Photonics technologies are being used in instruments and for communications in cabled ocean observatories.
Hank Hogan, Contributing Editor
With the new year, there will be new scientific outposts in the ocean. Unlike floating buoys or transiting ships, these cabled and fixed observatories should allow researchers to measure that which has been hidden and should enable them to do so potentially for decades. The scientific payoff could be immense. For landlubbers, the cabling that connects the observatories to the shore also may allow the viewing and virtual exploration of the sea from top to bottom.
Before the ocean observatories can operate, they first need to have cable laid. The ship shown here is putting down cable in Monterey Bay in California for the Monterey Accelerated Research System, or MARS (top). The instrumentation nodes along the cable will be made up of components that must be integrated (bottom). Courtesy of Keith Raybould, Monterey Accelerated Research System.
The ocean plays a key role in weather and climate, but scientists have faced a problem when trying to study it. To a large degree, the ocean is opaque to light. Thus, many tools that work on and for land cannot measure the ocean. For example, satellite-borne lasers can’t map the ocean floor from outer space. They can touch only the surface. Similarly challenged, ships and submersibles can stay on station only for short times, making it difficult to measure long-term phenomena or short, episodic events that come and go.
The solution, first conceived some 15 years ago, is ocean observatories. Distributed on the ocean floor but connected to land by fiber optics and copper, such observatories overcome the power and bandwidth limitations that have plagued oceanography.
In this artist’s rendering, an undersea laboratory is connected to land via a cable that provides power to the laboratory as well as a fiber optic link to facilities on shore. The power allows the operation of lights, of chemistry/biology experiments, of imaging sonar and of high-definition stereo cameras, while the fiber optics allows all of the collected data to be transmitted to shore. Here the setup is being used to investigate a black smoker, a type of hydrothermal vent found on the ocean floor where superheated and mineral-laden water spews. Courtesy of the regional scale nodes program at the University of Washington.
John Delaney, a professor of oceanography and project director of the regional scale nodes component of the National Science Foundation-funded $331 million Ocean Observatories Initiative at the University of Washington in Seattle, noted that a single cable can deliver kilowatts of power to areas of interest and that the optical fiber within the cable can handle high data rates.
The regional scale nodes component of the National Science Foundation’s Ocean Observatories Initiative — and the complementary NEPTUNE Canada program — will be associated with the Juan de Fuca tectonic plate, one of a dozen or so major plates that make up the surface of the earth. Fiber optic cables will run from shore landings to experimental sites (orange dots) located in the areas of highest scientific interest. The observatories will operate continuously and will provide unprecedented remote access to the ocean, the seafloor and the subseafloor. Courtesy of the regional scale nodes program at the University of Washington.
“In this day and age, you can load 10 Gb on a wavelength; so, in fact, you can go quite high in terms of bandwidth,” he said.
Both in terms of power and bandwidth, that is much more than is possible with remote, battery-operated oceanographic instruments. Communication via satellite, for example, requires a platform at the surface, and the data rates typically run less than 1Mb/s, and they often run much less.
The project that Delaney heads has a complementary and separately funded Canadian component, NEPTUNE Canada. Together, the two projects will place cabled observatories in the deep ocean.
But before observatories can be placed deep in the ocean, the technology and techniques must be tested. This is being done at the Monterey Accelerated Research System (MARS) in Monterey Bay off the coast of California and at the Victoria Experimental Network Under the Sea (VENUS) off the coast of Vancouver, British Columbia, Canada.
Adrian Round, the project manager for the science project VENUS, said that the observatories are at least partially in the water. “We have one array [of observatories] deployed, and the second array is just being set,” he said.
This observatory array is in coastal waters, with one segment being 3 km long and at 100 m depth while the second is 40 km long and at ~ 300 m depth. The cabling is standard submarine telecom cable from Alcatel-Lucent, consisting of an inner core of eight coated fibers and an outer jacket. In between the fiber and the jacket sits steel tubing, a copper conductor and a polyethylene sheath, and on the outside, up against the jacket, armor wires. The exact configuration of each cable used depends on the application, with cables intended for shallow water being more heavily armored.
Although the copper provides a path to get the power to the instruments, the return path is through the sea itself. The low-strength electric field that results does not disturb ocean life, and using the sea for a return path is standard for submarine telecom cables.
The underwater LAN ports that provide the connection from the cable to the instruments are being built by OceanWorks International Corp., a Vancouver-based company specializing in subsea equipment. The instruments attached to the ports can be removed or added as needed with a robotic vehicle.
The photonic sensors and devices used in the VENUS instrumentation include digital still cameras and scaling lasers that penetrate the water and provide size and aspect information for objects. Also used are transmissometers, which shine lasers through the water, measuring the absorption and scattering of the light to provide information about materials suspended in the water.
As for MARS, the technology test bed lies at a depth of 891 m in Monterey Bay. The observatory sits at the end of a 52-km undersea cable and allows the attachment of up to eight instrument packages and science experiments. Two of the proposed experiments involve instruments that move, with one crawling along the bottom and another traveling up and down a mooring.
