Advanced Imaging


Advanced Imaging Magazine

Updated: January 12th, 2011 10:01 AM CDT

Eye in the Sky

Latest Canadian SAR satellite delivers higher resolution, more flexibility
© Canadian Space Agency and MacDonald, Dettwiler and Associates
RADARSAT-2 is a second-generation Synthetic Aperture Radar (SAR) satellite with a number of advancements, including three-meter ultra-fine beam for high-resolution imaging and increased data storage.
A RADARSAT-2 image of Greenland.
© Canadian Space Agency and MacDonald, Dettwiler and Associates
A RADARSAT-2 image of Greenland.

By Barry Hochfelder

Resolution and Polarization

The flexibility of RADARSAT-2 enables it to image a wide range, from 500km at 100 meter resolution to 20km at just three meters. The phased-array antenna can be controlled to effectively zoom by changing the electronic characterization of the beam.

High-resolution is focused over a narrow region. In ice monitoring, for example, it's necessary to cover a wide area of the ocean. "You want maximum area coverage and don't care about resolution of the image," Rae says. "An intelligence analyst, however, looking for something like a new building will know the area, so he won't want wide coverage, but he will want fine resolution."

The ultra-fine resolution mode on RADARSAT-2 acquires images at a spatial resolution of three meters. In this mode, the radar operates with the highest sampling rate, so the ground coverage is limited (between 10km and 30km) to keep the acquisition within the recording limits. It can detect targets that are closely spaced and provide enhanced definition of other targets, reducing ambiguities.

Another improvement over RADARSAT-1 is in data polarization (polarimetric data). The original satellite provided only horizontal-transmit and horizontal-receive (HH) data. RADARSAT-2 can transmit horizontal (H) and vertical (V) polarizations and, depending on the selected mode, the sensor receives either H or V signals or both simultaneously. It generates products with VV polarization, cross-polarization (HV or VH), dual-polarization (HH+HV or VV+VH) or even quad-polarization (JJ+VV+HV+VH) over a range of spatial resolutions, allowing a better fit for each application.

RADARSAT-1 has wide-area coverage with its large accessibility swath, however, the revisit time for some latitudes can be limiting in some applications. Left- and right-looking modes on RADARSAT-2 reduce the revisit time by half while doubling the accessibility swath. In addition, in emergency situations, the choice of beam mode and position can be set to ensure the greatest repeat coverage of the region of interest.

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