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nsing,2001,vol.22,no.10,1999–2014
A remote nsing–GIS evaluation of urban expansion and its impact on surface temperature in the Zhujiang Delta,China
Q.WENG
Department of Geography,University of Alabama,Tuscaloosa,AL35487,USA
(Received26May1999;in nal form22November1999)
四月英文Abstract.The Zhujiang Delta of South China has experienced a rapid urban
expansion over the past two decades due to accelerated economic growth.Thisction
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paper reports an investigation into the application of the integration of remote
nsing and geographic information systems(GIS)for detecting urban growth
and asssing its impact on surface temperature in the region.Remote nsing
techniques were ud to carry out land u/cover change detection by using
multitemporal Landsat Thematic Mapper data.Urban growth patterns were
analyd by using a GIS-bad modelling approach.The integration of remote
nsing and GIS was further applied to examine the impact of urban growth on
surface temperatures.The results revealed a notable and uneven urban growth in
the study area.This urban development had raid surface radiant temperature
by13.01K in the urbanized area.The integration of remote nsing and GIS was
found to be e V ective in monitoring and analysing urban growth patterns,and in上海世博会介绍
evaluating urbanization impact on surface temperature.英语三级成绩
1.Introduction
外语教学法Land covers,as the biophysical state of the earth’s surface and immediate subsur-face,are sources and sinks for most of the material and energy movements and interactions between the geosphere and biosphere.Changes in land cover include changes in biotic diversity,actual and potential primary productivity,soil quality, runo V,and dimentation rates(Ste V en et al.1992),and cannot be well understood without the knowledge of land u change that drives them.Therefore,land u and land cover changes have environmental implications at local and regional levels,and perhaps are linked to the global environmental process.Becau of the interrelated nature of the elements of the natural environment,the direct e V ects on one element may cau indirect e V ects on others.
Urbanization,the conversion of other types of land to us associated with growth of populations and economy,is a main type of land u and land cover change in human history.It has a great impact on climate.By covering with buildings, roads and other impervious surfaces,urban areas generally have a higher solar radiation absorption,and a greater thermal capacity and conductivity,so that heat is stored during the day and relead by night.Therefore,urban areas tend to experience a relatively higher temperature compared with the surrounding rural areas.This thermal di V erence,in conjunction with waste heat relead from urban hous,transportation and industry,contribute to the
development of urban heat
International Journal of Remote Sensing
ISSN0143-1161print/ISSN1366-5901online©2001Taylor&Francis Ltd
uk/journals
2000
Q.Wengboring是什么意思
island(UHI).The temperature di V erence between the urban and the rural areas are usually modest,averaging less than1°C,but occasionally rising to veral degrees when urban,topographical and meteorological conditions are favourable for the UHI to develop(Mather1986).
In China,land u and land cover patterns have undergone a fundamental change due to accelerated economic development under its economic reform policies since 1978.Urban growth has been speeded up,and extreme stress to the environment has occurred.This is particularly true in the coastal region such as the Zhujiang Delta where massive agricultural land is disappearing each year,
converting to urban or related us.Evaluating the magnitude and pattern of China’s urban growth is an urgent need.Furthermore,becau of the lack of appropriate land u planning and the measures for sustainable development,rampant urban growth has been creating vere environmental conquences.Thus,there also is a need to asss the environmental impact of the rapid urban expansion.
The integration of remote nsing and geographic information systems(GIS)has been widely applied and been recognized as a powerful and e V ective tool in detecting urban land u and land cover change(Ehlers et al.1990,Treitz et al.1992,Harris and Ventura1995).Satellite remote nsing collects multispectral,multiresolution and multitemporal data,and turns them into information valuable for understand-ing and monitoring urban land process and for building urban land cover datats. GIS technology provides a exible environment for entering,analysing and displaying digital data from various sources necessary for urban feature identi cation,change detection and databa development.However,few of the urban growth studies has linked to post-change detection environmental impact analysis.The question of how to develop an operational procedure using the existing techniques of remote nsing and GIS for examining environmental impacts of rapid urban growth remains to be answered.
The goal of this paper is to demonstrate the integrated u of remote nsing and GIS in addressing environmental issues in China at a local level.Speci c objectives are to evaluate urban growth patterns in the Zhujiang Delta and to analy the impact of the urban growth on surface temperature.
2.Study area
The study area,the Zhujiang(literally‘the Pearl River’)Delta,is located between latitudes21°40N and23°N,and longitudes112°E and113°20E( gures1and2). It is the third biggest river delta in China and has an area of17200km2.Becau of the constraint of satellite data coverage,this rearch focus on the core area of the delta that includes the following15cities/counties:Guangzhou,Panyu,Sanshui, Nanhai,Foshan,Shunde,Jiangmen,Zhongshan,Zhuhai,Xinhui,Doumen, Zengcheng,Dongguan,Baoan and Shenzhen.Geomorphologically,the Zhujiang Delta consists of three sub-deltas formed by diments,the Xijiang,Beijiang and Donjiang Deltas,originated approximately40thousand years ago(Department of Geography,Zhongshan University1988).The process of dimentation still con-tinues today,extending award at a rate of40m per year(Gong and Chen1964). The delta has a subtropical climate with an average annual temperature between21 and23°C,and an average precipitation ranging from1600to2600mm.Becau of the impact of the East Asian Moonsoonal circul
ation,about80%of the rainfall comes in the period of April to September with a concentration in the months of May to July,when ooding is prone to occur(Ditu Chubanshe1977).Another
A remote nsing–GIS evaluation of urban expansion2001
Figure1.A map of the study area.
hazard is typhoons,which occur most frequently from June to October.The delta’s fertile alluvial deposits,in combination with the subtropical climate,make it one of the richest agricultural areas in China.The famous dike–pond ecological agricultural systems and silk production can be traced back to the beginning of the Ming Dynasty (1368–1644A.D.)(Zhong1980,Ruddle and Zhong1988).
