Category: Distributed Acoustic Sensing (DAS)

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. Distributed Sensing for Seismic Monitoring 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.

Fiber Optic Technology in earthquake monitoring

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

Fiber Optic Technology for 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

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.

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

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

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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Distributed Acoustic Sensing (DAS) in exploring the ocean

DAS in exploring the ocean Exploring the underwater environment that covers most of the Earth’s surface is one of the most difficult tasks. The easiest way is the usage of distributed acoustic sensing (DAS) technology. However, the fbgs sensors’ setting is also not so easy because of the environmental conditions. Despite this fact, distributed acoustic sensing has a huge potential for observing processes in the future.

Fiber optic solutions are the new methods of geophysical information registration that can be applied both onshore and offshore. The scientists used transmission time-of-flight of laser pulses inside transoceanic subsea fibers to note seafloor strain. To explore seafloor strain with higher spatial resolution, they utilized a distributed acoustic sensing (DAS) system.

Distributed acoustic sensing technology helps to observe the ocean and solid earth phenomena. The scientists applied a fiber optic cable and a distributed acoustic sensing (DAS) unit operating onshore. DAS technology uses a photonic device that sends short pulses of laser light through fiber optics. DAS detects the backscattering set by strain in the cable caused by stretching.

The researchers could get even more data than expected. They could record underwater earthquakes, volcanic activity, and a range of micro hydrodynamic signals. The scientists monitored the acoustic waves by alterations in laser light along the fiber optic cable. Recordings of a small earthquake wavefield demonstrated several fault zones underwater. Distributed acoustic sensing could picture earthquake hazards in the coastal oceans and give new data about fault orientations and seafloor structures. The DAS system displayed the state of the sea and its changes during a storm cycle. These observations proved the necessity and potential of this method for marine geophysics.

There are still aspects of this distributed acoustic sensing research that should be improved. One of them is the fact that current DAS instruments can only see lower frequencies. However, such frequencies are considered to be low for acoustics, but it is high for seismologists and enough to locate boat signals. The research team also explores the possibilities of tracking mammals, for example, whales with the help of distributed acoustic sensing technology. The second challenge is the fact that the scientists don’t know where exactly the fiber optic cable is. Because seabed bathymetry can affect the signals and influence DAS senses. Nowadays, it is possible to use only the initial part of the fiber optic cable, up to 200 km. But it already allows capturing a number of spheres of science.

As a result of the research, the observations with the DAS system during just a few days helped to create a map of an unknown fault system and detect several dynamic processes in the water. The distributed acoustic sensing technology could help to get rid of a huge gap in ocean sensing.

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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Distributed Acoustic Sensing (DAS) system for Arctic tests

DAS system for Arctic tests The USA researchers started a number of experiments that aim to analyze the first data about seafloor under Arctic sea ice with the usage of a new method. The research team was able to connect a distributed acoustic sensing (DAS) system with a fiber optic cable. The cable vibrations can record the data 24/7. That helped the scientists to get all the activities and changes within the ocean all day long. This was the first time in history when a DAS system was used on the seafloor of the Arctic or Antarctic oceans.

The appliance looks like an electronic box that is attached to the fiber optic cable on land. It uses a laser to send thousands of short pulses of light. The small amount of the light is reflected back. And the reflected light helps the appliance to monitor events along with the fiber and store the data on hard drives.

According to the research, the DAS technology showed the icequakes, different climate signals, and marine life. The researchers are expecting to note other climate signals like ocean wave height, timing, and distribution of sea ice breakup, and ice thickness, etc. The usage of the distributed acoustic sensing system has the potential to record a variety of Arctic phenomena so the scientists can better see the climate change effects and sea life. Moreover, the DAS system makes it cost-effective and safe in comparison with the other methods. The scientists have already recorded a number of events that the traditional hydrophone or ocean bottom seismometers couldn’t even detect. With the help of the DAS system, the scientists hope to also record whale songs.

However, the research team has to face challenges during the first week of the tests. And the most difficult one was the harsh climate. It was really cold, most of the territory is tundra. It’s snowing most of the time and it’s getting dark really early. No wonder, that the team should find new creative ways of data fixing like DAS technology to get everything working.

That’s why the researchers chose a distributed acoustic sensing system to cope with the weather conditions. Fiber optic cable is double-armored with copper and steel. All the network components are created to hold the extreme Arctic environment. They have no need in sending a boat to plant monitors, moving over the sea ice to install the sensors. This fiber optic cable can exist for years or decades without replacing it.

