Xia Zhen Chen Taihao
The Second Marine Geological Investigation Brigade,
Ministry of Land and Resources,
P.R.C. Guangzhou Second Marine Exploration Corporation
With the setting of the International marine year, the great importance is attached to marine not only due to its potential resource exploitation, but also because marine environmental change has influence on the living and development of the human beings. Furthermore, the coastal zone, the transition between the marine and continental deposit, which is the interacting area of the four spheres such as lithosphere, hydrosphere, biosphere and atmosphere, attracts great attention.
The rapidly developing remote sensing technology provides marine prospectors with a new way in which the spatio-temporal change can be detected by means of comparing different temporal remote sensing data. Thus it is especially useful for studying the coastline change because it can be used not only to analyze the spatio-temporal change process of the coastline, but also to identify the power condition and change factors that cause it. The result will provide evidence for the protection of the coastal environment.
2. Analysis of multi-temporal remote sensing data in Dayawan area
2.1 The study Area
Dayawan is located in the east of Pearl Reiver mouth with Honghai Bay in the east and Dpeng Bay in the west, covering a region from 22o20’00″N to 23o00’00″N and from 114o20’00″E to 115o20’00″E.
It is a U-shaped bay with mountains in the east, north and west. The bay mouth is 15 km wide and 30 km long from south to north. It has a 150-km long coastline. In the bay approximately 60 percent of the sea water is 10 meters deep and there are zigzag coastline and many islands, which altogether form three sub-bays with good shielding conditions: Dapeng Bay, yaling Bay and Fanhe Bay.
The Dayawan port has been building since the beginning of 1980s. Later on the nuclear power statinand other construction projects enabled a rapid development of economic construction of this area, which in turn promote the development of economic construction of this area, which in turn promote the development and exploitation of marine resources in Dayawan area (e.g. marine breeding). Consequently exploitationof marine resources in Dayawan area (e.g. marine breeding). Consequently these artificial factors greatly changed the natural environment of Dayawan area, and the current coastline is very different from original one. All these changes can be seen clearly on the multi-temporal remote sensing images.
2.2 Selection and processing remote sensing data
According to the requirement of our research project, four temporal satellite remote sensing data of Dayawan area selected. The earliest one is Landsat-MS data with the spatial resolution of 78 meters taken on October 31, 1973. Based on reasonable time intervals and the image quality, three temporal Landsat -TM remote sensing data are selected which were taken on Dec. 14, 1986, Dec. 7, 1995 and Nov. 10, 1997 respectively. The spatial resolution of them is about 30 meters.
The geometric correction of the TM data of 1995 was done in image processing data software (radiation correction was done by the Ground satellite Receiving Station of China). Based on the control of corrected 1995 TM data, the geometric correction for 1973, 1986 and 1997 TM data was also done in an image-by-image way. The each band remote sensing data is ready to be extracted from those corrected data.
Using the corrected four-temporal TM data of 1973, 1986, 1995 and 1997 can generate the color composite image. The composed data are interpreted cell-by-cell in the image processing system, and the sea area and non-sea can be distinguished from each other. After that the interpreted data are then corrected to the Yellow Sea geodetic surface to get rid of the tidal effect. Finally the grid data will be converted into vector format and be edited in Arc/info system, to generate a single temporal coastline vector format and be edited in Arc/info system, to generate a single temporal coastline map. The four period coastline data are overlaid together to create the dynamic change map. In order to improve the accuracy of the interpretation, the TM data are amplified for image interpreting.
3. The coastline change in Dayawan Area
The comparison of the four-temporal remote sensing image shows that the coastline of the area changed dramatically, especially in Aotou Port, Depeng Port, Fanhe Port and Qianliao Port. With the rapid development of the regional economics, a variety of developing and construction activities, and the active man-made land-reclaiming projects make the coastline extend into the sea with the maximum of more than one kilometer. Apart from artificial factors, only considering the effect of natural factors, the coastline changes can be classified into four types such as,
- Eroded coast, where the coastline shrinks backward because of the strong erosion. The maximum of erosion is up to 200 meters according to the four-temporal images of Dapongwan and Xichong area.
- Silting coast,
- Shrinking and extension coast, and
- Stable coast, mostly belonging to bedrock coast, such as Dashuiwan, Dongchong and Jueliao port etc.
4. Conclusion and suggestion
The overlaying analysis of multi-temporal remote sensing data, not only shows the coastline change very, also detects the power factors that cause the change, which is very useful for engineering constructiuon.
The coastal change map of this area shows that in the eroded coastal segments if there is not solid protection measures, the coast will be eroded repeatedly by the seawater. For instance, by comparing the coastal changes in 1973, 1986 and 1995 in Baishouwan area, the conclusion can be come up with that due to the strong erosion, the man-made coastline was destroyed and withdrew backward.
Although the natural condition in Dayawan area is relatively fine and there is abundant resource around the port with clear water and slow seawater flow, a variety of further studies are still necessary for engineering project. The detailed investigation and research will facilitate the engineering construction and the coastal protection.