Tag: DAS systems

Distributed Sensing for Seismic Monitoring Systems

We have already published a range of articles referring to different applications of fiber optic technology in various industries and fields. Geophysics has also applied distributed sensing as a powerful instrument for structural health monitoring, such in, the oil and gas industry, tunnel safety monitoring, etc.

Seismic monitoring has been no exception. Resistance to electromagnetic disturbance, cost-effectiveness and possibility of implementing into hard-to-reach regions or places that can be harmful for human health are undeniable advantages of distributed sensing systems.

What is Distributed Sensing Technology?

Distributed sensing is a technology that provides continuous measurements in real-time. Compared to traditional sensors, placed at certain points, distributed sensing acts as a sensing element along its entire length because the whole fiber optic cable is applied.

Due to the exploitation of the entire fiber optic cable all over its length, this method is considered to be one of the most cost-effective tools that can be placed in severe conditions.

Operation Principle of the Distributed Sensing Systems

In simpler terms, DAS systems as a part of the distributed sensing technology consist of several components including fiber optic cable and an attached optoelectronic device – FBG interrogator. The interrogator sends short pulses of the pulsed laser light into fiber optic cable. Then the backscattered light moves back up the fiber to the FBG interrogation unit. Due to the time that the laser pulse takes, there can be found the relation backscatter event and a fiber distance.

The FBG interrogator is connected to a processing unit that processes and stores the received data. This unit gets the raw data and transfers it into the information that is displayed in the program.

The software provides the visualized analysis that includes the previous data as well. In case there are any differences, fiber optic system alarms specialists. For instance, the system can display the location of the fiber optic cable on the map and highlight locations where the rates have changed or exceeded acceptable limits.

What’s the Difference Between DAS and DTS Systems?

Traditionally, distributed sensing systems are divided into distributed temperature sensing and distributed acoustic sensing.

The main difference between DTS and DAS systems is the type of signals they get to provide analysis. DTS systems are sensitive to temperature changes, while DAS is sensitive to acoustic vibrations. Therefore, their operation principle is also different. Due to the fiber qualities, the performance of DTS systems is able to stay at the necessary high injected pump power level. At the same time, DAS systems don’t require such high pump power as DTS systems because of the Rayleigh scattering.

DAS Systems and Their Applications in Seismic Monitoring

If we are talking about seismic monitoring, distributed acoustic sensing is used. DAS systems measure any vibrations that can’t be detected by DTS technology.

The goal of all seismic monitoring systems is warning before any accident occurs. Their effectiveness depends on the accuracy of the obtained data, lifetime and length. That’s why there is a necessity in a continuous operating system that is capable of working in severe environments and over long distances.

DAS systems were implemented as seismic monitoring systems due to the above-mentioned advantages as well as low cost, no special maintenance, robustness, etc. Therefore, distributed acoustic systems have provided new capabilities for seismic monitoring.

Field Projects Where Sensing Systems Were Applied

If we are talking about sensing systems, in most cases fiber optic sensors were more effective in comparison with the conventional electronic ones. That provides unrivaled performance, especially in critical applications.

For example, two years ago the specialists started a range of experiments in the Arctic and the Arctic Ocean. This is the first case when DAS systems were installed in the Arctic. Scientists wanted to get the analysis of the seafloor seismic activities and other processes under Arctic sea ice with a distributed acoustic sensing system. Fiber optic cable catches the vibrations about all the changes of the ocean 24/7.

The other project with DAS systems has also allowed scientists to see them in other severe environmental conditions. Since they are installed mostly in the ground, specialists have monitored their performance in snow. The most concerning parameters for them were the snow depth and severe frosts.

Finally, in the conditions of decreasing temperatures the reduction in background noise and better signal-to-noise ratio was noticed. In fact, the lower temperatures, the better results distributed acoustic sensing has provided. Cold temperatures don’t make fiber optic performance difficult or interfere with accuracy of the received data. Moreover, fiber optic cable is able to transfer signals at snow depths of at least 0.65m.

