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Methodological programs in a problem of definition of a microstructure of scattering objects by remote methods


A. V. Bukharin

Lidar systems of elastic scattering are applied, as a rule, in problems of atmospheric monitoring. For example, if scattering layer is located along a sounding line the on a backscatter signal make possible to define the size of a layer and its coordinate along a sounding line. The second problem is definition of a microstructure of a layer. Since creation of the first lidar, the existing methodological program is based on the decision of an ill-posed inverse problem. Such situation arises because of necessity to define a microstructure of a layer from two base coefficients. Basic coefficients are backscatter and extinction. The lidar’s signal which includes these coefficients, is described by the nonlinear integrated equation. Base coefficients are connected with particles size distribution by the integrated equations of Fredholm. The problem of a determination of this function is return and incorrect. For solution stabilisation of an incorrect return problem a priory information on probed object is actively used. A priory information can be the aerosol chemical compound, absent-minded radiation from extraneous light sources etc. The algorithm of the decision of a return problem is characterised by considerable volume of adjusting parameters and assumptions. It leads to occurrence of the subjective factor. Problems the basic lacks of the existing methodological program associate with a substantiation of reliability of the received decision and absence of the measured parameter which is the indicator of the size of particles. Additionally we note as necessity of intermediate calculations under the theory of Mie. As a result till now lidar systems are not used as tool means for definition of microphysical structure of scattering objects. Such situation remains within 50 years since creation of the first lidar. The further development of methods of the decision of an ill-posed inverse problem is connected with application of probing beams on several lengths of waves and directed on reception of the maximum possible volume of the information on probed object. However scattering particles, as a rule, have difficult distribution in the sizes, their structure and optical properties are unknown, particles can be not spherical etc. The alternative methodological program consists in introduction of the indicator of the sizes of particles on which probably to define and compare a microstructure of scattering objects. Such indicator is the forward scattering halo round a beam. The more the angular size of an halo, the is less size of particles. On the angular size of this halo, investigated object some equivalent object is associated. The equivalent object consists of mono disperse particles, has the same lidar ratio as real object. There is a possibility of calibration of a signal on con-centration of particles in an equivalent layer. On concentration of scattering particles it is possible to make comparison of a microstructure of atmosphere for an equivalent layer on different distances from a source of particles. Further development of the approach offered for non-spherical particles.

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