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NASA Radar Reveals Hidden Remains at Ancient Angkor

Douglas Isbell
Headquarters, Washington, DC                    February 12, 1998
(Phone: 202/358-1753)

Mary Hardin
Jet Propulsion Laboratory, Pasadena, CA 
(Phone: 818/354-0344)

RELEASE: 98-28

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 about 
100 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 one million 
people.  The famous temples were built from the eighth to 
thirteenth 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 Art 
and Archaeology Department 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 city.

    "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 twentieth 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 in its 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 five miles long 
and its function remains a matter of archaeological debate.

    "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 continued.

    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 Shuttle Endeavour. 

    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 Science, 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 ChoulŽan 
of the Cambodian Authority for the Protection and Management of 
Angkor and the Region of Siem Reap.

                       -end-