CHAPTER THREE
Synthetic Aperture Radar
Synthetic aperture radar (SAR) is a high-resolution airborne and spaceborne remote sensing technique for imaging remote targets on a terrain or more generally on a scene. In 1951, Carl Wiley realized that if the echo signal is collected when the radar is moving along a straight path, the Doppler spectrum of the received signal can be used to synthesize a much longer aperture so that very close targets in the along-track dimension can be resolved [1]. In 1953, the first measured SAR image was formed when a C-46 aircraft was used to map a section of Key West, Florida [2, 3]. The first on-board satellite SAR system was developed by the National Aeronautics and Space Administration (NASA) researchers and put on Seasat in 1978. This remarkable satellite provided a lot of data for oceanographic applications. After Seasat, several satellites carrying SAR systems have been launched by different countries. Russian Almaz (1987), European ERS-1 (1991) and ERS-2 (1995), and Canadian Radarsat (1995) were among some of them. The first space-shuttle mission that has a SAR module was SIR-A (shuttle imaging radar). After SIR-A was launched aboard the space shuttle Columbia in 1981, other spaceborne SAR missions were followed. SIR-B (1984) and spaceborne imaging radar-C/X-band synthetic aperture radar SIR-C/X-SAR (1994) acquired SAR images in multiple frequencies and polarizations for more advanced applications such as interferometric and polarimetric mapping ...
