Study Of Ship-borne ISAR Imaging

Inverse Synthetic Aperture Radar (ISAR) is one of the imaging radars. It relieson its transmitting broadband signals to realize the high range resolution, itscross-range resolution is achieved by targets’ rotation and Doppler information,so we can obtain the2-D high resolution images. At the same time the inversesynthetic aperture radar can image all kinds of non-cooperative moving targets,such as aircrafts, ships and missiles and so on, its2-D imaging can be not onlyover a long distance, but also under all day and all weather, so it has importantapplication value in each aspect. Generally speaking, ISAR fixed on the ground,its radar platform is stable, but in recent years people start to study the ISARimaging which is fixed on ships, vehicles and other moving platforms. In thispaper, we study further about the ship-borne ISAR imaging the plane target.There are six different modes of motion when the ship is under the influence ofthe waves, so the radar will follow the ship’s motion movement because the radaris fixed on the ship. Due to the instability of the radar platform, make the resultsof the imaging are greatly affected.Firstly, the turntable imaging model is introduced and the Range-Doppleralgorithm based on the turntable imaging model is derived. Assume that thetarget only exists rotary motion in the horizontal plane, we establish the model oftarget’s scattering points model. And the rotation matrix theory is derived, wealso get the stable platform ISAR imaging simulation results according to therotation matrix theory. The forms of the ship’s movement under the influence aredetailed analysis, and the expression of the ship’s rotation Angle is given.Then, we know that only the ship’s yaw and pitch motion will affect theimaging results through the analysis of the six different modes of motion.Following that the simulation experiment about the ship-borne ISAR imaging theplane target through the RD algorithm is done. The simulation experimentassumes that in one time the ship only exits one form of movement, namely theyaw or pitch respectively, and it achieves the results with different types of shipin different sea. The simulation results show the influence of the ship’s yaw and pitch motion.After the above work, the time-frequency imaging technology is put forwardto apply to the ship-borne ISAR imaging. Time-frequency imaging methodusually is used to solve the problem that the fuzziness of the RD imaging results,and here it is used to solve the influence of the unstable radar platform. Twocommonly used time-frequency transform methods are given in this paper, andthe distance-instantaneous Doppler imaging algorithm is introduced in detail.With the two time-frequency transform methods, we get the instantaneous imagesof the targets, also we can find that the results are good. Finally, we comparedthe simulation results from different imaging methods.