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Satellite-bad detection of water
我才不是唐三藏
surface variation in China’s largest
freshwater lake in respon to hydro-
春风的诗句climatic drought
Guiping Wu a & Yuanbo Liu a
a State Key Laboratory of Lake Science and Environment, Nanjing
Institute of Geography and Limnology, Chine Academy of
Sciences, Nanjing, China
Published online: 19 Jun 2014.
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Satellite-bad detection of water surface variation in China ’s largest
freshwater lake in respon to hydro-climatic drought
Guiping Wu and Yuanbo Liu *
State Key Laboratory of Lake Science and Environment,Nanjing Institute of Geography and
Limnology,Chine Academy of Sciences,Nanjing,China
(Received 15August 2013;accepted 11February 2014)Poyang Lake,the largest freshwater lake in China,is an important water resource and iconic ecosystem in a region that has been subjected to extreme drought in recent years.The lake ’s inundation area is heavily influenced by basin rainfall and also by the Yangtze River ’s water flows.Exploring the lake ’s inundation variation in respon to drought conditions is of great importance for developing effective management planning for local water resources and for mitigating future drought.Here we demonstrate how satellites can reflect the lake ’s inundation changes and process under typical hydro-climatic droughts.Using Moderate Resolution Imaging Spectroradiometer (MODIS)medium-resolution data collected between 2000and 2011,we documented the tempo-spatial variation characteristics of water inundation areas and two typical droughts in 2006and 2011.2006was a hydrologic drought year,which occurred due to an abnormal change in the Yangtze River ’s water flows.A dramatic shrinkage of the inundation area mainly occurred in autumn and winter.In contrast,2011was a hydro-climatic drought year,which resulted from the complicated influence of both the Poyang Lake basin and Yangtze River.The lake shrinkage appeared more vere during spring –summer,when about 70%of the inundation area disappeared before July.The results should be valuable for ecological conrvation and water resource management in the Poyang Lake region.1.Introduction Freshwater lakes are valuable economic resources for mankind and have regional ecolo-gical and environmental functions (Beeton
2002;Tiner 2005;Williamson et al.2009;Cui et al.2012).The lake area responds directly to climate change and also incorporates the effects of climate-driven changes occurring within its catchment.Changes in water inundation can affect other characteristics of the water body.For example,reduced
water inundation leads to lower water levels.The changes,in turn,can markedly affect the spatial availability of freshwater resources,which could be a critical influential factor in regional sustainable development (Ariztegui et al.2010;Du et al.2011).
Poyang Lake is the largest freshwater lake in China,and it has experienced vere drought in recent years.It is one of the most internationally important wetlands in terms of the provision of habitat for migratory birds (Finlayson et al.2010).However,there is a significant difference in benthic topography among the different lake gments,and the elevation generally decreas from south to north (Cai and Ji 2009).In addition,the varying discharges from different upstream catchments and the Yangtze River further complicate variation in the lake (Cui et al.2012)and cau the spatial distribution of the water surface to vary considerably in different regions (Shankman and Liang 2003;Feng *Corresponding author.Email:ybliu@niglas.ac .
