Retrieval of the aerosol extinction coefficient from scanning Scheimpflug lidar measurements for atmospheric pollution monitoring

Abstract

In this work, an 808-nm Scheimpflug lidar (SLidar) system, employing a laser diode as the light source and an image sensor as the detector, has been utilized for practical applications of air pollution monitoring in urban area. A comprehensive retrieval method has been proposed and developed for reliable and automatic retrieval of the aerosol extinction coefficient (AEC) from near-horizontal scanning SLidar measurements. The characteristics of the pixel-intensity curves measured by the SLidar system have been statistically examined, and a quality control process is developed to eliminate abnormal lidar profiles. An improved Douglas-Pucker algorithm has been utilized for the determination of the boundary value of the AEC. The AEC profile is thus obtained according to the Klett method with the boundary value as the input. Meanwhile, an angular iterative retrieval (AIR) algorithm has been developed with the AECs at neighboring scanning angles as references, which is able to significantly improve the retrieval reliability of the AEC for each scanning angle. Comparison studies with a local pollution monitoring station have also been carried out to verify the present retrieval method. Besides, the Scheimpflug lidar technique in combination with the retrieval method has shown promising performance in tracking pollution sources in urban area.