A Space Shuttle mission scheduled to be flown in May 2000 will carry a specially modified radar system that will produce the most accurate and complete topographic map of Earth's surface ever assembled.

The planned 11-day mission, called the Shuttle Radar Topography Mission (SRTM), is a cooperative project between NASA and the Defense Mapping Agency of the U.S. Department of Defense. A formal memorandum of understanding to develop and conduct the mission was finalized on July 8.

The mission is designed to collect three-dimensional measurements of nearly 80 percent of the Earth's land surface, except near the poles, with an accuracy of better than 16 meters (53 feet). The regions to be mapped are home to about 95 percent of the world's population.

SRTM will use the same radar instrument that comprised the Spaceborne Imaging Radar-C (SIR-C) that flew twice on Space Shuttle Endeavour in 1994. To collect the topographic images, engineers will add an almost 60- meter-long (200-foot) mast, additional C-band imaging antennas, and improved tracking and navigation devices.

The mast, which was developed using the design for the truss structure of the International Space Station, will extend sideways from the orbiter's cargo bay. The antennae at the tip will allow the system to acquire stereo-like radar images of Earth's surface through a technique called interferometry. Such space-based interferometry was successfully tested during SIR-C's second flight.

Scientists will then use the 3-D images to generate computer versions of topographic maps, called digital elevation models, that can be used for a large number of scientific, civilian and military applications.

"Excepting measurements from weather satellites, the topographic information produced from this mission will be the most universally useful data set about Earth that NASA has ever produced," according to NASA Program Scientist Dr. Miriam Baltuck. "Possible applications range from scientific uses such as planetary geophysics or hydrologic drainage system modeling, to more realistic flight simulators for military aircraft, to commercial uses like better locations for cellular phone towers and improved maps for backpackers."

Traditionally, topographic maps have been generated from stereo pairs of photographs acquired from high-altitude aircraft and satellites. However, such optical systems cannot penetrate the cloud cover that blankets nearly 40 percent of the Earth's surface. In some tropical regions the cloud cover is virtually continuous and, as a result, significant portions of Earths surface have never been mapped in detail.

"We have a better global map of Venus than we do for the Earth," said Dr. Michael Kobrick, co-originator of the SRTM mission concept at NASA's Jet Propulsion Laboratory. "Since radars can see right through clouds, SRTM's 11-day flight will give us enough data to produce an image of the Earth 30 times more precise than any that currently exist -- and the best part is that the image will be in 3-D."

The Defense Mapping Agency (DMA), Fairfax, VA, plans to use the radar data to fulfill a joint defense requirement for a digital global terrain elevation map with data points spaced approximately every 30 meters (100 feet). The DMA currently holds a digital terrain map over 65 percent of the Earth's land mass with data points every 100 meters (330 feet). Completion of this data set has been hampered by a lack of cloud-free photos over major portions of the world.

The SRTM mission will be implemented by the Jet Propulsion Laboratory for NASA's Office of Mission to Planet Earth, Washington, DC.

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