The surface urban heat island (SUHI) phenomenon has become increasingly severe due to the combined effects of global warming and rapid urban expansion, and the difference between urban and rural thermal environments has increased significantly. This trend has profound impacts on social, economic, and ecological environments. Research related to SUHI has achieved fruitful results; however, quantitative research methods for SUHI have not been unified with standards and systems, which will certainly affect the comparability of the results of SUHI research. Few studies have combined and compared multiple SUHI methods. Therefore, we designed a study of the Yangtze River Delta (YRD) urban agglomeration as a test case to quantitatively analyze the differences between SUHI results in different urban and rural contexts based on five different SUHI research methods. It was found that (1) there were significant differences in the SUHI intensity results among the different methods. The maximum difference in the SUHI intensity obtained by different methods can be up to 6 °C. The lowest SUHI intensity was observed during the day in the urban–buffer method, and the lowest SUHI intensity was observed at night in the urban–water method. (2) Different methods affected the distribution of SUHI areas and their evolutionary characteristics. The NHI (no heat island), WCI (weak cold island), and WHI (weak heat island) zones were larger, with proportions exceeding 70%. The expansion range of the heat island zone during the daytime was mainly in the west and north of the YRD urban agglomeration, whereas the expansion of the heat island range at night was mainly concentrated in the center and south. (3) The trend changes observed using different methods were significantly different. When we applied the urban–buffer and municipal–nonmunicipal methods, most cities showed an upward trend. However, when the other methods were applied, most cities exhibited a downward trend. The differences in trend results owing to the choice of different methods were greater with respect to values in the summer months and smaller in the winter months.

Using the China National Knowledge Infrastructure (CNKI) and Web of Science (WoS) databases, 487 articles that used remote sensing methods to study the intensity of surface urban heat islands (SUHIs) over the past 20 years were obtained using keyword searches. A multidimensional analysis was conducted on these articles from the perspectives of the research methods used, spatiotemporal distribution characteristics of the research area, research development trends, and main challenges. The research found that (1) the growth trend of the various SUHI research methods over the years was similar to the overall trend in the number of publications, which has rapidly increased since 2009. (2) Among the SUHI research methods, temperature dichotomy is the most widely used worldwide; however, defining urban and rural areas is a main challenge. The Gaussian surface and local climate zoning methods have gradually emerged in recent years; however, owing to the limitations of the different urban development levels and scales, these methods require further improvement. (3) There are certain differences in the application of SUHI research methods between China and other countries.

Surface urban heat islands (SUHIs) are essential for evaluating urban thermal environments. However, current quantitative studies of SUHIs ignore the thermal radiation directionality (TRD), which directly affects study precision; furthermore, they fail to assess the effects of TRD characteristics at different land-use intensities, on the quantitative studies of SUHIs. To bridge this research gap, this study eliminates the interference of atmospheric attenuation and daily temperature variation factors, in quantifying the TRD based on land surface temperature (LST), from MODIS data and station air temperature data for Hefei (China) from 2010–2020. The influence of TRD on SUHI intensity quantification was evaluated by comparing the TRD under different land-use intensities in Hefei. The results show that: (1) daytime and nighttime directionality can reach up to 4.7 K and 2.6 K, and occur in areas with the highest and medium urban land-use intensity, respectively. (2) There are two significant TRD hotspots for daytime urban surfaces, where the sensor zenith angle is approximately the same as the forenoon solar zenith angle, and where the sensor zenith angle is near its nadir in the afternoon. (3) The TRD can contribute up to 2.0 K to the results of assessing the SUHI intensity based on satellite data, which is approximately 31–44% of the total SUHI in Hefei.