One of the main deficiencies in the current meteorological global observing network is the lack of wind data. The only potential instrument to provide a three-dimensional coverage of wind data is a Doppler wind lidar mounted on a satellite platform. As part of the Living Planet Program, the European Space Agency (ESA) is preparing a mission to demonstrate the possibility of measuring wind profiles from space. The launch of the satellite is expected end of 2013.

Many trade-off studies have resulted in a lidar concept that is shortly described in a report together with the ADM mission objectives, background, requirements and implementation. For a more detailed description of the Atmospheric Dynamics Mission the reader is referred to the ADM Aeolus Science report.

At KNMI a software package, LIPAS (Lidar Performance Analysis Simulator), has been developed to simulate ADM-Aeolus wind profiles in realistic atmospheric conditions. Hereto an atmospheric database of combined ECMWF model winds, temperature and humidity and CALIPSO cloud and aerosol was developed. The ADM-Aeolus Doppler wind lidar (DWL) does not measure the complete wind vector but only the wind component along along the direction of the laser beam, also denoted the horizontal line-of-sight (HLOS) wind component. The figure below shows a slice of the HLOS wind along a CALIPSO track as obtained from ECMWF model zonal and meridional wind and laser pointing direction.

At KNMI an algorithm has been developed to retrieve atmospheric backscatter at 355nm from CALIPSO level-1 attenuated backscatter at 532nm at a high horizontal (3.5 km) and vertical (125 m) resolution. The figure below shows optically thin tropical cirrus, optically thick cumulus clouds, low-level stratus and an elevated aerosol layer.

ADM is operated in burst mode meaning that the laser is operated in cycles of 28 seconds of which the laser is active during 7 seconds (about 50 km along orbit track) and then turned off for 21 seconds (about 150 km). A wind profile is thus obtained every 200 km along the orbit track (blue dots in image below).

The laser wavelength of 355nm enables wind retrieval from both atmospheric particles (aerosols, cloud dropplets) and molecules. In principle two wind profile solutions are obtained; from molecules (Rayleigh channel) and particles (Mie channel). The vertical resolution of both channels is limited to 24 bins that may be freely distributed with a minimum binsize of 250 m and a maximum size of 2000 m. LIPAS simulates the signal that is coming back from the atmosphere (laser beam scattering at molecules and particles), detected on the telescope and further processed to retrieve the Doppler shift of the scattering molecules (Rayleigh channel) and particles (Mie channel) that move with the wind velocity. The figures below show the Rayleigh and Mie channel winds along half a CALIPSO respectively for the atmospheric scene displayed in the figures above. No winds are measured in the data void black regions because the laser is turned off here (burst mode). Dark blue regions indicate data void regions because of either orography or insufficient signal quality to retrieve a valid wind estimate for instance below optically thick clouds or in case of low aerosol loading (Mie channel).

Please contact Gert-Jan Marseille.

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