Abstract
A new viewpoint for understanding the urban expansion using impervious surface information, which is obtained using remote sensing imagery is presented. The purpose of this study is to understand and describe the urban expansion pattern with the view of impervious surfaces instead of the conventional view of land use/land cover. Six years' worth of impervious surface data (1990-2009) of Guangzhou are extracted via linear spectral unmixing analysis methods and spatial and temporal characteristics are discussed in detail. The area, density, and gravity centers changes of the impervious surfaces are analyzed to explain internal/external urban expansion. Meanwhile, five landscape indexes, such as patch density, edge density, mean patch size, area-weighted, and fragmentation index, are utilized to describe landscape changes of Guangzhou in past 20 years, which are influenced deeply by the impervious surface expansion. In order to detail landscape changes, two transects corresponding to the two urban expansion directions are designed and five landscape metrics in these two transects are reported. Conclusions can be drawn and shown as following: (1) temporally, the area of impervious sur- faces increases from 12,998 to 59,911 ha from 1990 to 2009. The amount of impervious surface varies in different periods. The annual growth rates of impervious surface area during 1990- 1995, 1995-1998, and 1998-2000 are 10.16%, 11.61%, and 10.78%, respectively; (2) annual growth rates decrease from 10.78% (1998-2000) to 5.67% (2000-2003). Nevertheless, from 2003-2009, the annual growth rate has a slight increase compared to a former period. The rate is 5.91%; (3) spatially, gravity centers of medium and high percentage impervious surfaces migrate slightly; and (4) according to the gradient analysis in the two transects, it can be observed that the high percentage of impervious surface increases gradually in new city districts (from west to east and from south to north). © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. (DOI: 10.1117/1.JRS.8.083609)
Highlights
Cities represent one of Earth’s fastest growing land-use types on a per-area basis, and over half of the planet’s 7 billion humans reside in cities.[1]
The spatial-temporal patterns of urbanization in Guangzhou have been investigated by using a subpixel linear spectral unmixing method in the periods from 1990–2009
Gradient analysis is finished based on two mutually perpendicular transects along the urban expansion directions, including 72 cells combined with landscape metrics
Summary
Cities represent one of Earth’s fastest growing land-use types on a per-area basis, and over half of the planet’s 7 billion humans reside in cities.[1]. Remote sensing provided the most convenient means to monitor and quantify urban expansion by taking advantage of its wide area coverage and regular orbiting period and it had proven useful for mapping urban areas and obtaining data for the analysis of urban land cover change.[2,3] In China, urbanization (urban expansion) has been experienced during different periods during the last two decades and many projects or researches on urban expansion have been launched.[4,5,6,7] These researchers mostly placed their attention on land use/. Land cover classification at the pixel level by using supervised or unsupervised classifications. These methods were limited by their precision of classification and image quality, such as spatial resolution, and they could not properly discriminate land cover classes in a heterogeneous context.[8]
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