Capabilities and limitations of a current FORTRAN implementation of the T-matrix method for randomly oriented, rotationally symmetric scatterers

We describe in detail a software implementation of a current version of the ¹-matrix method for computing light scattering by polydisperse, randomly oriented, rotationally symmetric particles. The FORTRAN ¹-matrix codes are publicly available on the World Wide We ba thttp://www.giss.nasa.gov/&crmim .W egiv eal lnecessar yformulas ,describ einpu tand output parameters, discuss numerical aspects of ¹-matrix computations, demonstrate the capabilities and limitations of the codes, and discuss the performance of the codes in comparison with other available numerical approaches. Published by Elsevier Science Ltd. 1. I NTRODUCTION The ¹-matrix method is a powerful exact technique for computing light scattering by nonspherical particles based on numerically solving Maxwell's equations. Although the method is, potentially, applicable to any particle shape, most practical implementations of the technique pertain to bodies of revolution. The method was initially developed by Waterman and has been significantly improved as described in Refs. 2—6. Specifically, Refs. 4 and 6 extend the method to much larger size parameters and aspect ratios, Ref. 2 presents an efficient analytical procedure for computing the scattering properties of randomly oriented particles, Ref. 3 describes an automatic convergence procedure convenient in massive computer calculations for particle polydispersions, and Ref. 5 presents benchmark ¹-matrix computations for particles with non-smooth surfaces (finite circular cylinders). A general review of the ¹-matrix method can be found in Ref. 7. In this paper we provide a detailed description of modern ¹-matrix FORTRAN codes which incorporate all recent developments, are publicly available on the World Wide Web, and are, apparently, the most efficient and powerful tool for accurately computing light scattering by randomly oriented rotationally symmetric particles. For the first time, we collect in one place all necessary formulas, discuss numerical aspects for ¹-matrix computations, describe the input and output parameters, and demonstrate the capabilities and limitations of the codes. The paper is intended to serve as a detailed user guide to a versatile tool suitable for a wide range of practical applications. We specifically target the users who are interested in practical applications of the ¹-matrix method rather than in details of its mathematical formulation.

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