| Accelerating urbanization is a common global phenomenon, and rapid urbanization brought us a lot of problems. With the increase of city limits expansion, massive population, pollutant emission and energy consumption, the urban ecological environment has become extremely fragile and unstable. Urban ecological environment changing has caused a series of problems, urban heat island and urban thermal environment changing are two of the most serious problems of them. Urban heat island effect and urban thermal environment changing can cause deterioration of the urban ecological environment, and effect human health, etc.. From macroscopical view, urban heat island effect and urban thermal environment changing are also important factors of global warming. Therefore, since urban heat island effect was found in the early 19th century, it has always been attracting wide attention.Xixian New Area, between Xi’an city and Xianyang city, which was built from 2010 is one of the state-level new areas. As a new state-level area, its urbanization pace will must be faster and faster. And this will must also cause the thermal environment changing and the formation of urban heat island. Therefore, we hope to monitor and analyze its urban land surface temperature(LST) and urban heat island distribution in its initial stage of construction, and hope this can play a positive role in its more scientific urban planning and urban construction.Remote sensing technology, which was gradually developed from the late 20th century, is an integrated earth observation technology. And has been widely using in research of urban heat island effect and urban thermal environment changing. By means of remote sensing technology, taking May 20,2000 Landsat5 TM image, May 24,2010 Landsat7 ETM image, May 11,2014 Landsat8 OLI/TIRS image as the main data source, this article completed the study area LST retrieval, and researched on the spatial distribution, spatial-temporal change and its reason of LST and heat island of the study area based on the retrieval result. The main contents of this article include:(1) This article summarized and contracted existing remote sensing LST retrieval method, including their math formula, retrieval parameters, applicable scope, retrieval accuracy, etc., and selected the appropriate method for the data of this article to do the study area LST retrieval.(2) Using Qin’s mono-window algorithm, combined with remote sensing images and meteorological data, this article did the study area LST retrieval of three phases, and discussed the solving method and process of each parameter in the retrieval process. Finally we got the retrieval results, and tested the retrieval accuracy.(3) By grading LST retrieval results, the article discussed the distribution of each LST range of each year, and identified the distribution range and area of the study area heat island of each year. And we also analyzed and discussed the distribution changes of the study area LST and heat island.(4) By analyzing the correlation of NDVI (normalized difference vegetation index), NDWI (normalized water index), NDBI (normalized construction index), BSI (bare soil index) changes and LST changes of the study area of 2000 and 2014, the article discussed the relationship between the changes of LST and underlying surface, and summarized the reason of the distribution changes of LST and heat island.The analysis results showed that, the study area LST distributions of year 2000,2010 and 2014 were all different from each other, and varying degrees of heat island existed in the study area in all of the three phases. In 2000, heat island area ratio was 26.97%, and the heat island area was mainly distributed in the bare soil areas including the Weihe River, Jinghe River riparian, In 2010 and 2014, heat island area ratio were 35.14% and 25.5%, and the heat island area was mainly distributed in city regions, Fengdong New City, Fengxi New City and Qinhan New City were the top three rate areas. The heat island distribution form was developed from discrete to centralized. From 2000 to 2010, the heat island area increased by 8.17%; from 2010 to 2014, the heat island area reduced by 9.64%, but the hot zone area increased. Over all, heat island area increased first and then reduced during these 14 years, and the main source of the heat island converted from nature bare soil area to city construction area. The correlations of NDVI, NDWI, NDBI, BSI changes and LST changes of the study area of 2000 and 2014, from high to low, were in the order of NDBI, NDWI, BSI, NDVI, but the differences between them was little. In which, the correlation coefficients of NDVI & TSI, NDWI & TSI were-0.32 and-0.42, and were negative; the correlation coefficients of NDBI & TSI, BSI & TSI were 0.42 and 0.38, and were positive. So we can make the conclusion that underlying surface change can be considered as one of the important factors of the study area LST change. Increase of urban construction land area and bare soil area can cause the increase of LST and the formation of heat island region. On the contrary, increase of high water content vegetation area and water area can cause the reduction of LST and the formation of heat island region.Comprehensive analysis showed that, the urbanization of study area significantly affected its LST and heat island distribution. But the new urbanization of the study area, since the beginning of its construction as a state-level new area, didn’t cause a sharp increase of heat island area. This showed that scientific and rational urban planning and construction are effective ways to control the distribution of LST and heat island and their changes. |
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