Evaluation of Higher-order Quadrature Schemes in Improving Computational
Efficiency for Orientation-averaged Single-Scattering Properties of
Nonspherical Ice Particles
Abstract
We evaluate several high-order quadrature schemes for accuracy and
efficacy in obtaining orientation-averaged single-scattering properties
(SSPs). We use the recently developed, highly efficient MIDAS to perform
electromagnetic scattering calculations to compare and evaluate the gain
in efficiency from these quadrature schemes. MIDAS is shown to be
superior to DDSCAT, a popular discrete dipole approximation (DDA)
method. This study is motivated by the fact that quality physical
precipitation retrievals rely on using accurate orientation-averaged
SSPs derived from realistic hydrometeors as input to radiative transfer
simulations. The DDA has been a popular choice for single-scattering
calculations, due to its versatility with respect to target geometry.
However, being iterative-solver-based (ISB), the most used DDA codes,
e.g. DDSCAT and ADDA, must solve the scattering problem for each
orientation of the target separately. As the size parameter and
geometric anisotropy of the hydrometeor increase, the number of
orientations needed to obtain accurate orientation-averages can increase
drastically and so does the computation cost incurred by the ISB-DDA
methods. MIDAS is a Direct-Solver-Based (DSB) code, using Method of
Moments (MoM) instead of DDA, its decomposition of the original large
matrix with a high rank into multiple more manageable smaller matrices
of lower ranks makes it much more computationally efficient and stable
while maintaining excellent accuracy. In addition, direct solvers
consider all requested orientations at once, giving MIDAS further
advantage over popular ISB-DDA methods. Combined with high-order
quadrature for orientation average, MIDAS can be orders of magnitude
more efficient in obtaining RTM-ready SSPs than existing ISB-DDA
methods.