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. Using an extended Huygens–Fresnel diffraction integral, we have derived analytical formulae that describe a partially coherent array of Gaussian beams passing through an optical target and going back along the entrance way in a turbulent atmosphere. These formulae include the light intensity distribution at the return place, as well as the light intensity distribution and the spatial correlation at the target place. Using numerical calculations, we have studied the effects of laser coherence length and turbulence strength on the interference fringe contrast and the spatial coherence degree at the target place, together with the light intensity distribution at the return place and the system operating range. We have found that the fringe contrast and the spatial coherence degree at the target place decrease with increasing turbulence strength and decreasing laser coherence length. Then the contrast of light intensity distribution at the return place decreases and the difficulties of identification of optical targets grow. The operating range can be as large as hundred kilometres under a weak-turbulence condition, decreasing rapidly to a kilometre level at strong turbulence.

Influence of atmosphere turbulence and laser coherence on the identification method based on interference multiple-beam scanning of optical targets