The molecular channel of the space-based Doppler lidar ADM-Aeolus relies on a double Fabry-Perot (FP) interferometer. The difference in photon numbers transmitted by the two FPs divided by their sum-the so-called Rayleigh response-is a function of the central frequency of the spectrum of the laser light backscattered by the atmosphere, so that a proper inversion enables the measurement of Doppler shifts and line-of-sight wind velocities. In this paper, it is shown that the relationship between the Rayleigh response and the Doppler shift does not depend on the sole characteristics of the instrument, but also on the atmospheric pressure and temperature (through the Rayleigh-Brillouin effect), and the likely presence of a narrow-band radiation due to particle scattering. The impact of these on the precision of inverted Doppler shifts (or line-of-sight winds) is assessed showing that a correction is needed. As they are lacking the appropriate precision, climatology profiles of pressure, temperature or aerosols cannot be used as an input. It is proposed to use data predicted by a numerical weather prediction system instead. A possible correction scheme is proposed. Its implication on the quality of retrieved Rayleigh winds is discussed.

The ground-based coherent lidar developped at LMD has been upgraded to make it more practical for atmospheric measurements. One experimental difficulty with our system is the time spent prior any backscatter or wind measurement for optical alignment, frequency offset tuning and stabilization. The overall procedure has to be repeated every time an experiment is to be conducted. The main modifications implemented last year deal with the TE-CO2 transmitter, the local oscillator, and a CCD camera to look at the remote targets we are aiming at for alignment or calibration purposes.