DRDC has been involved in the development of airborne SAR systems since the 1980s. The current system, designated
XWEAR (X-band Wideband Experimental Airborne Radar), is an instrument for the collection of SAR, GMTI and
maritime surveillance data at long ranges.
VideoSAR is a land imaging mode in which the radar is operated in the spotlight mode for an extended period of time.
Radar data is collected persistently on a target of interest while the aircraft is either flying by or circling it. The time
span for a single circular data collection can be on the order of 30 minutes. The spotlight data is processed using
synthetic apertures of up to 60 seconds in duration, where consecutive apertures can be contiguous or overlapped. The
imagery is formed using a back-projection algorithm to a common Cartesian grid. The DRDC VideoSAR mode noncoherently
sums the images, either cumulatively, or via a sliding window of, for example, 5 images, to generate an
imagery stream presenting the target reflectivity as a function of viewing angle. The image summation results in
significant speckle reduction which provides for increased image contrast. The contrast increases rapidly over the first
few summed images and continues to increase, but at a lesser rate, as more images are summed. In the case of
cumulative summation of the imagery, the shadows quickly become filled in. In the case of a sliding window, the
summation introduces a form of persistence into the VideoSAR output analogous to the persistence of analog displays
from early radars.