NASA/JPL TOPSAR Interferometric SAR

Authors: Thomas W. Thompson, Howard A. Zebker,
Richard E. Carande, Paul A. Rosen, Soren N. Madsen,
Scott Hensley, Ernesto Rodriguez, Jakob J. van Zyl,
Jan M. Martin and Timothy W. Miller

Contact: Jakob van Zyl
             Mail Stop 300-243
             Jet Propulsion Laboratory
             4800 Oak Grove Drive
             Pasadena CA 91109

Phone Number: (818) 354-1365
Fax Number: (818) 393-5285

e-mail : jacobv@blacks.jpl.nasa.gov

Title: The NASA/JPL Aircraft Topographic Synthetic Aperture
         Radar (TOPSAR) System for Rapid Production of Digital
         Terrain Models

We have developed an aircraft radar interferometer, TOPSAR, that
uses a synthetic aperture radar and interferometry to rapidly
produce topographic maps of the earth. In some applications, this
radar technique has the potential of replacing traditional
photogrammetry which uses aerial photography. In other
applications, this aircraft radar interferometer system can map areas
inaccessible to aerial photography because of darkness or weather.
Our aircraft radar is a processor to a possible satellite system, which
can produce a global digital topographic map of the earth.

We operate a C-band (6 cm wavelength) radar interferometer as an
adjunct to the JPL Aircraft Synthetic Aperture Radar (AIRSAR)
system that routinely acquires multi-polarization SAR images at P-
band (70 cm wavelength), at L-band (25 cm wavelength) and at C-
band. The TOPSAR/AIRSAR system flies on the DC-8 Airborne
Laboratory operated by the NASA Ames Research Center. The
TOPSAR system is implemented via two antennas mounted nearly
vertically on the left side of the DC-8 aircraft with a 2.6 meter
baseline spacing. Interferometric maps of the surface are constructed
by comparing the phase differences between SAR images from the
two antennas.  Statistical elevation errors for the TOPSAR system
range from 1.0 meters for flat land to 3.0 meters for mountainous
areas. Horizontal resolutions are 5 to 10 meters.

(NOTE-Jan Martin and/or Jakob van Zyl can provide you with details
of the output  Format, ordering products, etc.)

Typical data acquisitions are for areas of 10 km across-track (i.e. in
range) and up to 50 km along track (i.e. in azimuth). Analysis of
radar data obtained in the Galapagos Islands (Islas Fernandina and
Isabella) demonstrated that these 10 km-by-50 km topographic
maps could be mosaicked together for an area of about 50 km-by-
50 km. We improved the TOPSAR aircraft radar system in 1994 by
installing a new tightly-coupled Global Positioning/Inertia Navigation
System (GPS/INS) unit. This improved our topographic data and
enabled mosaicking via dead reckoning.

These aircraft observations are a precursor for a possible earth-
orbiting TOPographic SATellite (TOPSAT), which is currently in
premission studies at JPL. Current TOPSAT plans call for two nearly
identical spacecraft that will be launched and operated in tandem.
The L-band (25 cm wavelength) radar system on the TOPSAT two
satellites will be able to acquire a global topographic map of the
earth with height resolution of 2 to 5 meters for ground resolution
pixels with sizes of 30 meters.

TWT/13 Sept. 94

Updated 9/13/94
bruce.chapman@jpl.nasa.gov