A Novel Imaging Algorithm for Focusing High-Resolution Spaceborne SAR Data in Squinted Sliding-Spotlight Mode

To process squinted sliding-spotlight synthetic aperture radar (SAR) data, the azimuth preprocessing step based on the linear range walk correction (LRWC) and de-rotation operations is implemented to eliminate the effect of two-dimensional (2-D) spectrum skew and azimuth spectral aliasing. However, two key issues arise from the azimuth preprocessing. Firstly, the traditional chirp scaling (CS) kernel is not suitable for data focusing because the property of 2-D spectrum is changed significantly; secondly, the spatial variation of the targets’ Doppler rates along the azimuth direction due to the LRWC operation limits the depth-of-azimuth-focus (DOAF) seriously. In this letter, a modified accurate CS kernel is derived to realize range compensation. Thenˈan azimuth spatial variation removing method based on the principle of nonlinear CS (NLCS) is proposed to equalize the Doppler rates of the targets located at the same range cell, which can extend the DOAF and improve processing efficiency. Finally, a novel imaging algorithm is proposed, with its effectiveness demonstrated by simulation results.