Abstract Along with the development of SAR technique, imaging function cannot satisfy the requirement of the application of SAR systems in military and civil areas. Multi-function has become an important tendency of SAR. In this chapter, the development of SAR systems, GMTI and GMTIm algorithms are introduced, and the structure of this book is shown.
Development of SAR
SAR is originally designed as an advanced imaging sensor of high resolution, which is able to provide a high resolution 2-D radar image of a wide swath [1, 2]. SAR system acquires a high range resolution by transmitting and compression a large time-bandwidth product LFM signal, and achieves a high azimuth resolution by using the synthetic aperture technique [3-5]. Compared with optical remote sensing, SAR has the advantages of all-time, all-weather, and is also able to detect covered targets with the advantages of microwaves. By receiving and processing echoes with different polarizations, SAR is also capable of classifying and recognizing targets with different surface structures and materials [6, 7]. Based on these advantages, SAR is widely-used in civil and military areas .
SAR technique is firstly invented in the 50s, 20th century. Carl Wiley from Goodyear Company proposed the idea of increasing cross-track resolution by analyzing the Doppler spectrum of the echo on June, 1951. This idea is then named as DBS . In 1953, Illinois University proved the effectiveness of DBS technique by non-coherent radar experiment. Meanwhile, another team from this university acquired the first un-focused SAR image on July, 1953 . Willow Run Lab from Michigan University and the U.S. Army collaborated on the SAR system research and acquired the first focused SAR image by using the optical signal processing on August, 1957. Since then, the concept and principle of SAR was widely-known, and the application of SAR system was developed.
Based on the platform, SAR systems can be classified into spaceborne and airborne SAR. Along with the improvement of radar systems, other platforms, such
© Springer Nature Singapore Pte Ltd. 2017
J. Yang, Study on Ground Moving Target Indication and Imaging Technique of Airborne SAR, Springer Theses, DOI 10.1007/978-981-10-3075-8_1
as UAV-borne SAR [11, 12], aeroboat-borne SAR  and missile-borne SAR [14-16], are also developed. The research on spaceborne SAR started on 70s, 20th century. The first SAR satellite Seasat-A [17, 18] was launched on May, 1978 by NASA, which was capable of providing radar images from space [19-21]. Afterwards, SIR-A, SIR-B, SIR-C/X and Lacrosse series  were launched by the U.S. On March 1991, Almaz-1 SAR was launched by Soviet Russia. ERS-1, ERS-2 and Envisat-1 [23, 24] were launched by the European Space Agency (ESA). JERS-1 and L-band PALSAR were launched on February 1992 and 2006 by Japan, respectively. RadarSat-1 [25, 26] and RadarSat-2 [27, 28] were launched by Canada on 1995 and 2007, respectively. In 2007, German successfully launched TerraSAR-X [29-31], and are researching on the Tandem system . China, Italia, Israel, and India have also developed their own spaceborne SAR systems. The advantages of spaceborne SAR include: firstly, spaceborne SAR has wide swath, which is highly suitable for the ocean observation; secondly, the orbit of spaceborne SAR is steady, which is suitable for InSAR and Spotlight SAR modes.
Compared with spaceborne SAR, airborne SAR has the advantages of flexible working mode and simple system. Moreover, airborne SAR can be utilized to observe the interested area repeatedly without the constriction of revisit time. In 1966, a L-band airborne SAR was invented by Jet Propulsion Laboratory, which is installed on CV-900 of NASA. After sixty years’ development, the performance of airborne SAR is high improved, the resolution has been rise from 15 to 1 m , and new working modes, such as InSAR, scan-SAR, spotlight SAR and polarize SAR have been invented. At present, many countries, such as U.S., German, Canada and China have their own airborne SAR systems, for instance, Lynx, HiSAR, AN/APG-76 of U.S., E-SAR, PAMIR of German, and so forth. Up to now, the airborne SAR is still the most widely-used SAR system in the world.
China started its research on SAR systems in 70s, 20th Century. The first SAR image was obtained by Institute of Electronics, Chinese Academy of Science in 1979. Tsinghua University, Beijing University of Aeronautics and Astronautics, Beijing Institute of Technology and Xidian University have also published lots of researches on SAR technique. With these researches, the performances of SAR systems in China are improved, the finest resolution is up to 0.1 m .
Along with the development of the hardware and signal processing technology, the developing tendencies of SAR systems are as follows.