Moshe Kleiman

Scattering of electromagnetic radiation by multilayered spheroidal particles: recursive procedure

A formalism is developed for the calculation of the electromagnetic field scattered by a multilayered spheroidal particle. The suggested formalism utilizes the recursive approach with respect to passing from one layer to the next; thus it does not require an increase in the size of the equation matrices involved as the number of layers increases. The equations operate with matrices of the same size as for a homogeneous spheroid. The special cases of extremely prolate and weakly prolate spheroids are considered in more detail. It is shown that in such cases one can avoid the matrix calculations by instead using the iterative scalar calculations.

The recursive algorithm for electromagnetic scattering by tilted infinite circular multilayered cylinder

Abstract The purpose of the paper is to develop a formalism for solving the problem of scattering of electromagnetic waves by a tilted, infinite, multilayered cylinder. The approach allows us to obtain the Mie scattering coefficients without involving matrix calculations. This method provides the basis for constructing an efficient algorithm for the case of a multilayered cylinder, extending the procedure developed for a multilayered sphere. For the case of a cylinder, such a procedure does not follow directly from the boundary conditions, but requires a special mathematical justification. The proof is presented in this study.

Scattering by an arbitrary multi-layered spheroid: theory and numerical results

In this paper a simple algorithm is presented for calculating light scattering by a multi-layered spheroid for both normal and oblique incidence. Results of several numerical tests are given. They present the extinction efficiency for different aspect-ratio spheroids in comparison with that of the proper multi-layered sphere and cylinder.

Calculations of the Mie scattering coefficients for multilayered particles with large size parameters

Abstract The calculation procedure for the scattering coefficients appearing in the Mie theory is discussed for a case of multilayered particles with a large size parameter. There are two different aspects to the problem. The first aspect concerns a case where the imaginary part of the size parameters remains small. Shown here is the possibility for avoiding the canonical recommendations which prescribe using both upward and downward recursions for different types of Bessel functions. We have justified the procedure based on the upward recursions only where results are as stable as those in the canonical one. The second aspect concerns the case with a large imaginary part of the size parameter. The calculation procedure for a multilayered particle fails in such a case because of 0/0-type uncertainty. However, this problem can be overcome by using the proper asymptotic relations at crucial points. The numerical results are demonstrated for spherical and cylindrical multilayered particles.

Effect of dense atmospheric environment on the performance of laser radar sensors used for collision avoidance

The operation of laser radar in an automotive collision avoidance system under poor visibility conditions is analyzed. The equations were formulated to calculate (1) the signals returned to a laser radar system by a reflecting target positioned at a given range and (2) signals caused by the scattering of laser radiation by atmospheric particles only. The dependence of calculated signals on the density and the scattering properties of the atmospheric medium on one hand and on the geometry of the system on the other hand was studied. The multiple scattering processes were included in these calculations, and the polarization properties of the calculated signals were analyzed. An experimental verification of the theoretical results in a clear atmosphere and in a dense atmospheric environment has been performed. Good agreement was achieved only when multiple scattering was included in the theory. It is shown that multiple scattering is the main contributor to the signals received from the medium. Utilization of the results of this work can reduce significantly the very high false alarm rate typical for dense atmospheric conditions where successful anti- collision system performance is most crucial.

Instantaneous integrated Raman scattering.

Lidar detection of atmospheric molecules using a Raman scattering technique being usually limited by low signals is enhanced by integration of the forward Raman scattered light over a large atmospheric volume. This integral can be measured instantaneously in the presence of a reflector at one edge of the optical path, increasing the SNR by a factor of 100 in the case of a perfect reflector and a beam path of ~2 km. Natural reflectors such as clouds leading to the same effect are also discussed.

Evidence suggesting the shortening of the day from sunrise to sunset due to global change

The effect of global change in the past century, which led to increased levels of pollution and augmented values of cloud coverage, on the time of the apparent Sunrise and Sunset, is suggested to have shortened the day by 1 - 1.5 minutes in the past 4 decades in northern and mid-latitudes. This is supported by photographs of the setting Sun taken in Jerusalem during the months of July and August 2001, which reveal that in over 95% of the cases the Sun completely disappear to the naked eye below marked atmospheric layers at an average elevation angle of 0.5 - 2.5° above the solid earth horizon. Based on trends in past Sunshine Duration measurements, the day shortening effect is expected to increase in the future.

An Algorithm for Lidar Mapping of Aerosol Concentrations in a Varying Atmospheric Background Density

Abstract An algorithm for the determination of the number density profiles of a specific aerosol as a function of time and space is developed and discussed. The algorithm is applicable to atmospheric conditions in which a varying density particulate background contributes to the lidar backscatter a significant or even a major part of the total amount of the mattered light. The method is based on a priori knowledge of the dependence of the background aerosol mass backscatering coefficients on the varying lidar parameters (wavelength, polarization, scattering angle). The sensitivity of the method is also discussed. The theoretical approach is expanded to cases where the aerosol is mixed in two or more different backgrounds.

Analytical approximation for multiple Raman-Mie scattering

An analytical solution for calculation of double Raman-Mie scattering in the presence of a cloud is suggested. The model includes the Raman-Mie and Mie-Raman scattering processes occurring in the cloud volume as well as integrated Raman scattering signal from air molecules along the laser pulse from lidar to the cloud base. The developed algorithm allows for the comparison of relative contribution of these processes to the total Raman-shifted lidar signal. For typical lidar and cloud parameters, double scattering is not negligible and its contribution to the Raman signal is around 20%.

Scattering from a long helix

We consider here the electromagnetic wave scattering by a long and thin-wire helical particle. In contrast to several previous theoretical works, we adopt here the Mie theory to this case. In the present work a long helical particle is considered as a hollow cylinder with a thin non-homogeneous membrane for which the periodical boundary conditions are imposed.