Comparing MoM-CBFM and DDA Approaches in Solving EM Scattering of Realistic Solid Hydrometeors at Submillimeter Wavelengths

CubeSats with submillimeter ice-cloud radiometers are emerging as a promising low-cost approach for studying ice clouds to improve our understanding of Earth’s dynamic atmosphere and its impact on climate. Like for all microwave instruments, a crucial quantity for the physical (as opposed to empirical) quantitative retrieval of solid hydrometeors in the cloud is their single-scattering properties (SSPs). We previously applied the EM scattering solution method, MIDAS [1] (short for MoM Integral-equation Decomposition for Arbitrarily-shaped Scatterers), to calculate SSPs of arbitrarily shaped ice aggregates at select microwave frequencies, namely Ka, Ku, and W-bands. MIDAS applies a Method of Moments (MoM) with piecewise constant basis functions, followed by a domain decomposition method, namely the Characteristic Basis Function Method (CBFM). It has demonstrated a significant advantage in computational efficiency at the microwave frequencies mentioned above over the DDSCAT code based on Discrete Dipole Approximation (DDA), with comparable accuracy [1]. Volume-integral MoM and DDA formulations are mathematically equivalent and offer high versatility to scatterer geometry relative to other scattering solution methods, allowing calculations of SSPs for realistic complex-shaped ice hydrometeors [2]. Computational efficiency becomes thus a deciding factor in adopting one method or the other when both methods maintain satisfactory accuracy.