STRUCT · Harmonising forest structural metrics from LiDAR and passive optical instruments across scales

The structure of forests changes in response to environmental factors and human intervention (Calders et al 2020). It also determines the productivity capability of the forest, with corresponding impacts on the mass, momentum, and gas exchanges with the atmosphere (Béland et al., 2019). As such, it is key that measurements of forest structure are accurate and fit-for-purpose to enable understanding of forest structural changes and their underlying causes, as well as provide critical input into policy decisions related to nature-based solutions in the context of global change. Central to this is a measurement system capable of assessing these structural metrics at various scales such that each is consistent.The main aim of this research proposal is to assess the ability of multi-sensor approaches to measure forest structure and determine the consistency between these. This is both in the ability for a single measurement to be representative and for temporal changes to be discerned. This will be addressed in two parts: the first will be a detailed analysis at a field site within Belgium which has a corresponding virtual forest model (i.e. digital twin); the second part will extend this to a wider European network of sites used for forest structure monitoring. This will draw on radiative transfer modelling to simulate instrument responses in relation to the knowable true quantities and apply these insights to real measurement systems. Similarly, the project will utilise pre-existing infrastructure: an instrumented site in Belgium and a wider network of sites. As well as the overall aim of the project, several research questions will be addressed: 1) how can information from different sensors be combined to create better estimates of forest structural metrics? 2) what is the optimal sensing system to measure forest structural traits at different scales? and 3) what is the ability of satellite data to address temporal forest structural measurements at global scales?