Imaging Technology At Sea Clutter-speed Moving Target ISAR

The radar imaging technology is very valuable for military and civilian application. Considering the needs of the development of science and technology and national security, it is essential to study the radar imaging technology of high speed moving target. In this thesis, the main work is to study the inverse synthetic aperture radar (ISAR) imaging technology of high speed moving target. Since the high-speed and low-altitude target is often influenced by strong sea clutter, this thesis also carries out a study on sea clutter. The main work of this thesis is summarized as follows:1. The accurate echo model of ISAR for moving target is introduced, based on which the "stop and go" and "first-order approximation" models are summarized. Then, the matching functions of high speed moving target echo are constructed corresponding to these two kinds of echo model. According to the focusing results of the one-dimensional range profile, the most suitable echo model is chosen for high speed moving target imaging.2. The theory of high speed moving target ISAR imaging has been elaborated completely. Firstly, the process of estimating motion parameters and echo coherence has been done. Secondly, the correction of migration through resolution cell has been accomplished. The autofocus algorithm is utilized to remove the parameter estimation error and the influence of azimuth high order residual phase. Finally, the focused image is obtained. Considering that the autofocus algorithm is used repeatedly in the process of imaging, its performance has a great impact on the final imaging results. An improved autofocus algorithm named weighted eigenvector autofocus method is presented in this thesis, which has a better performance than dominant scatterer autofocus algorithm and traditional phase gradient autofocus algorithm under the condition of low signal-to-noise ratio.3. The high speed target flying with low altitude is often influenced by complicated sea clutter, so the sea clutter simulation is studied. A more efficient clutter simulation method is introduced, which is named gaussian variable weighted sum of productions. Subsequently, the one-dimensional and two-dimensional coherent K distribution simulation theory of sea clutter is given. Finally, the imaging results of high speed targets are shown under the condition of different signal-to-clutter ratio and low-grazing angle.