The influence of tree crowns on urban thermal effective anisotropy

A sensor view model is modified to include trees using a gap probability approach to estimate foliage view factors and an energy budget model for leaf surface temperatures (SUMVEG). The model is found to compare well with airborne thermal infrared (TIR) surface temperature measurements. SUMVEG is used to investigate the influence of trees on thermal anisotropy for narrow field-of-view TIR remote sensors over treed residential urban surfaces. Tests on regularly-spaced arrays of cubes on March 28 and June 21 at latitudes 47.6°N and 25.8°N show that trees both decrease and increase anisotropy as a function of tree crown plan fraction (λV) and building plan fraction (λP). In compact geometries (~ λP > 0.25), anisotropy tends to decrease with λV, whereas in open geometries the relation is reversed. Trees taller than building height cause anisotropy to increase with λV at all λP. These results help better understand and potentially correct urban thermal anisotropy.