High-resolution spectral mapping of urban thermal properties with Unmanned Aerial Vehicles

The integration of microclimatic information and physical properties of the materials into urban design is essential for adequately addressing the challenges related to climate change and to adaptation of urban environment to new climatic loads. Especially, the thermal and optical properties of materials used in the urban fabric play a fundamental role in determining the microclimate and building's energy balance. The present research approach aims at analyzing the thermal characteristics of the materials and the surface temperature distribution using airborne multispectral imaging sensors mounted on Unmanned Aerial Vehicle (UAV). Aerial surveys and in-situ measurements have been carried out in April 2016 at the Municipality of Ymittos in Athens (Greece). The applied multi-sensory survey included high resolution imaging of the materials in the visible and near infrared (VIS/NIR) wavelength region and IR part of the spectrum. The images have been analysed to form maps of surface temperature distribution and of material properties. The derived thermal maps show the changes in surface temperatures of the urban materials during a diurnal heating cycle. In addition, ground measurements of VIS/NIR reflection and albedo from the survey area were obtained and an albedo map and a map of apparent thermal inertia were derived. Thermal scanning of the asphalt in the area, allowed the estimation of the state of decay due to weathering and traffic. The combined maps of surface temperature, albedo and apparent thermal inertia give new perspectives of the urban features and enhance the classification of fine urban material and the energy balance models.