Exploring Influencing Factors for Differences in Integral and Complete Urban Surface Temperatures

Abstract

Complete urban surface temperature (UST) ( $T_{\textrm {c}}$ ) takes into account the total active surface areas and is used to estimate the surface temperature over a 3-D rough surface such as cities. Direct calculations of $T_{\textrm {c}}$ require temperatures of each surface of the urban canopy, which are hard to obtain in actual remote sensing observations. Moreover, solid-angle integral temperature ( $T_{\text {SI}}$ ) calculated using multiangle remote sensing observations has great potential for approaching $T_{\textrm {c}}$ . However, due to varying mechanisms, some differences remain between them. This study uses temperatures of urban facets in 3-D (TUF-3D) and surface-sensor-sun urban model (SUM) models to compute integral temperatures for multiple view angles over various urban forms and investigates the differences between $T_{\textrm {c}}$ and $T_{\text {SI}}$ and the influencing factors. The difference is minimized at VZA $=48^{\circ }$ –70° and VAA $=0^{\circ }$ –360°, and the mean absolute error (MAE) is 0.67 K. Urban canopy geometry (UCG) and solar zenith angles (SZAs) are the important influencing factors. Compared with $T_{\textrm {c}}$ , $T_{\text {SI}}$ underestimates the proportion of the wall. The MAE between $T_{\text {SI}}$ and $T_{\textrm {c}}$ decreases as the wall fraction in the integral domain increases but increases when the wall fraction exceeds a threshold. The upper limit of the optimal integral domain (OID) is basically 70° and the lower limit hovers around 48°, moving away from and then approaching the zenith as the SZA increases. This study evaluates the influencing factors for differences in $T_{\text {SI}}$ and $T_{\textrm {c}}$ . It offers a simple and high-accuracy method for approaching $T_{\textrm {c}}$ which can be used to facilitate research in urban energy balance and urban climate.