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 highly efficient MIDAS to perform electromagnetic
scattering calculations to evaluate the gain in efficiency from these
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 Models (RTMs). 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, 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 while maintaining excellent accuracy. In
addition, direct solvers consider all requested orientations at once,
giving MIDAS further advantage over popular ISB-DDA methods. MIDAS, when
combined with high-order quadrature for orientation averaging, can be
greater than three orders of magnitude more efficient in obtaining
RTM-ready SSPs of complex-shaped hydrometeors than existing ISB-DDA
methods, with the native quadrature schemes they offer.