By Thomas A., a radar engineer in the Acquisition Engineering office, National Geospatial-Intelligence Agency (www.nga.mil), Bethesda, Md.
As the number of commercial space radar satellites continues to grow, National Geospatial-Intelligence Agency (NGA) analysts and scientists are beginning to use these systems to advance geospatial intelligence (GEOINT). For example, in December 2009, the agency awarded three contracts for commercial satellite synthetic aperture radar imagery, data products and direct downlink services. Radar offers all-weather capability, providing NGA with a consistent, reliable way to gather intelligence in low-light and bad weather conditions.
The word "radar" is derived from the term "radio detection and ranging."
Radar imaging systems emit microwave radio signals that are reflected from Earth's surface and returned to the sensor. The radar measures the parameters of the reflected waves, which are processed into images and other radar products.
The pace of international commercial radar development has increased dramatically in recent years. From June 2007 through June 2010, six international commercial radar imaging satellites were launched. Italy launched three of its four-vehicle COSMO-SkyMed constellation; Canada launched RADARSAT-2; and Germany launched its TerraSAR-X and TanDEM-X satellites.
These commercial radar satellites represent a significant improvement over previous commercial radar systems, including images with resolutions as good as 1 meter and special collection methods that can vary the polarization of the energy their sensors transmit to the ground. This permits image collection in different polarizations simultaneously, which can characterize Earth's surface structure in interesting new ways.
Overview of the New Radars
The new commercial radar systems support large-area collection at medium and coarse resolutions. They also can collect pairs or series of images for use in change detection and other specialized applications such as measuring subtle changes and shifts in land surface structure. Each satellite operator also offers direct downlink services for fast regional support.
The COSMO-SkyMed system has four operating satellites, launched between June 2007 and November 2010. Of the three new commercial space radar systems, it provides the highest collection capacity and fastest access to any ground area.
This multisatellite constellation has the shortest time periods between so-called "coherent pairs" of images that are collected at different times from identical locations in space and used for change detection applications. COSMO also has the best native resolution of the three commercial systems. The resolution for commercial customers is limited to 1 meter.
To complete the full four-vehicle COSMO-SkyMed constellation, the Italians launched their fourth satellite Nov. 5, 2010 (see "Industry Updates," page 7). In addition, they're working with Argentina to possibly launch an L-band (long wave) radar constellation called SAOCOM. Such a system would be well suited to applications measuring small elevation changes in land surface and provide some foliage penetration capability.
Launched in December 2007, RADARSAT-2 is an improvement to the successful RADARSAT-1 vehicle that pioneered commercial space radar imaging and has been operating reliably for nearly 15 years. RADARSAT-2 is capable of imaging extremely wide swaths, as large as 500 kilometers. Of the set of new space radars, it has the longest collection time per orbit and is the only quad-polarimetric sensor.
RADARSAT-2 is expected to excel in ocean surveillance applications. Its best resolution mode is 1 meter by 3 meters. The Canadian Space Agency has funded a RADARSAT-2 follow-on program called the RADARSAT Constellation Mission, which may include up to six satellites.
TerraSAR-X and TanDEM-X
TerraSAR-X may be the most geometrically accurate commercial radar system. NGA's commercial imagery program recently evaluated TerraSAR-X accuracy to be 1 meter or better with known ground elevations. Such performance is possible because of the accurate orbit determination program the Germans use to enhance the raw radar measurements.
On June 21, 2010, the Germans began a mission called TanDEM-X by launching a second radar vehicle to fly in formation with the first TerraSAR-X launched in June 2007. This is similar to the NASA–NGA Shuttle Radar Topography Mission (SRTM), which flew on the space shuttle Endeavor for 11 days in 2000, except it will be a multiyear project and will generate global high-resolution elevation data that are more accurate and almost 10 times more dense than the best SRTM data. In addition, the Germans are making plans for a TerraSAR-X 2 vehicle, which will be a commercial system with even better resolution.
The Utility of Commercial Space Radar
These commercial systems offer unique space-based imaging opportunities. Taken together they're a constellation with daily access to locations virtually anywhere on Earth's surface. The systems can meet the swift demands of many GEOINT needs, including environmental and disaster support. They're particularly useful during hurricanes and volcanic eruptions when clouds and dust particles block other sensors.
These three international space radar systems have improved the resolution, collection capacity and other advanced radar-imaging methods available from commercial sensors. NGA finds value in these sensors because they provide unique GEOINT
support to national security missions.
Editor's Note: Thanks to the NGA Pathfinder staff for their assistance with this column.