Synthetic aperture radar (SAR) is a technique that allows high-resolution radar images to be formed from data acquired by side-looking radar instruments carried by aircraft or spacecraft (Curlander and McDonough, 1991).
Synthetic aperture radar (SAR) images are produced by an active system that sends a microwave signal from a sensor platform to the ground and detects backscattered waves that the ground reflects directly back to a receiver on the same platform, which can be borne aloft by either airplanes or satellites. When the source and receiver are on the same platform, the radar is said to be monostatic. If the source and receiver are on different platforms, the radar is said to be bistatic. Commercial SAR systems are monostatic and always collect images to the side of the flight path of the sensor platform, unlike most multispectral imaging systems, which commonly look straight down and are passive (consisting only of receivers of reflected sunlight and emitted thermal infrared radiation).