Airborne synthetic aperture radars, or SARs, process radar returns as if they were collected by an antenna as much as several hundred meters long. This "synthetic" antenna aperture is created by the movement of the aircraft itself - which is why airships do not make good SAR platforms - and allows a "parallax view" of the ground similar to a stereoscopic optical image. SARs were developed during the Cold War for their radio frequency ability to provide ground reconnaissance through the clouds and bad weather in Europe, unlike visual, infrared, and even hyperspectral sensors, and for ground moving target indication, which measures the displacement of vehicles and other objects during the radar scan.
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