Ray DuVarney explores
better pictures of outer space

From the Hubble Telescope have come stunning images-the births of new stars, the deaths of others. On the heels of the Discovery astronauts' Hubble tune-up, an Emory professor is helping give earthbound telescopes similar capabilities.

Ray DuVarney, associate professor and chair of the Department of Physics, has invented a camera that may some day retire the Hubble Telescope. His camera makes it possible for astronomy observatories around the world to capture images of the sun, moon and stars that are as good-or better-than Hubble's.

His camera will soon be delivered to NASA's Jet Propulsion Laboratory in Pasadena, Calif. Later this year, it will be installed at Mount Palomar Observatory, located in the foothills of Los Angeles.

The difficulty in obtaining sharp images from an Earth-based telescope, explained DuVarney, lies in turbulence caused by the motion of gases in the Earth's atmosphere. Every split second, the atmosphere shifts slightly. Such changes cause light to bend, creating distortion in photographs taken through telescopes. "It's why the stars twinkle," he explained.

However, it is possible to eliminate the effects of atmospheric turbulence. And over the past 10 years, scientists and engineers have been developing adaptive optics systems to do so.

DuVarney began developing space cameras about eight years ago with a group at Georgia Tech. They created an "electronic Speckle Camera," a high-speed camera that could photograph bright objects through the atmosphere with a one-millisecond exposure time. With this extremely high shutter speed, they eliminated blur because the atmosphere is relatively still over a one-millisecond interval. However, the images were still distorted, said DuVarney.

The distortion is similar to looking through a pane of old-fashioned glass-with its bumps and air bubbles, DuVarney explained. However, the distortion can be eliminated by combining mathematically many hundreds of images. It was this development that caught NASA's attention last year, when DuVarney was tapped to develop the camera that will be installed at Mount Palomar.

A high-speed, low-noise electronic camera such as the one developed by DuVarney can see the effects of atmospheric distortion on a millisecond-by-millisecond basis. His custom-made camera takes thousands of frames per second. To measure atmospheric changes in the low-light environment, the camera uses a "guide star," which provides enough bright light for it to read the distortions.

The camera then passes that information along to a computer, to which it is linked via fiber optics. The computer can adjust hundreds of actuators to bend the telescope's "adaptive" flexible mirror ever so slightly, yet enough to compensate for distortion.

Essentially, the fast-action camera allows DuVarney time to outwit nature. "The atmosphere changes noticeably about every 100-300ths of a second," he said. His camera captures the image, transmits the data, computes the distortion and adjusts the mirror before the atmosphere has time to make any significant changes.

This process creates the crystal-clear images that astronomers have sought for so long. "The resulting pictures look as if the atmosphere has been removed," said DuVarney. "In fact, they are clearer than those taken by Hubble."

As technology improves- including sensors and communication links-so does DuVarney's ability to improve the camera. His real challenge now is making the camera smaller, more rugged and more reliable under adverse conditions. "A camera like this has to perform in a harsh environment," he noted, "whether it's on a mountain in Chile or orbiting in outer space."

DuVarney also is contracting with the European Southern Observatory to develop a similar camera for a new observatory with four optically linked telescopes, under construction on a mountain in Chile.

NASA has a long-range goal of putting multiple telescopes in space and linking them optically, said DuVarney. His high-speed framing camera could capture images that would be used to maintain the integrity of the optical coupling. The level of resolution possible through such an optical system is tremendous, he said.

The same effect is possible on Earth, according to DuVarney. He compares the diameter of Hubble's telescope with six-meter diameter observatory telescopes on Earth. "We've got these wonderful, huge telescopes here, but because of the atmosphere, our images from earth are many times worse than Hubble's," he explained. "If we can remove the atmospheric effects, we will indeed be able to surpass Hubble's work from Earth."

-Jeanie Lerche Davis



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