Reference transmittance method constrained by the system constant for the retrieval of the aerosol extinction coefficient in scanning lidar measurements

Abstract

Mie-scattering lidar technique has been widely employed for atmospheric pollution source tracking based on scanning measurements, while it is still difficult to retrieve the aerosol extinction coefficient (AEC) in real-time from the scanning map with high precision and reliability owing to the ill-conditioned lidar equation and the variable atmosphere. This study proposes a novel reference transmittance constrained by the system constant (CSC-RT) method for real-time and accurate inversion in scanning lidar measurements. The CSC-RT algorithm employs a reference transmittance as the input to retrieve the AEC profile of a lidar curve that is challenging to obtain independently. The corresponding system constant is subsequently examined through comparison with neighboring scanning measurements to validate the retrieval results. Besides, long-term experiments have revealed that the temporal variation of the retrieved system constant is highly related to atmospheric conditions, especially the humidity, apart from the power fluctuations of the laser diode. Continuous atmospheric measurements carried out by using a scanning Scheimpflug lidar system in urban area have successfully demonstrated that the proposed algorithm is possible to reliably obtain the AEC scanning map for pollution source identification and tracking, and a good correlation between the obtained AEC values and particulate concentrations reported by a local pollution monitoring station has also been found. This method offers a robust and efficient tool for pollution source identification and environmental management, particularly in complex and dynamic atmospheric conditions.