A new look at spotlight mode synthetic aperture radar as tomography: imaging 3-D targets

A new 3-D tomographic formulation of spotlight mode synthetic aperture radar (SAR) is developed. This extends the pioneering work of Munson et al., who first formally described SAR in terms of tomography but who made the simplifying assumption that the target scene was 2-D. We treat the more general and practical case in which the radar target reflectivities comprise a 3-D function. The main goal is to demonstrate that the demodulated radar return data from a spotlight mode collection represent a certain set of samples of the 3-D Fourier transform of the target reflectivity function and to do so using a tomographic paradigm instead of traditional range-Doppler analysis. We also show that the tomographic approach is useful in interpreting the reconstructed 2-D SAR image corresponding to a 3-D scene. Specifically, the well-known SAR phenomenon of layover is easily explained in terms of tomographic projections and is shown to he analogous to the projection effect in conventional optical imaging.