Assessing the spatial-temporal impacts of underlying surfaces on 3D thermal environment: A field study based on UAV vertical measurements

The composition of underlying surfaces has a significant impact on the thermal environment within urban canopies. Current research predominantly focuses on surface temperature (Ts) and near-surface air temperature (Ta) at the pedestrian scale. However, studies on the Spatial-temporal distribution characteristics of the three-dimensional (3D) thermal environment within urban canopies remain scarce. This study selected 7 typical underlying surfaces and investigated the Spatial-temporal distribution characteristics of Ts and vertical Ta from 1.5 to 200 m by using unmanned aerial vehicle (UAV) and fixed measurement techniques. The results indicated that the largest differences in 3D thermal environment characteristics across different underlying surfaces occurred at 14:00, with the smallest at 05:30. Each underlying surface exhibited distinct day-night variations in their impacts on the 3D thermal environment, with the water body showing significant day-night difference. The dense forest positively regulated the urban thermal environment, but at night, it slightly adversely effected the thermal environment at the pedestrian scale. The bare soil had the second most adverse effect on the 3D thermal environment during the day, following the impervious pavement; thus, exposure of the land should be minimized in urban environments. There was a significant positive correlation between Ts and Ta at different heights (P