title: Satellite-derived subsurface urban heat island.
abstract: The subsurface urban heat island (SubUHI) is one part of the overall UHI specifying the relative warmth of urban ground temperatures against the rural background. To combat the challenge on measuring extensive underground temperatures with in situ instruments, we utilized satellite-based moderate-resolution imaging spectroradiometer data to reconstruct the subsurface thermal field over the Beijing metropolis through a three-time-scale model. The results show the SubUHI's high spatial heterogeneity. Within the depths shallower than 0.5 m, the SubUHI dominates along the depth profiles and analyses imply the moments for the SubUHI intensity reaching first and second extremes during a diurnal temperature cycle are delayed about 3.25 and 1.97 h per 0.1 m, respectively. At depths shallower than 0.05 m in particular, there is a subsurface urban cool island (UCI) in spring daytime, mainly owing to the surface UCI that occurs in this period. At depths between 0.5 and 10 m, the time for the SubUHI intensity getting to its extremes during an annual temperature cycle is lagged 26.2 days per meter. Within these depths, the SubUHI prevails without exception, with an average intensity of 4.3 K, varying from 3.2 to 5.3 K.
authors.affiliation: Jiangsu Provincial Key Laboratory of Geographic Information Science and Technology, International Institute of Earth System Science, and ⊥School of Earth Sciences and Engineering, Nanjing University , Nanjing 210093, China.
authors.forename: Wenfeng
authors.initials: W
authors.lastname: Zhan
authors.forename: Weimin
authors.initials: W
authors.lastname: Ju
authors.forename: Shuoping
authors.initials: S
authors.lastname: Hai
authors.forename: Grant
authors.initials: G
authors.lastname: Ferguson
authors.forename: Jinling
authors.initials: J
authors.lastname: Quan
authors.forename: Chaosheng
authors.initials: C
authors.lastname: Tang
authors.forename: Zhen
authors.initials: Z
authors.lastname: Guo
authors.forename: Fanhua
authors.initials: F
authors.lastname: Kong
mesh_terms: D002947:Cities / Q000706:statistics & numerical data*; D004784:Environmental Monitoring; D006358:Hot Temperature; D008962:Models, Theoretical; D058998:Remote Sensing Technology; D012621:Seasons; D013696:Temperature