Distributed Acoustic Sensing (DAS) has attributes that make it a potentially transformative technology in geosciences and engineering. DAS records ground motion along fiber-optic cables that are comparable to those obtained by single-component accelerometers or geophones. The transformative potential arises from the fiber itself being the sensor and allowing for a spatially continuous measurement. The fiber can be tens of kilometers in length and it can be located in shallowly buried trenches, in boreholes, or in some combination. The fiber geometry can encompass a large volume that can be tens of cubic kilometers in size. DAS inherently possesses properties of a large-N seismic array. The rapidly increasing interest in DAS arises from its potential to be used in continuous arrays that are kilometers in length while providing spatial resolution of meters and frequency response from millihertz to kilohertz.
DAS applications in geosciences and engineering are numerous and growing including transformative opportunities for deploying early warning systems for earthquakes, volcanic eruptions, continental and marine landslides, and avalanches, and for monitoring reservoirs and civil infrastructure. DAS can complement and supplement conventional seismic sensors and arrays already used across a wide range of disciplines.
The DAS Research Coordination Network (RCN) has four main goals:
Identify applications of DAS and develop a network of potential DAS users.
Train a community of DAS users in the acquisition, handling and processing of DAS data.
Identify needed technical development (engineering and scientific).
Identify major challenges and next steps for supporting DAS science beyond the RCN.
The proposed DAS RCN will use the mechanisms of workshops and short courses to engage a range of potentially interested groups. Workshops will focus on producing white papers in areas of science applications, data management, and future technology developments. Short courses will provide hands-on instruction in DAS-specific subjects such as data analysis, data management, and best field practices. The RCN is proposed for three years, after which it is expected that DAS will become permanently incorporated into new or existing facilities, and the community will become self-sustaining through community-wide facilities and professional societies. This research coordination network is supported by funding from the National Science Foundation under award EAR-1948737.
The DAS RCN plans to gather community input through a variety of methods. A DAS mailing list is available through the IRIS Message Center at: https://ds.iris.edu/message-center/topic/das/ to provide a forum for discussion and for announcements of events, workshops, meetings, or other opportunities in the DAS community. Please consider joining us at one or more of the following events to provide your input and get involved.
In addition to attending RCN-wide events, you can join one or more topical working groups simply by sending an email to the lead whose email is provided under the Working Group tab. They range in membership from half a dozen to two dozen. They meet with frequencies that range from monthly to twice a year. Meetings often include short presentations in order to discuss current topics. Working groups prepare resources for the RCN, such as bibliographies, event notices, and write brief reports on the state-of-the-art in their topical areas.
Please reach out to the working group leads to get involved. If groups have regular meeting times these are noted in the table below.
Fiber-Optic Seismology by Dr. Nathaniel J. Lindsey and Dr. Eileen R. Martin, Annual Review of Earth and Planetary Sciences, 2021
A DAS RCN Github has been set up to collect codes and examples. Contributions are welcome!
Frequently Asked Questions… and Answers!
What are average sample rates and data volumes?
That it is a tough question to answer as it would depend on applications. For example, in seismological applications sampling rates less than 100 Hz are adequate, for monitoring leaks on pipelines 1 kHz would be more appropriate, and for audio recording higher sampling rates (> 4kHz) would be required. However the data volume also depends on the number channels on the array and the length of the recording. The volume of data could be controlled with pretriggering while monitoring.
What is the difference between channel separation and gauge length?
Gauge length is the section of fiber that DAS uses to capture scattered signals. It is like a fingerprint that DAS uses to sense strains between consecutives laser pulses. The center of the change length is a channel and the distance between channels is the channel separation. The channel separation might be smaller than the gauges length, so channel overlap.
Is calibration necessary? How is it done?
It is necessary for applications involving amplitudes, such as moment tensor estimation. It can be done in the field by comparing known seismometer instrument response and DAS response. Another way for calibration is using fiber stretchers in the lab and comparing applied strain with recorded strain.
What is the future of DAS? Other than being optimized for earthquake source studies?
There are a number of current applications for DAS beyond earthquake source studies: from near surface geophysics, to surveillance, to civil infrastructure monitoring, to evaluation of deformations, to early warning systems.There is plenty of work in those areas. There are a few leads on the future use of DAS including the increasing use of dark fiber, using arrays to monitor storms, tapping into undersea cables, extending range by running DAS signals across internet communication devices. But the future really depends on researchers and investigators finding new and exciting applications for DAS.