GeoSAR: Geographic Synthetic Aperture Radar

By the end of this century, a new tool will be available for goelogists, earthquake researchers, emergency management agencies, and forestry and land use management agencies. An airborne radar system call GeoSAR will generate high-resolution, three-dimensional maps to explore and study California.

GeoSAR is being developed by a consortium consisting of the California Department of Conservation, Calgis Inc., and NASA's Jet Propulsion Laboratory, with funding provided the the Defense Advanced Research Projects Agency (DARPA). The project will develop a dual-frequency airborne radar system that will be able to collect 249 square kilometers (94 square miles) of data a minute.

A special feature of GeoSAR will be its ability to acquire three-dimensional images of the Earth's surface through a technique call interferometry. Because GeoSAR uses radar, the system will be able to operate both day and night, under almost any weather condition. GeoSAR will be the first instrument that will be able to map both above, through, and below the vegetation canopy providing important information such a data about landslides that are overgrown with vegetation. The GeoSAR radar system is a dual frequency design using both P- and X-band wavelengths. The longer P-band wavelength will penetrate deeper into the canopy and, coupled with computer modeling, map beneath the vegetation canopy. When combined with other remote sensing data such as Landsat multi-spectral information, it will be possible to not only determine land cover type such as tree species, but also tree height and perhaps even width, such as crown diameter. Maps created with the GeoSAR data will be used to assess potential goelogic/seismic hazards, such as landslides, classify land cover, map farmlands and urbanization, and manage forest harvests. This system will become operational in early 2000.

Interferometric System Parameters
	X-Band	P-Band
DEM height accuracy	0.5-1.2 m (relative) 1-3 m (absolute)	1-3 m (relative) 2-5 m (absolute)
Planimetric accuracy (1 sigma)	2.5 m (absolute) 1 m (relative)	2 m @ 5 km altitude (absolute) 4 m @ 10 km altitude (absolute)
Ground swath width	20 km	20 km
Wavelength at center frequency	3 cm	86 cm
Bandwidth	80/160 MHz	80/160 MHz
Polarization	VV*	HH & HV or VV & VH*
Baseline length	2.6 m	20 m

*H=Horizontal; V=Vertical

JPL will build the radar system and develop the data processing software that will be used to convert the raw data into digital elevation models (DEMs). Calgis Inc., a geographic information systems company based in Fresno, California, will construct a geographic information systems (GIS) work station that will convert the JPL radar images into user maps. Calgis will operate the radar system and acquire the data onboard a Gulfstream II. The California Department of Conservation will design and lead the user validation experiments during the final year of the three year project. GeoSAR will initially map areas in California with the project branching out into other states and countries as users request data.

Mission Goals

• Develop precision foliage penetrating mapping technology based upon dual-frequency interferometric radar.

• Procide military and civilian users with a significant increase in mapping technology.

• Produce true ground surface elevation models suitable for military and civilian applications.

This western Los Angeles County, California image, obtained with the NASA/JPL TOPSAR radar in 1996, is typical of the data that will be produced with the GeoSAR system. This digital elevation model is being used by the California Department of Conservation Seismic Hazard Mapping Program to identify potential earthquake hazards.

For more information on GeoSAR, see the Department of Conservation home page on the Internet at this World Wide address: http://www.consrv.ca.gov/geosar/ GeoSAR is sponsored by DARPA. "Approved for Public Release - Distribution Unlimited" (5/8/97)