Distributed sensing as a tool for seismic monitoring systems has proved to be effective in detection of any seismic shocks and flow changes. All in all, DAS provides capabilities for seismic monitoring of the near surface.

Optromix is a fast-growing vendor of fiber Bragg grating (FBG) product line such as fiber Bragg grating sensors, for example, FBG strain sensors, FBG interrogators and multiplexers, Distributed Acoustic Sensing (DAS) systems, Distributed Temperature Sensing (DTS) systems. The company creates and supplies a broad variety of fiber optic solutions for monitoring worldwide. If you are interested in structural health monitoring systems and want to learn more, please contact us at info@optromix.com

Fiber Optic Technology in earthquake monitoring

The improvement of life quality is the main factor in the development of every new technology including fiber optic technology. Scientists from all over the world have always looked for new solutions for the prevention of seismic events, which is one of the most essential points in life quality improvement.

Seismic data of the previous years, electric sensors, fiber Bragg grating sensors, and modern distributed acoustic sensing have an aim to predict all catastrophes connected to earthquakes in the future. Especially, it concerns areas with high rates of population. More accurate monitoring gives an opportunity to reduce the risks resulting from most common natural events like earthquakes, landslides, eruptions, etc.

FBG sensors in the prediction of seismic events

In the past, the only approach to all the natural phenomena was the information about the cases. Then electric sensors were applied. However, usual electric sensors are hard to comply with the monitoring requirements of high sensitivity and long lifetime. That is why scientists have tried to use different FBG sensors. In fact, fiber Bragg grating temperature sensors were produced for better monitoring and observation of seismic activity. Except for fiber Bragg grating temperature sensors, there are FBG strain sensors that can be also applied for collecting data as geothermal monitoring.

In comparison with the usual electric sensors, FBG sensors can offer ease in signal transmission and immunity to electromagnetic interference that plays an important role. In fact, temperature monitoring with the help of the FBG is considered to be one of the most popular applications. Moreover, modern sensors can be sensitive to both strain and temperature.

Distributed Acoustic Sensing in earthquake prediction

If we speak of seismic activity and the prediction of seismic events, we should definitely mention another fiber optic technology that helps in geothermal monitoring called distributed acoustic sensing. DAS systems are widely applied in various spheres, including vibroacoustic monitoring of the oil wells.

Scientists have already held a number of experiments with the help of the distributed acoustic sensing studying seismic activity in different areas such as metropolitan, oceans, etc. The results prove that DAS systems are able to accurately detect vibrations even in conditions of a highly noisy environment and far away from the epicenter. That’s why this fiber optic technology draws the attention of many researchers and is popular where there is a need for precise and robust information. The DAS’s improved performance has shown its potential to be a powerful instrument in geophysics studies thanks to its bandwidth, waveform fidelity, cost-effectiveness, and simplicity.

Despite all the achievements in fiber optic technology, scientists still consider that DAS technology for seismic monitoring is still in its infancy. However, they are sure that such promising opportunities will play a crucial role in the next seismic networks.

Optromix is a DAS system manufacturer that provides top-of-the-line distributed acoustic sensing systems suitable for monitoring commerce networks. If you have any questions or would like to buy a DAS system, please contact us at info@optromix.com

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Fiber Optic Technology for the earthquake warning

A research team from the USA has applied FBG sensors for detecting earthquakes and creating a system for subsurface imaging with the help of fiber optic technology. The sensors were installed above an existing fiber optic cable.

According to scientists, this fiber optic system can register seismic signals produced by trains and automobiles. These signals cause changes in the fiber optics’ length from the very beginning till the very end. This fiber optic system is also known as distributed acoustic sensing or DAS.

Scientists have also installed usual high-resolution seismometers along the fiber optic cable in addition to the new DAS technology. They have aimed to compare these two methods of signal detection. In distributed acoustic sensing the fiber laser light is sent through the fiber optic cable. DAS technology measures the perturbations in the backscattered light along the whole fiber optic cable.

