Sandia uses new underwater technology to carry out Arctic seabed data project
Image: In the first week of February, a rare and peaceful sunrise at Cape Oliktok, when researchers at Sandia National Laboratory began using distributed acoustic sensing and fiber optic cables to collect the first dataset from the Arctic ocean floor. see more
Image source: Photograph by Kyle Jones, Sandia National Laboratory
Albuquerque, New Mexico-Researchers at Sandia National Laboratory began to use a new method to analyze the first seafloor data set from under Arctic sea ice. They can capture ice shocks and traffic activity on the northern slopes of Alaska, while also monitoring other climate signals and marine life.
The team, led by Sandia geophysicist Rob Abbott, connected iDAS (a distributed acoustic sensor interrogator system made by Silixa) to an existing fiber optic cable owned by Alaska telecommunications company Quintillion. The cable reaches the bottom of the sea from Cape Oliktok. Capturing and recording cable vibrations 24 hours a day for 7 consecutive days helps researchers better understand the natural and man-made activities that occur in the data-poor ocean.
This is the first time that a distributed acoustic sensor interrogator system has been used to capture Arctic or Antarctic ocean bottom data, and the team has seen many advantages for future use.
"This is the first data collection. As far as the national laboratory is concerned, this is the type of high-risk, high-return research that may have a huge impact on how we can monitor the Arctic Ocean," Sandia manager Kyle Jones said. "This is really at the forefront of seismology and geophysics, as well as climate change and other disciplines."
The team hopes to record climate signals, such as the time and distribution of sea ice breaking, sea wave height, sea ice thickness, fault zones, and storm intensity. It can also record transportation, whale songs, and destruction. Abbott said that this new monitoring method has the potential to continuously capture various Arctic phenomena in a cost-effective and safe manner so that scientists can better understand the impact of climate change on this fragile environment.
The interrogator looks like an electronic box that can be connected to a fiber optic cable on land. It uses a laser to send thousands of short pulses of light along the cable every second. Due to the earth, sea ice, ocean currents, and animal activities, when the seabed to which the cable is attached moves, a small part of the light will be reflected back or backscattered along the cable. Backscattered light enables the interrogator to detect, monitor and track events along the optical fiber and store the data on the hard drive.
"Quintillion's fiber optic cables are in a vantage point on the North Slope of Alaska," Abbott said. "This technology is suitable for this project for several reasons. We will not send ships to plant monitors; we will not try to install sensors on sea ice. This cable will exist for decades, and we can get good data from it. This is a very safe way to make this measurement in a hazardous environment."
With funding from the laboratory-guided research and development program, this is the first eight-week data collection that the project will conduct in the next two years. The team will visit Alaska in each of the four Arctic seasons defined as frozen, ice-free, freezing and thawing. The third year will be used for further analysis of the data.
Abbott stated that the results will be communicated with the broader scientific community and will be provided to the climate modeling community for inclusion in algorithms. In addition, the team hopes that the results of the project will indicate the need for continuous distributed acoustic sensor monitoring in the Arctic.
"We want to provide data for high-fidelity climate models and raw data analysis," Abbott said. "I also hope to directly measure the thickness of sea ice, which is currently difficult. Now, you need a plane to fly over, or you need to get out on the ice. This can be very dangerous and expensive, and you can only do it once a year. Or twice. Using fiber optic cables, the distributed acoustic sensing system can operate 24/7/365, and you might take sea ice thickness measurements once a day."
Encouraging data captured in the first 168 hours
Abbott said that Sandia researchers have just begun to analyze the first 168 hours of data collected in February, and they are encouraged by what they have seen.
"We saw things that indicated that an ice quake had occurred. We saw events where there should be no human activity in the ocean as far as 33 kilometers," he said, referring to the first two hours of data he had read. "We must have seen some kind of natural event. It may be an ice shock, or it may be an underground microseismic event like an earthquake. We are not sure yet."
