Conference 7.286::space

771.0. "NASA develops new radar for environmental research" by PRAGMA::GRIFFIN (Dave Griffin) Mon Dec 16 1991 17:53

Brian Dunbar                                        December 13, 1991
Headquarters, Washington, D.C.

Jim Doyle
Jet Propulsion Laboratory, Pasadena, Calif.

RELEASE:  91-205

     Radar scientists and engineers at NASA's Jet Propulsion Laboratory,
Pasadena, Calif., 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, an interferometric radar mapper, 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 satellite mission to map the entire globe at high
topographic resolution, Zebker said.

     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 to achieve 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 6.6 feet and a
spatial resolution of 33 feet," he said.

     The present instrument has an accuracy of only 9.9 feet in height, Zebker
said, however, 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 are 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 ascertain the accuracy of the instrument.  TOPSAR was
tested in topographic mapping of several sites in the United States and Europe.

     Zebker said the instrument could be used to analyze geological processes
expressed in surface topography to study land use and water drainage and to aid
in management of disasters such as landslides and earthquakes.

     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.

     JPL managed the TOPSAR research and development for NASA's Office of Space
Science and Applications.
 

Article: 4296
From: [email protected] (UPI)
Newsgroups: clari.tw.aerospace,clari.tw.environment,clari.news.gov.usa
Subject: NASA to help study Central American rain forests
Date: Tue, 16 Mar 93 15:03:42 PST
 
	WASHINGTON (UPI) -- NASA experts are helping Central American nations
study the ecology of endangered rain forests.

	NASA scientists will train counterparts from Belize, Costa Rica, El
Salvador, Guatemala, Honduras, Nicaragua and Panama so they can use data
from U.S. weather satellites in their effort.

	``You can do many things with remote sensing technology that just
can't be done in the field or would take a long, long time,'' said Tom
Sever, a scientist at NASA's Stennis Space Center in Mississipi. ``The
technology has given us a way to monitor the region as it has never been
done before.''

	The data will help scientists estimate the amount of vegetation in
the rain forest regions and the area's biological productivity. It also
will help protect Mayan archaelogical sites, NASA said.