A novel envelope alignment algorithm based on splitting sub-apertures is proposed to improve the problem that it is hard for the envelope alignment to be accurately carried out under the condition of low signal to noise ratio(SNR)in inverse synthetic aperture radar(ISAR). The full-aperture is divided into several sub-apertures with same length
and a linear model is built for envelope error of each sub-aperture. The minimum entropy criterion is used to estimate the envelope error of each sub-aperture. Then a high-order polynomial is used to fit the full-aperture envelope errors
and estimations of sub-apertures are used to successfully achieve the final envelope alignment precisely. Simulation results and comparisons with the traditional envelope alignment algorithms show that the proposed method has advantages in envelope alignment
and the entropy of imaging results reduces by about 0.6 when the input SNR is as severe as -5 dB.
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