Inverse synthetic aperture laser radar imaging algorithm for maneuvering targets

When imaging maneuvering targets using Inverse Synthetic Aperture Laser Radar (ISAL), echo pulses disperse in range and the Doppler frequency varies with the slow time. The conventional Range-Doppler (RD) imaging algorithm is inapplicable of producing acceptable image. To solve these problems, an ISAL imaging algorithm for maneuvering targets is proposed. Firstly, the echo model of ISAL is established for a maneuvering target. Research reveals that, for a uniformly accelerated target, the ISAL signal after optical heterodyne processing can be approximated as a multi-component linear frequency modulation (MLFM) signal with a uniform chirp rate; when the Doppler frequency variation in azimuth can be estimated as a first-order polynomial, sub-echoes in each range cell are MLFM signals with different chirp rates related to the scatterers´ azimuth coordinates. Subsequently, fractional Fourier transform (FrFT) is in use for eliminating the range dispersion´s problem. A method combining FrFT and CLEAN technique (FrFT-CLEAN) are proposed after motion compensation for azimuth imaging. Simulation results demonstrate the validity of the proposed algorithm.