Ground Moving Target Indication and Imaging in WAS Mode
Abstract This chapter mainly discusses the GMTI and GMTIm algorithms in WAS mode. The signal mode of moving target is established in WAS mode, and a new system design scheme is presented to maintain the sharpening ratio constant without increasing the system and signal processing complexity. Moreover, a real-time DBS algorithm is proposed based on CZT, and a GMTI and motion parameter estimation algorithm based on multiple revisits has been presented. Finally, simulations and real data have been utilized to prove the effectiveness of these algorithms.
Besides the stripmap SAR mode, scan mode is also a typical working mode of a SAR system. Different from the fixed antenna LOS in the stripmap SAR mode, the LOS scans with a rotating speed along the azimuth direction in the scan SAR mode. Therefore, larger observation areas can be obtained in the scan SAR mode under the same observation time. Also, the reciprocation of the antenna allows the system to revisit the same target, and more information of the target can be acquired to the target indication and imaging. Based on these two advantages, scan SAR mode is more suitable for moving target processing compared with the stripmap SAR mode, and it is also called WAS mode.
WAS mode can be classified into phased-array scanning mode and mechanic scanning mode. In the phase-array scanning mode, the LOS is controlled by altering the phase of the transmitted signal in each channel, and multi-channel signal receive can be realized . However, the phase-array antenna is relatively expensive, and the signal processing burden is very heavy. The mechanic scanning mode achieves azimuth scanning by mechanic rotation of the single antenna. The antenna control accuracy of the mechanic scanning mode is worse than the phased array scanning mode, but it has a simpler system structure, and can be achieved using the same stripmap SAR system. Therefore, this chapter mainly focused on the mechanic scanning mode.
© 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_4
In the mechanic scanning mode, the traditional RD and CS algorithms of the stripmap SAR mode cannot be used to acquire a focused SAR image. DBS algorithm is used to improve the azimuth resolution. This chapter firstly analyzed the geometry and signal model in the mechanic scanning mode, and the principle and processing steps of the DBS algorithm are introduced. To maintain the sharpening ratio constant, a system design scheme suitable for the airborne SAR mechanic scanning mode is presented, and a real-time DBS imaging algorithm based on CZT is proposed. Since the GMTI processing in the mechanic scanning mode is operated in the imagery domain, the qualities of the images are highly important for the indication.
In the phased-array scanning mode, the indication and parameter estimation of a moving target is achieved by using multi-channel GMTI algorithms, such as DPCA. However, these algorithms are not suitable for the mechanic scanning mode since only single-channel images can be obtained. To solve this problem, a GMTI and parameter estimation algorithm based on multiple revisits is proposed in this chapter. The indication of the moving targets in each image is achieved by the Spectrum filtering algorithm, and the motion parameters are estimated by using the location changes of the targets between each image. Real SAR data is used to prove the effectiveness of this algorithm.
This chapter is organized as follows. In Sect. 4.2, the signal model and the system design scheme are discussed. Section 4.3 introduces the proposed algorithm based on CZT. In Sect. 4.4, the GMTI and parameter estimation algorithm based on multiple revisits is presented. Finally, conclusive remarks are provided in Sect. 4.5.