In fact, scientists made a conclusion that the fiber optic system is sensitive enough to detect footsteps. The other research team from one of the US universities proved that fiber optic technology can provide data about street traffic and demonstrated the results of the lockdown 2020. The fiber optic system could locate vibrations from cars and pedestrians above and demonstrated that the pedestrian traffic almost disappeared in April and stayed almost the same in June.

However, according to this scientific research, the fiber optic cable can even detect the jet airplanes that fly by. The scientific work was much easier because DAS systems are easy-to-install devices in comparison with the traditional methods. Scientists just needed to use a single fiber optic cable instead of thousands of geophones to detect ground vibration. Researchers got the same information using fiber optic technology faster. The DAS system continuously monitors the modifications in the fiber optics’ length down to changes in the length of less than 1 nanometer.

Thanks to the DAS technology the research team will calculate the velocity structure in the subsurface by measuring the strain changes. The velocity is a crucial factor in the determination of how the ground and civil infrastructure may respond to an earthquake.

Thanks to the new fiber optic technology, scientists and engineers are going to improve velocity and ground motion models in urban areas by collecting more information. Moreover, they hope to find a better understanding of the seismic risks and assess the resilience of our infrastructure.

Besides, the research team has a plan to spread this fiber optic technology for a vast territory to develop a better early-warning system for earthquakes. This is a totally new way of thinking about monitoring and designing for earthquakes that can give people time to get to shelter.

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Fiber Optic Technology in humans movement tracking

A team of researchers from the US university applied fiber optic technology to demonstrate the changes in city traffic because of the lockdown. Scientists had tapped into an underground telecommunication fiber optic cable and made a scientific monitoring device. Thanks to this fiber optic system, they could watch how Covid-19 brought life to a halt.

According to researchers, they shined a laser through the fiber optics and could locate vibrations from cars and pedestrians above. The fiber optic cable could detect the movement through the unique seismic signals from them. That allowed scientists to create a detailed picture of how a community ground to a halt, and then slowly came back to life when the lockdown eased.

This experiment with the fiber optic cable showed that the pedestrian traffic almost disappeared in April and stayed almost the same in June. However, the car traffic started increasing after initially declining. As a result, the vehicle traffic is actually back to normal, while people walking is still minimal. Moreover, scientists could distinguish the vibration signals from fiber optic cable from construction vehicles. In April there was no industrial activity as the construction halted. But in June the construction vehicles’ movement had started again.

Fiber optic cables trap light pulses and transport them to vast distances as signals. And when a car or person passes, the vibrations introduce a disturbance, and a scattering light returns. The researchers measured vibrations at different lengths of the fiber optic cable by estimating the time it took the back-scattered light to travel. This method is well-known as distributed acoustic sensing (DAS).

Distributed acoustic sensing (DAS) can become an instrument for tracking people’s movement instead of cell phone location data studying. Researchers can apply fiber optic cables to monitor pedestrians and cars. However, DAS can’t help in identifying a particular car or person. It can only identify a type of vehicle, for example, truck or bike.

In comparison with usual seismometers, such fiber optic cable is cost-effective and doesn’t need a source of power. There is a need for just an FBG interrogator that gets the information.

Engineers have already produced DAS systems to detect soil deformation, biologists use offshore fiber optic cables to listen in on whales, and scientists made measurements of earthquakes and water temperature in the Arctic with the help of FBG sensors. Every day fiber optic technology gets a new application.

DAS systems distributed acoustic sensing FBG sensors fiber optic cables

Distributed Acoustic Sensing (DAS) in the oil and gas industry

According to scientists, nowadays we can see newly developed distributed sensing systems that can have many appliances including monitoring of wells’ conditions in the oil and gas industry. Mostly, distributed acoustic sensing (DAS) is applied in these spheres.

