Front. Earth Sci. 2012, 6(1): 75–82 DOI 10.1007/s11707-011-0188-8 RESEARCH ARTICLE Extraction of palaeochannel information from remote sensing imagery in the east of Chaohu Lake, China Xinyuan WANG1,2, Zhenya GUO2,LiWU(✉)3, Cheng ZHU3, Hui HE2 1 Center for Earth Observation and Digital Earth, Chinese Academy of Sciences, Beijing 100094, China 2 College of Territorial Resources and Tourism, Anhui Normal University, Wuhu 241000, China 3 School of Geographic and Oceanographic Sciences, Nanjing University, Nanjing 210093, China © Higher Education Press and Springer-Verlag Berlin Heidelberg 2011 Abstract Palaeochannels are deposits of unconsolidated 1 Introduction sediments or semi-consolidated sedimentary rocks depos- ited in ancient, currently inactive river and stream channel The palaeochannel, which was formed by the natural or systems. It is distinct from the overbank deposits of anthropogenic factors, is a geological-geomorphologic currently active river channels, including ephemeral water body of the abandoned channel resulting from its changes fl courses which do not regularly ow. We have introduced a (Wu, 2008). Many studies about the palaeochannel have spectral characteristics-based palaeochannel information been done, combined with practice, by scientists including extraction model from SPOT-5 imagery with special time domestic and foreign scholars (Bridge, 1985; Kalickl, phase, which has been built by virtue of an analysis of 1987; Khan, 1987; Wu et al., 1996; Xu et al., 1996; Wu, remote sensing mechanism and spectral characteristics of 2002; Brown et al., 2010; Kemp and Rhodes, 2010; Smith the palaeochannel, combined with its distinction from the et al., 2010). However, traditional methods of investigation spatial distribution and spectral features of currently active into palaeochannels and changes of drainage pattern need river channels, also with the establishment of remote more investment of manpower, material and financial sensing judging features of the palaeochannel in remote resources, and a longer time must be consumed. The use of sensing image. This model follows the process of remote sensing technology solves this problem. The fi ! supervised classi cation farmland masking and extraction of remote sensing information, such as the ! primary component analysis underground palaeochan- information extraction of water, residential areas, roads, ! nel information extraction information combination geological structure, etc., has been extensively studied in ! palaeochannel system image. The Zhegao River Valley recent years, and various methods about the information in the east of Chaohu Lake was selected as a study area, extraction have been proposed (Du et al., 2001; Yin et al., and SPOT-5 imagery was used as a source of data. The 2005; Rathore et al., 2010; Smedt et al., 2011). Remote result was satisfactory when this method has been sensing application for extracting information of palaeo- successfully applied to extract the palaeochannel informa- channels not only serves the comprehensive management tion, which can provide good reference for regional remote of watershed systems, territorial planning within the sensing archeology and neotectonic research. However, the catchment and regional sustainable development, but is applicability of this method needs to be tested further in also important for the regional remote sensing archeology other areas as the spatial characteristics and spectral and revealing how much palaeochannels’ changes affect response of palaeochannel might be different. human activities. Since 1950s, extracting information about palaeochan- Keywords palaeochannel, remote sensing, information nels and analyzing the changes of drainage pattern by use extraction, spectral characteristic, Chaohu Lake of remote sensing technology have been carried out extensively. The best representative is the discovery of paleodrainages in the Eastern Sahara (McCauley et al., 1986). The Columbia Space Shuttle carried SIR-A flight through the Sahara in November 1981. Study of the radar Received July 17, 2011; accepted September 30, 2011 echo by the bedrock under the sand layer from SIR-A E-mail: [email protected] images brought out the palaeochannels several meters 76 Front. Earth Sci. 2012, 6(1): 75–82 under the sand, which indicated that there used to be a river system larger than the Nile River in the north of Africa, and negated the argument that there was not a main water system in this area. The palaeochannels provided oases for Paleolithic human in the desert, showing the Sahara’s environmental conditions at that time. Many similar studies have been conducted in China. Bai (1994) extracted the change information of the Tarim River after the enhancement of MSS image, and found that the modern Tarim River was the merger of two major river systems from the north and south, proposing that the main reason of the changes was the atmospheric circulation adjustments and neotectonic movements. An