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Globle Change of Environment
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Integrated analysis of Remote Sensing data for natural environment changes
Zhao Yingshi
The Graduate school, Academic Sinica
Beijing 100039, China
Abstract
Study on changes of natural environment in historical time by using remote sensing, in fact is a type of recognition of traces, that is to find traces of objects related to historical environment features on images, delineate range of their changes, and to recover the paleo-geographic environment based on their characteristics in spatial pattern, spectrum, and temporal changes. Coastal change is a reflect of global climate change, and is of get importance in environmental research. In this paper, the coastal change in North-China plain is studies. Nine Plaeo-coastal lines since the Holocene Epoch have been determined through processing and analyses of multitemporal Landsat MSS, TM image data, and integrated analysis of remote sensing data, archaeological data, and lightfaces data.
Introduction
Study on changes of natural environment using remote sensing is to find traces of objects related to environmental change remained on remote sensing images according to their characteristics in spatial pattern, spectrum, and temporal changes, and then through the recognition of the traces to analyze geographical range of their changes, to lecur macroscopically paleo-geographic environment and study its relationship to contemporary environment.
Research on coastal changes is of great importance in study of natural environment change. Coastal changes are synthetic reflection and real records of eustasy and ground level changes. Affected mainly by global climate change, the transgression and regression of seawater resulted in differences of land forming time, geomorphic types, material composition, characteristics of ground water, as well as divergence in pattern of landuse in the coastal are. Some of these differences remained on remote sensing images.
The North-china Plain along the Bohai Bay is selected as the study area on coastal changes since Holocene Epoch using remote sensing imagery.
Characteristics of Remote Sensing imagery on coastal changes
- Coast - debouch geomorphy
- Ridged Accumulated Body
Various types of coastal accumulation are often formed along coastal zone under the sea water action, such as wave, tide, and coastal current. For example, coastal dune and dam in the Luanhe debouch, chell ridge, shell-sand ridge on the west shore of Bohai Bay, littoral sand dams along light the color North Jiangsu seashore, are composed of coarse and light color bean material ad have higher location, good permeability, lower ground water level and good water quality, with higher reflectance. They assume light strips on images, which are often disturbed partly by human activities, for example, village, road, construction, or planting of fruit trees, cotton and peanuts. Lower land between ridges composed of silt and clay with good water holding capacity and higher ground water level, shows dark tone on images. This has caused on the image light and shade strips of is different width parallel to the contemporary coast-line. (See fig. 1)
- Littoral Depression
In the coastal zone, there are littoral depressions of different types in cause of formation, such as lagoon, lagoonal depressions and swamp, which are often distributed as group of depressions. Substantial composition of dark clay and subclay with more.
- Littoral fan-shaped land
When sand and silt material carried by rivers deposited a outlets to plain or sea, alluvial fans and deltas developed. It is easy to recognize fan-shaped bodies with distinct form. There are depression in the fan front are, and braided channels on the fans. They can often be connected with the developed of paleo-coastal line. In the pas-glacial period the climate became warmer, which caused a global transgression. Paleo-coastal lien arrived upto these fan-front on the north shore of the Bohai Bay, on the south shore of the Laizhou Bay. Al-paleo-coastal lines, but it is possible to trace them crossing fan bodies by enhancing processing.
- Sudden change points of river pattern
The change of river pattern happened at the river mouth due to sudden change of water dynamic conditions (e.g. push of sea water and elimination of energy) as well as composition and relief of waterbed. In this connection, sudden change points of river pattern are often related to the paleo-debouch.
- Distribution of Ground Water and characteristics of Chemical Composition of Water.
In the study area, there is close relationship between distribution and quality of ground water, and invasion, salinization of paleo-sea water. Following regression, the extent of desalination, depth and distribution chemical composition of underground water shows the feature f horizontal zoning parallel to the coastal line. For example, in the Hebei Plain, there exists ground salt water wedge with width of 5-150 m and mineralization of more than 2 g/l., which is increased up to 20 g/l as well as types of water quality changed from chloride sulphate (Na-Mg) to sodium chloride similar to sea water with the direction from land to the sea. Sea facies fossils have been found in many drill holes in the salt ground water area. It proves the existence of sea water invasion at that time there and the range of the transgression is mainly within the salt ground water distributed region, and partly coincides with he boundary between salt and fresh ground water. In the Jiaowei Plain, to the south of Laizhou Bay, there exists underground bittern water with mineralization of more than 50 g/l and up to 200 g/l which are called underground bittern
mine, and used directly for salt production. This bittern body is also distributed parallel to shore line, and is considered to be formed as a result of evaporation and concentration of intertidal beach and lagoon. It seems that the formation of underground bittern bodies along the coastal zoen has direct relationship with paleo transgression.
The differences in distribution and chemical characteristics of ground water have controlled water-heat conditions and water - salt dynamic status, affected development of soil and vegetation in this are, and caused differences of color tone and pattern on remote sensing images. Figure 3 shows classification of ground water types in the Hebei Plain by integrated processing of enhanced multi-temporal Landsat images. The middle part of the picture is salt water are, which is the region involved by the transgression. Since later river developed in this region, shallow fresh water floated on the ground salt water wedge, which forms dark strips and islands on images, and shows disorder and coarse pattern combined with light piebald-shaped saline land. It is very different from full fresh ground water area in the east part of the study area. These arched zones, roughly parallel to today's coastline, have proved to be coincided basically with paleo-coastal line by other verified data.
- Human Activities
Different types of high land developed along coastal zone are often the proper places for human living. Regular distribution of villages, roads and farming structure around sea shore is an another indicator of paleo-coastal lines. (see figure 4)
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