Motion Compensation Of Bistatic Forward-Looking Synthetic Aperture Radar

To get knowledge of topography and targets in front of aircraft, and solve the technical challenge which troubles forward-looking high-resolution imaging for a long time period, is an urgent issue in the field of autonomous landing and autonomous navigation. By setting the transmitter and receiver on different platforms, the orthogonal partition between equi-distance line and equi-DoppIer line can be formed in front of aircraft, thus bistatic synthetic aperture radar (SAR) has the potential of forward-looking high-resolution imaging. Hence, bistatic forward-looking SAR (BFSAR) is the focus of current research.Motion compensation with high efficiency and high precision is of great significance to guarantee high quality image of BFSAR. In this paper, following works involving signal properties, error model, parameter estimation and compensation methods of BFSAR are carried out,1. The range migration properties and Doppler properties of BFSAR are analyzed as well as high-order phase error. The point target spectrum for BFSAR with motion error is derived, and the relationships between motion error and Doppler parameter are established. The work of this part will lay theotical foundation for parameter estimation and motion compensation.2. Using prior information of sensors, converting intensity data into binary data and dividing Radon transform into coarse and fine Radon transform, an improved Radon-transform-based Doppler centroid estimation scheme is proposed, thus Doppler centroid without ambiguity for BFSAR can be obtained with rapid speed. By searching for range walk slope based on the minimum entropy, an iterative scheme of Doppler centroid estimation is proposed, thus the Doppler centroid can be estimated for BFSAR. Meanwhile, the range walk is corrected.3. Combining time-Doppler rate distribution with improved Radon transform, the high-order Doppler parameter estimation scheme is proposed. By detecting slope in time-Doppler rate domain, high-order phase error of BFSAR can be estimated and compensated. 4. The estimation strategy of Doppler rate in low-contrast scene is proposed. According to the strategy, the Doppler rate in high-contrast scene is estimated firstly by detecting slope in time-frequency domain, and then Doppler rate in full scene can be acquired using the relationship of Doppler rates in different range bins.5. To overcome the problem that conventional wavenumber-domain imaging can not be combined with second-order motion compensation, the extended wavenumber domain imaging based on hyperbolic-equivalent model is proposed, and then high-resolution imaging of BFSAR with large range migration can be realized.Both the simulated and real data are used to verify the proposed methods, and the results show that these methods can be used to estimate Doppler parameter and compensate phase error of BFSAR, and the image quality is improved greatly.