A new lidar design for operational atmospheric wind and cloud/aerosol survey from space

Abstract

Abstract. Global wind profile measurement has, for a long time, been a first\npriority for numerical weather prediction. The demonstration, from\nground-based observations, that a double-edge Fabry–Perot interferometer\ncould be efficiently used for deriving wind profiles from the molecular\nscattered signal in a very large atmospheric vertical domain has led to the\nchoice of the direct detection technique in space and the selection of the\nAtmospheric Dynamics Mission (ADM)-Aeolus by the European Space Agency (ESA) in 1999. ADM-Aeolus was\nsuccessfully launched in 2018, after the technical issues raised by the\nlidar development had been solved, providing the first global wind profiles from\nspace in the whole troposphere. Simulated and real-time assimilation of the\nprojected horizontal wind information was able to confirm the expected\nimprovements in the forecast score, validating the concept of a wind profiler using a single line-of-sight lidar from space. The question is raised here about consolidating the results gained from\nADM-Aeolus mission with a potential operational follow-on instrument.\nMaintaining the configuration of the instrument as close as possible to the\none achieved (UV emission lidar with a single line of sight), we revisit the\nconcept of the receiver by replacing the arrangement of the Fizeau and\nFabry–Perot interferometers with a unique quadri-channel Mach–Zehnder (QMZ)\ninterferometer, which relaxes the system s operational constraints and extends\nthe observation capabilities to recover the radiative properties of clouds.\nThis ability to profile wind and cloud/aerosol radiative properties enables\nthe meeting of the two highest priorities of the meteorological forecasting community\nregarding atmospheric dynamics and radiation. We discuss the optimization of the key parameters necessary in the selection\nof a high-performance system, as based on previous work and development of\nour airborne QMZ lidar. The selected optical path difference (3.2\u2009cm) of the\nQMZ leads to a very compact design, allowing the realization of a high-quality interferometer and offering a large field angle acceptance.\nPerformance simulation of horizontal wind speed measurements with different\nbackscatter profiles shows results in agreement with the targeted ADM-Aeolus\nrandom errors, using an optimal 45 ∘ line-of-sight angle. The\nDoppler measurement is, in principle, unbiased by the atmospheric\nconditions (temperature, pressure, and particle scattering) and only weakly\naffected by the instrument calibration errors. The study of the errors\narising from the uncertainties in the instrumental calibration and in the\nmodeled atmospheric parameters used for the backscattered signal analysis\nshows a limited impact under realistic conditions. The particle backscatter\ncoefficients can be retrieved with uncertainties better than a few percent\nwhen the scattering ratio exceeds 2, such as in the boundary layer and in\nsemi-transparent clouds. Extinction coefficients can be derived accordingly. The chosen design further allows the addition of a dedicated channel for aerosol and cloud polarization analysis.