application of satellite remote sensing was also used to explore the mystery of Loulan’s disappearance, which found that two landslides in the upstream of Peacock River blocked the channel and cut off the water supply that led to the abandonment and dying out of ancient Loulan City (He Fig. 1 Location map of the study area and Sun, 2001). It was the first time that the riddle of Loulan’s disappearance has been answered by use of main eastern rivers flowing into the Chaohu Lake (Fig. 1). satellite remote sensing images. With a broad research on With the total length of 35 km, the Zhegao River originates historical documents, historical maps, large scale topo- in the eastern foot of Fucha Mountain, and flows from the graphic maps, satellite images and other data, Zhang et al. north-west to the south-east, and turns south at Zhegao (2004) revealed the channel changes of Santun River and Town. At last, it passes by Qingtai Mountain to the west. It Hutubi River in the past 300 years, finding out a close crosses the Wudu Bridge of the Heyu Road and the relationship between the spatial distribution of river system Zhonghan Bridge of the Huainan Railway, then flows into and the historical changes of Manas Lake. He then the Chaohu Lake at the Hekou Village to the north-west of analyzed the main factors of drainage changes in different the Guishan Mountain, which is one of the four major bays time stages. Radar remote sensing technique has also been (Chorography Compiling Commission of Chaohu City. widely used in the extraction of palaeochannel informa- 1992). The Zhegao River Basin is located in 117°34′–117° 2 tion. By use of the remote sensing archeological method, 52′E, 31°38′–31°55′N, covering an area of about 507 km , 2 2 Wang et al. (2006) researched the ancient Tongji Grand including 46 km of massif area and 41 km of polders. The Canal in Sui and Tang Dynasties and explored the reasons branches present trellis drainage going from north-east to for its traffic function transformation from a narrow south-west or from south-west to north-east. The whole ScanSAR image (300 km  300 km) that was obtained basin is surrounded by hills and mountains from three by Canadian Radar Satellite 1 in 1997. A number of old sides, with one side facing the lake that consists of river valley and lake basins buried by wind-blown sand piedmonts alluvial and lacustrine plains. The well-devel- were recognized based on analyses of SIR-A, SIR-B, SIR- oped river system of this basin, as well as the dense C, Radarsat ScanSAR, Landsat MSS and Landsat TM vegetation and fertile lands, are suitable for human activity. images acquired on different dates and the investigations Within the basin, there are a large number of relics from the made in several field trips in Alxa Plateau of Inner Neolithic Age to the Shang and Zhou Dynasties (Gao et al., Mongolia (Guo et al., 2000a, b; Wang et al., 2002; Wang et 2008). al., 2004). This study also establishes a preliminary The data used is the multi-band image obtained by drainage evolution model in this area since the Tertiary, SPOT-5 on January 4, 2004 (K/J: 288-286/3), with 10 m and finds that the Alxa Plateau was once an area with many spatial resolution (the short-wave infrared band is 20 m), rivers and lakes amid a warm and humid climate. including five wavebands (Table 1). To facilitate the According to the results of previous studies, this study explored the paleaochannels within the Zhegao River Table 1 Spectral wavelength and resolution of SPOT-5 Basin in the east of Chaohu Lake using the SPOT-5 Sensor Spectral waveband Ground Wavelength images, and produced an effective method for remote resolution/m range/µm sensing information extraction of palaeochannels. SPOT-5 Panchromatic 10 0.48–0.71 B1: green 10 0.50–0.59 B2: red 10 0.61–0.68 2 Study area and data sources B3: near infrared 10 0.78–0.89 – The Zhegao River, located in Chaohu City, is one of the B4: short-wave infrared (SWIR) 20 1.58 1.75 Xinyuan WANG et al. Extraction of palaeochannel information from remote sensing imagery 77 research, data formed in winter is selected to reduce the characteristics of palaeochannels formed in the images can influence of vegetation cover. Thus, it is convenient to establish appropriate information extraction model for investigate the palaeochannels and exhibit the small palaeochannels research. beaded lakes, swamps and micro-geomorphologic struc- ture, etc. Besides, there are other data: 1∶50000 topo- 3.2 Establishment of interpretation keys for palaeochannels graphic maps and the land use maps of the study area. To improve the geometric precision of the image, the first step In regard to the interpretation of palaeochannels in the is to make the image registration with multi-band and study area, the visual interpretation method is mainly used panchromatic image by use of the cubical polynomial to interpret the SPOT-5 B3-B2-B1 false color composite transform model in the software of ERDAS IMAGING image.