Transient response characteristics in identification and imaging

Three different solutions to problems in identification and inverse scattering using restricted far-zone scattering data are reviewed and illustrated. The data are restricted in the sense that the frequencies, aspects, and polarizations are limited. All three solutions are based in part on a fundamental time domain viewpoint whereby the far-zone scattering characteristics of any finite object are uniquely summarized by its impulse response waveforms. Insight provided by these waveforms is exploited via geometrical characteristics extracted from steady-state, forced, and free responses of the object. For the present purposes the fundamental importance of signaling waveforms whose wavelengths are within an order of magnitude of the object dimension is demonstrated. The basic methods discussed have been previously identified in the literature as natural resonance estimation, radar imaging from ramp response signatures, and low frequency classification. Related common features, additional insight, and some new results are given. Applications of all three methods to objects ranging from simple to complex geometries are described.