Statistical estimate of the deformation of a light pulse in the location of plane stratified clouds

The study of clouds in the lower atmosphere by means of laser location (lidar) started in the second half of the sixties. The first investigations in this direction by Ligda [1] and Collis [2–5] indicated the extensive prospects of optical probe systems in studying the structure and dynamics of clouds. The powerful lasers used in these systems (lasers with pulses as short as 10^–9 sec) help in identifying the upper and lower boundaries and the spatial inhomogeneity of clouds of fairly low density with the resolution necessary for projector probing. As in the case of radar, methods of studying atmospheric objects with lidars are based on an analysis of the information included in the reflected signal. The reflected signal in these cases is formed by the back-scattering of light on diffuse interaction with atmospheric inhomogeneities. The different meteorological nature (shower, fog, haze, etc.) and internal structure of the inhomogeneities reflect differently on the parameters of the signal. In general the intensity, the state of polarization, the shape of the envelope of the pulse, and the energy and frequency spectrum all vary. However, the extraction and analysis of the information contained in these changes in order to solve the inverse problem present an extremely complicated problem, as yet only solved in individual simple cases. In problems relating to the laser probing of clouds and mists, one of the most informative and easily-analyzed characteristics is the degree of deformation of the initial pulse by reason of the repeated scattering of photons. A number of preliminary estimates establishing a relationship between the parameters of the cloud layer and the shape of the reflected light pulse were presented in [6–9]. In [6, 9], in particular, the authors estimated the time characteristics of a diffusely-reflected light signal by the method of statistical tests [10], which is particularly suitable for solving multidimensional problems of atmospheric optics [11]. The algorithm of the Monte Carlo method proposed in [6, 9] and used in the present investigation enables us to allow for the complicated boundary conditions arising in the propagation of a divergent, spatially-limited light beam in a layer-like inhomogeneous scattering medium, and also the transient nature of the process.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 50–53, February, 1973.