Daytime Thermal Anisotropy of Urban Neighbourhoods: Morphological Causation
Daytime Thermal Anisotropy of Urban Neighbourhoods: Morphological Causation
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DOI：
10.3390/rs8020108
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发表时间：
2016-02-01
期刊：
影响因子：
5
通讯作者：
Voogt, James A.
中科院分区：
文献类型：
--
作者：
Krayenhoff, E. Scott;Voogt, James A.
地表温度是边界层气象学中的一个关键变量，通常通过对发射的热辐射进行远程观测而获得。然而，城市的三维结构使问题变得复杂：城市表面不均匀的太阳能加热在邻里尺度上产生了地表热发射的有效各向异性。因此，遥感城市地表温度会随着传感器视角的不同而变化。将微尺度城市地表温度模型与热遥感模型相结合，预测了简化邻域结构的有效各向异性。前一个模型提供了一系列城市形态的详细地表温度分布，而遥感模型计算了多个视角的总温度。根据加拿大温哥华附近地区的测量结果，评估了组合模型再现观测到的各向异性的能力。与之前的建模研究一样，各向异性被低估了。小(小平面尺度)结构的适度覆盖可以解释缺失的大部分各向异性。随后，用该模式组合进行了1900多次敏感性模拟，并评估了白天有效热各向异性对日太阳路径(即纬度和时刻)和钝化邻域形式的依赖关系。有效各向异性的范围，以及与最低观测亮温的最大差值，中等建筑高度与间距比(H/W)的峰值，以及与峡谷(建筑之间)面积的比例；分散的高层城市形态产生最大的各向异性。最大各向异性随太阳高度的升高而增大，随短波辐照度的增大而增大。此外，对于H/W<；1.25，它与H/W呈线性关系，斜率取决于最大偏置传感器角度。最小亮度温度的降低是最大各向异性线性增长的主要原因。这些结果允许一阶估计作为建筑高度与间距比、建筑平面面积密度和短波辐射的函数的城市街区的最小有效各向异性大小。最后，对两个纬度的四个局地气候带进行了模拟。去除这些区域的邻街方向规律性，最大各向异性减少3%-31%。此外，与邻近形态相比，热和辐射材料属性对各向异性的预测作用较弱。本研究首次系统评价了城市景观的有效各向异性大小及其成因。
Surface temperature is a key variable in boundary-layer meteorology and is typically acquired by remote observation of emitted thermal radiation. However, the three-dimensional structure of cities complicates matters: uneven solar heating of urban facets produces an effective anisotropy of surface thermal emission at the neighbourhood scale. Remotely-sensed urban surface temperature varies with sensor view angle as a consequence. The authors combine a microscale urban surface temperature model with a thermal remote sensing model to predict the effective anisotropy of simplified neighbourhood configurations. The former model provides detailed surface temperature distributions for a range of urban forms, and the remote sensing model computes aggregate temperatures for multiple view angles. The combined model's ability to reproduce observed anisotropy is evaluated against measurements from a neighbourhood in Vancouver, Canada. As in previous modeling studies, anisotropy is underestimated. Addition of moderate coverages of small (sub-facet scale) structure can account for much of the missing anisotropy. Subsequently, over 1900 sensitivity simulations are performed with the model combination, and the dependence of daytime effective thermal anisotropy on diurnal solar path (i.e., latitude and time of day) and blunt neighbourhood form is assessed. The range of effective anisotropy, as well as the maximum difference from nadir-observed brightness temperature, peak for moderate building-height-to-spacing ratios (H/W), and scale with canyon (between-building) area; dispersed high-rise urban forms generate maximum anisotropy. Maximum anisotropy increases with solar elevation and scales with shortwave irradiance. Moreover, it depends linearly on H/W for H/W < 1.25, with a slope that depends on maximum off-nadir sensor angle. Decreasing minimum brightness temperature is primarily responsible for this linear growth of maximum anisotropy. These results allow first order estimation of the minimum effective anisotropy magnitude of urban neighbourhoods as a function of building-height-to-spacing ratio, building plan area density, and shortwave irradiance. Finally, four local climate zones are simulated at two latitudes. Removal of neighbourhood street orientation regularity for these zones decreases maximum anisotropy by 3%-31%. Furthermore, thermal and radiative material properties are a weaker predictor of anisotropy than neighbourhood morphology. This study is the first systematic evaluation of effective anisotropy magnitude and causation for urban landscapes.