Optical Property Retrieval for Urban Climate Digital Twins

Urban heat stress is one of the most pressing climate risks in the Netherlands, with strong impacts on public health, infrastructure, and energy demand. A major driver of urban heat is the radiative budget of cities, which governs how much solar radiation is reflected, absorbed, and stored by urban materials such as roofs, roads, walls, and vegetation. This radiative budget directly controls surface temperature, sensible heat flux, and ultimately the intensity of the urban heat island (UHI). Accurate quantification of urban radiative exchange is extremely challenging due to three-dimensional (3D) structure of cities, shadowing, material heterogeneity, and directional reflectance effects. Traditional satellite-based approaches often rely on simplified assumptions which break down in complex 3D urban canopies. 

Recent advances in high-resolution remote sensing using hyperspectral aerial imagery and multi-spectral satellite imagery, 3D city models (3DBAG, LiDAR, digital twin) and physics-based 3D radiative transfer models (DART, Figure 1) now enable a deterministic, physics-based inversion of urban optical properties. These optical properties (albedo, emissivity) form a critical input for urban microclimate models (Figure 3). The goal of this research topic is to derive optical properties over one or more Dutch cities using high-resolution (1-m resolution) hyperspectral aerial imagery and 3D radiative transfer model DART for providing realistic inputs to the 3D urban microclimate models. This topic will be critical generating next-generation physics-based digital twins of Dutch cities capable of producing accurate estimations of radiative budget.