Combining sub-facet scale urban energy balance and sensor-view models to investigate the dependence of effective thermal anisotropy on city structure

A new micro-scale urban energy balance model (TUF-3D) is coupled to an existing urban sensor-view model (SUM; Soux et al. 2004) to investigate the dependence of effective anisotropy in thermal remote sensing on variations in the structure of simple urban surfaces. Results for a summer clear-sky midlatitude scenario show that modelled maximum diurnal anisotropy peaks for roughness element plan area fractions (λ_p) of approximately 0.35 for aligned, evenly-spaced arrays of identical cubic buildings. When both building height and λ_p are varied, a linear relationship between canyon H/W and maximum diurnal anisotropy is found for H/W < 1.5, and maximum anisotropy occurs at H/W ≈ 1.5-2.0. The impact of regularity of street orientation on anisotropy is noticeable, but not dominant. Finally, a parameterization of effective anisotropy as a function of solar angle and of shaded and sunlit facet temperatures is proposed for aligned, evenly-spaced arrays of identical buildings, and is compared with model results.