The JPL UAVSAR

by Bruce Chapman, Scott Hensley, Yunling Lou, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California

History
The Jet Propulsion Laboratory’s (JPL) Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) project began as an Instrument Incubator Program (IIP) task in 2004, funded by the National Aeronautics and Space Administration’s (NASA) Earth Science Technology Office. After a year of study, JPL presented to NASA, a SAR instrument concept that would meet IIP science and instrument objectives, and could be expanded to meet future airborne radar science needs. This led to a 4-year program in that the SAR radar system was designed, fabricated, installed, and flight tested. A Gulfstream G-III aircraft at NASA Dryden was modified to support UAVSAR, including the development of a precision autopilot that would keep the aircraft within a planned 10-meter flight tube during radar acquisitions.

The primary objectives of the UAVSAR development phase were to develop a compact polarimetric L-band SAR for use on a UAV, or minimally-piloted vehicle, including an electronically-scanned antenna and the associated processing algorithms for repeat-pass differential InSAR; followed by the acquisition of measurements of geophysical interest to demonstrate the system, particularly observations of rapidly deforming surfaces such as volcanoes or earthquakes. The system was designed to support a wide range of science investigations including cryospheric studies, vegetation mapping and land-use classification, archeological research, soil-moisture mapping, geology and cold land processes.

UAVSAR became operational in 2009 and began acquiring data for a variety of science investigations. NASA Dryden operates the aircraft; JPL maintains the radar hardware, plans the missions, and processes the data. ASF is the designated Distributed Active Archive Center (DAAC) for the UAVSAR data products.

Instrument Characteristics
UAVSAR is an L-band SAR with a bandwidth of 80 Mhz. The antenna measures 0.5 meters in range by 1.5 meters in azimuth and is contained within a pod that hangs beneath the fuselage of the Gulfstream G-III aircraft. The antenna may be electronically steered along track; typically, it is steered to zero Doppler. The power transmitted is greater than 2 kW, and the noise equivalent for most of the swath is better than -45 dB. The single-look-complex data (SLC) have a pixel spacing of 0.6 m x 1.6 m. The Rosamond Calibration Array is used to calibrate the UAVSAR data to the required accuracy of one dB.

UAVSAR typically flies at an altitude of 41,000 feet on the NASA Gulfstream G-III, at a nominal ground speed of 430 Knots (Figure 3). The typical flight duration is 6 hours. In a typical mode of operation, full quad-polarization data are acquired. The cross-track image swath is about 20 km, and a typical flight line is 100 km in length.

Data Acquisitions
UAVSAR first acquired data on 18 September 2007. Since 2009, over 1,800 flight lines have been acquired during more than 160 flights, acquiring over 40 terabytes (TB) of raw signal data. Data have been acquired across several NASA Earth Science and Applications disciplines, such as solid Earth science, terrestrial ecology, cryospheric science, and hydrology.

In 2009, UAVSAR participated in the International Polar Year, and in addition to acquiring L-band data in Greenland and Iceland, also supported the development of a Ka-band system and subsequent acquisition of data in Greenland. Since 2009, UAVSAR has been monitoring deformation of the San Andreas Fault every 6 months from the Mexican border to North of San Francisco. Several terrestrial ecology missions have been conducted, from the Northeastern United States of America to Central America. Solid Earth-science campaigns have taken place from Central America to Hawai’i to the Aleutian Islands.

In 2010, UAVSAR was deployed to Haiti and to the Gulf Oil-Spill region to acquire data in support of assessing the impact of those disasters. Also in 2010, UAVSAR acquired repeat-pass InSAR results from the Baja 2010 earthquake (Figure 4). UAVSAR has been supporting several other investigations, such as regular monitoring of the Sacramento Delta, and the development of a real-time, on-board processing system.

Data Products
UAVSAR processes acquired data to high-resolution, fully-polarimetric data products. These products are available to anyone at no charge and may be downloaded by file transfer protocol from the data archive at ASF. Currently, over 1,400 fully-polarimetric images (almost 20 TB of data volume) are available for download, covering over 3 million-square kilometers. Included in the available products are 36-look slant-range polarimetric products at 5 m x 7.2 m pixel spacing; ground-projected polarimetric products in an equiangular geographic projection corresponding to 6 m x 6 m pixels; legacy Airborne SAR compressed stokes format data for the multilook slant-range data; and a full-resolution KMZ-formatted color composite image. SLC data products are available by request.

At the request of investigators, pairs of images are processed interferometrically to form interferograms. In addition to slant-range interferometric products, ground-projected products are also generated, as well as KMZ-formatted color overlays. These products are also available at no charge to an interested user.

Polarimetric data may be searched for and downloaded from both the ASF SAR Data Center’s Web site (https://ursa.asfdaac.alaska.edu/cgi-bin/login/) and from the UAVSAR Web site (http://UAVSAR.jpl.nasa.gov). Interferometric products will be available from ASF and are currently only available for search and download from the UAVSAR Web site.

Future
UAVSAR is continuing to conduct L-band science investigations on the NASA Gulfstream G-III aircraft for a variety of science objectives. The flexibility and modularity of UAVSAR allows for modifying the radar to operate in other frequencies and platforms. In fact, a P-band SAR capability, funded through NASA’s Earth Venture program and led by the University of Michigan, is being developed to measure subcanopy and subsurface soil moisture. A Ka-band, single-pass interferometry capability, funded through the NASA Airborne Instrument Technology Transition program and led by Remote Sensing Solutions, Incorporated, is being developed to study polar ice sheets. Work is also being undertaken to add L-band, single-pass interferometry capability to UAVSAR via two wing-pod-mounted antennas on the Global Hawk UAV platform.

For More Information
If you are interested in requesting UAVSAR data acquisitions for science investigations, please visit the UAVSAR Web site at https://uavsar.jpl.nasa.gov/cgi-bin/login.pl to plan flights, estimate the flight costs, and submit a flight request. For more information, please visit the UAVSAR Web site at http://uavsar.jpl.nasa.gov.

©2011 California Institute of Technology. Government sponsorship acknowledged. This work was performed at the JPL, California Institute of Technology, under contract with NASA.