SILVO, a lightweight 3D illumination model to characterise the spatial structure of heterogeneous vegetation canopies

In the framework of vegetation modelling, the accurate representation of spatial heterogeneity is a challenge for remotely sensed radiative transfer models (RTMs). On the one hand, one-dimensional RTMs are highly realistic on homogeneous surfaces but have limitations when modelling complex structures, while three-dimensional RTMs, although physically detailed, have a high computational cost and greater complexity in parameterisation. In this paper, we present the SILVO (Simplified Light-Vegetation Overlay) model as a streamlined ray-tracing tool that allows the generation of basic spatial metrics (gap fraction, scene vegetation density) on a geometrical representation of the canopy. The model is driven by a simplified scene description and solar illumination conditions, and has been implemented in parallel with OpenMP to provide a computationally efficient solution. The results obtained in a real heterogeneous forest scene demonstrate the ability of the model to capture the essential aspects of the canopy’s spatial structure, facilitating the extension of 1D RTMs for more realistic representations of heterogeneous canopies. An indicative comparison with LiDAR-derived structural proxies is also reported (R2 = 0.774 for vertical vegetation density; NRMSE = 11.7% for gap fraction), while acknowledging that this does not constitute a full validation exercise. As it is an active project, and in search of integration with future developments, its code is available under the AGPL license in a public repository.