Physical constraint method to determine optimal overlap factor of Raman lidar

Abstract

Overlap factor is an instrumental phenomenon caused by the incomplete overlay of the transmitting and receiving systems of a light detection and ranging (lidar) system. Conventional methods of overlap calculation for Raman lidar by combining Mie and N2-Raman signals is based on a user-assumed lidar ratio, assumption of which may introduce larger uncertainties when the characters of an aerosol loading is unknown. In this study, a physical constraint method is proposed to obtain an appropriate lidar ratio for overlap profile calculation of Raman lidar. The experiment of six representative cases verified that the correction of the overlap profile obtained by our method is practical and feasible. The signal of the experiment was derived from the Raman lidar at the Southern Great Plains site (SGPRL) of Atmospheric Radiation Measurement Program. The particle extinction coefficient of Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation was used as a reference value. The mean absolute errors of the particle extinction coefficient derived based on the proposed method is small (7.0–22.9 Mm−1) for 0–2 km by comparing the reference value. Additionally, the large bias below 0.8 km between the particle extinction coefficient corrected by the SGPRL-released overlap profile and the reference value suggest that the overlap profile applied in SGPRL still has larger room to be improved.