TY - JOUR
T1 - Global mapping of urban thermal anisotropy reveals substantial potential biases for remotely sensed urban climates
AU - Du, Huilin
AU - Zhan, Wenfeng
AU - Liu, Zihan
AU - Scott Krayenhoff, E.
AU - Chakraborty, T. C.
AU - Zhao, Lei
AU - Jiang, Lu
AU - Dong, Pan
AU - Li, Long
AU - Huang, Fan
AU - Wang, Shasha
AU - Xu, Yuyue
N1 - We gratefully acknowledge the National Natural Science Foundation of China (42171306, 42001270, and 42201337) for providing support for this current study. We also thank the support from the National Youth Talent Support Program of China. TC Chakraborty’s contribution was supported by Coastal Observations, Mechanisms, and Predictions Across Systems and Scales- Great Lakes Modeling (COMPASS-GLM), a multi-institutional project supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research as part of the Earth and Environmental Systems Modeling program. Pacific Northwest National Laboratory is operated for the Department of Energy by Battelle Memorial Institute under contract DE-AC05-76RL01830. We would like to thank Dandan Wang from China University of Geosciences (Beijing) for providing thermal anisotropy results of 25 cities to assist comparative analysis, and to thank the anonymous reviewers for their insightful comments.
We gratefully acknowledge the National Natural Science Foundation of China (42171306, 42001270, and 42201337) for providing support for this current study. We also thank the support from the National Youth Talent Support Program of China. TC Chakraborty's contribution was supported by Coastal Observations, Mechanisms, and Predictions Across Systems and Scales- Great Lakes Modeling (COMPASS-GLM), a multi-institutional project supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research as part of the Earth and Environmental Systems Modeling program. Pacific Northwest National Laboratory is operated for the Department of Energy by Battelle Memorial Institute under contract DE-AC05-76RL01830. We would like to thank Dandan Wang from China University of Geosciences (Beijing) for providing thermal anisotropy results of 25 cities to assist comparative analysis, and to thank the anonymous reviewers for their insightful comments. Wenfeng Zhan designed research; Huilin Du and Wenfeng Zhan performed data analysis; Huilin Du, Wenfeng Zhan, and Zihan Liu wrote manuscript; E. Scott Krayenhoff, TC Chakraborty, Lei Zhao, Lu Jiang, Pan Dong, Long Li, Fan Huang, Shasha Wang, and Yuyue Xu contributed ideas to data analysis, interpretation of results, or manuscript revisions.
PY - 2023/8/30
Y1 - 2023/8/30
N2 - Urban thermal anisotropy (UTA) drastically impacts satellite-derived urban surface temperatures and fluxes, and consequently makes it difficult to gain a more comprehensive understanding of global urban climates. However, UTA patterns and associated biases in observed urban climate variables have not been investigated across an adequate number of global cities with diverse contexts; nor is it known whether there are globally measurable factors that are closely related to the UTA intensity (UTAI, quantified as the maximum difference between the nadir and off-nadir urban thermal radiation). Here we investigate the UTAI over more than 5500 cities worldwide using multi-angle land surface temperature (LST) observations from 2003 to 2021 provided by Moderate Resolution Imaging Spectroradiometer (MODIS). The results show that the global mean UTAI can reach 5.1, 2.7, 2.4, and 1.7 K during summer daytime, winter daytime, summer nighttime, and winter nighttime, respectively. Using nadir LST observations as a reference, our analysis reveals that UTA can lead to an underestimation of satellite-based urban surface sensible heat fluxes (H) by 45.4% and surface urban heat island intensity (Is) by 43.0% when using LST observations obtained from sensor viewing zenith angles (VZAs) of ±60°. Practitioners can limit the biases of H and Is within ±10% by using LSTs from sensor VZAs within ±30°. We also find that UTAI is closely related to urban impervious surface percentage and surface air temperature across global cities. These findings have implications for angular normalization of satellite-retrieved instantaneous LST observations across cities worldwide.
AB - Urban thermal anisotropy (UTA) drastically impacts satellite-derived urban surface temperatures and fluxes, and consequently makes it difficult to gain a more comprehensive understanding of global urban climates. However, UTA patterns and associated biases in observed urban climate variables have not been investigated across an adequate number of global cities with diverse contexts; nor is it known whether there are globally measurable factors that are closely related to the UTA intensity (UTAI, quantified as the maximum difference between the nadir and off-nadir urban thermal radiation). Here we investigate the UTAI over more than 5500 cities worldwide using multi-angle land surface temperature (LST) observations from 2003 to 2021 provided by Moderate Resolution Imaging Spectroradiometer (MODIS). The results show that the global mean UTAI can reach 5.1, 2.7, 2.4, and 1.7 K during summer daytime, winter daytime, summer nighttime, and winter nighttime, respectively. Using nadir LST observations as a reference, our analysis reveals that UTA can lead to an underestimation of satellite-based urban surface sensible heat fluxes (H) by 45.4% and surface urban heat island intensity (Is) by 43.0% when using LST observations obtained from sensor viewing zenith angles (VZAs) of ±60°. Practitioners can limit the biases of H and Is within ±10% by using LSTs from sensor VZAs within ±30°. We also find that UTAI is closely related to urban impervious surface percentage and surface air temperature across global cities. These findings have implications for angular normalization of satellite-retrieved instantaneous LST observations across cities worldwide.
KW - Global urban climates
KW - Thermal remote sensing
KW - Urban heat island
KW - Urban surface fluxes
KW - Urban thermal anisotropy
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U2 - 10.1016/j.scib.2023.06.032
DO - 10.1016/j.scib.2023.06.032
M3 - Article
C2 - 37468411
AN - SCOPUS:85165209267
SN - 2095-9273
VL - 68
SP - 1809
EP - 1818
JO - Science Bulletin
JF - Science Bulletin
IS - 16
ER -