Study Of General Bistatic SAR Properties And Image Formation

With separation of transmitter and receiver, bi- and multi-static synthetic aperture radar (SAR) could provide more abilities and more performance, such as resolution improvement, extended mapping swath, elevation information acquirement and moving target detection, and so on, than the mono-static SAR system. The general Bi-SAR system, which has different velocities of transmitter and receiver, is the heading of development in the future because of its flexibilities and more abilities. However, the new system is azimuth variant. And the new radar imaging theories with regard to the new system receives increasing interest in the past few years.This thesis focuses on signal processing theories for general bi-static SAR system which is azimuth variant with different velocities of transmitter and receiver, with respect to system characteristic and general bi-static SAR imaging.Elementary problems for general bi-static SAR imaging, such as signal model and characteristic of echo, are studied in Chapter 2. Based on the study of movement of transmitter and receiver, the changing travel-distance of electromagnetic wave and its azimuth variance are analyzed. Then the calculation of Doppler centric frequency and Doppler FM rate of general bi-static are given and their azimuth variance is analyzed. These are the basis of the following work.The two-Dimensional point target spectrum for general bi-static SAR is derived in Chapter 3. The instantaneous Doppler contribution ratio is proposed to represent the difference between the instantaneous Doppler contributions of transmitter and receiver. By this, the problem of double square roots included in bi-static phase is reduced to solving two individual weighted stationary phase equations. Then the two- Dimensional spectrum is obtained by using the stationary phase principle and Taylor series expansion for general bi-static SAR. The derived spectrum is also compared with the existing ones for general bi-static SAR. The analysis shows that our spectrum has the better precision, more applicability and more concision comprehensively. It will be useful for developing efficient bi-static algorithms operating in the two-dimensional frequency or the range Doppler domains.The general bi-static SAR focusing algorithms are studied in Chapter 4. Firstly the two-dimensional special variance of the spectrum is analyzed. Then, on the trait that the spectrum could be regard as the scaled Fourier transform of the echo, the Chirp-Z algorithm is proposed for general bi-static SAR. It used inverse Chirp-Z transform twice to solve the problem of range and azimuth variance for general bi- static SAR. Only the Fourier transform and multiplication of complex number are used, so the Chirp-Z algorithm is an efficient imaging method for general bi-static SAR.Spaceborne/airborne hybrid bi-SAR system characteristics and imaging method are studied in Chapter 5. For sliding spot mode the spatial relationship of transmitter, receiver and targets is analyzed, echo of the target is modeled for hybrid bi-SAR and the Doppler parameters are derived. The results are basis of the hybrid bi-SAR system implementation. For hybrid bi-SAR imaging the proposed algorithm is applied. It is verified to work well in the case of spaceborne/airborne hybrid bi-SAR by simulation results.Azimuth invariance SAR imaging is studied in Chapter 6. For high squint and bi-static angle SAR it is difficult to obtain a precise spectrum of echo, which leads to difficulty in setting up effective algorithm. The proposed spectrum is applied and the RMA algorithm is proposed for high squint and bi-static angle SAR. The simulation results show that it work well in the case of high squint and bi-static angle SAR. For low squint bi-static SAR the CS algorithm is proposed and verified by simulation.