NASA Dryden's Gulfstream III banks over Edwards AFB with
the UAVSAR pod visible beneath the aircraft 3/6/07
Photo: Lori Losey
11/27/2007 - EDWARDS, CA - NASA is evaluating a compact L-Band
synthetic aperture radar for potential use on unmanned aircraft.
The sensor detects and measures small changes in the Earth's
surface of geophysical interest, such as volcanoes, earthquake
faults, landslides and glaciers.
NASA's Dryden Flight Research Center, Edwards, Calif., and
the Jet Propulsion Laboratory (JPL), Pasadena, Calif., are partnering
in the development of the Unmanned Aerial Vehicle Synthetic
Aperture Radar (UAVSAR). A modified NASA Gulfstream III aircraft
carries the JPL-developed radar in a custom-built pod under
the aircraft's fuselage during its development phase.
"The system is an imaging radar. It is like a camera that
uses microwaves to make an image," said Scott Hensley,
chief scientist for the UAVSAR project. "It collects data
to measure the deformation of the Earth's surface, for example
from an earthquake or volcano. This will help us better understand
how earthquakes and volcanoes work. The way we do that is through
the signatures of how they deform the Earth's surface."
"The UAVSAR is a flying testbed for developing the tools
and technologies for future space- based radars," said
Robert Smith, UAVSAR program manager for NASA's Earth Science
Technology Office. "Once operational, it will also be a
powerful airborne instrument providing calibration data and
rapidly repeated images scientists need to augment data obtained
During these validation flights, the aircraft is using a technique
known as repeat pass interferometry that requires the aircraft
to fly each pass as close to the original flight line as possible.
For the UAVSAR experiment, two data passes, flown from minutes
to months apart, are compared to examine changes in the Earth's
surface. Flying this technique enables the data collected by
the synthetic aperture radar to be converted into surface displacement
measurements with a sensitivity equal to a fractional part of
the radar wavelength.
To ensure the accuracy of the flight paths, a precision autopilot
designed by engineers at Dryden has been installed on the test
aircraft. The autopilot guides the aircraft using the differential
Global Positioning System and the aircraft's inertial navigation
system to repeat the flight path to an accuracy of within 15
feet. With the precision autopilot engaged, the synthetic aperture
radar will be able to acquire repeat pass data that can measure
changes with a resolution measured in millimeters.
"We're very pleased with the performance of the Platform
Precision Autopilot, and feel confident that this new system,
along with the structurally modified G-III aircraft, is ready
to fully support UAVSAR interferometry studies," said Frank
Cutler, project manager for the Gulfstream III UAVSAR flight
testing at NASA Dryden.
During the 1990s scientists used NASA's DC-8 airborne science
laboratory to collect data with the airborne synthetic aperture
radar (AIRSAR) system, also developed at JPL. The UAVSAR instrument
currently under development has benefited from technology advancements
in the 20 years since AIRSAR was built.
The prototype UAVSAR is smaller, fitting into a pod about 10
feet in length. The radar pod is a self-contained instrument
package that requires only electrical power from the aircraft.
The instrument has its own navigation system consisting of a
high-accuracy inertial navigation unit and a differential GPS
developed at JPL that provides the aircraft's location to an
accuracy of less than three feet. The radar's electronically
steered antenna compensates for aircraft attitude changes as
the radar makes repeated passes over areas of interest.
The pod also contains a two-terabyte recorder to store the
large amounts of data generated by the radar. The pod is designed
to operate autonomously by loading commands to the system's
computer prior to flight. Along with the autopilot, the design
of the pod allows it to be flown on a variety of aircraft, including
The sensor is currently undergoing a one-year development and
test period to improve robustness and validate its ability to
meet the science objectives. The UAVSAR will be extensively
tested through 2008, after which it will become a community
science tool for NASA.
Source: NASA Dryden Press Release