Vol. 129, No. 1 * Pages 1–105 * January - March 2025

This research aims to evaluate a quantitative comparison of the visibilities detected by three different methods: (i) human eye-based observations; (ii) calculated from the measured values of forward scatter visibility sensor; and (iii) evaluated from ceilometer’s vertical backscattering profiles. Visibility data observed at two meteorological stations, Pestszentlőrinc and Szeged (Hungary) were analyzed. The paper focuses on the fog events observed during the periods of October-December in 2019 and November 21-24 in 2020. The results reveal that the visibility observed by the three methods can be significantly different. Comparison of the values of visibility detected by the three different techniques shows, that visibility evaluated from the ceilometer data is the largest, and the human eye-based observation detects the smallest values. Analysis of the data about fog detection (yes or no) reveals that the ceilometer detects significantly shorter duration of the fog than the other two methods.