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加强绿化可有效缓解城市热岛(UHI)效应,但植被降温规律如何,如何科学绿化一直模糊不清。以南京市ETM+影像为数据源,经ATCOR2模块大气校正后,提取了南京城区地表温度(LST)、归一化植被指数(NDVI)和减化比值植被指数(RSR),基于实测值和同时相ASTER数据反演结果的双重验证,拟合了两种植被指数与地表温度的定量关系,并进行了对比研究。结果表明:南京市存在明显的UHI,城区水体和绿地为显著的低温区,除水体外,植被覆盖度高的区域地表温度明显低于植被稀少或无植被区;地表温度与NDVI呈显著线性负相关,与RSR呈显著幂函数负相关,后者的相关性高于前者;以RSR=3.2为界,此值之前,地表温度随着植被覆盖增加而锐减,此值之后,植被覆盖继续增加,地表温度却趋于恒定,呈现植被降温效应“饱和”现象;RSR能直接说明对于不同下垫面,增加相同的植被覆盖度其降温效果存在差异,而不进行土地利用分类,NDVI无法揭示此现象。
Strengthening greening can effectively relieve the urban heat island (UHI) effect, but how the vegetation cooling rules and how scientific greening has been vague. Taking Nanjing ETM + image as data source and atmospheric correction of ATCOR2 module, the LST, NDVI and RSR of Nanjing urban area were extracted. Based on the measured data and simultaneous phase ASTER data inversion results of the double validation, fitting the two vegetation index quantitative relationship with the surface temperature, and conducted a comparative study. The results show that there is obvious UHI in Nanjing, and the urban water bodies and greenbelt are obviously low temperature areas. Except for water body, the surface temperature in the area with high vegetation coverage is obviously lower than that in vegetation or no vegetation area. The surface temperature is significantly negative with NDVI , And RSR was negatively correlated with a significant power function, the latter was higher than the former; with RSR = 3.2 as the boundary, before this value, the surface temperature dropped sharply with the increase of vegetation coverage. After this value, vegetation coverage continued to increase , The surface temperature tends to be constant, showing the phenomenon of “saturation” of the vegetation cooling effect. RSR can directly explain that for the different underlying surfaces, the same vegetation coverage has different effects on the cooling effect without land use classification, and the NDVI can not Reveal this phenomenon.