The engineers have an opportunity to make decisions on operational optimization onsite with the usage of the data provided by distributed fiber optic sensors. The fiber optic technology can help in well performance improvement as well as in keeping safety at the well site. And as a result, it optimizes production from oil and gas wells. In comparison with distributed sensing, there is no such method that could provide such quality and extent of detail about physical conditions.

Mostly, distributed acoustic sensing (DAS) is produced to record fluid and gas flow signals, listen to hydraulic fracturing-related signals, etc. Distributed sensing systems trace changes in acoustic vibrations along the entire length of a fiber optic cable in real-time. In the fiber optic cable, there are thousands of detection points at minimal spatial intervals. Compared to the usual sensing systems, distributed sensing does not rely on discrete sensors at predetermined points. Distributed sensing system uses the whole fiber optics itself as a sensing unit.

Therefore, fiber optic technology is suitable for those who want to apply environmental monitoring in sensitive geologic operations. Thanks to the length of the fiber optic cable and its working ability in severe environmental conditions for long, it is quite popular for such use. The down hole fiber optic sensor application provides for oil and gas wells, flow-back operations, geothermal wells, etc.

The ability of measurement along the complete length of the fiber optic cable can be applied for many other applications like the characterization of contaminated bedrock aquifers and monitoring of geologic carbon sequestration projects. In addition to that, distributed sensing systems can also register the conditions of the near-wellbore area of subsurface rock formations.

DAS system manufacturers always have an aim of making their fiber optic solutions better. For the DAS systems, it is the regulation of acoustic and vibratory noise sensing. The ambient noise is always in sites and should not be measured.

That is why the next scientific goal for DAS technology is the creation of a portable vibration isolation system to maximize the distributed acoustic sensing system’s dynamic range.

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Distributed Acoustic Sensing (DAS) and its applications

In southwest Iceland, there is a fiber optic cable that connects two geothermal power plants. It is used as every casual fiber optic cable for data transmitting. However, in 2015 a research team decided to apply it for detecting seismic waves of earthquakes, so they could draw a map of the underground features including geological faults. And distributed acoustic sensing (DAS) made it possible.

Scientists made their discovery thanks to distributed acoustic sensing (DAS). This technique measures any tiny changes to the phase of fiber optic laser pulses that reflect from many points on fiber optics. The thing is an acoustic or seismic wave stretches and compresses fiber optics when it passes through the ground where the fiber optic is attached. DAS systems can provide the necessary information at a reasonable cost. Moreover, the usual seismometers couldn’t reach such kind of information.

In fact, Iceland is not the first country where the distributed acoustic sensing (DAS) technology was applied. Before that, fiber optic cables were produced in other seismic regions, for example, in the USA. The precise information on earthquakes’ location, nearby faults was got thanks to the fiber optics both on the seabed and on land. Scientists consider that by using a million kilometers of fiber optic cable around the world, we can broaden quake monitoring thanks to the network of seismometers with fiber optic sensors.

Distributed acoustic sensing (DAS) has been previously applied mostly in the fossil-fuels industry. The sensing technology helped to monitor boreholes and image deposits of oil and gas. Nowadays, it has many other applications for extracting data from vibration in the ground. Distributed acoustic sensing can even shed some light on global warming by studying the glaciers’ movements in the Antarctic and Alaska.

Besides earthquakes, researchers proved that they can use DAS systems for studying other natural hazards. The research team from Italy showed that they can detect the strain changes connected to the volcanic phenomena which include explosions. They also discovered seismic waves slowing through presumed fault zones on the volcano.

In the meantime, scientists from Japan demonstrated that DAS technology can monitor submarine volcanoes. The researchers measured the signals from the fiber optic cable on the seafloor. They found out that fiber optic sensors could produce coherent measurements that are needed for underwater eruptions’ recording.

Distributed sensing is an effective instrument that provides us with a lot of data that we can’t observe with the naked eye. Considering how widely fiber optic lines are used, distributed acoustic sensing (DAS) can give many possibilities to scientists and society.

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