Inverse synthetic aperture ladar imaging algorithm for spinning targets

Due to the limitation of the laser modulation technique and the interference of the atmospheric turbulence, inverse synthetic aperture ladar (ISAL) has the problems of azimuth Doppler ambiguity and echo noncoherence when imaging a spinning target. Meanwhile, the large relative rotation angle of the spinning target results in a poor correlation between adjacent echoes that makes the present phase error compensation methods fail to work. Hence, the traditional coherent integration algorithms are incapable to obtain a well-focused 2-D image. In order to solve these problems, the envelope of the echo is considered for imaging. The ISAL imaging geometry of a spinning target is established, and the characteristic of the echo is analyzed. An ISAL imaging algorithm based on the generalized radon transform (GRT) is proposed for spinning targets. Firstly, the spinning velocity of the target is estimated by autocorrelation with the range-compressed envelope in the range-slow-time domain. Then, noncoherent integration with the range-compressed envelope is realized by using the GRT, and hence the 2-D image of the spinning target with high resolution is obtained. Since the phase is not used in imaging, the phase errors are avoided. Simulation results show that, the traditional range-Doppler algorithm fails to work, while the proposed algorithm successfully obtained a well-focused ISAL image in the case of low signal-to-noise ratio, Doppler ambiguity, and echo noncoherence.