The Effects of Aberrations in Synthetic Aperture Systems.

Recent interest in the use of synthetic aperture optical systems for astronomical and reconnaissance applications prompted this study. The imaging characteristics of a synthetic aperture system consisting of six circular elements positioned on a circle were determined for the case when piston error, tilt, defocus, spherical aberration, astigmatism or coma was introduced into one element of the array. In addition, system defocus was introduced across all elements of the array. The effects of the aberrations on the optical wavefront, the point spread function, and the image of an extended object were determined. The optical transfer function was calculated by a digital computer for the case of small aberrations and was measured experimentally for the case of large aberrations. Synthetic aperture systems produce imagery having an unconventional appearance which is accentuated by aberrations. Special demands are placed on the photointerpreter and on photointerpretation equipment from degrading already low contrast imagery.