Abstract:The imaging of ship targets is an active area in ISAR research field. Its key is to obtain the valuable side view and top view ship images. In this paper, by measuring the Doppler spreads and the centerline slopes of the ship from a sequence of sub-images generated with successive short time data, the variations of the resultant effective rotation vector and its vertical component are estimated. Subsequently, the sea state and the rock intensity of the ship are evaluated according to the two estimated rotation vectors, and the imaging processing is separate into several different cases. In each case, the imaging instants for ship side view and top view are determined. At the same time, the optimal duration centered with the chosen instant is searched by minimizing the image entropy. Simulated data and real data verify the effectiveness and practicability of the method. The ship top view or side view image can be obtained under unknown sea state, which much benefits the subsequent ship identification.