Motion-Extended Array Synthesis—Part III: An Offset Imaging System Perspective

Motion-extended array synthesis (MXAS) is a concept for the realization of a 1-D or 2-D synthetic array, accomplished specifically without recourse to a reference waveform. The essential idea is that the relative motion between a minimum of two collection platforms with different velocity vectors can be exploited to create a virtual array, the size of the virtual array being the space swept out by the relative motion of the collectors. From fundamental imaging theory, the process is properly described as an offset imaging system (OIS) for which the range of baselines engendered is similar to that for a real aperture of the same size, but is offset by some potentially very large distance. For a far-field scenario, this may be equivalently described in terms of spatial frequencies, with the real and virtual imaging systems differing by the presence (in the latter) of an offset spatial frequency. We show that the MXAS construct is properly understood as an OIS, the MXAS processing method yields a form of the principal solution for an OIS, and the MXAS method is advantageous relative to conventional aperture synthesis processing measures, for an OIS. We consider imaging performance implications due to the offset nature of the imaging system, for spatially coherent and incoherent scenarios, and conclude that for many applications of interest, the process introduces no appreciable degradation.