This paper considers an active vision system with spaced light source and receiver that simulates illumination and observation conditions typical for a car driver in fog. The objects of the investigations are image contrast and limiting visibility range for a characteristics non-Lambertian target, namely for a retroreflector. Calculations are made for a Gaussian angular dependence of its radiance factor centered near the direction opposite to the incident light direction. We concentrate our attention on studying effects of the angular retroreflectance scale on contrast and limiting visibility range of such a retroreflective marker. Here is shown the optimal retroreflective characteristics to exist that provide the maximal contrast and the best visibility of the marker under other equal conditions. The estimations of the angular scale are presented for various practical situations. The limiting visibility range values of retroreflective and Lambertian markers are compared.
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