A Combination of the Separation of Variable and the T-matrix Method for Computing Optical Properties of Spheroidal Particles
Schulz, F.M., Eide, H.A., and Stamnes, K., University of Alaska, Fairbanks;
Stamnes, J.J., University of Bergen, Norway
Eighth Atmospheric Radiation Measurement (ARM) Science Team Meeting
The growing interest in nonspherical particles in recent years has led to significant improvements of various light scattering models for different kinds of nonspherical particles. One approach is to model size-shape distributions of randomly oriented particles by spheroids, whose light scattering properties can be rigorously calculated with the separation of variable method (SVM). The SVM can be used to model particles with spheroidal shapes departing significantly from sphericity. In contrast, the extended boundary condition method (EBCM, or T-matrix method) becomes increasingly ill-conditioned as the particle becomes more aspherical. The EBCM has, however, the advantage that the averaged optical properties of ensembles of randomly oriented particles can be obtained analytically and thus very efficiently from the T-matrix. In order to reconcile the SVM and the EBCM in such a way that we can benefit from the advantages of either method, we developed a method to calculate the T-matrix with the SVM, rather than with the EBCM. We have also developed a method to transform the T-matrix obtained with the SVM into the corresponding (EBCM) T-matrix in spherical coordinates. Thus, we circumvent the notorious ill-conditioning associated with the EBCM for strongly aspherical particles, while we retain its advantage of averaging analytically over orientational angles of randomly oriented particles. Direct comparison of the T-matrices of spheroidal particles computed with the traditional EBCM and with our new SVM approach shows very good agreement of results within the range of applicability of the EBCM. A comparison derived optical properties (scattering and extinction coefficient, asymmetry parameter, Stokes scattering matrix) for randomly oriented, monodisperse particles is equally satisfactory.
Note: This is the poster abstract presented at the meeting; an extended version was not provided by the author(s).
