Retrieval of aerosol profiles by Raman lidar with dynamic determination of the lidar equation reference height

Abstract

A reference height that often needs to be assumed in aerosol retrieval from Raman lidar tends to cause high uncertainty in retrieving the vertical distribution of aerosol optical properties. Here, a novel method is proposed to determine the height-revolved reference height, which is then used to retrieve aerosols from Raman lidar. This method can automatically avoid the atmospheric layers with the presence of aerosols, clouds and low signal to noise ratio (SNR). Based on elastic (at 355 nm) and inelastic (at 387 nm) signals collected during the period from 5 December 2016 to 5 March 2017 by a ground-based Raman lidar in Beijing, China, the aerosol optical properties, such as extinction coefficient, backscattering coefficient and lidar ratio have been successfully retrieved. Results show that the averaged nighttime aerosol optic depth (AOD) from Raman lidar is in good agreement with early morning AOD retrieved from a collocated sunphotometer. The AOD exhibits a strong diurnal variation with a peak at 1500 Beijing time. On average, the nighttime AOD at 355 nm is 0.32, whereas the daytime AOD is 0.72 over Beijing during the study period. The column averaged lidar ratio is 44 sr at 355 nm, roughly consistent with previous studies. Our findings shed light on the pathways towards improving the retrieval of vertical distribution of aerosols optical properties during nighttime.