Comparison of In-Situ FOG Observations with Insat-3D Satellite FOG Product for North Indian Cities

Low visibility events due to fog cause an adverse impact on transportation in North India during the winter season. In this study, in-situ visibility (METAR) observations and satellite (INSAT -3D) fog product are used to detect the fog for 7 North Indian cities from 2013–2021. Both fog products have a different spatial scale and theoretical background. One should have an idea of an agreement between these two fog data sources before making a combined use. Hence, equivalent visibility for the satellite fog is found out, keeping overall accuracy and Kohen's Kappa coefficient as measures of the agreement. The equivalent visibility for INSAT -3D fog product is 306 m, with an overall accuracy of 0.96 and Kohen's Kappa coefficient of 0.29. The non-fog observations outnumber fog observations and make the dataset imbalanced, leading to a smaller value of Kohen's Kappa coefficient despite a large overall accuracy. The equivalent visibility varies between 161 to 998 m for different cities, indicating some spatial variability altering the agreement.