Miniaturization of elastic scattering lidars: determination of the microstructure of the atmospheric surface layer

The article considers models of miniature elastic scattering lidars with similar optical schemes, analyzing the possibility of their application in determining the microstructure of the atmospheric surface layer. A microlidar model is proposed, whose main feature is a small sensed volume of the atmosphere. It is assumed that on short sensing paths in the limiting case, a small sensed volume may contain no particles. In this case, the minimum backscatter signal corresponds to molecular scattering, while the exceeding of this minimum by the signal is associated with the presence of a particle. The molecular component of the backscatter signal is constant and comparable to the tabulated value of the backscattering coefficient in the optical model of the atmosphere. This allows the average value of the total backscatter signal (from molecules and particles) to be put into correspondence with the overall backscattering coefficient. The authors consider a model of a minilidar whose optical scheme is similar to that of a microlidar but increased in scale. The minilidar can be used to determine the microstructure of the atmospheric surface layer on longer paths as compared to the microlidar. For both schemes, the average values of atmospheric backscatter signals are the same. When using a minilidar, the backscatter signal is formed by a layer measuring from a few meters to several tens of meters. In this case, the sensed volume can be determined using perforated screens and reflecting spheres. It is shown that the minilidar-to-microlidar sensed volume ratio is equal to the similarity coefficient to the fourth power, which enables the comparison of data measured by means of these lidars. These complementary measurement results allow the model of an equivalent atmosphere containing monodisperse aerosol to be put into correspondence with the examined atmosphere. The obtained results provide a means to develop a detailed procedure for determining the concentration of equivalent particles in the surface layer of atmospheric aerosol using micro- and minilidars.