DEVELOPMENT OF LIDAR TECHNIQUES TO ESTIMATE ATMOSPHERIC OPTICAL PROPERTIES
Johns Hopkins University
The modified methodologies for one-directional and multiangle measurements, which were used to invert the data of the JHU elastic lidar obtained in clear and polluted atmospheres, are presented. The vertical profiles of the backscatter lidar signals at the wavelength 1064 nm were recorded in Baltimore during PM Supersite experiment. The profiles of the aerosol extinction coefficient over a broad range of atmospheric turbidity, which includes a strong haze event which occurred due to the smoke transport from Canadian forest fires in 2002, were obtained with the near-end solution, in which the boundary condition was determined at the beginning of the complete overlap zone. This was done using an extrapolation from the ground level of the aerosol extinction coefficient, calculated with the Mie theory. For such calculations the data of the ground-based in-situ instrumentation, the nephelometer and two particle size analyzers were used. An analysis of relative errors in the retrieved extinction profiles iii due to the uncertainties in the established boundary conditions was performed using two methods to determine the ground-level extinction coefficient, which in turn, imply two methods to determine aerosol index of refraction (using the nephelometer data and chemical species measurements). The comparison of the three analytical methods used to solve lidar equation (near-end, far-end and optical-depth solutions) is presented. An improved measurement methodology and modifications of a data processing technique are proposed to process the multiangle elastic-lidar data in clear atmospheres. The technique allows one to determine more accurate profiles of the optical depth and relative backscattering versus height. It is also shown that these profiles and the measured range-corrected signals can be used to determine the lidar overlap function versus range. The retrieved data allow one to analyze the influence of the local horizontal heterogeneity and measured lidar-data distortions, and thus, to estimate the retrieved data quality. The methodology and the data processing technique were tested with experimental data of two simultaneously scanning lidars operating in clear atmospheres. The experimental results obtained with the two lidars at different wavelengths are discussed. The results show that the multi-angle method is most suitable for the shortest wavelength (355 nm).