Retrieving aerosol backscatter coefficient using coherent Doppler wind lidar.

Coherent Doppler wind lidar (CDWL) has been widely used for wind detection, but retrieving aerosol optical properties remains challenging, due to its high sensitivity to turbulence and beam focusing. This study comprehensively evaluates the capabilities and limitations of pulsed CDWL in retrieving aerosol backscatter/extinction coefficient profiles, with a special focus on calibration and error analysis. A self-calibration method for the telescope focus function is proposed and validated through horizontal observations. Both forward and backward retrieval approaches are reviewed, with and without auxiliary co-located measurements. Key sources of uncertainty, including the carrier-to-noise ratio (CNR), heterodyne efficiency, lidar constant, and assumed lidar ratio, are analyzed. It's indicated that maintaining a controlled system environment is important for achieving a stable heterodyne efficiency profile. The lidar constant, calibrated using non-precipitating thick stratocumulus clouds, can achieve an uncertainty within 15% at 1550 nm, but the uncertainty increases with wavelength, as predicted by Mie theory. Under typical clear-sky conditions, an assumed lidar ratio with a 20% relative error introduces a relative error of less than 2% in the backscatter coefficient, whereas the extinction coefficient error is entirely dependent on the assumed lidar ratio. The influence of turbulence is further assessed using an equivalent experimental setup. With the deployment of thousands of CDWL systems worldwide, the ability to retrieve aerosol optical properties alongside simultaneous wind measurements is expected to significantly enrich datasets for aerosol transport studies, fog monitoring, and joint inversions with other instruments.