Performance assessment of the Aeolus Doppler wind lidar prototype

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Performance assessment of the Aeolus Doppler wind lidar prototype

Paffrath, Ulrike

The Atmospheric Dynamics Mission ADM-Aeolus by ESA (European Space Agency) will be the first mission worldwide to provide global observations of wind profiles by applying a Doppler wind lidar on a polar-orbiting satellite. An instrumental prototype was developed to validate this lidar system during ground and flight campaigns at DLR. This thesis introduces a newly end-to-end simulator, representing the properties of the prototype and various atmospheric models, to study wind measurements for different atmospheric and instrumental parameters, and to analyse the performance of the prototype from ground and aircraft. The random error of simulations at 10 mJ laser energy of an airborne system, for a flight altitude of 10 km, is smaller than 0.5 m/s, whilst for a ground system, it is smaller than 1 m/s (simulations up to 10 km altitude). The results of the simulations are used to develop and optimise the signal processing algorithms, knowing the properties of the modelled signal. The wind is determined by the Doppler shift from the molecular and aerosol backscatter signal with respect to the transmitted laser pulse. The algorithms are evaluated, optimised and compared, and those that provide results with a random error smaller than 0.15 m/s are the most suitable for this type of receiver. Simulations show the benefit of the system measuring both Rayleigh and Mie backscatter, because the wind speed measurements cover a larger atmospheric range. Atmospheric wind is not derived but the wind speed measurement accuracy was determined by the backscatter signal of the surface of a building. The random error is larger than 0.59 m/s. Besides, cloud backscatter is demonstrated and the attenuation of backscatter signal above clouds. It is shown that the Rayleigh signal was be detected up to altitudes of 8 km in clear air. First measurements of atmospheric backscatter with the prototype were performed at DLR (Deutsches Zentrum for Luft und Raumfahrt, or German Aerospace Centre) from ground and aircraft, and it was the first time that a direct detection Doppler wind lidar had been deployed on an aircraft. The very first measurements from these airborne studies are presented and discussed. Signals between the aircraft and ground, along with backscatter from clouds, and signals of the Earth's surface, were detected by the instrument, showing the capability to identify the ground and cloud return at the receivers.