A new lidar design for operational atmospheric wind and cloud/aerosol survey from space
Authors: Bruneau Didier , Pelon Jacques 
Published: June 2021

Abstract. Global wind profile measurement has, for a long time, been a first
priority for numerical weather prediction. The demonstration, from
ground-based observations, that a double-edge Fabry–Pérot interferometer
could be efficiently used for deriving wind profiles from the molecular
scattered signal in a very large atmospheric vertical domain has led to the
choice of the direct detection technique in space and the selection of the
Atmospheric Dynamics Mission (ADM)-Aeolus by the European Space Agency (ESA) in 1999. ADM-Aeolus was
successfully launched in 2018, after the technical issues raised by the
lidar development had been solved, providing the first global wind profiles from
space in the whole troposphere. Simulated and real-time assimilation of the
projected horizontal wind information was able to confirm the expected
improvements 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
ADM-Aeolus mission with a potential operational follow-on instrument.
Maintaining the configuration of the instrument as close as possible to the
one achieved (UV emission lidar with a single line of sight), we revisit the
concept of the receiver by replacing the arrangement of the Fizeau and
Fabry–Pérot interferometers with a unique quadri-channel Mach–Zehnder (QMZ)
interferometer, which relaxes the system's operational constraints and extends
the observation capabilities to recover the radiative properties of clouds.
This ability to profile wind and cloud/aerosol radiative properties enables
the meeting of the two highest priorities of the meteorological forecasting community
regarding atmospheric dynamics and radiation. We discuss the optimization of the key parameters necessary in the selection
of a high-performance system, as based on previous work and development of
our airborne QMZ lidar. The selected optical path difference (3.2 cm) of the
QMZ leads to a very compact design, allowing the realization of a high-quality interferometer and offering a large field angle acceptance.
Performance simulation of horizontal wind speed measurements with different
backscatter profiles shows results in agreement with the targeted ADM-Aeolus
random errors, using an optimal 45∘ line-of-sight angle. The
Doppler measurement is, in principle, unbiased by the atmospheric
conditions (temperature, pressure, and particle scattering) and only weakly
affected by the instrument calibration errors. The study of the errors
arising from the uncertainties in the instrumental calibration and in the
modeled atmospheric parameters used for the backscattered signal analysis
shows a limited impact under realistic conditions. The particle backscatter
coefficients can be retrieved with uncertainties better than a few percent
when the scattering ratio exceeds 2, such as in the boundary layer and in
semi-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.