International Journal of Remote Sensing ,2014
V ol.35,Nos.11–12,4544–4558,dx.doi/10.1080/01431161.2014.916444
©2014Taylor &Francis
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et al.2012).For this reason,the classic method of water level –area relationship cannot be applied to such a complex lake to obtain a reasonable inundation area,especially in the low-water period (Alsdorf and Lettenmaier 2003).Remote-nsing techniques have tre-mendous advantages for large-scale studies,offering remotely nd images at different spatial and spectral resolutions with a short revisit time.As a result,veral rearchers have begun to investigate changes in the water surface area of Poyang Lake using remote nsing (Alsdorf,Rodríguez,and Lettenmaier 2007;Hui et al.2008;Zhao et al.2011;Feng et al.2012;Liu,Wu,and Zhao 2013).Drought may create a direct effect on a lake ’s ecosystem,including water inundation (Kratz et al.1997).Although remote-nsing techniques have proved uful for monitor-ing lake surface areas,accurate and effective water inundation information may be affected by multiple factors such as the temporal –spatial resolution of images,lake complexity,and water extraction accuracy.Therefore,the capability of remote nsing t
o reflect lake inundation changes and process under different drought conditions needs to be examined.The main goal of this study is to explore the temporal –spatial distribution characteristics of the Poyang Lake inundation area under different drought conditions in typical drought years.Through this work,we demonstrate the water surface variation of the lake in respon to hydro-climatic drought.2.Study area and data 2.1.Study area Poyang Lake (28°22′–29°45′N,115°47′–116°45′E)is the largest freshwater lake in China.It is the primary component of the Poyang Lake wetland,which was included in the first batch of the Ramsar Convention List of Wetlands of International Importance (Finlayson et al.2010).The lake plays a critical role in modulating local dry/wet conditions and ecological functions of the Poyang Lake wetland (Finlayson et al.2010).As shown in Figure 1,water from the rivers Xiushui,Ganjiang,Fuhe,Xinjiang,and Raohe flows into the Yangtze River through this lake,which is shaped like a gourd.Therefore,the lake region is influenced by the water systems and can be divided into five zones corresponding to hydrological and topographic features (Zhou,Wan,and Jiang 2011).Zones I and II are water body zones,parated by Songmen Mountain.The northern part is a deep,narrow channel that exchanges water with the Yangtze River via the Hukou.In contrast,the southern part is wider and shallower.Tributaries parate the remaining lake area into three different estuary deltas –the western branch of the Ganjiang and Xiushui rivers (Zone III),the southern central branch of the Ganjiang and
烟花的英语Fuhe rivers (Zone IV),and the Raohe River (Zone V)(Figure 1).In the high-water ason,the five tributaries are flooded due to concentrated rainfall,resulting in a maximum lake surface area of over 3000km 2(Shankman and Liang 2003).In the low-water ason,the surface is remarkably changeable due to its varied benthic topography.When this occurs,the water surface area of the lake shrinks to less than 1000km 2(Liu,Wu,and Zhao 2013).The disconnected gments are parated by expod floodplains,which provide esntial habitats for thousands of winter migratory birds (Leeuw et al.2010).
2.2.Data acquisition and processing
Moderate Resolution Imaging Spectroradiometer (MODIS)Level-1B data (MOD02_QKM and MOD02_HKM)from 2000to 2011were acquired from the NASA Goddard International Journal of Remote Sensing 4545
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Space Flight Center (ladsweb.v ).A total of 466cloud-free images were ud in
this study.The data were ud to quantify the intra-and inter-annual variability of the Poyang Lake inundation area.MOD02_HKM was extracted for digital number (DN)values in the green band (0.54–0.57μm)at 500m resolution,and MOD02_QKM was extracted for DN values in the NIR band (0.84–0.88μm)at 250m
resolution.To match the spatial resolution of the MODIS NIR band,the 500m green band data were resized to 250m resolution by using a nearest-neighbour resampling algorithm.Nearest-neighbour resampling was lected becau it better maintains original reflectance values while providing sufficient accuracy and reducing the potential introduc-tion of unwanted geometric distortions with no ground control points to provide preci control (Muukkonena and Heiskanenb 2005;Reich,Aguirre-Bravo,and Bravo 2008).All of the acquired MODIS images were projected into Universal Transver Mercator (UTM)with a World Geodetic System (WGS-84)datum.In addition,24scenes of cloud-free Landsat TM/ETM+images with the same overpass date were lected to validate the lower-resolution (250m)MODIS obrvations.The data were acquired from the Global Land Cover Facility (GLCF)and have a finer spatial resolution of 30m.TM/ETM+band 2(green band)and band 4(NIR band)were ud to delineate the relatively accurate lake
surface.Figure 1.Geographical location of Poyang Lake in China.The lake is divided into five zones corresponding to different hydrological and geographic features.The ba map is a fal-colour composite of Landsat TM bands 4,3,and 2(marsh vegetation appears in shades of red,water areas are blue,and soils vary from dark to light brown).4546G.Wu and Y.Liu
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>龙井怎么泡
