Sandia LabNews

Synthetic aperture radar comes of age

Beyond images: SAR’s precision tracking and mapping

In her presentations to New Mexico employees and to the community, Ireena Erteza offered a glimpse of why there is so much excitement about the capabilities of synthetic aperture radar (SAR). She has worked in Jack Jakowatz’s Radar Algorithm Development Laboratory Dept. 5912 for the past five of its 15 years. Much other SAR work is in Electronics Systems Center 2300.

SAR is a computed imaging technique, like medical tomography, relying on a "synthetic aperture" created by flying the device above the target area. Sandia first got started on SAR because of a strong radar hardware heritage for weapons systems. That expertise, based in Center 2300, has been coupled with Sandia’s strong signal processing research. That combination, said Ireena, "made it natural for Sandia to become a world leader in SAR systems."

"Through continued steady funding from DOE and an outstanding group of researchers, Sandia has been able to make significant contributions to the national radar community during the past decade and a half," said Ireena. "It is really inspiring to work with this group."

SAR was originally seen only as a day/night, all-weather imager. Sandia has made "significant enhancements to the imaging capabilities of SAR, but more important, we have shown the community that SAR offers much more than just imagery," she said.

The work has resulted in "many significant and unique capabilities" to exploit SAR imagery. In fact, she said the goal is to develop innovative techniques for exploiting SAR imagery, applied specifically to nuclear nonproliferation, arms control, and national security.

She showed two examples of innovative SAR products produced at Sandia:

Coherent change detection (CCD). CCD, developed at Sandia, compares a pair of SAR images taken of the same scene but at different times. "CCD allows us to detect physical changes on the order of a wavelength on the surface of a scene. A radar wavelength is measured in a few centimeters." She showed two SAR images of Hardin Field north of Sandia’s Tech Area 1 taken 20 minutes apart. The resulting computed comparison shows the path of a lawn mower and the footsteps of the operator walking around the machine and of two people walking diagonally across the field to lunch (from the bending of the grass). It even reveals the different positions of leaves on the tree caused by the wind. And this is from computed images made from an aircraft flying 10,000 feet up and three miles laterally away.

Interferometric terrain mapping.Here pairs of images are used to determine the heights of objects in a scene. Through a breakthrough in automation of a complicated technique called phase unwrapping, Sandia has been able to build completely automated terrain mapping systems. The aircraft-based system can in a day provide maps of a 30-square-mile area with height data every 3 meters and 0.8 meter relative accuracy.

"These high-accuracy maps are critical for security and military mission planning and training," said Ireena. Sandia’s new system produces maps that are more than 1,000 times more detailed than current maps that exist worldwide.

Concluded Ireena: "Sandia’s SAR program has produced many technical breakthroughs that give our nation information that couldn’t be obtained otherwise."