Developing Component-Based Models for Hemispherical and Complete Urban Surface Temperatures and Analyzing the Relationships

The complete urban surface temperature ($T_{\text {c}}$) considers the temperatures of all the urban surfaces and is not restricted by the viewing biases inherent in remote sensors used to estimate surface temperature over rough urban surfaces. However,$T_{\text {c}}$is not typically directly measured but can be estimated. The hemispherical radiometric temperature ($T_{\text {H}}$), which integrates both horizontal and vertical surfaces, has the potential to approximate$T_{\text {c}}$.$T_{\text {H}}$is more easily obtained through remote sensing. However, view factors for individual surfaces will be biased for$T_{\text {H}}$. The current researches on the relationship between$T_{\text {c}}$and$T_{\text {H}}$are limited to specific experimental conditions. A systematic analysis of their differences is still lacking. We developed component-based$T_{\text {H}}$and$T_{\text {c}}$models based on a geometric method. The impact of component weights on the relationship between$T_{\text {H}}$and$T_{\text {c}}$was studied from a mathematical perspective based on building structure and solar zenith angle (SZA). The results were also validated using a coupled simple 3-D energy balance and sensor view model system. The results show that: 1) the difference of$T_{\text {H}}$and$T_{\text {c}}$($T_{\text {H}}-T_{\text {c}}$) varies with SZA in the range of −3 to 3 K.$T_{\text {H}}-T_{\text {c}}$approaches 0 at a moderate SZA of 45° and is positive in summer and negative in winter; 2) in the impact of building structure on$T_{\text {H}} -T_{\text {c}}$, the h/w effect is greater than$\lambda _{\text {p}}$. As building density increases, the absolute value of$T_{\text {H}}-T_{\text {c}}$increases; 3) the effect of SZA on$T_{\text {H}} - T_{\text {c}}$is larger than that of the building structure. After removing the effect of component temperature differences, the ranges of influence for SZA and building structure are −1.7 to 2.7 K and −1 to 2 K, respectively. SZA can affect the component temperatures and weights. Building structure mainly affects the component weights; and 4) when h/$w\lt 0.75, T_{\text {H}} -T_{\text {c}}$from the geometric method is closer to the referenced coupled model. When h/$w\ge 0.75$, the error is primarily caused by the “Boolean” assumption in regularly distributed urban scenes, which introduces differential biases in the modeling of$T_{\text {c}}$and$T_{\text {H}}$. This study facilitates the use of remote sensing to obtain a more representative urban surface temperature for energy balance estimation.

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