Backscattering measurements of atmospheric aerosols at CO2 laser wavelengths: implications of aerosol spectral structure on differential-absorption lidar retrievals of molecular species

The volume backscattering coefficients of atmospheric aerosol were measured with a tunable CO2 lidar system at various wavelengths in Utah (a desert e nvironment) along a horizontal path a few meters above the ground. In deduc ing the aerosol backscattering, a deconvolution (to remove the smearing eff ect of the long CO2 lidar pulse and the lidar limited bandwidth) and a cons trained-slope method were employed. The spectral shape beta(lambda) was sim ilar for all the 13 measurements during a 3-day period. A mean aerosol back scattering-wavelength dependence beta(lambda) was computed from the measure ments and used to estimate the error Delta(CL) (concentration-path-length p roduct) in differential-absorption lidar measurements for various gases cau sed by the systematic aerosol differential backscattering and the error tha t is due to fluctuations in the aerosol backscattering. The water-vapor con centration-path-length product CL and the average concentration C = (CL)/L for a path length L computed from the range-resolved lidar measurements is consistently in good agreement with the water-vapor concentration measured by a meteorological station. However, I was unable to deduce, reliably, the range-resolved water-vapor concentration C(r), which is the derivative of the range-dependent product CL, because of the effect of residual noise cau sed mainly by errors in the deconvolved lidar measurements. (C) 1999 Optica l Society of America.