Surface albedo and emissivity for Belgian cities (SuaBe)

Urban areas, with their abundance of materials that absorb solar radiation and high population density, are particularly vulnerable to the heat island effect. Mitigating this phenomenon requires accurate estimates of surface albedo and emissivity, yet such measurements are often unavailable at a citywide scale. High-resolution optical and thermal-infrared satellite sensors offer a solution, overcoming the spatial and temporal limitations of in-situ observations. However, satellite measurements are constrained by limited acquisition geometries and spectral bands, which prevents the accurate computation of neded quantities such as urban albedo maps.

This contribution describes the SuaBe project (https://stereoiv-suabe.eu/en), which focuses on designing and implementing a fast, and robust algorithm, that uses the 3D radiative transfer code DART (https://dart.omp.eu/#/) to invert remote sensing images of cities as a 3D distribution of optical properties and temperature, using a geometric urban database. This approach enables us to obtain a 3D model of a city to simulate urban surface albedo, emissivity, and net radiation maps at any date as long as the optical properties of urban elements remain constant. These optical properties can be up-dated with the inversion of recently acquired satellite imagery.

As a case study, we will apply it to Brussels to retrieve  surface albedo and emissivity maps at a neighbourhood scale. These results can be considered an asset to be used by urban planners and decision-makers to identify what urban areas should be considered priority candidates for an intervention to mitigate heat pollution, which in turn, shall allow authorities or civil organisations to maximise benefits from limited financial resources. Since the SuaBe’s methodology is based on a robust and rigorous physical model, it can be seamlessly implemented in any other city worldwide, provided that a geometric urban database is available.