ISAR imaging of helicopter

Conventional envelope alignment method of ISAR imaging assumes that the target is a rigid body, and therefore, the correlation between one-dimensional range profiles at neighboring time slots gives a larger value compared to correlation between time separated range profiles. But this is not the case for targets such as helicopter which have rotating body parts. In this paper, an envelope alignment algorithm for helicopter target ISAR imaging is proposed. For every range profile, correlation with other range profiles are done, and the range profiles with larger correlation value are used to provide an initial estimate of the target motion parameters by polynomial fitting. Then the estimated parameters are averaged to get a better estimation. The position of the rotor signals are obtained by taking the difference of the range profiles in the slow time domain. The rotor signals are then suppressed by zero-force windowing technique. Simulation results have shown the effectiveness of this algorithm.