Is fog really decreasing everywhere? - A new longterm fog climatology for Europe based on cross-generation satellite data from the geostationary orbit (SatFogClim)

• Applicants: Professor Dr. Jörg Bendix; Dr. Sebastian Egli
• Subject Area: Physical Geography ; Geodesy, Photogrammetry, Remote Sensing, Geoinformatics, Cartography
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 449977557

Fog has a high socio-economic and ecological relevance (source of water, obstruction in traffic, destabilisation of power grids, etc.). Due to its high albedo, it also influences the radiation balance of the atmosphere. Also, the exact quantification of the influence of low clouds and fog on the radiation budget of the atmosphere is a major uncertainty factor in the evaluation of future climate scenarios.Current long-term studies on fog occurrence on the basis of station data have shown that (at least) since the 1960s there has been a worldwide decrease in fog frequency. However, these are only punctual observations that cannot capture the influence of different land cover types and are also not very representative for exposed locations in mountain ranges.In order to be able to investigate these influences, the need for a long homogeneous time series of spatially explicit data on fog distribution is growing. The applicants have been able to obtain area-wide information on fog distribution in Europe since 2006 on the basis of a geostationary satellite system (Meteosat Second Generation - MSG). However, this time series is not yet sufficient for climatological studies.Currently, the data set of the predecessor satellite series (Meteosat First Generation - MFG) has been homogenised by intercalibration and adjustment of sensor degradation and is therefore available for scientific evaluation for the period 1982-2004. In principle, the data set is thus suitable for the derivation of a long-term fog climatology, but it must be processed consistently with the much more advanced MSG system.Altogether, two research deficits result: There is no consistent methodology with which a homogeneous fog product (day and night, 30 minute resolution) can be created for Europe for the entire data set of MFG and MSG (1982 until today). It is not clear how fog develops over all areas (low to high altitudes) and in different weather situations (e.g. radiation situations versus advection situations) in the course of environmental change.Based on these research deficits, the following objectives result for the research project: The fog detection method developed by the applicants is to be further developed and adapted to the MFG satellite series (1982-2006) by means of machine learning methods. Based on this, a consistent fog data set with a high spatio-temporal resolution and extensive coverage over the entire time series is to be created, as well as a weather situation-based fog climatology that can be derived from the data set. The data set will also be used to investigate spatio-climatological trends in fog distribution separately for different fog types and depending on topography and land use as well as the prevailing weather conditions.

• DFG Programme: Research Grants