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The study on landscape pattern is an important field of urban land use and ecological change. Since 1990s, the widely accepted Patch-Corridor-Matrix model is generally used in qualitative description of landscape pattern. In recent years, quantitative evaluation on urban landscape dynamics is becoming hot in research. By making a critical review on existing research methods of landscape pattern, a new approach based on RS/GIS is put forward in this paper, comprising three steps, "General pattern characteristics - Gradient differentiation feature- Directional signature of the landscape", and we call it GGD. This method is applied to the case study of Xi'an metropolitan area in China. The result shows that the method is effective on quantitative study of urban landscape.
The preparation of the method GGD is setting up research platform based on RS and GIS. By using the software of Geographical Information System (Arcgis9.0 & Erdas), the authors got the interpretation of remote sensing images of different years, and carried on the division of the landscape type of the research region. By calculating various index of landscape level with software Fragstats3.3 as an assistant tool and adopting three steps of GGD combined with landscape index, this paper can assesses the landscape spatial pattern of urban area: 1) General pattern characteristics analysis is to get transition probability of various landscape through Markov chain and to predict the landscape transformation by introducing CA model. The analysis emphasizes on total landscape structure and its change over time; 2) Gradient characteristic analysis, which makes gradient zone by taking city as a center outwardly with certain distance and contrastively analyzes the landscape index of each subarea, stresses the spatial character of landscape pattern, verifies urban morphology theories and provides the quantitative warranty for establishment of urban modality. Therefore, the analysis is useful for supervising urban expanding speed; 3)Direction characteristic analysis, which is setting up radiate strip on west-east, south-north, southwest-northeast and northwest-southeast and form certain width on each direction, can precisely and quantitatively indicate different characteristic of urban landscape at each development direction, and by combined with gradient analysis it is highly advantageous to the examination and planning of urban expanding direction.
In the case study on Xi'an metropolitan area, remote sensing images of 1988 and 2005 Landsat-TM were handled, and the division of the landscape type of the region was also carried on. According to the above approach, the result was got and some valuable information was showed as follows:
1) The diversity of overall landscape of Xi'an metropolitan area tends to increase and the degree of fragmentation tends to deepen. With the increase of urbanization level, the visual component of landscape is more and more diversified, the shapes of landscape is more and more complicated and ecologically more and more fragmented. In the region where urbanization level is low, natural landscape is the main component of the landscape, the diversity of the landscape is low. And because landscape is seriously disturbed by human activities with urbanization, fragmentation of the landscape emerges periodically.
2) In the process of transect gradient analysis, the landscape pattern index can explore the urbanization gradient, and its trend to reduce gradually towards the suburban. The landscape of area with a high urbanization level is mainly man-created, and its patches show large number, small area, simple shape and higher landscape heterogeneity. The transect gradient analysis on different time series indicates the relationship between urbanization level and landscape pattern. The landscape of urban area suffers intensely from human being, and its pattern component and spatial collocation depends on the interference intensity to a large degree. In the area with a high urbanization level, its pattern component is more man-created and less natural landscape. The landscape collocation characteristic of its patches takes on a large number, little average area, simple shape and low polymerization degree.
3) Analysis of direction and gradient of Xi'an metropolitan area can quantitatively reflect influence of urbanization and characteristics of urban landscape in the main development axes of north-south and east. Result shows that the degree of internal integration between Xi'an city and Xianyang city is gradually enhanced with the quickly urbanization course in China.
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