point set on the optical fiber. It also captures the vibration of the vacuum pump installed in the tunnel.
This time, we created an observation environment different from before, such as burying optical fibers with mortar cement, and made observations.
(1) One-dimensional distribution measurement over the entire optical fiber is possible with one measurement.
(2) The distance resolution is determined by the light pulse width incident on the optical fiber, and changes in a range narrower than the light pulse width are observed as averaged values, so it is difficult to measure physical values at points.
(3) The scattered light generated by impurities and defects in the optical fiber is weak, and processing such as averaging is performed to reduce noise.
(4) There is a distance resolution determined by the sampling frequency.
(5) Due to the transmission loss of the optical fiber, the signal strength of the scattered light at a farther distance becomes weaker than that near the device. The maximum measurable distance exists.
However, the physical quantity of the data observed by the DAS is a strain rate, different from the physical quantity obtained by the seismometer and is an averaged value in a certain section.
We are investigating whether the vibration intensity is linear with respect to seismic motion. A single-mode 4-core 1km optical fiber is laid in a tunnel in the Funagira district of Tenryu-ku, Hamamatsu City, Shizuoka Prefecture, and DAS test observations are being conducted. We observed natural earthquakes with DAS and confirmed seismic waves corresponding to P and S waves at each point set on the optical fiber. It also captures the vibration of the vacuum pump installed in the tunnel.
This time, we created an observation environment different from before, such as burying optical fibers with mortar cement, and made observations.