[AAS15-03] Intense weather event observation using surface optical fiber cable and DAS technology
Keywords:DAS, hDVS, optical fiber, micro-scale meteorology, dense observation, Intense weather
DAS (Distributed Acoustic Sensing) technology has been introduced to the oil and gas industry since the beginning of the century for the purpose of monitoring pipelines and detecting intruders. However, its application to geophysical exploration began only from around 2011. The latest optical fiber sensing technology "heterodyne Distributed Vibration Sensing" (hDVS), using a differential phase data began to be used from around 2014. This system can record high-quality seismic data, including Vertical Seismic Profile (VSP)1). Three-dimensional imaging can be performed by the 3DVSP method, and it has already come to be used in Japan2). It has been reported in recent years such as SEG and the Seismological Society of Japan conferences that the natural earthquake data recorded using optical fiber and hDVS have been confirmed to be similar to data recorded using seismometers3) 4).
From 2017, demonstration tests of hDVS including earthquake observations using optical fiber cables buried at a depth of less than 50 cm, have been conducted in Japan. Fiber lengths can range from hundreds of meters to greater than 10 km. The observation period can be several days or more than a month. When the continuously recorded vibration data was roughly evaluated, occasionally, data with high average background noise was recorded. hDVS responds to vibrations with sensitivity nearly equivalent to seismometers for all phenomena that change the strain of optical fiber. It has been known to be affected by traffic of vehicles and artificial noise from factories and construction sites in addition to natural earthquakes. However, at night, data with a high noise level may be recorded for a long period of time in a time zone in which these factors are unlikely. When the cause was investigated, it became obvious that more data with high noise level was recorded during the time of heavy rain compared with the data of AMeDAS installed near the experimental site.
This suggests that DAS technology using fiber optics as a vibration sensor can be used to observe intense weather events. If a single hDVS device can observe severe weather conditions reaching up to 40 km with a resolution of several tens of meters, it will be possible to issue warnings with more detail.
In Japan, optical fiber for communication is often installed in the air such as in an utility pole and iron tower, except for the trunk communication network in the metropolitan area. Although such optical fibers are directly affected by rain and wind, they are less affected by artificial noise sources generated on the ground surface such as vehicles, factories, and construction sites. In other words, if an hDVS device is connected to an optical fiber on the transmission line named OPGW (optical fiber composite overhead ground wire), it may be possible to construct an observation network for severe weather phenomena in an instant. In the case of rain, when the rain is calm, the rate at which rain strikes the OPGW decreases, vibration or the dynamic strain of the optical fiber appears less, therefore, the signal is small. When the rain intensifies, the rate at which rain hits OPGW increases, vibration appears greatly, the signal is large. Therefore, there is a possibility that local rainfall can be quantitatively observed at intervals of several tens of meters. In addition, it may be possible to understand the size of raindrops and the difference between rain and hail.
Typhoons that have landed in Japan in recent years have been affected by global warming, leading to more intense weather phenomena. It has been reported that utility poles and towers have collapsed. In such a situation, identifying the damaged location is essential for swift recovery. With DAS technology and fiber optics, it is possible to determine, with a few meters accuracy, where the fiber optic broke or where a severe shock occurred after collapsing. In addition, observations can be continued up to the point where the condition of the optical fiber is acceptable.
Connecting hDVS to underground, submarine, or terrestrial fiber optic networks could create a comprehensive disaster preventing observation network for earthquakes, volcanoes, tsunamis, typhoons and Guerrilla rainstorm.
References:
1) Kimura, T. et al, Optical Fiber Vertical Seismic Profile using DAS Technology, JpGU 2016 (RAEG 2016) STT17-12
2) Fujisawa, M. et al, Acquisition and Imaging of the Kijiyama DAS-VSP + SSP Experiment Data, SEG-J 2019
3) Kasahara, J. et al, Comparison of DAS and seismometer measurements to evaluate physical quantities in the field, ACQP2, Expanded abstract of SEG 2018
4) Nishimura, T. et al, Seismic observation at Azuma volcano using fiber optics and DAS system, SSJ 2019 (S02-04)
From 2017, demonstration tests of hDVS including earthquake observations using optical fiber cables buried at a depth of less than 50 cm, have been conducted in Japan. Fiber lengths can range from hundreds of meters to greater than 10 km. The observation period can be several days or more than a month. When the continuously recorded vibration data was roughly evaluated, occasionally, data with high average background noise was recorded. hDVS responds to vibrations with sensitivity nearly equivalent to seismometers for all phenomena that change the strain of optical fiber. It has been known to be affected by traffic of vehicles and artificial noise from factories and construction sites in addition to natural earthquakes. However, at night, data with a high noise level may be recorded for a long period of time in a time zone in which these factors are unlikely. When the cause was investigated, it became obvious that more data with high noise level was recorded during the time of heavy rain compared with the data of AMeDAS installed near the experimental site.
This suggests that DAS technology using fiber optics as a vibration sensor can be used to observe intense weather events. If a single hDVS device can observe severe weather conditions reaching up to 40 km with a resolution of several tens of meters, it will be possible to issue warnings with more detail.
In Japan, optical fiber for communication is often installed in the air such as in an utility pole and iron tower, except for the trunk communication network in the metropolitan area. Although such optical fibers are directly affected by rain and wind, they are less affected by artificial noise sources generated on the ground surface such as vehicles, factories, and construction sites. In other words, if an hDVS device is connected to an optical fiber on the transmission line named OPGW (optical fiber composite overhead ground wire), it may be possible to construct an observation network for severe weather phenomena in an instant. In the case of rain, when the rain is calm, the rate at which rain strikes the OPGW decreases, vibration or the dynamic strain of the optical fiber appears less, therefore, the signal is small. When the rain intensifies, the rate at which rain hits OPGW increases, vibration appears greatly, the signal is large. Therefore, there is a possibility that local rainfall can be quantitatively observed at intervals of several tens of meters. In addition, it may be possible to understand the size of raindrops and the difference between rain and hail.
Typhoons that have landed in Japan in recent years have been affected by global warming, leading to more intense weather phenomena. It has been reported that utility poles and towers have collapsed. In such a situation, identifying the damaged location is essential for swift recovery. With DAS technology and fiber optics, it is possible to determine, with a few meters accuracy, where the fiber optic broke or where a severe shock occurred after collapsing. In addition, observations can be continued up to the point where the condition of the optical fiber is acceptable.
Connecting hDVS to underground, submarine, or terrestrial fiber optic networks could create a comprehensive disaster preventing observation network for earthquakes, volcanoes, tsunamis, typhoons and Guerrilla rainstorm.
References:
1) Kimura, T. et al, Optical Fiber Vertical Seismic Profile using DAS Technology, JpGU 2016 (RAEG 2016) STT17-12
2) Fujisawa, M. et al, Acquisition and Imaging of the Kijiyama DAS-VSP + SSP Experiment Data, SEG-J 2019
3) Kasahara, J. et al, Comparison of DAS and seismometer measurements to evaluate physical quantities in the field, ACQP2, Expanded abstract of SEG 2018
4) Nishimura, T. et al, Seismic observation at Azuma volcano using fiber optics and DAS system, SSJ 2019 (S02-04)