Assessment of an Urban Sensor View Model for thermal anisotropy

The surface-sensor-sun relations model (SUM) of Soux et al. [Soux, C.A., Voogt, J.A., & Oke, T.R. (2004). A model to calculate what a remote sensor 'sees' of an urban surface. Boundary-Layer Meteorology, 111, 109-132.] is modified to include a coupling of SUM with the actual building structure of a study area, thereby allowing variable building heights and shapes to be represented within SUM as well as the provision for an inter-building spacing that provides a more realistic urban block structure in the internal SUM urban surface representation. Model simulations using both modifications are performed and compared with airborne observations of surface temperature made over a Light Industrial area and a downtown area of Vancouver, BC. The results are generally good, although there is a general tendency to underestimate the overall thermal anisotropy. Use of mean facet temperatures in the validation limits validation statistics for one study area; improvements are made when facet temperatures are updated from individual flight lines. Performing a sensitivity analyses on the contributions to the thermal anisotropy suggests that surface structure and microscale temperature variability both make substantial contributions to the total anisotropy. This finding underscores the importance of including microscale temperature variability in assessments of urban thermal anisotropy. Full hemispheric plots of directional temperature and statistics for each study area are presented as an application of the model and show smooth variations in directional temperature when averaged over the study area. (C) 2007 Elsevier Inc. All rights reserved.