基于亚像元估测的城市硬化地表景观格局分析
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Q96,Q149

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Urban landscape pattern study based on sub-pixel estimation of impervious surface
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    摘要:

    城市硬化地表不仅是影响城市生态环境质量重要因子,也是定量描述城市地表物理特征,进行城市景观分类的基础。基于多种分辨率遥感影像亚象元分类提取硬化地表成为近年来的研究热点。利用TM/ETM+和Quickbird不同分辨率遥感数据,以北京市中心城区为研究区域,对比分析回归树法和多元回归法的估测精度,选出预测硬化地表指数(Impervious surface index,简称为ISI)最优估测模型,并进行景观分类与城市景观格局分析。结果表明:(1)回归树亚象元估测法是提取硬化地表信息的一种有效的方法(最大相关系数=0.94),不同季节遥感影像可以挖掘地物在不同时期光谱差异,提高分类精度。(2)根据硬化地表指数划分城市用地类型,提供了量化分类的依据;(3)北京城市硬化地表景观格局表现出极强的空间梯度性,从北京市中心到郊区,ISI逐渐降低:城市二环以内,ISI平均值为67.32%,集中分布在高于60%范围;二环—四环分布比较相似,平均值分别为65.91%、66.13%;四环—五环区域ISI下降迅速(ISI=46.42%),存在两个高峰,分别是低于<20%和>70%;六环以外区域,非硬化地表成为主要类型(ISI=9.32%);(4)北京市景观格局在不同区域差异巨大:从市中心到市郊,景观破碎化程度加强,平均斑块面积逐渐增加,高密度城市用地比例逐步下降,自然地表平均面积呈现U形分布;中等密度城市用地斑块密度最高,破碎度最高;城市用地形状比自然地表复杂,低密度城市用地形状最为复杂。(5)运用回归树亚象元估测法提取出北京中心城区硬化地表信息,为城市地表景观特征提取与高精度量化分类提供了新的研究方法与研究思路,在此基础上进行了景观分类及景观格局分析,进一步推广并论证了硬化地表在景观生态学研究中的应用价值。

    Abstract:

    The urban impervious surface (IS) refers to any nonporous land cover that prevents water from infiltrating into sub-surface layers, e.g., buildings, roads, parking lots, sidewalks, and other built surfaces. In addition to its use as an indicator of environmental influences, IS has also been applied to determine the spatial extent, intensity, and type of urban land use/cover changes. In recent years there has been increased interest in the use of classification and regression tree model (CART) technology to map sub-pixel impervious surfaces. This process uses medium-resolution Landsat imagery to extrapolate IS over large-scale areas with high-resolution imagery as training data to represent the urban land-cover heterogeneity. The main advantage of the regression tree algorithm is that it can account for non-linear relations between predictive and target variables, and thus allows both continuous and discrete variables to be used as input (predictive) data. The distribution of impervious surface index (ISI) distribution was deriveded fom Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+) data by comparing it with CART and multi-stepwise regression (MSR). The results demonstrated that CART provided with the correlation coefficient of 0.94 and the average error of 8.59% with consistent and acceptable accuracy, which was better than MSR. The average ISI value for the total study area was 20.80% with standard deviation of 0.29. However, in most grids (58.60%) the average ISI was less than 10%. ISI percentage values in different regions also varied dramatically ranging from 67.32% in Zone 1 to 9.32% in Zone 6. Further, the spatial distribution patterns of IS exhibited spatial gradients increasing in value from the city outskirts to the inner urban areas. Utilizing ISI a new landscape classification system was developed, composed of the following four categories: natural cover (ISI≤10%), low-density urban (10< ISI≤40), medium-density urban (4160). The results of landscape pattern analysis demonstrate that high-density urban is the dominant landscape within the 4th ring-road covering 67.41% of the surface area, while natural cover is the dominant form of land cover outside the 5th ring-road. Landscape patterns varied extremely with landscape fragmentation index and average patch area, and the average area of natural cover exhibits a U shape as you moved from the inner urban area to the outskirts. It can be concluded that ISI is able to serve as a useful indicator for landscape classification and landscape pattern analysis.

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肖荣波,欧阳志云,蔡云楠,李伟峰.基于亚像元估测的城市硬化地表景观格局分析.生态学报,2007,27(8):3189~3197

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