PUBLIC FACT SHEET
During the last 15 years, the National Aeronautics
and Space Administration (NASA) space shuttle has
been used to study many aspects of space and Earth.
Now the shuttle, with an instrument called an imaging
radar, will be used to provide the most precise "picture"
ever of Earth's land surface. The radar will bounce signals
off the surface; these signals will be received by two
onboard antenna systems and combined by computers at
a ground facility to produce three-dimensional (3-D)
images. Because the shuttle will fly over most of the
globes' surface, enough data will be acquired to generate
the most complete topographic map of Earth's land surface
ever produced.
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How the Radar Works
SRTM will build on technology used during two shuttle
flights of the Spaceborne Imaging Radar-C/X-Band Synthetic
Aperture Radar (SIR-C/X-SAR). These missions
tested the radar technology and used imaging radar as a
tool for improving our understanding of how Earth' surface
is changing. A key SRTM technology is radar interferometry,
which compares two radar images taken at
slightly different locations to obtain elevation or surface-change
information. Unlike earlier missions, SRTM will
use single-pass interferometry, which means that the two
images will be acquired at the same time -- one from the
radar antennas in the shuttle's payload bay, the other from
the radar antennas at the end of a 60-meter (200-foot)
mast extending from the shuttle. Combining the two
images produces a single 3-D image.
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Working toward a Common Purpose
The Shuttle Radar Topography Mission (SRTM) will
collect these important data during an 11-day space
shuttle mission in 1999. The mission is a partnership
between NASA and the Department of Defense's
National Geospatial-Intelligence Agency (NGA). In
addition, the German and Italian space agencies are
contributing an experimental high-resolution imaging
radar system. Analysts will use the SRTM data to generate
3-D topographic maps called digital elevation models.
These digital topographic maps can be combined
with other data for analysis.
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The SRTM data will also be used to generate 3-D pictures
-- called visualizations -- of Earth's surface that
scientists will use for studies of flooding, erosion, land-slide
hazards, earthquakes, ecological zones, weather
forecasts, and climate change. The data's military applications
include mission planning and rehearsal, modeling,
and simulation. Other possible uses include
optimizing locations for cellular phone towers and improving
topographic maps for backpackers, firefighters,
and geologists.
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Seeing through the Clouds
Topographic maps can be produced by combining two
photographs taken by aircraft or satellites, but these images
are sometimes difficult to obtain when clouds obscure
the surface. A key advantage to radar is that it can
"see" the surface through clouds and in darkness. Imaging
radar was used by NASA's Magellan spacecraft from
1989-1994 to produce spectacular pictures of the cloud-covered
surface of the planet Venus. SRTM's goal is to
produce a similarly detailed map of Earth. The 11-day
SRTM flight will yield enough data for a digital model
of Earth that is more detailed than what is currently
available.
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A Global Perspective
SRTM will collect radar data over nearly 80 percent of
Earth's land surface, home to nearly 95 percent of the
world's population.

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Because of the complexity in converting the raw radar
data into topographic maps, data processing will require
one year. The resulting data formats will be compatible
with standard cartographic data-analysis software and
tailored to the needs of the civil, military, and scientific
user communities. Much of the data from the mission
will be made available to these users in accordance with
release guidelines mutually developed by NGA and
NASA.
The Jet Propulsion Laboratory, California Institute of
Technology, manages the Shuttle Radar Topography
Mission for NGA and for NASA as part of its Earth
Science program. This program uses data from satellites,
aircraft, and ground research to help scientists better understand
Earth's systems of land, water, air, and life, how
they interact, and how they are changing.
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Using Imaging Radar Data
These examples show how radar data are used to generate
highly detailed maps and 3-D images. This topographic map
![[Topographic Map Example]](images/bin/factsheet_pub_4.gif)
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(left image) of an area in the California
Sierra Nevada was created using SIR-C interferometry
data. The same digital data were used to create a 3-D
visualization (right image) that can be used by scientists
to help them understand drainage patterns and land-surface
changes.
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To Learn More about SRTM and Imaging Radar
We invite you to visit our World Wide Web site at
http://southport.jpl.nasa.gov -- or write to us at
Jet Propulsion Laboratory
MS 186-113, 4800 Oak Grove Drive
Pasadena, California 91109-8099.
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National Aeronautics and
Space Administration
Jet Propulsion Laboratory
California Institute of Technology
Pasadena, California
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