Dynamic Mapping Of Urban Impervious Surfaces In Nanjing Based On Landsat Long-term Time Series Observations

As an important part of urban ecosystems,urban impervious surface(UIS)is an important index of urbanization process.Clarifying the spatio-temporal patterns of urban impervious surface plays an important role in deeply mastering the ecological,economic and social benefits of UIS.Taking advantage of yearly Landsat long-term observations(1984 to 2016),in tandem with high spatial resolution Google Maps,mapping the spatio-temporal patterns of UIS in Nanjing was conducted in this study.The Landsat 5 TM satellite images from 1984 to 2011 and the Landsat 8OLI satellite image data from 2013 to 2016 were collected and atmospherically corrected to support the extraction of UIS.Eight remote sensing based UIS extraction indices including the urban index(UI),the normalized difference built-up index(NDBI),the index-based built-up index(IBI),the visible red-based built-up index(VrNIR-BI),the visible green-based built-up index(VgNIR-BI),the negative normalized difference vegetation Index based impervious surface(NNDVI-IS),the corrected negative normalized difference vegetation Index-Impervious Surface and the Impervious Surface Based on Tasseled Cap(ISBTC)were derived and applied to map UIS in Nanjing.Afterwards,500 random points were generated within the study area and overlaid onto the historical Google Earth imagery with high spatial resolution to evaluate the UIS extraction accuracies of the eight methods.The results showed that the overall accuracy of the eight methods was more than 60%.The CNNDVI-IS and ISBTC models outperformed other models in the extraction of UIS.The highest extraction accuracy of 88.2%,with a Kappa coefficient of 0.85 was made by ISBTC model..VgNIR-BI and VrNIR-BI models under-performed in the extraction of UIS compared to others,and the UI,IBI and NDBI models are moderately performed.Ultimately,the best ISBTC model was determined to map the UIS in Nanjing to depict its spatio-temporal trends.Through the analysis of the spatial and temporal patterns of UIS in Nanjing from 1984 to2016,several key points can be summarized as follows:(1)The UIS area ratio in Nanjing increased from 6.17% in 1984 to 28.19% in 2016,increased by 22.02%,and a continuous ascending trend in UIS was witnessed;(2)After 1995,the increment rate of UIS in Nanjing was higher than that before 1995,which indicating that the year of 1995 was the turning point of accelerating urbanization.(3)The UIS of Nanjing mainly concentrated on the area along the Yangtze River Banks,where the development of UIS was faster than other regions.(4)The UIS in the sorthern portion of the Yangtze River was higher that of the north,so did the increment rate of UIS(5)The driving forces contributing to the observed rapid sprawl of UIS were the growth of population,policy shift and economic development.This study provides the following reference for the healthy development of urban impervious surface in Nanjing:(1)develop a scientific land use specification;(2)reasonable development to reduce the difference between the north and south of the Yangtze River(3)toimprove the using of land(4)Rational planning of urban infrastructure construction;(5)reasonable planning of traffic lines.