# Correlation Analysis between UBD and LST in Hefei, China, Using Luojia1-01 Night-Time Light Imagery
## 4 Results and Analysis  
### Spatial Distribution of UBD and LST  
Taking the main urban area of Hefei City as the research area (including the urban waterbody), the UBD obtained from Luojia1-01 NTL imagery is consistent with the spatial pattern characteristics of the LST obtained from Landsat8 TIRS. From the overall distribution results of the study area UBD (Table 1), we can state the following: The proportion of the low-density area is the largest, reaching 47.06%; and the low-density areas are mainly distributed in the outer suburbs with high vegetation coverage, few buildings, and small human development space. Besides this, the area ratio of the middle-density area is 24.60%, and the high-density area and sub-high-density area take up less than 10%. The UBD value of Binhu New Town is the highest, reaching 48.25%. This area is an emerging urban circle developed in Hefei City in recent years, and it has had a new agglomeration effect on the UBD. Table 3 shows that the LST range of the study area is between 19.21 \({}^{\circ}\)C and 46.14 \({}^{\circ}\)C, with an average LST of 27.44 \({}^{\circ}\)C and a standard deviation of 4.72 \({}^{\circ}\)C. The spatial distribution of the LST is shown in Figure 10. The area of the sub-low temperature zone in the study area is the largest, accounting for 33.87%, and the sub-high temperature zone is also large (25.77%); the high-temperature zone and the low-temperature zone is the smallest. The area with LST larger than 26.97 \({}^{\circ}\)C is basically concentrated in the urban area, while the LST in the suburbs is mostly between 23.06 \({}^{\circ}\)C and 26.97 \({}^{\circ}\)C. The LST is quite different between the urban and suburban areas, and the UHI effect is significant. The partial views of Figures 9 and 10 show that there are three typical areas in the entire study area: the high-concentration areas for the LST and UBD are different in terms of geographic location. Figure 9 (I.) shows that the most concentrated areas of the high-density area are located at the intersection of four jurisdictions in Hefei City, with an average UBD greater than 25%. The area is an old town with numerous high-rise buildings, a dense population, low greening rate and fragmentation, and dense road networks. In Figure 10 (I. ), the densest and most continuous location in the high-temperature zone is in the southern part of the study area. By comparing remote sensing images, it was found that in addition to industrial production and anthropogenic heat emissions, there are a large number of low-rise industrial buildings and hard pavements which absorb a large amount of heat and lead to an increase in temperature. As shown in Figure 10 (II.a. and III.a.,b.,c. ), the low-temperature area is mainly concentrated in urban water bodies and forest parks. The water body and vegetation effectively cut off the high-temperature area and increase the fragmentation degree of the urban LST, while playing an essential role in relieving the UHI effect and the local thermal environment. Besides this, the values of LST and UBD at II.b. are significantly lower than those in the surrounding area. The remote sensing image showed that the area is an abandoned airport in Hefei which has high vegetation coverage and low UBD. The obtained UBD layer and the inversion LST layer were superimposed and analyzed. The results showed that the average temperature of the high-density area in the study area is 30.50 \({}^{\circ}\)C, and the average temperature of the sub-high-density zone is 27.35 \({}^{\circ}\)C. The average temperature of the sub-low-density zone is 23.32 \({}^{\circ}\)C, and the average temperature of the low-density zone is only 21.05 \({}^{\circ}\)C. Therefore, UBD has a warming effect on the thermal environment inside the city. Moreover, the LST increases with the UBD; especially at a specific scale, this warming effect is more obvious.