The cable was successfully deployed in March 2007, and all the subsystems have been delivered and are being integrated into the final observatory configuration at the Monterey Bay Aquarium Research Institute (MBARI), according to project manager Keith Raybould. Investigators at the institute are working through issues related to the medium-voltage 10-kW power convertor and the low-power system, which Raybould noted was the most technically challenging MARS component.
However, he does not think that these problems will delay deployment. “If all goes well with the rest of the integration at MBARI, the node should be installed in January 2008.”
One of the instrument packages that will be on MARS is the Eye-in-the-Sea device from the Ocean Research & Conservation Association of Fort Pierce, Fla. Association president and senior scientist Edith Widder noted that creatures in the ocean don’t like bright lights and even shy away from dim ones. The Eye-in-the-Sea gets around this problem by using the right light and camera, making it possible to see in the nearly complete darkness at the bottom of the ocean without scaring away the animals.
Widder said that the version of the device that will be deployed in MARS has benefited from work done elsewhere with earlier incarnations of the instrument. The new version will use 680-nm LEDs, with a cutoff filter close to 700 nm. Because of the low-light situation, the imaging will be done by a commercial intensified ITT Night Vision CCD camera with a sensitivity of a millionth of a lux, or roughly one-thousandth the light of a moonless and clear night sky.
This is a great improvement over the cameras found in the original instrument, but there are still some limitations, Widder noted. “The resolution is much better, but they’re still not high resolution. And it’s a black-and-white camera.”
The Eye-in-the-Sea also includes red scaling lasers spaced a known distance apart on the instrument. When their red dots appear on an object, they provide a way to determine how big something is, which can be difficult to do underwater with no reference points.
Researchers imitate the bioluminescence of deep-sea jellyfish, Atolla wyvillei (above), with an electronic version that has 16 blue LEDs (below). By imitating the same pinwheel display as the real thing, the electronic jellyfish lures sea life into view of cameras. Courtesy of Edith Widder, Ocean Research and Conservation Association.
The other photonics part of the Eye-in-the-Sea is its light lure, which has been dubbed an electronic jellyfish. Using blue LEDs that flash in a predetermined pattern, the lure attracts animals by mimicking the bioluminescence often found on the ocean bottom.
Into the deep
Information gained from the two projects will help with the deployment and operation of the 2000-km network of fiber optic/power cables of the combined US-Canada effort, called the North-East Pacific Time-Series Undersea Networked Experiments (NEPTUNE). NEPTUNE Canada already has deployed its full 800-km backbone cable. The US part of the network, now called the regional scale nodes component of the Ocean Observatories Initiative, should begin deployment this year and is scheduled to finish in 2010.
When completed, the network will encircle and cross the Juan de Fuca tectonic plate off the coast of Washington and British Columbia, an area roughly 550 × 450 km in size. Between 15 and 20 experimental sites will be established at nodes along the cable, providing an array of temperature, acoustic, chemical, biological and visual sensors. Some will be fixed, while others will move, gathering data over an area or up and down the water column.
A water-column mooring of the type that will be connected to the regional scale nodes cabled ocean observatory is shown. The mooring will include an instrument called a vertical profiler, which will sample the entire length of the mooring cable by crawling up and down continuously. The result is a detailed picture of the water conditions and the currents at all depths. As the profiler crawls, sensors measure water temperature, salinity, depth, oxygen level, and backscatter and fluorescence. The latter two measurements help indicate how much microscopic life is in the water. Courtesy of regional scale nodes program at the University of Washington.
Benoît Pirenne, associate director for information technology at NEPTUNE Canada, said that technology will keep the various locations synchronized to within a few milliseconds. Researchers therefore will be sure that a reading at one point can be correlated with a reading at another.
Some of the data will be as simple as a temperature measurement taken at regular intervals, while other readings will be streaming acoustic and video data. The latter will be compressed, which will cut down the storage requirements considerably and which Pirenne said must be done to keep the storage costs down. “In particular, it’s very critical for high-definition video,” he said.
Even with compression, estimates by NEPTUNE Canada are that 45 TB of data will be generated every year. Part of that will be metadata, or data about the data, that will contain such bits of information as device configuration. The data will be freely available and stored for the life of the project, which is expected to be 20 to 30 years.
Mairi Best, associate director of science for NEPTUNE Canada, noted that such cabled ocean observatories will stress technology in a number of ways. For example, plans for the joint US-Canada effort off the Pacific Northwest coast call for getting close to an active underwater volcano with both sensors and cabling.
There also will be a strong educational component, with the ability to pipe images directly into classrooms, thus bringing oceanography to areas far from the ocean. Other plans will allow end users to tilt, pan and zoom cameras, bringing the ocean into everyone’s view.
But it is the science that could gain the most benefit from these and other cabled observatories, Best said. “It’s going to completely change how we do ocean science. It’s going to change our view of 70 percent of our planet.