The authors consider migration based synthetic aperture radar (SAR) imaging of surface or shallowly buried objects using both down-looking and forward-looking ground penetrating radar (GPR). The well known migration approaches devised to image the interior of the Earth are based on wave equations and have been widely and successfully used in seismic signal processing for oil exploration for decades. They have the potential to image underground objects buried in complicated propagation media. Compared to ray-tracing based SAR imaging methods, migration based SAR imaging approaches are more suited to imaging underground objects owing to their simple and direct treatment of oblique incidence at the air-ground interface and propagation velocity variation in the soil. The authors apply the phase-shift migration approach to both constant-offset and common-shot experimental data collected by PSI GPR systems. They address the spatial aliasing problems related to the application of migration to the GPR data and the spatial zero-padding approach to circumvent the problem successfully.