Bistatic Sar Imaging Algorithm And Motion Compensation

Bistatic SAR is a type of synthetic aperture radar (SAR) , whose transmitting system and receiving system are located on separated platforms. Compared with monostatic SAR, Bi-SAR has several more advantages, such as, acquiring multi-direction electromagnetic scatter information from the target scene far away from the interest zone, the quiet passive receiver being more difficult to be detected and jammed, and low cost of manufacturing the Bistatic SAR system et al. Therefore, Bi-SAR which is used as a new measure to observe the earth in the space will have extensive development in military application or civil application.Based on the need of the systematic research of airborne Bi-SAR, the researches including the Bi-SAR imaging algorithm, motion compensation, time synchronization adjustment are carried out in this dissertation. They are listed as follows:1. The geometry and echoed signal models of airborne bistatic SAR in general flight configuration are introduced. And the theoretical relationship between the resolution and bistatic SAR system parameters is suggested. The imaging model of Bi-SAR is described. All kinds of Bi-SAR imaging algorithms are analyzed and compared. Additionally, their advantages and disadvantages are pointed out.2. A bistatic SAR imaging algorithm based on Chirp-Z Transform is presented, which is suitable for the flight configuration that the transmitter and receiver follow parallel path with equal velocity in broadside looking mode. In the thesis, derived from the geometry model and echoed signal model of this particular flightpath for airborne bistatic SAR, the two dimension frequency spectrum of point target is deduced in detail, and the phase of the frequency spectrum is disassembled into the quasi-monostatic term phase and the bistatic deformation-term phase. The two dimension discrete frequency spectrum is also presented. The quasi-monostatic term is divided into the one with reference to the slant R_0Rcen and the other one with reference to the variable r. Then the method of making use of inverse transform of Chirp-Z to eliminate range migration is deduced. The flowchart of Bi-SAR imaging algorithm based on the CZT is introduced in detail. What's more, the calculation of the CZT algorithm is also analysed. The algorithm is validated by simulation and the real Bi-SAR data. Eventually, the focusing result of Bi-SAR is obtained.3. The airborne Bi-SAR motion compensation technique based on the GPS/INS is presented. The method of how we make use of the parameters provided by GPS to compensate the motion error is proposed. The analysis of motion error groud on the prominent scattering point is introduced.. And then the phase tracking algorithm is proposed. This algorithm designs a series of narrow-band filters to restrain the clutter echo next to the strong scattering point and obtains the estimation of the phase of the strong scattering point. After the phase-unwrapped and the second curve fitting of the phase, the phase error is calculated. It can be used to compensate the motion error to improve the Bi-SAR image. Finally, the Bi-SARω-K algorithm integrating with the phase-tracking is shown and validated by the real Bi-SAR data, obatining the good Bi-SAR image.4. Two situations which result in the time synchronization error are discussed. And the effect of the time synchronization error on the Bi-SAR imaging is analysed. The research on echo signal envelop adjustment is accomplished through making use of the direct-wave signal to extract the range walk unitsΔt_err.The algorithm is validated by simulation and the real Bi-SAR data. In the end, the best result of Bi-SAR is acquired.