The Earth's atmosphere: measuring wind with lasers for weather forecasting
Atmospheric wind measurements are very important for climate models and weather forecasting, as the processes in the atmosphere depend very much on the dynamics of the air. Nowadays, atmospheric wind can of course be measured using laser light. The laser light is sent into the atmosphere and the wavelength of the backscattered photons provides information, reference counter, information desk, information counter. Thanks to the Doppler shift, the movement of the air molecules can be determined.
Laser light in the atmosphere is scattered by air molecules (Rayleigh scattering) and by slightly larger particles such as dust, aerosols and soot (Mie scattering). Rayleigh scattering is, for example, the scattering of sunlight in the atmosphere, which can be seen as a blue sky. This scattering depends on the temperature, as the air molecules move more at higher temperatures than at lower temperatures (Brownian motion). Mie scattering can be recognized as the scattering of sunlight in the dustier layer of air 1-2 km above the ground; it can be seen as a red evening sky on the horizon. The Mie spectrum is not temperature-dependent and is very narrow-banded.
70% of the earth is covered by oceans - which makes it impossible to have a uniform distribution or coverage of measuring stations. These measuring stations provide data for weather forecasting and climate research. In order to obtain data from the entire atmosphere, satellites are nowadays placed in orbit around the earth. They use various methods to measure atmospheric parameters such as wind, humidity, pressure and temperature.
The European Space Agency (ESA) has launched a satellite mission to take wind measurements in the Earth's atmosphere in order to collect data for weather forecasting and climate research. The main objective of this Atmospheric Dynamics Mission ADM is to measure wind profiles with global coverage using a satellite-borne Doppler wind LIDAR. The first-time development of a Doppler LIDAR system on a satellite platform represents a major scientific and technological challenge until the planned launch of the mission.
As part of this mission, a prototype was developed - in other words, an instrument that is comparable to the principle of the satellite measurement system. This prototype was used in several measurement campaigns at the German Aerospace Center. Numerous wind measurements were taken from the ground and from the aircraft and compared with reference devices. An important part of the work included analyzing the signals at the receiver and developing the algorithms for evaluating the data and optimizing them. The aim of such a prototype is to validate the equipment and develop algorithms before the satellite mission begins.
