7 October 2014 Turbulence mitigation methods and their evaluation
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In general, long range detection, recognition and identification in visual and infrared imagery are hampered by turbulence caused by atmospheric conditions. The amount of turbulence is often indicated by the refractive-index structure parameter Cn2. The value of this parameter and its variation is determined by the turbulence effects over the optical path. Especially along horizontal optical paths near the surface (land-to-land scenario) large values and fluctuations of Cn2 occur, resulting in an extremely blurred and shaky image sequence. Another important parameter is the isoplanatic angle, θ0, which is the angle where the turbulence is approximately constant. Over long horizontal paths the values of θ0 are typically very small; much smaller than the field-of-view of the camera. Typical image artefacts that are caused by turbulence are blur, tilt and scintillation. These artefacts occur often locally in an image. Therefore turbulence corrections are required in each image patch of the size of the isoplanatic angle. Much research has been devoted to the field of turbulence mitigation. One of the main advantages of turbulence mitigation is that it enables visual recognition over larger distances by reducing the blur and motion in imagery. In many (military) scenarios this is of crucial importance. In this paper we give a brief overview of two software approaches to mitigate the visual artifacts caused by turbulence. These approaches are very diverse in complexity. It is shown that a more complex turbulence mitigation approach is needed to improve the imagery containing medium turbulence. The basic turbulence mitigation method is only capable of mitigating low turbulence.
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Adam W. M. van Eekeren, Adam W. M. van Eekeren, Judith Dijk, Judith Dijk, Klamer Schutte, Klamer Schutte, "Turbulence mitigation methods and their evaluation", Proc. SPIE 9249, Electro-Optical and Infrared Systems: Technology and Applications XI, 92490O (7 October 2014); doi: 10.1117/12.2067327; https://doi.org/10.1117/12.2067327


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