Research On Impervious-surface-based Urban Expansion And Ecological Effect

Impervious surface is defined as any area consisting of constructed surface which water cannot infiltrate to reach the soil.It not only serves as a key indicator of the degree of urbanization,but also has been widely applied in micro-ecosystem quality evaluation.The increasing replacement of nature landscape by impervious surface leads to the change of natural factors,such as hydrological character,soil quality,thermal environment and land use status.Human factors,including population density,economic situation,agricultural development,are also within its radius of influence,to a certain extent.Therefore,it is essential to monitoring impervious surface distribution timely and accurately to ensure urban development is sustainable.Remote sensing technology has become an important method,and may be the only viable way,to effectively extract impervious surface due to its high efficiency and low cost with large coverage.Taking Jiaozhou Bay region as research object,this paper extracted the impervious surface distribution information with the utilization of medium resolution Landsat imagery.Combined with humane statistics,the ecological effect of urban expansion was analyzed.Extraction of impervious surface distribution,analysis of urban expansion and ecological effect evaluation were accomplished.The understanding and results are as follows.1.The spectral characteristics of typical urban landscapes,especially the easy-confused impervious surface and soil,were analyzed,laying a foundation for the proposition of new impervious surface index.Different from traditional band-ratio approach,which using multispectral bands as components in the index directly,feature extraction was introduced in this paper.The new index,referred to as combinational build-up index(CBI),is based on the new features derived from three lower-level indices,the first component from principal components(PC)transformation,Soil Adjusted Vegetation Index(SAVI)and Normalized Difference Water Index(NDWI),representing high albedo,vegetation and low albedo respectively.The new index was tested using various remote sensing images at different spectral and spatial resolutions.Qualitative and quantitative assessments of the accuracy and separability of CBI,together with the comparison with other existing indices,were performed.The result of this study indicates that CBI is able to serve as an effective impervious index and can be applied widely.2.This paper analyzed the over or under estimation of impervious surface,inconsistency between endmember model and biophysical composition in mixed pixels,and presents a biophysical adaptive spectral mixture analysis(BASMA)for impervious surface mapping.It integrate the feature space of minimum noise fraction(MNF)and two biophysical indices,named CBI and NDVI,to determine the spectrum features of endmembers and pixel-level endmember model with the utilization of classification tree.Then linear spectral mixture analysis(LSMA)was applied to obtain the abundance of impervious surface.Results indicate that the BASMA method achieves a better performance than four-endmember SMA.3.Taking the impervious surface abundance imagery in 2009 and 2013 achieved by BASMA as research objects,hierarchical statistical analysis method was applied to clarify the changes in impervious surface distribution patterns.Qualitative and quantitative analysis was conducted to illustrate the variation characteristics and the driving force of urban expansion.4.With the combination of remotely sensed data and humane statistics,an eco-environmental quality evaluation index system was established based on the pressure-state-response framework.Necessary ecological evaluation indices and weights of indicators were extracted and assigned weights of indicators were extracted and assigned according to the practical situation of the research area during the design of the evaluation model.It is indicated that,during this period,the quality of ecological environment in the study area showed a downward trend on the whole.Urban fringe region,new urban areas,such as Huangdao District and Jiaonan District,showed an obvious decline,while area mainly made up of mixed landscape along the coast,inner city and rural area didn't witness significant variations.5.Ecological effect of urban expansion was illustrated through analyses about impervious surface distribution and eco-environmental quality evaluation index in the study area.It can be concluded that the expanded areas partly consistent with the regions that suffer from the detrimental effects.The worsening quality of ecological environment strongly associated with increasment of impervious surface fraction in urban fringe region,suburban and new city areas.On the other hand,however,this regularity didn't go to most parts of countryside and mixed landscape along the coast of Jiaozhou Bay.That's because the rich vegetation and water resources in these areas help to maintain the stability of the ecological environment.