Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/jplnews2/1407.pr

Text File | 1993-05-03 | 4KB | 72 lines

PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE [phone]

Contact: Jim Doyle, JPL
FOR IMMEDIATE RELEASE                   December 13, 1991
    Radar scientists and engineers at NASA's Jet Propulsion
Laboratory have developed a new, more accurate, airborne radar
system for topographic mapping of the Earth's surface.
    The instrument, called TOPSAR for topographic synthetic
aperture radar, has many potential commercial and scientific uses
and will be about three times more accurate than any topographic
mapper now readily available, said Dr. Howard Zebker of JPL.
    TOPSAR is an interferometric radar mapper and is carried
aboard NASA's DC-8 aircraft.
    Radar interferometry measures the difference from each of
the two antennas to a point on the ground to determine the height
of that point by triangulation. The separation of the antennas,
which forms the third side of the triangle, is called the
baseline.
    The instrument, developed in collaboration with an Italian
consortium, is a prototype for a possible NASA satellite mission
to map the entire globe at high topographic resolution, Zebker
said.
    The mission, TOPSAT, may be launched later in this decade.
    JPL currently operates a multifrequency radar, called
AIRSAR, aboard the NASA aircraft and TOPSAR uses much of the
AIRSAR hardware. But several modifications were implemented toachieve optimum performance in topographic mapping, Zebker said.
    "Our goal here is to provide an operational instrument
capable of delivering digital elevation models at a height
accuracy of 2 meters and a spatial resolution of 10 meters," he
said.
    The present instrument has an accuracy of only three meters
in height, however, Zebker said, while the scientists continue to
work eliminating phase errors that result from, among other
things, aircraft motion.
    The radar pulses are transmitted from a single antenna and
received simultaneously at two different antennas. The best
performance is achieved by minimizing errors in baseline length
distance to each point in the image, and distortion in the data
processor, Zebker said.
    But the aircraft attitude is also important, he said,
because the roll angle of the aircraft can be translated into an
error in look angle of the radar.
    Modifications in AIRSAR hardware and new computer software
on board the plane are being used to get the accuracy the
instrument is capable of achieving. TOPSAR was tested in
topographic mapping of several sites in the United States and
Europe.
    Zebker said the instrument could be used scientifically to
analyze geological processes expressed in surface topography.
Commercially, he said, it could be used for land use and water
drainage studies and to aid in management of disasters such as

landslides and earthquakes.
    "It's potentially a much cheaper way of mapping large areas
than anything now available and is roughly three times more
accurate than the U.S. Geological Survey's standard product," he
said.
    The instrument was described in a paper by Zebker and co-
authors Soren Madsen and Jan Martin of JPL. The interferometric
antennas mounted on the DC-8 were developed by Alenia S.p.A.
under contract from the Italian Consortium for Research and
Development of Advanced Remote Sensing Systems.
    The research and development at JPL was under contact to
NASA's Office of Space Science and Applications.
_____
#1407
12/13/91jjd