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FOR IMMEDIATE RELEASEFebruary 12, 1998
NASA RADAR REVEALS HIDDEN REMAINS AT ANCIENT ANGKOR
New evidence of a prehistoric civilization and remnants of
ancient temples in Angkor, Cambodia have been discovered by
researchers using highly detailed maps produced with data from an
airborne imaging radar instrument created by NASA.
Experts say the findings, made possible by the Airborne
Synthetic Aperture Radar (AIRSAR) developed by NASA's Jet
Propulsion Laboratory (JPL), Pasadena, CA, may revolutionize the
way archaeologists view the ancient city's development.
Angkor is a vast complex of some 1,000 temples covering more
than 160 square kilometers (about 60 square miles) of northern
Cambodia. Little is known of the prehistoric occupation of this
fertile flood plain, but at its height the city housed an
estimated population of 1 million people. The famous temples were
built from the 8th to 13th century AD and were accompanied by a
massive hydrological system of reservoirs and canals. Today,
much of the civilization of Angkor is hidden beneath a dense
forest canopy and is inaccessible due to poor roads, land mines
and political instability.
"The radar data have enabled us to detect a distribution of
circular 'prehistoric' mounds and undocumented temples far to the
northwest of Angkor," said Dr. Elizabeth Moore, Head of the
Department of Art & Archaeology at the School of Oriental and
African Studies at the University of London. "The site's
topography is highlighted by the radar, focusing our attention on
previously neglected features, some at the very heart of the
"The radar maps not only bring into question traditional
concepts of the urban evolution of Angkor, but reveal evidence
of temples and earlier civilization either absent or incorrect on
modern topographic maps and in early 20th century archaeological
reports," she said.
"The radar images make apparent many features that are not
readily identifiable on the ground," said Dr. Anthony Freeman, a
radar scientist at JPL who has collaborated with Moore for the
past three years studying the use of radar on the Angkor site.
"We can see differences in vegetation structure and some features
that are obscured by vegetation cover."
In December 1997, Moore surveyed a small mound on the
perimeter of the famous 12th century AD temple, Angkor Wat, that
Freeman had first noticed in the radar image. "Previous
archaeological accounts from 1904 and 1911 note only two temples
and make no mention of the distinct circular form of the mound.
We found four to six temple remains, including pre-Angkorean
structures," Moore said. "This suggests occupation of the 12th
century site some 300 years earlier, radically changing accepted
chronologies of Angkor."
Angkor's beauty is seen its in temples, but the greatness
of the Khmer city lies in the multitude of water-related
constructions, according to Moore. The Khmer kings nominally
dedicated temples to Hindu and Buddhist deities, but the
underlying significance was veneration of ancestral spirits,
ensuring fertility of the land. Management of water was
essential, both for control during the monsoon rains and
conservation during the dry season and involved the construction
of moats, dikes, canals, tanks, and reservoirs. The largest of
these reservoirs, dated to the 12th century AD, is eight
kilometers (five miles) long and its function remains a matter of
"These new detailed topographic maps have shown us many
more hydrological features and highlighted how they function in
the rituals and daily life of the Khmer people," Moore explained.
"Using a technique known as radar interferometry, which
combines two images to create a three-dimensional topographic
map, we can construct a map of the area surrounding Angkor that
is more accurate than most maps we have of the United States,"
said Dr. Scott Hensley, a radar engineer at JPL. "This map lets
us see both natural and human-made water management features at
the site with great clarity."
"Angkor is situated on the edge of the Tonle Sap lake, a
unique body of water that doubles in size during the rainy
season. These maps give us new insights into the human impact on
this ecosystem, from the ancient Khmer to the present day, and
are of importance in the study of our changing Earth," Freeman
The Angkor radar images were taken in late 1996 as part of
the AIRSAR Pacific
Rim Deployment and were a follow-up to the 1994 study of Angkor
with data collected by the Spaceborne Imaging Radar-C/X-band
Synthetic Aperture Radar (SIR-C/X-SAR) that flew on NASA's Space
Like SIR-C/X-SAR, AIRSAR transmits and receives three radar
frequencies in both horizontal and vertical polarizations. While
both systems use C-band and L-band wavelengths, AIRSAR has the
added benefit of P-band, a longer wavelength that can penetrate
below the forest canopy. In addition, AIRSAR can be flown in a
mode called TOPSAR that allows it to measure topography and
create three-dimensional images of the surface.
AIRSAR images of the Angkor region will be posted to the
Internet at this address: http://www.jpl.nasa.gov/news/
AIRSAR flies on a NASA DC-8 aircraft that is managed at
NASA's Dryden Flight Research Center, Edwards, CA. The AIRSAR
instrument is managed by JPL, a division of the California
Institute of Technology for NASA's Office of Earth Sciences,
Washington, DC. This office manages NASA's Earth Science
enterprise, an internationally coordinated effort to study
natural and human-induced changes in the Earth's land, oceans,
atmosphere, ice and life.
The AIRSAR flight over Cambodia was funded by the Government
of Thailand. Ground verification has been made possible by Vann
Molyvann, Minister of State for Culture and Fine Arts,
Territorial Management, Urban Planning and Construction; and Dr.
Ang Chouléan of the Cambodian Authority for the Protection and
Management of Angkor and the Region of Siem Reap.