An Optimization Method for Surface Urban Heat Island Footprint Calculation Based on Anisotropy Assumption

Footprint (FP) is the main indicator for quantitatively analyzing the surface urban heat island (SUHI) effect. Existing SUHI FP calculation methods ignore the interference caused by city shape and are mostly based on the isotropic expansion assumption, resulting in too rough FP. Therefore, this paper proposed an optimization schema leveraging the angle segmentation and anisotropy assumption. This method divided urban area and its buffer rings into 16 sectors with equal central angles and selected appropriate land surface temperature (LST) curves for exponential decay fit. The final FP was determined by the SUHI extension distance and reference suburban LST. The study extracted the SUHI FPs of 27 cities in the central region of the Yangtze River Delta (YRD) in summer 2019 and compared it with traditional methods. The results showed that the FPs calculated by this method were more detailed because it minimized the influence of urban form, topography and the surrounding landscape. Moreover, this method revealed the vital role of the allocation and proportion of land use types around the urban area on the SUHI effect. This state-of-the-art method is meaningful for unveiling the SUHI spatial distribution pattern and providing scientific support for land planning of sustainable urban development