Economically,the Zhujiang Delta is the largest area of economic concentration in South China.Guangzhou,China’s sixth largest city,Hong Kong and Macao are located here.Since1978,the delta has become a rising star due to its dramatic economic expansion under China’s economic reform policies,and therefore has been regarded as a model for Chine regional development.The establishment of Shenzhen and Zhuhai Special Economic Zones in1979and the Zhujiang Delta Economic Open Zone in1985has stimulated Hong Kong and foreign rms to locate their factories there as village–township enterpris.The labour-intensive industries, in association with the cash crop production,notably,afood,poultry,vegetables, fruit and owers,have transformed the spatial economy of the delta(Lo1989,Weng 1998).The rapid economic development has brought about fundamental changes in land u and land cover patterns.The integrated approach developed in this paper is to analy the changing patterns of urban land u/cover and its impact on surface tempera
ture.
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Figure2.Major rivers,counties and cities in the Zhujiang Delta(after Lo1989).
钢铁侠3英语3.Methodology
3.1.Urban expansion detection and analysis
Land u/cover patterns for1989and1997were mapped by the u of Landsat Thematic Mapper(TM)data(Dates:13December1989and29August1997).Seven land u and land cover types are identi ed and ud in this study,including: (1)urban or built-up land,(2)barren land,(3)cropland,(4)horticulture farms, (5)dike–pond land,(6)forest,and(7)water.With the aid of Erdas Imagine computer software,each Landsat image was enhanced using histogram equalization(in order to gain a higher contrast in the‘peaks’of the original histogram)to increa the volume of visible information.This procedure is important for helping identify ground control points in recti cation.All images are recti ed to a common UTM (Universal Transver Mercator)coordinate system bad on the1550000topo-graphic maps of Guangdong Province produced by the Chine government.Each image was then radiometrically corrected using relative radiometric correction method(Jenn1996).A supervid classi cation with the maximum likelihood algorithm was conducted to classify the Landsat images using bands2(green),3(red) and4(near-infrared).The accur
acy of the classi cation was veri ed by eld checking or comparing with existing land u and cover maps that have been eld-checked.
In performing land u/cover change detection,a cross-tabulation detection method was employed.A change matrix was produced with the help of Erdas Imagine software.Quantitative areal data of the overall land u/cover changes as well as gains and loss in each category between1989and1997were then compiled. In order to analy the nature,rate,and location of urban land change,an image of urban and built-up land was extracted from each original land cover image.The
A remote nsing–GIS evaluation of urban expansion2003 extracted images were then overlaid and recoded to obtain an urban land change (expansion)image.
The urban expansion image was further overlaid with veral geographic reference images to help analy the patterns of urban expansion,including an image of the county/city boundary,major roads,and major urban centres.The layers were constructed in a vector GIS environment and converted into a raster format(grid size=30m).The county/city boundary image can be utilized to nd urban land change information within each county/city.Becau proximity to a certain object, such as
major roads,has an important implication in urban land development,urban expansion process often show an intimate relationship with distance from the geographic objects.Using the bu V er function in GIS,a bu V er image was generated, showing the proximity to the major roads of the study area.Ten bu V er zones were created around a major road with a width of500m.Local conditions have been taken into account in lecting the bu V er widths.The bu V er image was overlaid with the urban expansion image to calculate the amount of urban expansion in each zone.The density of urban expansion was then calculated by dividing the amount of urban expansion by the total amount of land in each bu V er zone.The values of density can be ud to construct a distance decay function of urban expansion.
3.2.Urbanization expansion impact analysis
treat her like a ladyUrban development usually gives ri to a dramatic change of the Earth’s surface, as natural vegetation is removed and replaced by non-evaporating and non-transpiring surfaces such as metal,asphalt and concrete.This alteration will inevitably result in the redistribution of incoming solar radiation,and induce the urban–rural contrast in surface radiance and air temperature.The di V erence in ambient air temperature between an urban and its surrounding rural area is known as the e V ect of UHI.Given the relationship between surface radiant temperature and the texture of land co
ver,the impact of urban development on surface temperature in the Zhujiang Delta can be assd.
Studies on surface temperature characteristics of urban areas using satellite remote nsing data have been conducted primarily using NOAA AVHRR data (Kidder and Wu1987,Balling and Brazell1988,Roth et al.1989,Gallo et al.1993a). The1.1km spatial resolution of the data are found suitable only for small-scale urban temperature mapping.The much higher resolution(120m)Landsat TM thermal infrared data were ldom ud to derive surface temperature.Recently, Carnahan and Larson(1990)have ud the TM thermal infrared data to obrve mesoscale temperature di V erences between urban and rural areas in Indianapolis, while Nichol(1994)ud it to monitor microclimate for some housing estates in Singapore.However,no rearch has yet attempted to detect urban-induced surface temperature change over time at a local level using multidate TM thermal infrared data.
To measure the surface temperature change from1989to1997,surface radiant temperatures were derived from radiometrically corrected TM thermal infrared data (band6),using the following quadratic model to convert the digital number(DN) into radiant temperatures(Malaret et al.1985):
T(K)=209.831+0.834DN0.00133DN2(1) Then,corrections for emissivity(e)were applied to the radiant
temperatures according to the nature of land cover.In general,vegetated areas were given a value of0.95
