Low-earth-orbit (LEO) synthetic aperture radar (SAR) can achieve advanced remote sensing applications benefiting from the large beam coverage and long duration time of interested area provided by a geosynchronous (GEO) SAR illuminator. In this paper, an imaging method for GEO-LEO SAR is proposed. After analyzing the sampling characteristics of GEO-LEO SAR, it is found that only 12.5 % sampling data can be acquired in azimuth direction. To handle the serious sub-Nyquist sampling problem and achieve good focusing results, an imaging method combined with multi-receiving technique and compressed sensing is proposed. The multi-receiving imaging model is firstly obtained based on the inverse process of a nonlinear chirp scaling imaging method. Then, the imaging problem of GEO-LEO SAR is converted to an L1 regularization problem. Finally, an effective recovery method named complex approximate message passing is applied to obtain the final nonambiguous image. The simulation results show that the proposed method can suppress 8 times Doppler ambiguity and obtain the well focused image with 3 receiving channels.

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