Multispectral Monte Carlo radiative transfer simulation by the maximum cross-section method

A Path‐Tracing Monte Carlo Library for 3‐D Radiative Transfer in Highly Resolved Cloudy Atmospheres

“…Since most MC codes remain sensitive to the size and refinement of the volume description due to the nonlinearity of Beer's extinction law, the end of this section is devoted to the well‐established family of null‐collision algorithms (NCAs), presented here as a way to bypass this nonlinearity (Galtier et al, ), thus opening the door to acceleration grids for volumes as well. To the best of our knowledge, the most advanced proposal along these lines in the field of cloud radiation is in Iwabuchi and Okamura (). However, while they use NCAs in acceleration grids, they do not achieve insensitivity of computing times to the resolution of the volumetric data.…”

“…Among the first consequences of the analysis of NCAs in their integral forms is the fact that acceleration grids could indeed be introduced for volumes (Iwabuchi & Okamura, ; Kutz et al, ; Novák et al, ). Such structures are expected to ensure fast traversal of the ‐field used in NCAs, and fast access to the true k value when a collision is found in the transformed field, all the while minimizing the computational cost of handling null collisions by locally adjusting the ‐field to the true k field.…”

“…If is entirely uniform, then the sampling is ideally fast, but it remains fairly simple if is only uniform by parts. Therefore, the acceleration grid should be composed of voxels where is uniform (super‐cells in Iwabuchi & Okamura, ), and the voxels should be constructed with the constraint that k n be small enough, ideally null, so as not to add too many null collisions.…”

“…nonlinearity , thus opening the door to acceleration grids for volumes as well. To the best of our knowledge, the most advanced proposal along these lines in the field of cloud radiation is in Iwabuchi and Okamura (2017). However, while they use NCAs in acceleration grids, they do not achieve insensitivity of computing times to the resolution of the volumetric data.…”

“…• Figure S2 • Figure S3 Correspondence to: N. Villefranque, najda.villefranque@gmail.com The theoretical reasons for this weak sensitivity were identified early on (e.g., in Marshak et al, 1995), but it is only quite recently that MC codes have been able to handle highly refined cloud fields such as those produced by today's high-resolution atmospheric models (with typically hundreds of millions to a few billions grid points). This new capability has paved the way for numerous applications in atmospheric science (see, e.g., Iwabuchi & Okamura, 2017) and beyond. For example, the cinema industry has recently started to make use of MC for the physically based rendering of cloudy scenes (Kutz et al, 2017).…”