# SAR Ground Moving Target Indication and Imaging Theory

**Abstract **This chapter mainly introduces the basic principles of SAR imaging, signal model, GMTI and GMTIm algorithms. The geometries of stationary and moving targets are established, and the characters of their echoes are analyzed. Based on the analysis, three classical single-channel GMTI algorithms are introduced in this chapter, and their limitations are discussed. Moreover, the principle of GMTIm algorithms with Keystone transform and time-frequency analysis algorithm is introduced, and the limitations in Doppler centroid ambiguity and motion parameter derivation are studied.

## Introduction

Signal modeling and phase analyzing are the basis of SAR GMTI and GMTIm theories. Both the characters and processing problems of moving targets in real data can be explained by the signal model. Therefore, it is necessary to study on the signal model in the beginning of this book. After modeling the echo signal of a moving target, a detailed analysis of the impact of motion parameters on the echo phase in this chapter, and the different characters of moving targets with different motions, which are both the problems and clues of GMTI and GMTIm algorithms, are discussed.

In real applications, single-channel SAR systems still outnumber multi-channel SAR systems in China, due to the high expense and complex system structure of a multi-channel SAR system. In the signal processing point of view, the performances of multi-channel GMTI algorithms are higher due to the expense of complex system structures and algorithms. Although single-channel GMTI algorithms have been studied for years, there are many problems in real applications, considering the unknown and complex motions of moving targets. Compared with spaceborne SAR, airborne SAR has a lower speed and a higher resolution, which endows airborne SAR a lower detectable speed and a finer indication pixel. Therefore, this book mainly focuses on the single-channel GMTI and GMTIm algorithms of airborne SAR systems.

© 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_2

In this chapter, the signal model of a moving target is established, and the principles of several traditional single-channel GMTI and GMTIm algorithms are introduced, which is organized as follows. In Sect. 2.2, the principle of a SAR system is briefly introduced, and the signal model of a stationary target is established. In Sect. 2.3, the signal model of a moving target is established, and the relationship between the echo property and the motions is deeply analyzed. In Sects. 2.4 and 2.5, traditional single-channel SAR GMTI and GMTIm algorithms are presented respectively, and their limitations are discussed. Finally, conclusive remarks are provided in Sect. 2.6.