Sensor Fusion for the Observation and Nowcasting of Winter Weather Condition

Despite advanced technologies, modern air traffic can be considerable derogated with adverse weather conditions like thunderstorms and snow fall. Although, adverse weather conditions can't be impeded, it is possible to reduce the impact on aviation, especial in the terminal area. Even though numerical weather forecast is able to provide reasonable forecasts, nowcasting applications based on observations are necessary to perform short term forecasts on a time range up to one hour. While there exists a number of algorithms for the identification, tracking and nowcasting of deep convection; techniques for nowcasting of winter weather conditions like the transition of rain to snow (and vice versa) or the occurrence of freezing rain and drizzle are rare. Dual-polarization radar has shown that fuzzy logic algorithms allow classifying hydrometeors in distinct classes. However, some uncertainty exists in the distinction between light rainfall and light snowfall. The identification of super-cooled liquid water is a priori not possible. The knowledge of temperature can help in this situation, but often observations are not available with the desired quality and for three-dimensional the region of interest. Further uncertainty is caused by the fact that scanning weather radar does not measure at the surface but at several hundred meters above the surface.

With the fusion of different sensors like dual-polarization weather radar, vertical pointing radar, temperature measurement at the surface and from aircraft it is possible to improve the detection of the transition from rain to snow or freezing rainfall. We will present a novel technique to identify winter weather objects based on a fuzzy-logic orientated approach of the fusion of the instrumentation available in the terminal area of Munich airport. The key instruments are the C-band dual-polarization weather radar POLDIRAD, vertical pointing micro rain radar, optical disdrometer and temperature measurements at the surface and from aircraft.