Microphysical particle parameters from extinction and backscatter lidar data by inversion with regularization: theory

A method is proposed that permits one to retrieve physical parameters of tr opospheric particle size distributions, e.g., effective radius, volume, sur face-area, and number concentrations, as well as the mean complex refractiv e index on a routine basis from backscatter and extinction coefficients at multiple wavelengths. The optical data in terms of vertical profiles are de rived from multiple-wavelength lidar measurements at 355, 400, 532, 710, 80 0, and 1064 nm for backscatter data and 355 and 532 nm for extinction data. The algorithm is based on the concept of inversion with regularization. Re gularization is performed by generalized cross-validation. This method does not require knowledge of the shape of the particle size distribution and c an handle measurement errors of the order of 20%. It is shown that at least two extinction data are necessary to retrieve the particle parameters to a n acceptable accuracy. Simulations with monomodal and bimodal logarithmic-n ormal size distributions show that it is possible to derive effective radiu s, volume, and surface-area concentrations to an accuracy of +/-50%, the re al part of the complex refractive index to +/-0.05, and the imaginary part to +/-50%. Number concentrations may have errors larger than +/-50%. (C) 19 99 Optical Society of America.