The positive micro-climate effects of urban greenery are well-known. During hot summers they reduce high temperatures caused by urban heat islands but also provide numerous other positive environmental effects, such as higher humidity and reduction of dust. The primary root of heat islands in cities is due to the absorption of solar radiation by mass building structures, roads and other hard surfaces. The absorbed heat is subsequently re-radiated to the surroundings and increases ambient temperatures. The vegetation can stop and absorb most of incoming solar radiation mostly via photosynthesis and evapotranspiration process. Moreover, the cooling effect of urban greenery goes beyond its boundary, in many cases in several hundreds of meters. The key components of the simulation representing these processes are: 3-D city model representing the morphology and building materials absorbing the solar radiation, solar radiation model capable of assessing the spatial distribution of solar radiation in a complex urban environment and urban vegetation model representing the varying properties of plants throughout the year.
Sentinel-2A is a new generation of ESA sensors particularly targeted to monitoring the land cover changes within the Copernicus Earth observation programme. Sentinel-2A will be launched to the orbit in June 12, 2015. The multi-spectral imagery data collected with a high time frequency of 10 days at a high spatial resolution (up to 10 m) and spectral resolution (13 spectral bands in visible near infrared and shortwave infrared spectrum) make this sensor particularly attractive for monitoring urban greenery. While the greenery (such as trees) is usually mapped by conventional methods in a much higher spatial resolution, the seasonal changes related to phenology remain uncaptured due to the low temporal resolution of airborne photogrammetric or ground surveys. Therefore, the remote sensing parameters of the Sentinel-2A mission make it attractive for monitoring urban vegetation especially in moderate climate zones, such as in Slovakia. The acquired imagery is planned to be used for derivation of various vegetation indices based on diverse reflectance in visible and infrared spectral bands. These characteristics are particularly important for assessing cooling effects of urban greenery and heat island mitigation in many cities.
This project will serve as a preparatory study to assess the applicability of the multispectral satellite imagery for approximating the dynamics of solar radiation transmittance of urban greenery to assess the cooling effects of the greenery via modelling the spatial distribution of solar radiation in a complex urban environment represented by a 3-D city model.