Effect of a nonplanar wavefront in spotlight-mode synthetic aperture radar

The tomographic formulation of spotlight-mode synthetic aperture radar (SAR) is based on a plane-wave assumption that requires the dimension of the target scene to be much smaller than the range to the target. When this assumption is violated, the resulting image exhibits target smearing and target shift. For severely squinted SAR operation, which arises in runway imaging (for aircraft landing applications), the authors have observed that the smearing is not serious, but that targets are shifted considerably from their correct locations, especially for targets near the edges of the scene. They analyze this problem by first deriving an expression for the spatial shift of a reconstructed point reflector for bandpass Fourier data with phase error. Then, they analyze the point target shift in squint-mode SAR, by incorporating the higher-order terms of the range function. Simulation results for isolated point reflectors are presented