Development of a nationwide approach for large scale estimation of green roof retrofitting areas and roof-top solar energy potential using VHR natural colour orthoimagery and DSM data over Thessaloniki, Greece

Buildings, and other engineered structures that form cities, are responsible for a significant portion of the local and global impacts of climate change. Therefore, there is a need for the increase and large-scale implementation of energy-efficient and renewable energy-generation technologies. In this paper, we investigate a remotely sensed approach for assessing the potential capacity of installing rooftop photovoltaic systems and/or implementing green roof retrofitting measures in an urbanized area. In particular, we analyse the ways in which freely available, no-cost, very high spatial resolution orthoimagery and Digital Surfaces Models, along with geospatial vector data, can assist in delineating available roof area at the level of individual buildings across a Mediterranean city. The available data-sets are integrated and processed within a Geographical Object Based Image Analysis framework. The method was developed on the basis of a test area consisting of the town of Thessaloniki in Northern Greece. The correlation between the automated extracted roof area and the manual digitized reference data had a value of up to 0.9. The described approach can be applied nationwide across Greece, considering the national availability coverage of the data-sets, while the semantics can readily be transferred to neighbouring Mediterranean countries.