Investigation of full polarization characteristics of aerosols and cloud particles with Stokes lidar

Traditional polarization lidar has been widely used in the observation of atmospheric aerosol and cloud. To study the full polarization characteristics of aerosol and cloud particles and their variation with height more accurately, a new full polarization vector Stokes lidar system has been developed. A new method of eight-point online calibration of full Stokes parameters is proposed. The total root-mean-square (RMS) deviation of the full polarization vector Stokes after online calibration is 0.0016. The full polarization vector Stokes of aerosol and cloud can be detected in real time and with high precision by the system. Vertical structural changes in the full polarization characteristics of atmospheric aerosol and cloud particles under clear and cloudy skies were observed using the system. Results show that in clear sky, the absolute values of S₁, S₂, and S₃ above 3.2 km tend to be 0, with most aerosol particle morphologies spherical or spheroidal. Below 3.2 km, their absolute values are non-zero, indicating the presence of many non-spherical particles with directional scattering properties or complex structures. In cloudy sky, the absolute values of S₁, S₂, and S₃ at 3.4 km all show a second peak. The microphysical processes are active, with the highest number of non-spherical ice crystals or cloud droplets, and the particle morphology is complex. The study shows that the fully polarization vector Stokes is extremely sensitive to aerosol concentration, morphology and cloud particle detection. The lidar provides new methods for studying of aerosol classification, cloud phase detection, aerosol-cloud interaction, and microphysical properties.