Double-passage imaging of partially coherent objects through turbulent atmosphere

The double-passage effects of atmospheric turbulence on the imaging quality and resolution of partially coherent objects are discussed in terms of the information content and number N-d of degrees of freedom of an imaging sys tem. The Karhunen-Loe've expansion of the generalized prolate spheroidal fu nction is used to investigate the effective number of freedom and informati on content of the imaging system. When waves double-passage in week atmosph eric turbulence, the object is placed in the far field of the pupil plane o f the illumination-and-viewing system. If a correlation scare of an object is much larger than the turbulent coherent radius and the radius of the rec eiving aperture is larger than the short-term spread of backscattered propa gated beam, the turbulent spread of the beam will lead to a positive effect , and there is a potential supperresolution that is the resolution (or the number N-d of degrees of freedom) and the quality (or information N-r) of t he short-term imaging of the double-passage imaging system can be higher th an that of the line-of-sight propagation system. (C) 1999 Elsevier Science B.V. All rights reserved.