Influence of nonuniform ground reflectance on horizontal visibility

One of the assumptions made in calculating the horizontal visibility of black targets is that every volume element of the atmosphere or medium is illuminated by the same amount of light. This assumption has always been interpreted as a homogeneous illumination, without considering the importance of the reflectance properties of the ground extending between observer and horizon along the path of sight. This paper is a theoretical and experimental study of the effect of ground, with varying reflectance properties, on the horizontal visibility. The laboratory simulation shows that, if that part of the ground extending between observer and target has a higher reflectance than the one extending between target and horizon, the visibility may decrease by up to 15%. In the opposite case, the visibility increases.