Scientists of the Institute of Atmospheric Physics performed measurements with a laser instrument - a Lidar - at the highest mountain of Germany the Zugspitze. Within the next years this lidar (light detection and ranging) will fly on a satellite of the European Space Agency ESA within the frame of the Atmospheric Dynamics Mission (ADM-Aeolus). The study was performed at the unique mountain observatory – the research station Schneefernerhaus at an altitude of 2650 m. Objective was the measurement of the physical properties of the scattering on molecule with an extremely stable laser in the atmosphere.
The scientists point their laser beam above the white mountain summits of the Alps into the clear and deep blue sky, resulting from the Rayleigh scattering of sun light on air molecules. Although this effect was discovered by Lord Rayleigh already in 1871, it was not possible up to now to measure the wavelength spectrum of Rayleigh scattering precisely in the atmosphere. It is known from laboratory measurements, that the spectrum is almost a Gaussian curve due to the thermal motion of the molecules. Small deviations from the Gaussian curve by a few percent are caused by density fluctuations in the atmosphere. The scientists want to determine this effect with a laser, which scans the spectrum with more than 200 observations with a distance of only 20 femtometer (one femtometer corresponds to 10-15 m). The exact knowledge of the spectrum is relevant for future lidar instruments on satellites, like the first worldwide wind lidar on ADM-Aeolus or the aerosol lidar on EarthCARE.