This project of watching the Arctic ocean with the usage of the distributed acoustic sensing system is going to last over the next two years. The research team will collect the data. And the next third year will be spent on its analysis.

According to the researchers, the production of fiber optic systems based on the DAS technology can be easily automated. However, there is still a space for developing and finding new ways of optimization.
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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Distributed acoustic sensors (DAS) are applied underwater

DAS are applied underwater Scientists are looking for new ways of employment for distributed acoustic sensors (DAS). The fiber optic system contains a mandrel with a wounded with sensitized optical fiber. It is the acoustic sensor for a heterodyne that is protected for underwater use.

Nowadays, the DAS system can be used both for military purposes as well as for peaceful life. In the military, they are mostly utilized for submarine locations. While they are also in active use for monitoring sea animals’ life or finding and exploring marine mineral sources. The fiber optic systems based on the DAS technology have more advantages over the other items. First of all, they are thin and reliable. Secondly, there are no underwater electrical devices. And finally, the systems with acoustic sensors are immune to electromagnetic interference.

These devices usually contain an array of DAS sensors along with the fiber. Herewith, the arrays are up to a hundred or even fewer acoustic sensors because of the technical restrictions. The spacing between these acoustic sensors is fixed. That’s why there are some limitations in marine acoustic detection, for example.

The recent researches from China exploited a distributed acoustic sensing based on heterodyne coherent detection and demonstrated its field-testing. The optical cable contains a supporting mandrel, special optical fiber, and cable sheath. Acoustic signals from the fiber optic system disturb the mandrel and the fiber. That all causes phase changes which are the desired signal. The whole model was created to analyze the equivalence and specific character of the acoustic wave response.

With the array signal processing, the DAS device can easily find underwater acoustic signal sources and track motion trajectories. Moreover, the results of the experiments are highly accurate.

There are also obvious benefits of distributed acoustic sensors (DAS) in various industries. Most of which are elements of longer-term goals.

Some of the potential advantages of a distributed acoustic sensing are numbered below:

a low-cost acquisition system;
a simple design;
no electrical energy required in the fiber optic cable;
the fiber optic cable is suitable for harsh environments (dust, temperature, harmful gases);
the fiber optic cable is immune to the radiations such as EMI (Electromagnetic Induction) & ESD (Electrostatic Discharge);
the fiber optic system can transform several kilometers long sensor that enables it to monitor on a truly distributed basis.

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Distributed Acoustic Sensing (DAS) for glaciated areas

DAS for glaciated area detection Nowadays scientists pay more attention to the process of Alpine microseismicity. The thing is that the sensing of seismic activity is important for studying landscape-shaping processes and predict dangerous mass movements. Nonetheless, the amount of modern fiber optic sensors is still low in Alpine regions. Therefore, distributed acoustic sensing (DAS) promotes solving the problem.

The application of advantageous fiber cables makes DAS technology very promising in seismic monitoring of glacier movements and natural hazards. Additionally, DAS technology has significantly changed the portability of seismic devices. This is why the performance of seismic monitoring in difficult-to-reach areas becomes more and more accessible.

It should be noted that the purpose of distributed acoustic sensing “focus on processes near the Earth’s surface rather than on traditional seismology subjects like the deeper crust and mantle.” DAS applies fiber optic sensors into which an interrogator enters a sequence of laser beam pulses. Herewith, fiber optic systems as distributed acoustic sensing are widely used in geophone chain deployments.

Fiber optic systems allow for sensing local earthquake signals, which are too weak to be recorded by conventional seismometers. Moreover, DAS enables the record of anthropogenic noise. Even though individual channels of distributed acoustic sensing have some disadvantages as a lower signal-to-noise ratio, they overcome seismometers. The thing is that there are a lot of unused fiber optic systems with unprecedented sensor coverage and density.

Novel DAS technology performs the records of microseismic signals and ambient noise in glacier areas. Compared to standard fiber optic systems, new distributed acoustic sensing offers important improvements in stick-slip event location and determines weak seismic waves. Herewith, the potential and utility of DAS systems are doubtless for sensing glacial processes.

According to scientists, DAS technology performs measuring seismogenic glacier flow and even small Alpine mass movements, for example, rockfalls. The benefits of distributed acoustic sensing include better limitation of static and dynamic properties of the glacier and its surroundings. The most significant thing is DAS technology provides precise arrival time measurements despite spatial averaging.

Finally, the advantages of DAS channels increase the location quality of stick-slip events significantly. The density of distributed acoustic sensing detects numerous reflections and extremely refracted waves. Herewith, spaced seismometer networks can not carry out it.

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