By combining small SAR systems with a unmanned aerial vehicle platform, Sandia is providing radar imaging capabilities for a variety of applications.

The outcome of World War II’s Battle of Britain might have turned in favor of the Nazis and changed the course of history if Robert Watson-Watt of the British Radio Research Station had not demonstrated in the mid-1930s the capabilities of radar for aircraft detection. Significant developments in radar have been occurring since, many of which have implications for national security.

During the postwar 1950s, a significant development in the form of Synthetic Aperture Radar (SAR) occurred at the Goodyear Aircraft Co. that quickly became an alternate imaging modality to airborne photography. SAR was further developed at Sandia National Laboratories (Sandia) in Albuquerque, New Mexico, where scientists have honed in explicitly on real-time performance, physical size and image exploitation needs to drive SAR modifications.

“SAR is an all-weather (clouds, dust, rain), day or night technique that can also provide key information unavailable through traditional optical means,” said Bill Hensley, manager, SAR Applications at Sandia. “Besides imagery, SAR can provide 3-D maps, reveal minute changes in terrain and be used for navigational guidance. Many national security organizations could use SAR to ‘own the night’ and reveal details unavailable through any other technique.”

Sandia has a long history of developing components and technologies applicable to SAR. Over the last decade, Sandia’s scientists have applied technologies to imaging radars to meet the needs of advanced weapon systems, verification and nonproliferation programs and environmental applications.

“SAR requires world-class expertise in nearly every engineering discipline, including system, electrical, electromechanical, mechanical and materials engineering,” said Bryan Burns, senior scientist, who has been involved in Sandia’s SAR development activities for well over two decades. “It also requires detailed understanding of many scientific concepts, ranging from the physics of atmospheric transmission to electromagnetic interactions to real-time embedded computing. Through a long legacy of capabilities developed under the nuclear weapons program and refined by key projects for national security, Sandia has developed the expertise in these areas to deliver a unique combination of performance, size, and image processing algorithms.”

While the U.S. Army sponsored development of STARLOS (SAR Target Recognition and Location System), a real-time SAR with image-formation and automatic target recognition of multiple and simultaneous targets, between 1986 and 1991, Sandia scientists worked to reduce SAR’s size from 2,000 to 500 pounds and introduced further imaging capabilities.

In 1999, Sandia worked with General Atomics, Inc. (GA) to design and develop the Lynx SAR, which further reduced SAR size and weight to less than 85 pounds. This made them capable of accommodating small unmanned aerial vehicles (UAVs) for reconnaissance and surveillance in adverse weather conditions. That same year, Sandia and GA delivered the first prototype compact SAR. The sensor offered one to ten foot resolution strip-map capability and spotlight (higher-resolution, single-area imaging) resolutions as high as four inches, with a maximum range of 25 to 85 kilometers.

Since then, Lynx radar and subsequent designs have been successfully demonstrated on mediumpayload UAVs. In fact, the Lynx SAR is now performing day-to-day border search operations onboard a Customs and Border Protection (CBP) Predator B UAV.

As sponsors worked to build more effective operational SAR systems and image-exploitation approaches, DOE’s Laboratory of Directed Research and Development (LDRD) began funding SAR improvements, which led to further reducing package weight and adding multiple new imaging and image-exploitation capabilities. In 2000, a three-year LDRD project was accompanied by a supplementary LDRD to fabricate a new compact digital receiver, a miniaturized waveform synthesis prototype and an advanced application-specific integrated circuit. In FY 2004–05, LDRD developed highly modular software architecture and advanced image-formation algorithms for lower-resolution images. The efforts resulted in the MiniSAR, a functional radar weighing less than 30 pounds. Its prototype was successfully demonstrated in May, 2005, on a UAV.

“A number of key technical advances were achieved to yield a high-performance, ultra-fine resolution, all-weather, day-or-night imaging capability that can be integrated onto small, low-cost airborne platforms such as class III UAVs (nominal 50-pound payload) as well as larger aircraft, depending on the application,” said Kurt W. Sorensen, manager of Sandia’s SAR Sensor Technologies Department. “Since 2005, MiniSAR-derived systems and technologies have been engaged in a wide variety of missions, ranging from crevasse detection in Antarctica to incorporation in NASA’s Lunar Reconnaissance Orbiter mission.”

MiniSAR filled a void in remote sensing technology by providing unequaled real-time image quality and resolution for tactical warfare systems, while achieving four- to five-fold reductions in size, weight and cost. In particular, it gave even small UAVs the ability to see through smoke, dust, clouds and rain.

LDRD projects have since concentrated on developing better moving-target imaging and improved image resolution. Focus areas include Enhanced Inverse SAR (ISAR), which seeks to coherently process a set of radar-pulse echo data to image a target object whose motion is unknown. These advancements exemplify how, by combining MiniSAR-based systems with a UAV platform, Sandia today can provide the United States with capabilities that up until now would have been unachievable.