Forests are one of Europe’s most important renewable resources and a key repository of biological biodiversity. Also, the forest sector is one of Europe’s most important economic sectors. In recent years, widespread forest mortality related to drought or temperature stress has been described in drought-prone forests throughout the world. Such mortality events can radically transform biodiversity, fire risk, ecosystem function, land-atmosphere interactions and ecosystem services. Remote sensing offers the unique possibility to derive spatially explicit information on vegetation status at local, regional or landscape scale. Great benefits would be expected from remote sensing techniques that quantify the photosynthetic carbon fixation dynamics of the vegetation as a reference measurement of forest health. Increasing efforts are currently been carried out by Europe Space Satellite Missions (ESSM) for sensing solar-induced Fluorescence (F). Satellite missions have recently been launched (GOSAT/TANSO) or are currently under evaluation (ESA-FLEX), and will open interesting perspectives for the early detection of plant stress at landscape level. However, upscaling of these methodologies still requires investigation on challenging issues regarding the interpretation of F retrieved from mixed pixels of hundreds of meters that aggregate vegetation, soil and shadow components and a better understanding of the influence of heterogeneous forest canopy structure, background and viewing geometry on steady-state fluorescence. For the first time, this work proposed the integration of FluorMODleaf with the three-dimensional ray-tracing model (FLIGHT) for investigating these interactions by means of the simulation of forest canopy reflectance and fluorescence signals for varying canopy variables and viewing geometries. This work is highly relevant because is a novel approach to study F on heterogeneous forest canopies structures and for the validation of current and future ESSM.