Lidar measurements for the investigation of Rayleigh-Brillouin scattering in the atmosphere

Kurzfassung

The global observation of atmospheric wind profiles remains to be the highest priority need for weather forecast. Therefore, the European Space Agency ESA decided to implement the Atmospheric Dynamics Mission ADM-Aeolus to demonstrate the potential of the Doppler lidar technology for global wind profiling. Thereby, the laser of the Doppler lidar sends short pulses into the atmosphere where they are scattered by aerosols and molecules. Some of the backscattered light is collected by a telescope and analyzed concerning its frequency. The frequency shift between emitted and received light, caused by the Doppler shift of moving particles, is directly proportional to the atmospheric wind speed. The accuracy of this measurement technique is significantly depending on the knowledge of the spectral distribution of the backscattered light from molecules. For the validation and the improvement of spectral line shape models of Rayleigh-Brillouin scattered light, atmospheric lidar measurements have been performed from the mountain observatory Schneefernerhaus. For this, the unique location of the Schneefernerhaus was an eminently advantage which made such kind of accurate measurements possible. During high-pressure weather conditions in wintertime, the altitude of the UFS is usually higher than the atmospheric boundary layer and therefore, the lidar measurements are not disturbed by scattered light from aerosols. Furthermore, a number of in-situ measurement data of temperature, pressure, humidity and aerosol content, performed by the German Weather Service (Deutscher Wetterdienst, DWD) and the Federal Environmental Agency (Umweltbundesamt, UBA), is available and can be used to monitor the atmospheric state. Moreover, data from radiosondes daily launched from the airport Innsbruck (~30 km from the UFS) are available. Another advantage is that the UFS allows performing horizontal lidar measurements over long distances. This kind of measurement is favorable as the data of horizontal lidar measurements can be averaged over several kilometers, which leads to an improvement of the signal to noise ratio in the measured line shapes. In addition, despite its remote location, the UFS offers a very good laboratory infrastructure and the possibility of delivering bulky equipment using a cog railway. On my poster, the Doppler lidar principle is introduced and the need of an accurate line shape model for molecular scattered light is demonstrated. The results of the atmospheric measurements performed from Schneefernerhaus are introduced and discussed.