Distributed Acoustic Sensing (DAS): A Quick Overview

Distributed acoustic sensing systems (DAS) are optoelectronic instruments based on fibre optics that measure acoustic interactions along the length of a fibre optic sensing cable. To collect acoustic sound or data, DAS uses fibre optic cable. Light pulses are sent down the thread before returning to the sensor. Acoustic events disrupt the fibre, resulting in “backscatter,” or variation in the return signal. To convert light information into acoustic information, the backscatter pattern can be analysed and interpreted. Wave patterns vary depending on the type of acoustic event, e.g. seismic, foot traffic, vehicles, etc.

Almost any existing fibre optic cable, such as telecommunications cables, can be converted to an acoustic sensor using Distributed Acoustic Sensing. The system only requires a small amount of power to send and receive the light signal, and it is immune to electromagnetic and radio frequency interference. Distributed Acoustic Sensing is ideal for long-term, continuous monitoring of acoustic signals in remote locations because of these attributes.

Distributed Acoustic Sensing Application

Continuous monitoring of pipelines for unwanted interference, leaks, or flow irregularities; monitoring roads, borders, and other sensitive perimeters unusual activity; and even oil well monitoring applications where the technology allows the state of the well to be determined in real-time all along its length are all examples of Distributed Acoustic Sensing applications. Because of the optic fibre’s capacity to function in hostile settings, it’s particularly well suited to situations where traditional sensing devices are either useless or impracticable owing to environmental factors.

Acquisition of data, signal processing, and visualisation

A strategy for data management, processing, and visualisation is critical because of the large amounts of data produced by distributed acoustic sensing systems. At a rate of more than 10 kHz, these systems collect data from up to 20 sensing points. This equates to the ability to fill a terabyte drive in a matter of days.

The interrogation units are usually connected to a processing unit, such as an industrial PC or server, that handles data storage and processing. As it is rarely practical to store more than this amount of raw data, there is usually a rolling buffer for it.

The processing unit is pre-programmed with a variety of smart algorithms for interpreting raw data and determining whether it matches predefined events such as an intruder event or a pipeline leak. The fibre optic sensing cable will be divided into a number of zones, each with its own set of algorithms and alarms.

These events can be visualised in a variety of ways. One option is to use DTS-specific visualisation software, which, for example, can display the fibre optic path against a site map or diagram and, if an event occurs, highlight the location of the event and display an alarm. Another option is to integrate the Distributed Acoustic Sensing software with an existing third-party SCADA, control, or security software package. The event will be highlighted in the third-party software. We hope this article will help you to know more about Acoustic Sensing software.

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