Sensitive and accurate dual-wavelength UV-VIS polarization detector for optical remote sensing of tropospheric aerosols

摘要

An UV-VIS polarization lidar has been designed and specified for monitoring aerosols in the troposphere,showing the ability to precisely address low particle depolarization ratios,in the range of a few percent. Non-spherical particle backscattering coefficients as low as 5 × 10~(-8) m~(-1).sr~(-1) have been measured and the particle depolarization ratio detection limit is 0.6 %. This achievement is based on a well-designed detector with laser-specified optical components (polarizers,dichroic beamsplitters) summarized in a synthetic detector transfer matrix. Hence,systematic biases are drastically minimized. The detector matrix being diagonal,robust polarization calibration has been achieved under real atmospheric conditions. This UV-VIS polarization detector measures particle depolarization ratios over two orders of magnitude,from 0.6 up to 40 %,which is new,especially in the UV where molecular scattering is strong. Hence,a calibrated UV-VIS polarization-resolved time-altitude map is proposed for urban and free tropospheric aerosols up to altitude of 4 kilometers,which is also new. These sensitive and accurate UV-VIS polarization-resolved measurements enhance the spatial and time evolution of non-spherical tropospheric particles,even in ur- ban polluted areas. This study shows the capability of polarization-resolved laser UV-VIS spectroscopy to specifically address the light backscattering by spherical and non-spherical tropospheric aerosols.