Robot Glider Detects Rogue Waves

When the robotic Papa Mau completed its 16,668-kilometer scientific expedition across the Pacific Ocean last month, the surfboard-sized submarine did more than set a new world record for the longest distance traveled by an autonomous vehicle. The wave-powered sub reached Australia’s Hervey Bay with a load of data that will keep marine biologists, oceanographers and other scientists busy for quite some time, including observations of rogue waves that satellites failed to detect during the Papa Mau’s year-long voyage.

On what appeared to be a calm, sunny day last February, Papa Mau transmitted data indicating rough weather—six- to 7.6-meter rolling seas and winds blowing at 50 knots. The sub had been at sea since November 17, 2011, the first of a fleet of four robot subs (called Wave Gliders) launched from San Francisco Bay by Liquid Robotics, Inc.

“There was not a cloud in the sky, nothing was on the satellites,” says Bill Vass, CEO of Sunnyvale, Calif.-based Liquid Robotics, a provider of ocean data services for shipping, energy and environmental companies. “And we said, ‘Oh, there must be something wrong with [the submarine’s] sensors.’ But when all four robots saw [the waves], we turned on the cameras. It was pretty astounding.” Nearby, an unfortunate sailboat lost its mast and was rescued by a Dutch freighter. “Besides that sailboat, the freighter, and us, no one would have seen those waves,” Vass adds.

Maritime history is filled with fantastical stories of rogue waves that appear suddenly, like walls of water, to swamp unsuspecting sailors and their vessels. As recently as 2010, several such monstrous waves hit the cruise ship Louis Majesty in the Mediterranean off the coast of Spain, an incident that killed two people and injured six.

Satellites in the worldwide communications system used for transmitting data from offshore locations “make their best guess” from 400 kilometers up about weather conditions at sea, including wind speeds and wave heights, according to Vass. They not only miss giant waves but are “tremendously inaccurate” in estimating the speeds of current and wave direction, he says

After comparing satellite data with his robots’ findings, Vass believes satellites detect surface shear, which comes from winds and broad currents. There are two dimensions to surface shear. One is the difference in currents at the ocean’s surface compared with those flowing at lower levels of the water column. The second occurs when two currents collide and generate smaller localized eddies and turbulence. Both are important to know when determining circulation and its effect on shipping energy usage and fuel consumption.

“We’re finding the satellites are way off for microcurrents,” Vass says. “In many cases, the satellite models were showing currents 180 degrees off from the currents we actually experienced, and off by a factor of two to three in speed. Our robots feel the first eight meters of ocean.” A drifter—a buoy that may submerge to a depth, then rise to the surface while tracking the path of a current—might detect a surface current, and a satellite might “see” the first few inches of the ocean, but Vass says his robot gliders “feel the full breadth of the current.” As such, the gliders ran through a series of eddies that were invisible to the satellites. They also crossed the equator where, according to satellite models, a huge shear current was thought to run east to west. Yet the flotilla experienced none of that. Upwellings, rising masses of water that can be small or enormous and that often carry deep ocean nutrients to the surface, were also in the wrong places compared to what the satellites indicated, he adds.

“The speed and directions of currents have major effects on the shipping industry, oil and gas and marine operations, as well as global weather,” Vass says. “The robot gliders’ ability to show measurements will change the way many of these industries work in the future.”

Others are more skeptical of the significance of the gliders’ findings and point out that the limitations of satellite observations are already well known. Oscar Schofield, a Rutgers University professor of bio-optical oceanography thinks that Liquid Robotics is overstating the importance of its findings. “I wouldn’t take such a negative tone,” he says. “We’ve been well aware for a long time––since we put the satellites up––that they are limited. They are the only way to provide a global view of the ocean, albeit weighted to the surface, but they are still the most effective tool.”

The question is how to fill in the subsurface, 3-D structure, Schofield says. Robotic gliders—including those made by Liquid Robotics and Falmouth, Mass.-based Teledyne Webb Research—as well as scientific buoys like the Argos drifter are filling the data gap, he adds.

In June, Liquid Robotics’ gliders also documented a more than 1,900-kilometer-long chlorophyll and plankton bloom—the largest ever and not usually seen that time of year—initially undetected by satellites. “At this resolution, the chlorophyll bloom provides a groundbreaking link between scientific modeling and in-situ measurement and real-time data transmission,” says Liquid Robotics oceanographer Luke Beatman. The finding is significant because algae and phytoplankton are the base of the oceanic food chain and also regulate climate by absorbing carbon dioxide from the atmosphere.

Commenting on algal bloom, Scott Glenn, a Rutgers University professor who specializes in physical oceanography, says he finds that “the near-surface spatial maps of temperature and phytoplankton distributions obtained by satellite combined with the vertical profiles obtained from underwater profiling robots and gliders are very powerful observational tools, illuminating a chronically undersampled ocean that varies rapidly in space and time.”

Satellites provide maps of instants in time whereas surface wave gliders and underwater profiling gliders provide time series that move around underneath these maps, and can be redirected by these maps to the areas of greatest interest, Glenn says, adding that he prefers to use all three means simultaneously for “sustained sampling trajectories through this unseen world.” Both Glenn and Schofield are part of Rutgers’ Institute of Marine and Coastal Sciences Coastal Ocean Observation Lab.

Papa Mau’s journey came to a close when it arrived in Bundaberg, Australia, on November 20, having weathered gale-force storms, fended off sharks, skirted around the Great Barrier Reef, and finally battled and surfed the East Australian Current to reach its destination Down Under. The robot gliders could change the economics of sea exploration and monitoring. The average research vessel costs $37,500 per day due to fuel, crew and maintenance, so an expedition like Papa Mau’s by ship could cost tens of millions of dollars. Instead, each robot glider costs up to $3,000 per day.

Next up, Liquid Robotics has chosen five teams of scientists to study the new data. Researchers from University of California Merced, University of California Santa Cruz, Scripps Institution of Oceanography, University of Texas and Boston-based software firm Wise Eddy will use the information to analyze the ocean’s health and respiration, its biomass and other information about organisms critical to ocean life.

The second robot glider, Benjamin, is expected to arrive in Australia in early 2013. The two others are being repaired in Hawaii and will eventually swim to Japan. Liquid Robotics is next contemplating a robot sub mission circumnavigating Antarctica.

Courtesy of www.scientificamerican.com

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