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OCEANOGRAPHY

An ocean of scientific change

New ways to map seas, save whales

SIGGRAPH 2006: From idea to image
It’s an academic conference. It’s a digital art exhibit. It’s drawing 25,000 people to Boston this week to see how emerging technologies are being used to educate, entertain, and study everything from the sea floor to the human body.

Off the North Atlantic coast, Marine biologists maintain a vigilant watch over the few hundred right whales left in the world.

This year, they'll have a new tool: Using photographs taken underwater and above the surface, they will construct three-dimensional models of the animals to monitor weight changes or new scars from run-ins with ships and fishing gear.

It's just one example of how computer imaging and other technologies are transforming oceanography -- the subject of a special session at SIGGRAPH 2006 , a major conference on computer graphics and emerging technologies drawing more than 25,000 people to the Boston Convention & Exhibition Center this week.

The terrestrial part of the world is now easily searched by Google Earth, but scientists have ventured into just a tiny fraction of the world's oceans. Computer graphics are crucial for developing images of places where humans can't go.

``The oceans are mostly unexplored," said Dave Gallo, director of special projects at the Woods Hole Oceanographic Institution.

``They're incredibly hostile to humanity, the average depth is 2 miles, the pressure is enough to crush the Titanic like a paper cup, and if you're down there, you wouldn't be able to see your hand," Gallo said.

The institution is pioneering some of the latest advances in underwater imaging and is monitoring everything from ocean currents to seismic activity on the ocean floor. ``To explore that world, you have to have computer graphics," Gallo said.

In the case of right whales, scientists need three-dimensional models because they can't capture and assess each of the estimated 350 animals left every year. Instead, they use stereoscopic imaging to turn two-dimensional photographs into three-dimensional representations, by taking into account the different angles of the photos.

The models will let marine biologists check on the remaining population, which was decimated by centuries of whaling. If the models show weight loss in many whales, for example, scientists can infer that there might be a disruption in the food supply.

Similar technology is allowing another Woods Hole scientist, senior engineer Jonathan Howland , to create panoramic images and accurate maps of shipwrecks. Armed with the equivalent of a flashlight in the depths of the ocean, underwater vehicles can only shoot photos of small parts of a shipwreck at any time. Pasting together dozens or hundreds of these individual photos to make a panorama is problematic, because the edges of the images won't match completely.

``It's an imperfect process," Howland said. ``The world isn't flat, so flat pictures of three dimensional things don't work."

Secondly, having images alone isn't enough. If scientists want to send rovers to explore a wreck, they need to have accurate distances to avoid crashing the vehicle or ensnaring its tether.

Howland is working on technology to resolve this, called photomosaicing. It will piece together two-dimensional photographs, taking into account the different angles and correcting distortions. The same principles of stereoscopic imaging apply here, as well. Calculating the rover's coordinates and the different images, Howland can determine how far, for example, a ship's deck is from the seafloor, all from a set of photos.

Other researchers can use this data to investigate the reasons why a ship sank, learn about a new ecosystem, or excavate artifacts without disturbing an archaeological site.

New imaging techniques and better equipped underwater vehicles are also allowing scientists to map the ocean floor in detail never seen before. Satellite technology creates a relatively crude map of global ocean topography by measuring the strength of the gravity emanating from the earth, based on the sea's surface. More gravitational pull indicates more mass, and therefore higher elevation in an area.

Chris German, chief scientist for deep submergence at Woods Hole, uses a combination of satellite, sonar, temperature data, and photographs to construct maps of the seafloor. He also uses a pair of underwater vehicles to investigate seafloor topography. One does a fly-over at 100 meters above the seafloor, while another zooms in for a close-up.

German and his team identify 300-square-foot areas of interest, usually with mysterious hydrothermal vents. The vents, which have piqued great interest from the scientific community, leak lava and house a panoply of odd creatures that live in an environment rich with hydrogen sulfide, deadly to most other life forms. It's an ecosystem unlike any other in the world, and may offer insight to Earth's first life forms.

Once scientists have zeroed in on a patch of terrain, an underwater vehicle called ABE, or Autonomous Benthic Explorer , flies over the area in a tightly wound zigzag pattern, taking photos, sensing temperature, and measuring depth. All this data -- the gravity pull, the sonar response, and the photos -- are translated into a three-dimensional topographical map.

``We can go from 200 kilometer by 10 kilometer section in the beginning to mapping a 200 by 100 meter area," he said.

German will be testing a deep-sea vehicle called Nereus next year that can descend to 11,000 meters below sea level in the Pacific Ocean. Areas that extend this deeply tend to happen when one tectonic plate slips beneath another, in a process called subduction. The best known examples exist off the coasts of Japan, Chile, and Indonesia, the latter near where a tsunami struck in 2004.

Changes in the seafloor could help explain geological phenomena like movements in tectonic plates or even the origin of life. But historically, little has been known about ocean floors; for centuries, people assumed they were flat. The scientific community only learned about the mid-ocean ridges, which are like underwater mountain ranges, in the middle of the 20th century.

``Until we had good maps, you could have a city the size of Manhattan or Boston sitting on the bottom of the ocean and you'd be hard-pressed to find it," Gallo said. ``Today you can see a Coke can on the ocean floor."

These graphics and photography techniques are also used to study the sea's tiniest creatures.

Woods Hole scientist Cabell Davis developed a camera that swims and dives hundreds of feet while taking photos of plankton by the microsecond. Studying plankton, which are the foundation of the ocean ecosystem, is difficult because the microscopic creatures are often so fragile that they disintegrate upon contact, so scientists can't round them up for laboratory observation.

The camera allows plankton to swim undisturbed between the camera lens and the flash. Trailing Woods Hole's research ship for thousands of miles through the Atlantic, Davis's invention has shot pictures of flamboyant Caribbean plankton with flashy protrusions and the more plain-looking East Coast plankton. ``It's like candid camera for plankton," Davis said.

Kim-Mai Cutler can be reached at kcutler@globe.com.

SIGGRAPH 2006
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