Detection of Day Time Fog Over India Using INSAT-3D Data

A simple and new fog detection algorithm using any geostationary satellite data that is having at least one visible and one thermal channel is developed. The visible channel observation is used to detect fog, whereas the thermal infrared channel data are used to eliminate the medium/high clouds and snow area. This method is based on temporal differencing technique. Thresholds used in this technique are derived dynamically for each data. It also includes the spatial homogeneity test, which is a unique characteristic of fog. The algorithm is tested with half hourly data of INSAT-3D imager from 0400 to 0930 UTC of 2013–2014 winter months. The fog maps were validated with visibility data available at hourly interval for five different locations over the Indo-Gangetic plains of India for January 2014. The main advantage of this algorithm is its capability to detect day time fog without using the $3.9\hbox{-}\upmu {\text {m}}$ channel, which is having both emissive and reflective components during day time. This technique is found to have potential for operational use.