News

12 October 2026

MONKI paper published

After six years of development, our MONKI paper is now published in Geoscientific Model Development. It brings together the physics, numerical methods, and validation behind the code that I built from scratch in modern Fortran. MONKI, short for Monte Carlo KNMI, simulates how sunlight travels through planetary atmospheres: how it is scattered by molecules, aerosols, and clouds, absorbed by gases, and reflected from surfaces. Throughout these interactions, the code follows both the intensity and polarisation of the light.

A key part of this work was going back to the fundamental physics. I derived a new theoretical framework that allows MONKI to converge robustly even in thick atmospheres where light is scattered many times, such as that of Venus. MONKI is already being used to investigate 3D cloud effects in TROPOMI and SEVIRI satellite measurements and to predict signals for ESA’s upcoming EnVision mission to Venus. In principle, MONKI can be used to simulate reflected light signals from any planet.

27 May 2026

MONKI used at KNMI to study 3D cloud effects in weather satellite measurements

MONKI was used in a study led by Job Wiltink to quantify how three-dimensional cloud-radiation interactions affect satellite-based estimates of global horizontal irradiance: the amount of sunlight that reaches the surface on a horizontal plane.

Such 3D effects are often hidden within large satellite pixels. Light can be transported horizontally between cloudy and cloud-free parts of a scene, and cloud shadows can reduce the radiation that reaches the surface. As new geostationary weather satellites observe clouds with smaller pixels, these effects become increasingly important for interpreting and correcting satellite-based irradiance products.

The study combines MONKI with realistic cloud fields from MicroHH, a large-eddy simulation cloud model, and shows how pixel size, cloud structure, and horizontal photon transport shape the retrieved signal.

9–13 February 2026

Venus habitability workshop at the Lorentz Center

I spent the full week at the Lorentz Center in Leiden for the workshop “Roadmap to the Exploration of Venus Habitability”. The meeting brought together researchers working on Venus geology, interior structure, atmospheric evolution, and future mission concepts.

We discussed which observations and mission strategies are needed to understand how Venus evolved and whether it may once have been habitable. I contributed from the perspective of reflected-light modelling and argued for polarimetry as a way to constrain Venus’s clouds, hazes, and atmospheric structure.

14 July 2025

MONKI preprint published in EGUsphere

The MONKI preprint is available on EGUsphere. The paper presents MONKI from the radiative-transfer equations to the numerical implementation, including polarisation-dependent sampling, forward and backward Monte Carlo modes, and validation against established benchmark models.

MONKI computes total and polarised radiation reflected by planetary atmospheres and can handle both horizontally homogeneous scenes and three-dimensional cloudy atmospheres. The paper also includes sample simulations for Earth and Venus, showing how the altitude of photon scattering helps explain features in the total and polarised reflected-light signals.

30 April 2025

Modelling Venus’s spectropolarimetric signatures for EnVision

I presented MONKI simulations of Venus reflected-light spectra and polarisation at the EGU General Assembly in Vienna. The simulations support the interpretation of future VenSpec-U and VenSpec-H measurements by ESA’s EnVision mission.

The results show how Venus’s clouds, hazes, gaseous absorption, Rayleigh scattering, and viewing geometry shape the measured fluxes and polarisation. This work is part of adapting MONKI for Venus, including challenging twilight and limb geometries that are relevant for future mission observations.