Sub-aperture imaging in SAR: results and directions

The complex phase history of the synthetic aperture radar (SAR) image can be broken up into a series of overlapping crossrange sub-apertures from which time-dependent information can be extracted from the scatterers that make up the image. The change in the image characteristics from one sub-aperture window to the next can be correlated to generate a stability map of the scene; i.e., areas that change rapidly as the sensor viewpoint changes can be identified. These changes in pixel characteristics over the aperture may be due to many sources: scatterers interfering with each other differently as acquisition geometry is swept out, scatterer sources being created and destroyed as the geometry changes, and aspect-dependent scatterers (e.g. dihedrals) being interrogated differently over the width of the aperture. The stability analysis reported earlier(1) for the peak feature has been extended to arbitrary pixels in the SAR image, and the application of this analysis to other features of interest can be made. An example using measured MSTAR data of the stability of a characterized scatterer from the Slicey phantom, imaged in a self-obscuring state, is presented in the context of the stability analysis. Further generalizations of the approach to polarimetric SAR are also presented.