Reciprocal path imaging: A technique for the mitigation of image degradation due to atmospheric turbulence

A naturally-occurring, conjugate-wave phenomenon in mono-static laser imaging applications is caused by reciprocal scattering paths which experience identical phase delays during the double passage of an electromagnetic wave through a random phase screen or turbulent medium. This opposition effect or enhanced backscatter phenomenon is known to be caused by constructive interference between reciprocal multiple scattering paths. Reciprocal path imaging (RPI) is an attempt to exploit this phenomenon for obtaining diffraction-limited images of extended objects obscured by a random phase screen or turbulent atmosphere. We report upon our current effort to investigate RPI with sparse array receivers and its potential as a mechanism for achieving high-resolution imaging through a turbulent atmosphere without the use of adaptive optics for image compensation. Preliminary work is reviewed and several RPI concepts to be evaluated in the laboratory are discussed