Using urban canyon geometries obtained from Google Street View for atmospheric studies: Potential applications in the calculation of street level total shortwave irradiances

Abstract

This paper presents an implementation of digital image processing tools, in order to reconstruct building geometries and urban sky view factors for individual street canyons around the world. By using the Google Street View image database, it is possible to reconstruct canyon fisheye images at any point where a Google panorama is available. The Hugin software allows the geometrically correct merging of independent images in order to create a fisheye projection, covering the upper hemispheric view of the sky. Sky view factor calculations may then be performed by specialised software on the reconstructed fisheye image. In order to analyse the fitness of reconstructed panoramas, control images taken with a fisheye lens camera were used for comparison. The Rayman model was then used to calculate total shortwave global irradiances from the restricted canyon view and from a full hemispheric view. Finally, total shortwave global irradiances were measured for the same position in the street canyon and compared against observatory measurements under a full sky view, this in order to evaluate the performance and usefulness of idealised calculations. The reconstructed urban geometries returned acceptable fine-scale descriptions, and their potential utility for scientific purposes in the atmospheric sciences was demonstrated with the examples provided.