Application of X-band radar and lidar wind measurement at Frankfurt and Munich airports for air traffic management (ATM)

At the international airports Frankfurt (FRA) and Munich (MUC) two high-performance remote wind measurement instruments namely an X-band polarimetric radar and a 1.6 μm lidar has been installed. As a fact of the combination of both sensors the wind field of the atmospheric boundary layer (ABL) at the terminal maneuvering areas (TMA) can be observed in rain as well as in clear air conditions. Initially, the measurements are applied to detect, quantify and alert automatically on the presence of horizontal and vertical low-level wind shear. As a consequence of numerous aircraft accidents due to wind shear ICAO recommends that wind shear information between runway level and 1600 ft AGL shall be updated at least every minute. For the purpose of monitoring wind shear along the glide paths both instruments radar and lidar perform a 3° PPI scan every minute. A volume scan using several elevations is performed every 5 minutes to detect wind at different heights above the airport as well as to observe atmospheric convergences and divergences such as gust fronts or microbursts in the field of sensors view. In general, horizontal wind shear alerts at runway and glide paths (ROSHEAR) are referred mostly of X-band radar data at FRA and MUC since a large amount of horizontal wind shear is related to precipitation; vertical wind shear events are mostly obtained from vertical velocity processing (VVP) wind profiles based on lidar velocity data as a fact of low-level temperature inversions connected with low-level jets. However, the high-resolution wind measurements can also be used as back-up of operational radar measurements and as input for analyzing systems and models as well as for precise time based separation of aircrafts. In order to summarize all available wind data in the vicinity of airports within one domain for MUC a 3D wind prototype is under development (domain: 100 km x 100 km x 10 km, resolution: 1 km x 1 km x 1 km). Basically, X-band radar and lidar measurements are merged by a 3D variational analysis scheme with additional measurements from C-band radar and radiosondes as well as wind retrievals from aircrafts using the selective mode (Mode-S) of the tracking and ranging radar (TAR) at the airport. Comparison studies with model results show a high benefit of the 3D wind system. Further applications are on model assimilation of the velocity fields of the X-band radar and lidar and the additional measurements. For MUC a highly regionalized version of the operational German model COSMO-DE has been developed the so-called COSMO-MUC model (1.4 km, 1h update cycle). During rapidly changing weather precise short-range and now-cast forecasts are important to support the ATM process. In view of improving the prediction quality of very-short range weather forecasts first results of radar and lidar assimilation by nudging show a distinctly higher sensitivity than conventional simulations. Enhanced studies will be on development of now-casting of wind by a linear Kalman filter using the X-band radar and lidar measurements. Instead of assimilating measurements in models, model data could be used for the now-casting of wind. Wind now-casting would be useful information for separation of aircrafts. According to the executive order no. 716/2014 of the European Commission distance based aircraft separation shall be replaced by time based aircraft separation for example at FRA, MUC and Düsseldorf airport. The replacement aims on enhancement of airport capacities by reduction of distances between aircrafts when wind speed thresholds are reached. However, wind speed and wake-vortices dissipation are correlated; when the aircraft head wind component increases wake-vortices dissipate faster thus distances can be reduced. Since the X-band radar and lidar at FRA and MUC are located in such a way that scanning directions are rather parallel of all runways head and tail wind can be approximated precisely. By summary, these high-resolution X-band radar and lidar wind data (1 min, 100 – 150 m radial) are suitable as input for time based aircraft separation.