Close to the shore, Abbott said the team is most likely to record the frequency of production and reinjection wells that recover wastewater and indicate ocean tides and currents. A surprising result is that the system picked up the frequency of the low-altitude hovering aircraft.
Abbott says that the interrogator can record events at a spatial density three to four orders of magnitude higher than traditional hydrophone or subsea seismograph deployments.
"In the first data collection, we did not expect to see a lot of ocean currents and ice shocks, because there are stable ice sheets throughout the region, but we did see some of them, which is very exciting," Abo In particular.
Abbott said he looks forward to capturing data on whales and seals during the migration season. The Arctic is home to bowhead whales and beluga whales, and each whale has its own song. The system should be able to record these songs in the same way as earthquakes, because the vibrations in the ocean will be transmitted to the earth and then to the cable. For whales, as the pitch of the song changes, a characteristic pattern is formed.
"This is called gliding, and over time, the frequency starts from low to high, and then decreases again," Abbott said. “Frequency like this is characteristic of biological sources and is easily distinguished from other sources such as earthquakes. Whales often sing for more than 30 minutes, individual repeating notes lasting for a few seconds, sliding up and down.”
Weather on the North Slope increased the intensity of the key first week of the experiment
The expected but intense North Slope climate is a challenge. Abbott said that in February, the area was dark for about 18 hours a day, and because it was snowing most of the time and the roads were not well marked, everything looked new. The team was still dealing with the severe cold. Although they were prepared, the temperature was about 10 degrees lower than expected and dropped to minus 45 degrees Fahrenheit (minus 77 degrees Fahrenheit including wind chill). Abbott said that even people working there have closed all outdoor activities.
Quintillion’s Chief Revenue Officer Michael McHale said: “The American Arctic region is daunting, and it’s common for winter temperatures to fall below 30 degrees Celsius.” It is difficult to cross in good weather. Working here requires a wealth of experience and hard-won expertise. The engineering impact is huge. Most networks and satellite ground stations can tolerate minus 70 degrees without operating in areas where they are needed."
McHale said that due to harsh conditions, Quintillion's fiber optic cables are double-armored with copper and steel sheaths to prevent cutting, squeezing, or abrasion damage.
"All of the company's network components, including cabling, are carefully designed to withstand the extreme Arctic environment and prevent network outages," he added. "The seabed part of the cable is mainly buried under the seabed."
Due to the uncertainty of the success of data collection, the nerves lasted for the whole week
The day after the team arrived, the researchers met at the Quintillion cable landing facility, where the distributed acoustic sensing system was installed with the help of the company. Team members from Silixa (from which Sandia purchased the distributed acoustic sensing system) are also there to help.
McHale said that Sandia researchers were able to use approximately 30 miles of submarine fiber optic cable, and the setup went smoothly. He added that so far, the project has been a great experience.
"It is exciting and honored to have the opportunity to work with some of the most knowledgeable geophysicists and data scientists in the country," he said. "Supporting the work of the scientific community has been Quintillion's goal for a long time. Achieving this goal with a respected client like Sandia Labs has exceeded our expectations."
A few days before the initial collection, tension was expected in the team because this was something that had never been done before. Although Abbott used fiber optic cables to record explosions for Sandia, he did not use them on the seabed, nor did he use them on such a large object.
Abbott said that the interrogator collects 2 GB of information every minute, and because it comes in so fast, it's difficult to know if the data is correct. Three or four days later, the team showed signs that the system was working well, and it took them a whole week to be confident in the experiment.
"What excites me is that we saw a lot of interesting phenomena in this data set, which may be the quietest data set with the least ice shock or wave effect," Abbott said. "Once we start to see ice breaks and icebergs collide with each other in other seasons when there is no ice at all, we will see better things, such as tides, ocean currents and storms."
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Manette Fisher mfisher@sandia.gov Office: 505-844-1742
Copyright © 2021 American Association for the Advancement of Science (AAAS)
Copyright © 2021 American Association for the Advancement of Science (AAAS)