Images from the international Space Radar Laboratory may help researchers find previously unknown settlements near the ancient city of Angkor in Cambodia.

The radar data were obtained during the October 1994 flight of the space shuttle Endeavour, processed and then sent in January to the World Monuments Fund in New York City. The group had approached the radar science team about observing the Angkor area after the Space Radar Laboratory's first flight in April 1994.

"I had read about the radar mission while the April mission was in progress and instantly surmised that it would have applications to the international research efforts at Angkor," said John Stubbs, program director of the World Monuments Fund. "I didn't really know where to start, but I was hopeful NASA would be willing to image the area around Angkor."

Angkor is a vast complex of more than 60 temples dating back to the 9th century that served as the spiritual center for the Khmer people. In its heyday the city housed a population of about 1 million people and was supported by a massive hydrological system of reservoirs and canals.

The April 1994 flight of the Space Radar Laboratory's complementary radars -- the Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar (SIR-C/X-SAR) -- first demonstrated their capability to obtain vast amounts of data that could be used to advance many disciplines, including ecological, oceanographic, geologic and agricultural investigations.

"We realized after the huge success of the first flight that we could be more flexible in adding new sites to the timeline of flight two," said Dr. Diane Evans, the SIR-C project scientist at NASA's Jet Propulsion Laboratory. "Since our science team was interested in studying as much of the tropical rainforest as possible, Cambodia and the Angkor site complemented our ecology objectives."

Today Angkor is hidden beneath a dense rainforest canopy. Its temples have been ravaged by weather, war and looters. Remnants of an extensive irrigation system, which fell into disuse long ago, have intrigued archeologists studying the ruins.

"The radar's ability to penetrate clouds and vegetation makes it an ideal tool for studying Angkor," Stubbs explained. "I can see the hydrological system very clearly in the radar imagery and preliminary analysis reveals what may be evidence of organized settlement of large tracts of land to the north of the present archeological park, which until now, has gone unnoticed."

The SIR-C/X-SAR data will be used by the World Monuments Fund, the Royal Angkor Foundation and research teams from more than 11 countries to understand how the city grew, flourished and eventually was abandoned over an 800-year period.

"The 'temple mountain' monuments at Angkor, such as Angkor Wat and the Bayon, are not unlike some of the pyramid-like forms encountered in Central America," Stubbs said. "The sheer size and sophistication of Angkor's great city plan, now enveloped in dense jungle, set this ancient capital apart as the ultimate jungle ruin."

SIR-C/X-SAR is a joint mission of the United States, German and Italian space agencies. The Jet Propulsion Laboratory built and manages the Spaceborne Imaging Radar-C portion of the mission for NASA's Office of Mission to Planet Earth.

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