Interferometric synthetic aperture detection of sparse non-surface

Abstract

A technique for detecting non-surface objects from a moving platform using radiant ranging. The platform moves perpendicular to a line through a pair of first and second transducers. A transmitter repeatedly transmits a radiant signal via a first transducer. The return reflection signals in both transducers include return reflection signals from sparse non-surface objects in the presence of surface clutter reflections. Respective synthetic aperture complex images of resolution cell in slant range and Doppler frequency are formed from the received reflections of the two transducers. The complex phase factor between received reflections for each resolution cell in the absence of non-surface objects is determined. This is feasible because the non-surface objects are sparse, that is rare and generally encountered individually. Each resolution cell of the first synthetic aperture complex image is multiplied with the complex conjugate of the corresponding resolution cell of said complex phase factor. The resulting product signal is subtracted from the second synthetic aperture complex image. The resulting signal is non-zero (except for second order effects) only in the presence of a non-surface reflecting target. The technique may employ a third transducer permitting detection of non-surface objects at otherwise blind heights.