An accurate and computationally cheap microwave scattering method for ice aggregates: the Independent Monomer Approximation

The Discrete Dipole Approximation (DDA) is widely used to simulate scattering of microwaves by snowflakes, discretising the snowflake into small ‘dipoles’ which oscillate in response (a) incident wave, and (b) scattered waves from all other dipoles particle. It this coupling between dipole pairs makes solving DDA system computationally expensive, that cost grows nonlinearly as number crystals n within an aggregate increased. Motivated this, many studies have ignored (the Rayleigh–Gans Approximation, RGA). However, use RGA leads systematic underestimation both absorption, inability predict polarimetric properties. To address we present a new approach Independent Monomer IMA) solves for each crystal ‘monomer’ separately, then combines them construct full solution. By including intra-monomer coupling, but neglecting inter-monomer save factor computation time over DDA. Benchmarking IMA against solutions indicates its accuracy greatly superior RGA, provides ensemble cross-sections closely agree with their more expensive counterparts, particularly at size parameters smaller than ∼ 5 . Addition rime aggregates does not significantly degrade results, despite increased density. radar remote sensing evaluated, show multi-wavelength multi-polarisation are successfully captured few tenths dB probed frequencies 3 200 GHz, contrast where errors up 2.5 observed. Finally, explore realism greater detail analysing internal electric fields, discuss some broader insights physical features important microwave scattering.