Lidar Studies on Atmospheric Aerosols at a Semi-Urban Station Cheeryal (17.51° N, 78.62° E) near Hyderabad, India with Range Dependant Lidar Ratio

摘要

Deriving the optical properties of aerosols and clouds from the experimentally obtained lidar data is one of the most interesting and challenging tasks. Various lidar methods have been developed so far, to obtain the quantitative profiles of extinction /backscattering coefficient of aerosols and clouds from the pulsed backscattering lidar measurements. In order to obtain an analytical solution to the lidar equation, it has been a common practice to assume that these parameters are related in the form of the extinction-to-backscatter ratio or Lidar Ratio (LR). The LR depends on the size distribution, shape and chemical composition of the aerosols. These properties of aerosols are highly variable and mainly depend on their sources and the local meteorological parameters. In order to enhance the accuracy of the derived extinction/backscatter profile, it is necessary to obtain the lidar ratio also along with the backscattered signal, called as Range Dependant Lidar Ratio (RDLR). In this study, we derive the RDLR while carrying out investigations on aerosol characteristics in the Cheeryal Village (17.51° N. 78.62° E). which is located at a distance of about 20 Km in the suburbs of Hyderabad, India. For this study the Multi-wavelength laser radar which is developed in-house and made operational at this location is used. The Nd:YAG laser (M/S Bright Solutions. Italy) based multi-wavelength lidar operates at 532 nm and 1064 nm with a pulse energy of 50uJ at both the wavelengths. The two wavelengths are generated coaxially with a pulse width of 10ns and the laser operates up to a PRF of 4 KHz. The receiver system consists of a 360 mm Newtonian optical telescope, 10 nm of interference filters and the Licel Gmbh, Germany make 250 MHz Photon Counting recorder.