Study On ISAR Imaging Of Ship Targets

Inverse synthetic aperture radar (ISAR) has the capability of getting high resolution images of noncooperative targets at long range under all weather and all day, so it is with great military and civil values. The detection and recognition of targets on the sea (such as ship targets) is an active topic in ISAR study all over the world. The airborne ISAR imaging of ship targets depends on the ship's rotation relative to the radar line of sight (RLOS), which is constituted by two parts: the relative tangential movement between the radar and the ship; and the ship's own sway. Moreover, the practical sea-state changes frequently and is unpredictable. All of these increase the difficulty in achieving high quality images. In this article, some technologies of ISAR ship imaging are mainly discussed.In the preface to this dissertation, the development of the ISAR is introduced briefly. Subsequently the Range-Doppler principle and many kinds of methods for motion compensation and imaging are detailed. Finally, the main contents of this thesis are summarized.Range alignment of ISAR motion compensation is studied in Chapter 2. A method by minimizing the entropy of the average range profile is mainly intrcduced. At last the method is compared to the traditional range alignment methods to demonstrate its validity and effectiveness.When the rotation induced by the relative tangential movement between the radar and the ship cannot be neglected, the images obtained by RD method are the mixture of the ship top view and side view, which are not suitable for the ship recognition. A method to obtain the ship side-view images under this circumstance is presented in Chapter 3. The side-view images are obtained by formatting the derivative of the Doppler frequencies, which are estimated from the echoes. Side-view images are very important in recognition of ship targets. At last, some results under certain simulation environments are presented.Chapter 4 exposits a method of optimum time selection for ship ISAR imaging and scaling for ship images when the depression angle can not be neglected. It is based on the estimation of the ship motion in horizontal and vertical components. Proper imaging intervals in order to obtain high quality ship images are selected using the estimated rotating angular velocity. At the same time, the scaling of the obtained ship images will be easily done. In the end, conclusions and future work are explained.