Use of satellite images for fog detection (AVHRR) and forecast of fog dissipation (METEOSAT) over lowland Thessalia, Hellas

In this work, both AVHRR and METEOSAT data are used in order to detect fog areas and to predict fog dissipation. Since fog is created during the night, AVHRR data is used for fog detection at night and METEOSAT data is used for fog observation and fog dissipation forecast during the day over a specific area of Greece, lowland Thessalia. For fog detection at night only the three infrared AVHRR channels are used. The difference between channel 4 and channel 3 is used to distinguish fog or low stratus from land and sea. A cloud classification method applied in this work is based on multispectral box classification. Classification classes are fog and low clouds, sea, land, middle and high clouds. There is also a class for unclassified pixels. For fog dissipation detection, the visible channel of METEOSAT is used, normalized according to the vertical Sun viewing angle. Fog persistence after the first morning calculations is examined versus fog duration. Also, the percentage of the same area affected by fog in the following hours is examined versus fog duration. A case study is presented and the results of the method are discussed.