A FUZZY APPROACH TO THE DEFINITION OF STANDARDIZED VISIBILITY IN FOG

The problem of defining the physical concept of standardized visibilit y is addressed by means of a fuzzy logic approach. Assuming that sever al hypotheses hold, it is possible to evaluate a standardized visibili ty V(k) (or meteorological visual range) as the ratio of a psychometri c coefficient k and the extinction coefficient sigma of the aerosol. T he main disadvantage of this relationship due to Koschmieder [7] stems from the fact that the meteorological visual range can be very differ ent from visibility estimated by a human observer with normal sight. T his is particularly true during fog occurrences. A fuzzy approach is u sed to evaluate a relationship between the fog extinction coefficient supplied by a transmissometer and the corresponding visibility evaluat ed by an expert. Calculations are performed according to two different approaches. First, a so-called fuzzy hyperbolic model based on a dist ance defined by Bardossy et al. [2] is presented, yielding a crisp (no nfuzzy) value of the coefficient k. Next, we use the multiplication of two fuzzy numbers, taken as triangular, to build an average fuzzy num ber k that accounts for the different values found in the literature. The defuzzification of k confirms the result obtained by the first app roach.