PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov
Contact: Mary A. Hardin
FOR IMMEDIATE RELEASE
April 18, 1996
SPACE RADAR REVEALS ANCIENT SEGMENTS OF CHINA'S GREAT WALL
Scientists in China are using space radar images to locate
and study two generations of the Great Wall of China that have
been eroded and buried in places by centuries of blowing sand.
"In the images we can recognize two different dynasties that
built the Great Wall. One was built in the Ming Dynasty and is
about 600 years old. The other was built during the Sui Dynasty
and is more than 1,000 years old," said Dr. Guo Huadong, a
Spaceborne Imaging Radar C/X-band Synthetic Aperture Radar (SIR-
C/X-SAR) science team member from the Institute of Remote Sensing
Applications at the Chinese Academy of Sciences in Beijing.
The radar images were taken by the SIR-C/X-SAR instrument
that flew on Space Shuttle Endeavour in April and October of
1994.
The Great Wall is one of several archeological sites being
studied through the use of the space radar images. Other sites
include Angkor, Cambodia, the Lost City of Ubar in Oman and the
Silk Road along the desert of northwestern China.
"Archeology wasn't one of our original science objectives,
but imaging radar data have been found to be very useful for this
type of research. It's an exciting spin-off," said Dr. Diane
Evans, the SIR-C project scientist at NASA's Jet Propulsion
Laboratory.
Evans is discussing the radar's role in archeological
research this week at a symposium at the University of Florida in
Gainesville, organized by the World Monuments Fund, the Royal
Angkor Foundation and the university, with support from the J.M.
Kaplan Fund and the Samuel H. Kress Foundation.
The Great Wall of China dates back to the third century
B.C., when it was built to protect the country from northern
invaders. The wall, which spans more than 3,000 kilometers (1,860
miles), has been periodically rebuilt and modified throughout
history by each reigning dynasty.
The scientists are studying a segment of the wall about 700
kilometers (430 miles) west of Beijing in a remote region of the
north-central China desert. The most recent version of the wall
was built by the Ming Dynasty during the 14th century and it is
clearly visible both on the ground and in the radar data. An
older version, built during the Sui Dynasty, runs parallel to the
present wall.
"Part of the wall is visible on the surface, but part of it
is buried by the strong winds that blow sand dunes across this
part of the desert," Guo said. "In this region the wall was made
out of loose soil and mud, not bricks or rocks. Usually you
cannot find these segments even if you go there, so the radar
data are helping to show us the whole wall."
"Using radar to look at archeological structures has been
very powerful because the radar is sensitive to vertical
structures, such as walls. Even if they are highly eroded, like
these segments of the Great Wall, the radar is able to capture a
reflection off it and the wall shows up quite clearly in the
radar image," said Dr. Jeffrey J. Plaut, the SIR-C experiment
scientist at JPL.
"This is a part of the world where we can also take
advantage of the radar's ability to penetrate through layers of
dry sand to image buried structures," Plaut added. "The multiple
channels of the SIR-C/X-SAR system increase our ability to detect
different kinds of structures that a single-channel radar system
would not see."
The Spaceborne Imaging Radar project is managed by JPL for
NASA's Office of Mission to Planet Earth, Washington, DC. SIR-
C/X-SAR is a joint mission of the United States, German and
Italian space agencies.
Radar images of the Great Wall at various resolutions are
available via the World Wide Web at the following address:
http://www.jpl.nasa.gov/radar/sircxsar/
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