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Digital Acoustic Sensing – Turn telecom fibres into microphone arrays
DAS is a new technology for using fiber optic cable as a sensor to measure temperature and vibration, e.g., in bedrock or underwater. The technology transforms optical telecom fiber into a long series of fiber optic hydrophones capable with high spatial and temporal resolution along many kilometers of fiber cable.
Purpose
Seismic activity can be mapped and analyzed in both time and frequency domains. The DAS technology can, for example, provide relevant information about the nature of the bedrock by determining the propagation speed of surface waves. Fiber optic measurement methods create distributed acoustic sensors (DAS) for seismic measurements instead of conventional hydrophone cables.
Advantages of DAS technology
- Robust and corrosion resistant - Withstands harsh environments
- Low power comsumption: the optical fibre does not need elecrticity to operate
- Immune to electromagnetic interference
- High spatial resolution of seismic data, providing more detailed results for seismic tomography and enabling surface wave analysis
- Flexible - measurement area and resolution can be easily changed during an ongoing measurement
- Suitable for underground installations
- Can continuously monitor large areas along an optical fiber, up to several kilometers, and enables measurement with high spatial resolution (1-10 m) along the fiber (equivalent to a geophone every 1-10 meters)
- All measuring instruments can be placed far from the measurement points on the fiber, increasing operator safety
- DAS can measure vibrations from a few millihertz to tens of kilohertz with a single fiber optic cable installation, requiring access to only one end of the fiber. The DAS instrument can thus be placed several kilometers from the area of interest, increasing operator safety and ensuring long-term monitoring possibilities as the fiber can be permanently installed in the monitoring area
Examples of areas:
- Underwater passages
- Tunnels of all kinds - train, car, road, public transport
- Rock engineering in general
- Underwater cables, ports
Method
We support customers in performing advanced measurements in various ways:
- Preliminary investigations and feasibility studies
- Field measurements, with or together with the customer
- We combine equipment with our expertise in fiber optics and photonics
Fast installation
A typical delivery in a "DAS project" is a study with measurement protocols to help the customer better assess seismological impact (for example), but it depends entirely on the application area, and the delivery is discussed on a case-by-case basis.
Mer information
DAS is a passive acoustic (seismic) technology based on the use of optical fibers. There are many applications within seismology - rock engineering such as mines, tunnels, but also in urban contexts - wherever we need better data on how rock masses move.
DAS enables, for example, monitoring of passive acoustic vibrations generated by moving infrastructure or mining and is a powerful method for reading rock quality. Passive data collection, where the source of acoustic energy comes from underground activities, makes it possible to investigate the deeper part of the rock volume.
In this scenario, the advantages of DAS technology compared to traditional seismic sensors are the higher spatial resolution and the ability to provide multiple measurement points in a single and completely passive optical fiber that functions as both a sensor and data transmission cable. The ability to install fiber optics in complex environments, such as in boreholes or along tunnels, is likely to improve 3D characterization of the rock volume even in these environments.
