Airborne ISAR imaging of ship side view

In airborne ISAR imaging of ship targets, the complexity of the ship's rotation relative to the radar line of sight (RLOS) increases the difficulty in achieving high quality ship images. When imaging from long distance, the rotation induced by the tangential motion between the radar and the ship can always be neglected. The images obtained by exploiting the ship's own sway are generally the ship side view. However, when the rotation induced by the relative tangential motion cannot be neglected, the obtained images are the mixture of the ship top view and side view, which are not suitable for the ship recognition. In this paper, a method of obtaining the ship side view images under this circumstance is presented. Its main idea is to estimate the Doppler frequency derivative, which can be approximated by the chirp rate in a short imaging interval. A concentration measure is introduced to increase the estimation precision of the chirp rate in the dechirp process. The effectiveness of the proposed method is verified by the experiments on the simulation data.