Far-field laser spot image detection for use under atmospheric turbulence

Abstract. In wireless laser communication, the effects of atmospheric turbulence cause laser spots to appear as irregular speckles in the far-field plane, which may make automatic acquisition, pointing, and tracking systems unable to locate a spot position. We propose an innovative and precise anti-interference, spot-detection algorithm for far-field irregular speckles based on the intensity characteristics of the far-field spots. Before obtaining the spot center coordinates through two-dimensional vector space circle fitting, the proposed algorithm employs computer graphics combined with mathematical morphology to fill the connected domains and extracts light-spot edges using the Canny operator, thus resulting in an accurate detection of far-field spots. The algorithm validation, using an automated experimental platform (atmospheric turbulent refractive-index structure parameter Cn2 is 10  −  15  m  −  2/3), yields a detection threshold accuracy of 30 to 32 pixels (each pixel represents 3  μrad) for 10.2 km far-field spot images. The corresponding deviation satisfies the two-dimensional aiming platform for a minimum step distance of 17.45  μrad, verifying the feasibility and effectiveness of the algorithm.

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