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.
KeywordsRadiative transfer Street canyon Urban meteorology
Robert Schoetter and Sue Grimmond are thanked for useful discussions. The building geometry for London was obtained from Emu Analytics, whose data combine building outlines from Ordnance Survey Open Map with building height from lidar data collected in 2014 and 2015. Building geometry data for Los Angeles were obtained from the Los Angeles County GIS Data Portal, with the original data generated from aerial imagery. A number of the integrals were calculated using the online symbolic integration tools at www.wolframalpha.com and www.integral-calculator.com.
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