Simultaneous reconstruction of two microphysical aerosol characteristics from the lidar data

Abstract

A method is proposed for joint determination of two aerosol microphysical characteristics: the complex refractive index m = mreal + i*mimage and the spherical-particle size distribution function U(r) from the data of the nighttime vertical lidar sensing at the wavelengths 355–1064 nm. The values of the refractive index are nonlinearly related to the size distribution function. During their simultaneous estimation it is useful to minimize the discrepancy functional Φ(m) in the range of the physically justified m. The variation in the functional behavior with absorption is investigated. The principal limitations due to a wider region of the global minima of Φ(m) appear at mimage ∈ [0.01, 0.04] and give rise to a potential shift of the resulting values of mrealest and mimageest. A simultaneous use of several functionals gives a better estimate of mdue to different sets of the respective optical characteristics. The problem in retrieving the distribution function is caused by the information content of the coarse particle measurements. The statistical regularization method offers an unambiguous estimation of U(r)for the mean radius up to 3 µm, and gives an admissible estimate for larger radii. The algorithms have been tested using 50 empirical models obtained from the Zvenigorod AERONET site. In addition, the vertical profiles of aerosol parameters reconstructed from the data of the LOZA-S lidar measurements during the polar air mass transfer are presented.