(From The New York Times) In 2005, two Silicon Valley engineers, Joe Rizzi and Roger Hine, began building a device that would allow them to listen to the calls of humpback whales off the coast of Rizzi's vacation home in Puako, on the Big Island of Hawaii.

What they produced, with their two-year-old company, Liquid Robotics, is the Wave Glider, a vehicle that will not only allow them to eavesdrop on the whales but could also become a powerful tool that helps scientists to understand climate change better and the military to monitor the high seas.

"This is a transformational development," said Jim Bellingham, the chief technologist at the Monterey Bay Aquarium Research Institute. "I wish I had invented it."

The Wave Glider is a sensor-carrying vehicle that moves through the ocean propelled entirely by wave energy. The glider's engine is about five feet long and sits 22 feet below the surface, tethered to a floating instrument platform equipped with sensors and the command center.

Rizzi, the chairman of Liquid Robotics, said the glider could record wide-ranging, long-term oceanic and atmospheric observations in a way never before possible.

Scientists use various techniques to record sea surface and atmospheric conditions. "Over 80 percent of the heat that enters the climate system goes into the ocean," said Dean Roemmich, a professor of oceanography at the Scripps Institution of Oceanography. "Measuring ocean temperature is the best way to measure global warming."

Each method has its limitations. Weather and distance are limiting factors for satellites, and buoys are costly and stationary.

The glider has a negligible operating cost, said Tim Richardson, the chief operating officer of Liquid Robotics. It can be deployed from shore by two people and controlled via satellite through an Internet interface. Wave energy has no cost, and solar panels on the surface float power the glider's command, control and sensor systems. Batteries provide a 10-day backup energy source. Richardson declined to say how much the gliders would cost in full production.

The concept for the glider was developed several years ago when Rizzi anchored a hydrophone, housed in a waterproof box, in the shallows during Hawaii's winter whale season. Instead of picking up the haunting calls of humpbacks, Rizzi said, "I heard the sound of frying bacon." Snapping shrimp, near-shore crustaceans that stun prey with sound waves generated by their snapping claws, had drowned out the vocal giants.

Rizzi tried mooring hydrophones in quieter offshore waters hundreds of feet deep, but several were destroyed in rough seas. "We needed a buoy that could stay in place without an anchor," he said, adding, "Fundamentally, that's an energy problem."

He called Hine, a robotics specialist who worked in the semiconductor field. With little experience in marine engineering, Hine approached the problem as an outsider.

"The concept of harnessing wave energy isn't new," said Justin Manley, chairman of the Unmanned Maritime Vehicles Committee for the Marine Technology Society, "but the traditional outlook is to convert wave energy into electricity." Instead, the wave glider passively converts wave energy into forward thrust. "I think Roger was so successful because he wasn't limited by conventional thinking."

The design is simple. When the surface buoy rises with a swell, it pulls the glider upward. When the buoy falls, so does the submerged glider. Water pushing on the glider's wings allows it to move horizontally while it rises and falls, and a tail rudder controls its direction. Traveling in a shallow saw-tooth pattern, it can move into the wind and swell and reach speeds up to two knots.

Scientist use battery-powered gliders now to study the ocean, but these devices take measurements vertically through the water column to depths of thousands of feet, while the green-powered Wave Glider records surface conditions. But there are other efforts to make vertically traveling gliders that draw energy from the ocean. Last April, Teledyne Webb Research, in Massachusetts, completed a four-month, 1,864-mile Caribbean test flight of a thermal glider that used the ocean's temperature gradients to propel itself through the water column to depths of 3,937 feet.

The Wave Glider's longest voyage covered some 3,000 nautical miles in about five months. In January, a glider completed a nine-day, 343-mile trip around the Big Island in heavy seas. The objective, Hine said, was to build a glider that could stay at sea for a year.

The National Oceanic and Atmospheric Administration is seeking financing for full-scale testing of the glider, said Chris Meinig, director of engineering at the agency's Pacific Marine Environmental Lab, in Seattle. The agency plans to use the glider to determine the extent of the oceans' rising levels of carbon dioxide, a heat-trapping gas produced by the burning of fossil fuels.

In addition, in 2004, the Defense Advanced Research Projects Agency issued a call for an oceangoing device that could both move and hold a position as the glider does, with sensors to detect things like submarines.

An agency spokeswoman, Jan Walker, said that after financing early research and testing (which did not include the Wave Glider), the agency closed the program because of "engineering challenges identified in high seas." Last year, Richardson said, Liquid Robotics signed a government contract to further test and evaluate gliders, but he would not say what agency was involved.

Other potential uses for the Wave Glider include mapping the seafloor, improving tsunami warning systems, patrolling marine reserves and monitoring coastal pollution.

"My vision is that we're going to populate the ocean with different types of robots, each with a different specialty," said Bellingham of the Monterey lab. "The wave glider adds a missing piece."

That vision is already coming into focus. In 1999, off the coast of Australia, an oceanographic coalition called Argo, which includes 25 countries, released the first of its free-drifting sensor-carrying devices. Today, more than 3,300 populate the oceans. But the devices travel at the whims of the currents.

"The nice thing about gliders," said Roemmich, who is as a co-chairman of the coalition, "is that they go where you tell them to go."