MONKI: a three-dimensional Monte Carlo simulator for transfer of polarised light in planetary atmospheres
- 1Delft University of Technology (Delft, Netherlands)
- 2Royal Netherlands Meteorological Institute (De Bilt, Netherlands)
Abstract
Spectropolarimetry is a powerful tool for characterising planetary atmospheres and surfaces. For the design and operation of spectro(polari)metric instrumentation, numerically simulated signals of the measured radiation are essential. We present MONKI (Monte Carlo KNMI), an efficient and accurate Monte Carlo radiative transfer code written in Fortran. MONKI computes total, linearly polarised, and circularly polarised radiances reflected by and transmitted through planetary atmospheres, fully accounting for the polarisation of light in all orders of scattering. Unlike classical Monte Carlo approaches that rely on post-sampling weight corrections and can therefore produce rare but disproportionately large photon weights, MONKI samples scattering directions from the full polarisation-dependent distribution, consistently in both forward and backward Monte Carlo modes. We provide the corresponding theoretical framework in the appendices. Because of this exact polarised sampling approach, the code converges robustly for optically thick and/or strongly polarising atmospheres. MONKI can handle horizontally homogeneous atmospheres as well as atmospheres with horizontal inhomogeneities, such as three-dimensional (3D) patchy clouds. We validate MONKI through comparisons with other radiative transfer codes. Finally, we present sample simulations of sunlight reflected by the Earth and Venus, and explain the total and polarised radiance features by analysing the altitudes at which photons are scattered. We conclude that MONKI is a versatile and accurate tool for simulations and detailed analyses of total and polarised light emerging from the atmospheres of the Earth, Venus, and, in principle, any other planet.
Versions
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BibTeX
@article{trees2026monki,
title = {{MONKI: a three-dimensional Monte Carlo simulator for transfer of polarised light in planetary atmospheres}},
author = {Victor J. H. Trees and Ping Wang and Job I. Wiltink and Piet Stammes and Daphne M. Stam and David P. Donovan and A. Pier Siebesma},
journal = {Geoscientific Model Development},
year = {2026},
month = oct,
doi = {10.5194/gmd-19-9677-2026},
url = {https://gmd.copernicus.org/articles/19/9677/2026/},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - MONKI: a three-dimensional Monte Carlo simulator for transfer of polarised light in planetary atmospheres
AU - Victor J. H. Trees
AU - Ping Wang
AU - Job I. Wiltink
AU - Piet Stammes
AU - Daphne M. Stam
AU - David P. Donovan
AU - A. Pier Siebesma
PY - 2026
DA - 2026/10/12
JO - Geoscientific Model Development
DO - 10.5194/gmd-19-9677-2026
UR - https://gmd.copernicus.org/articles/19/9677/2026/
AB - Spectropolarimetry is a powerful tool for characterising planetary atmospheres and surfaces. For the design and operation of spectro(polari)metric instrumentation, numerically simulated signals of the measured radiation are essential. We present MONKI (Monte Carlo KNMI), an efficient and accurate Monte Carlo radiative transfer code written in Fortran. MONKI computes total, linearly polarised, and circularly polarised radiances reflected by and transmitted through planetary atmospheres, fully accounting for the polarisation of light in all orders of scattering. Unlike classical Monte Carlo approaches that rely on post-sampling weight corrections and can therefore produce rare but disproportionately large photon weights, MONKI samples scattering directions from the full polarisation-dependent distribution, consistently in both forward and backward Monte Carlo modes. We provide the corresponding theoretical framework in the appendices. Because of this exact polarised sampling approach, the code converges robustly for optically thick and/or strongly polarising atmospheres. MONKI can handle horizontally homogeneous atmospheres as well as atmospheres with horizontal inhomogeneities, such as three-dimensional (3D) patchy clouds. We validate MONKI through comparisons with other radiative transfer codes. Finally, we present sample simulations of sunlight reflected by the Earth and Venus, and explain the total and polarised radiance features by analysing the altitudes at which photons are scattered. We conclude that MONKI is a versatile and accurate tool for simulations and detailed analyses of total and polarised light emerging from the atmospheres of the Earth, Venus, and, in principle, any other planet.
SN - 1991-9603
ER -