Abstract
The Aeolus satellite mission of the European Space Agency (ESA) has brought the first wind LiDAR to space to satisfy the long-existing need for global wind profile observations. Until the successful launch on 22 August 2018, pre-launch campaign activities supported the validation of the measurement principle, the instrument calibration, and the optimization of retrieval algorithms. Therefore, an airborne prototype instrument has been developed, the ALADIN Airborne Demonstrator (A2D), with ALADIN being the Atmospheric Laser Doppler Instrument of Aeolus. Two airborne campaigns were conducted over Greenland, Iceland and the Atlantic Ocean in September 2009 and May 2015, employing the A2D as the first worldwide airborne direct-detection Doppler Wind LiDAR (DWL) and a well-established coherent 2-µm wind LiDAR. Both wind LiDAR instruments were operated on the same aircraft measuring Mie backscatter from aerosols and clouds as well as Rayleigh backscatter from molecules in parallel. This paper particularly focuses on the instrument response calibration method of the A2D and its importance for accurate wind retrieval results. We provide a detailed description of the analysis of wind measurement data gathered during the two campaigns, introducing a dedicated aerial interpolation algorithm that takes into account the different resolution grids of the two LiDAR systems. A statistical comparison of line-of-sight (LOS) winds for the campaign in 2015 yielded estimations of the systematic and random (mean absolute deviation) errors of A2D observations of about 0.7 m/s and 2.1 m/s, respectively, for the Rayleigh, and 0.05 m/s and 2.3 m/s, respectively, for the Mie channel. In view of the launch of Aeolus, differences between the A2D and the satellite mission are highlighted along the way, identifying the particular assets and drawbacks.
Highlights
The understanding of the dynamics in the troposphere and stratosphere is essentially based upon wind measurements
Two airborne campaigns were conducted over Greenland, Iceland and the Atlantic Ocean in September 2009 and May 2015, employing the A2D as the first worldwide airborne direct-detection Doppler Wind LiDAR (DWL) and a well-established coherent 2-μm wind LiDAR
Both wind LiDAR instruments were operated on the same aircraft measuring Mie backscatter from aerosols and clouds as well as Rayleigh backscatter from molecules in parallel
Summary
The understanding of the dynamics in the troposphere and stratosphere is essentially based upon wind measurements. ALADIN features two interferometers that are sensitive to molecular and aerosol or cloud backscatter This unique combination assures optimal coverage within the whole altitude range which constitutes a main difference compared to coherent wind LiDARs. To reduce the inherent risk in such new technologies, the A2D has been developed, being the first direct-detection Doppler wind LiDAR to be operated from an aircraft in a viewing geometry comparable to Aeolus (Durand et al [37]; Reitebuch et al [30]). Using the Keflavik airport on Iceland as the base, more than 20 flights in total have been performed during two airborne campaigns over the North Atlantic region in September 2009 and May 2015 During the latter, two LiDARs, namely the direct-detection TWiliTE (Gentry et al [26]) and the coherent DAWN instrument (Kavaya et al [25]), were deployed on the NASA DC-8 aircraft and likewise performed research flights in this North Atlantic region which is important regarding the evolution of weather systems that move towards Europe.
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