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

To process squinted sliding-spotlight synthetic aperture radar data, the azimuth preprocessing step based on the linear range walk correction (LRWC) and derotation operations is implemented to eliminate the effect of 2-D spectrum skew and azimuth spectral aliasing. However, two key issues arise from the azimuth preprocessing. First, the traditional chirp scaling (CS) kernel is not suitable for data focusing because the property of the 2-D spectrum is changed significantly; second, 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. Then, an azimuth spatial variation removing method based on the principle of nonlinear CS 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.