Laser radar characterization of atmospheric aerosols in the troposphere and stratosphere using range dependent lidar ratio

Laser radar (lidar) provides an excellent tool for characterizing the physical properties of atmospheric aerosols which play a very important role in modifying the radiative budget of the Earth's atmosphere. One of the important issues in lidar research is to derive accurate backscattering or extinction coefficient profiles required for understanding the basic mechanisms in the formation of aerosols and identifying their sources and sinks. Most of the inversion methods used for deriving the aerosol coefficients assume a range independent value for the extinction-to-backscattering ratio [lidar ratio, (LR)]. However, it is known that in a realistic atmosphere the value of LR is range dependent and varies with the physical and chemical properties of the aerosols. In this paper, we use a variant of widely applied Klett's method to obtain the range dependent LR values and derive the aerosol extinction profiles with good accuracy. We present the lidar derived aerosol extinction profiles in the upper troposphere and lower stratosphere corresponding to different seasons of the year of two distinctly different stations in the Indian subcontinent namely Trivandrum (8.33° N, 770 E), Kerala, India, a coastal station and Gadanki (13.5° N, 79.2° E), Tirupati, India an inland station. The range dependent LR is derived corresponding to different seasons of the year at the two stations. The lidar ratio, aerosol extinction coefficient (AEC), aerosol scattering ratio, and aerosol optical depth show strong to medium seasonal variation at both the stations. The optical properties of the aerosols at the two stations differ considerably as evident from the various parameters obtained. The lidar ratio values at Trivandum vary in the range of 11-38 sr whereas the values range from 20-34 sr at Gadanki. AEC values at the Trivandum station vary from 7.9 × 10-6 to 6.9 × 10-5 m-1 and at Gadanki station the variation is from 1.27 × 10 -5 to 6.9 × 10-5 m-1. It is proposed to use back-trajectory analysis to understand the sources of aerosol at the two stations. © 2010 Society of Photo-Optical Instrumentation Engineers.