On the Impact of the Gauge Length Value on Distributed Acoustic Sensing Data Quality

2020 ◽  
Author(s):  
C. Jestin ◽  
G. Calbris ◽  
V. Lanticq ◽  
M. Røed ◽  
C. Ringstad
Keyword(s):  
Data Quality ◽  
Gauge Length ◽  
Acoustic Sensing ◽  
Sensing Data ◽  
Distributed Acoustic Sensing ◽  
The Impact

On the use of Distributed Acoustic Sensing for seismic divergence and curl estimations

2021 ◽  
Author(s):  
Pascal Edme ◽  
Patrick Paitz ◽  
David Sollberger ◽  
Tjeerd Kiers ◽  
Vincent Perron ◽  
...  
Keyword(s):  
Strain Rate ◽  
Rayleigh Scattering ◽  
Axial Strain ◽  
Vertical Component ◽  
Real Data ◽  
Gauge Length ◽  
Acoustic Sensing ◽  
Rotational Components ◽  
Distributed Acoustic Sensing ◽  
The Impact

<p>Distributed Acoustic Sensing (DAS) is becoming an established tool for seismological and geophysical applications. DAS is based on Rayleigh scattering of light pulses conveyed in fibre optic cables, enabling unprecedented strain rate measurements over kilometers with spatial resolution of less than a meter. The low cost, logistically easy deployment, and the broadband sensitivity make it a very attractive technology to investigate an increasing number of man-made or natural phenomena.</p><p>One key restriction however is that DAS collects axial strain rate instead of the vector of ground motion, resulting in a poor sensitivity to broadside events like (at the surface) vertically incident waves or surface waves impinging perpendicular to the cable. Helically wound cables partially mitigate the issue but still do not provide omni-directional response as the typical vertical component of seismometers or geophones.</p><p>The present study is about the potential of using unconventional DAS cable layouts to replace and/or complement traditional sensors. We investigate the possibility of estimating the divergence and the vertical rotational components of the wavefield from cables deployed in a square or circular shape. The impact of the size of the arrangement as well as that of the interrogation gauge length is discussed.  Real data are shown and the results suggest that DAS has the potential to offer additional seismic component(s) useful for wave type identification and separation for example.</p>

scholarly journals The seismic wavefield as seen by Distributed Acoustic Sensing (DAS) arrays: local, regional and teleseismic sources

2021 ◽  
Author(s):  
Brian Kennett
Keyword(s):  
Strain Rate ◽  
Seismic Waves ◽  
Strong Dependence ◽  
Laser Pulses ◽  
Gauge Length ◽  
Additional Contribution ◽  
Acoustic Sensing ◽  
Distributed Acoustic Sensing ◽  
The Difference ◽  
Seismic Wavefield

Distributed acoustic sensing (DAS) exploiting fibre optic cables provides a means for high-density sampling of the seismic wavefield. The scattered returns from multiple laser pulses provide local averages of strain rate over a finite gauge length, and the nature of the signal depends on the orientation of the cable with respect to the passing seismic waves. The properties of the wavefield in the slowness-frequency domain help to provide understanding of the nature of DAS recordings. For local events the dominant part of the strain rate can be extracted from the difference of ground velocity resolved along the fibre at the ends of the gauge interval, with an additional contribution just near the source. For more distant events the response at seismic frequencies can be represented as the acceleration along the fibre modulated by the horizontal slowness resolved in the same direction, which means there is a strong dependence on cable orientation. These representations of the wavefield provide insight into the character of the DAS wavefield in a range of situations from a local jump source, through a regional earthquake to teleseismic recording with different cable configurations and geographic locations. The slowness domain representation of the DAS signal allows analysis of the array response of cable configurations indicating the important role of the slowness weighting associated with the effect of gauge length. Unlike seismometer arrays the response is not described by a single generic stacking function. For high frequency waves, direct stacking enhances P, SV waves and Rayleigh waves; an azimuthal weighted stack provides retrieval of SH and Love waves at the cost of enhanced sidelobes in the array response.

Precise Distributed Acoustic Sensing measurements by using seafloor optical fiber cable system for seismic monitoring

2020 ◽  
Author(s):  
Masanao Shinohara ◽  
Tomoaki Yamada ◽  
Takeshi Akuhara ◽  
KImihiro Mochizuki ◽  
Shin'ichi Sakai
Keyword(s):  
Optical Fiber ◽  
Single Mode ◽  
Gauge Length ◽  
Observation System ◽  
High Signal ◽  
Seismic Observation ◽  
Acoustic Sensing ◽  
Seafloor Observation ◽  
Optical Fiber Cable ◽  
Distributed Acoustic Sensing

<p>Distributed Acoustic Sensing (DAS) measurements which utilize an optical fiber itself as a sensor can be applied for various purposes. An observation of earthquakes using an optical fiber deployed on the seafloor with DAS technology is attractive because DAS measurements enable a dense seismic observation as a long linear array. Spatial resolution of the observation reaches a few meters. The length of the array is determined by the measurement range of the DAS interrogator deployed on the optical fiber, and a fine spatial sensor interval can be configured. DAS measurements have become increasingly accurate and the current state of technology exhibit high signal quality. Because DAS measurement is useful for earthquake observation, there were some trials for an observation of earthquakes using an optical fiber deployed on the land or the seafloor. However, There are few observations using DAS technology on seafloor until the present.</p><p>In 1996, a seafloor seismic tsunami observation system using an optical fiber cable was deployed off the coast of Sanriku by Earthquake Research Institute, the University of Tokyo. The system has three seismic stations and two tsunami-meters, and a length of the cable is approximately 115 km. The system has six spare (dark) optical fibers which are dispersion shifted single mode type, and have been incorporated for future extension of the observation system. We have started development of a seafloor seismic observation system utilizing DAS technology on the Sanriku cable observation system as a next generation of marine seismic observation system. In 2019, we performed DAS measurements using a dark fiber from Sanriku seafloor observation system three times. An interrogator was installed in the cable landing station temporarily. Data were recorded with various values of parameters, such as length of data collection (array aperture), gauge length, ping rate, acquisition offset, for evaluation of data quality and signal to noise ratios. The total recording period for three measurements was approximately three weeks. As a result, many earthquakes including micro-earthquakes were recorded. The obtained data will be used to develop data processing techniques for seismic observations utilizing DAS measurements.</p><p> </p>

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