Research and application of city ventilation assessments based on satellite data and GIS technology: a case study of the Yanqi Lake Eco-city in Huairou District, Beijing

A method of performing city-scale ventilation assessments based on remote sensing (RS) and geographic information system (GIS) technology is proposed and applied effectively in an assessment of the local ventilation environment before and after the construction of the Yanqi Lake Eco-city in Huairou District, Beijing. The ventilation environment of a city is dependent on its background wind environment and ventilation potential. The background wind environment can be assessed through meteorological statistical analyses or numerical simulations, whereas the ventilation potential can be estimated using the underlying surface dynamic roughness length (RL) and the surrounding sky view factor (SVF). Based on the principle of morphology, the RL of a vegetation area is determined mainly by the vegetation types, vegetation canopy area index and vegetation height, whereas the RL of an urban area is defined mainly by the building area coverage and building height. The SVF can be estimated according to high-resolution digital raster elevation data. Based on the combination of the RL and SVF, the ventilation potential is graded, and the ventilation potential index (VPI) is defined and used to assess quantitatively the ventilation capacity of the city. The present study calculates the RL of the Yanqi Lake Eco-city using Landsat-TM5 satellite data from 26 July 2011, Geoscience Laser Altimeter System (GLAS) satellite data from 2005 and Beijing basic geographical data at 1:2000 from 2009. Subsequently, the RL and ventilation potential distribution of the Yanqi Lake Eco-city is mapped at a 100m spatial resolution. The ventilation conditions before and after the construction of the Yanqi Lake Eco-city are evaluated using the VPI in combination with the background wind field. According to changes in the ventilation capacity, relevant policy suggestions for urban buildings and design factors for ventilated corridors are postulated.