Ray DuVarney explores
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.
better pictures of outer space
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
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,
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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