DEVELOPMENT OF LIDAR TECHNIQUES TO ESTIMATE ATMOSPHERIC OPTICAL PROPERTIES
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Date
2006-08-03T15:25:14Z
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Johns Hopkins University
Abstract
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
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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).