An Exponential Model of Urban Geometry for Use in Radiative Transfer Applications

In radiative transfer schemes for urban areas it is common to approximate urban geometry by infinitely long streets of constant width, or other very idealized forms. For solar and thermal-infrared radiative transfer applications, we argue that horizontal urban geometry is described uniquely by the probability distribution of wall-to-wall separation distances. The analysis of building layout from contrasting neighbourhoods in London and Los Angeles reveals this function to be well fitted by an exponential distribution. Compared to the infinite-street model, this exponential model of urban geometry is found to lead to a significantly more accurate description of the rates of exchange of radiation between the sky, the walls and the streets of an urban canopy.