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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
  1. Coast - debouch geomorphy

    1. 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)


      Fig 1. Arch-shaped strips of paleo-ridged accumulation
      (enhanced composition of TM)

    2. 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.

    3. 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.

    4. 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.


  2. 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.


    Figure 3. Differences of ground water features (by integrated processing of enhanced multi-temporal Landsat images)

  3. 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)

Figure 4. Regular distribution of villages, roads and farming structure along paleo-coastal zones

Determination of paleo-coastal lines
  1. Processing and Analysis of Multi-temporal Remote Sensing Imagery

    Features of historical migration of coastal lines on images have become very dim after seal-land interchange and human reconstruction in a long history. Besides, variety of object types makes difficult in extraction of thematic information on paleo-coastal zone. Here the selection of remote sensing data and processing methods is very important. As objects to be studies are characterized in spatial pattern, in this study, multi-temporal images of Landsat MSS, TM were collected, and in addition, infrared airphoto images were use. Through the contrast analysis of these images, the annual and seasonal change of landscape in this region can be easily reflected. It helps with recognition of traces of coastal change.

    Considering that costal change is reflected by distinct geomorphological features and spatial pattern, and also closely related to water salt dynamics, on the basis of multi temporal analysis, season (later March-earlier April), when climate is dry, ground is bare, salinization is heavy, so that the feature of water-salt dynamics and land form is clear; the second is end spring or end autumn (later may or later September), when it is the mature period, and difference in condition of water, salt and soil have a concentrated reflection on types and growing of crop. Through optical-digital mixed processing of image, such as color enhancement, contrast modification, ratio analysis and integration of multiland and multi temporal data, good results in extracting paleo-coastal zone information have been achieved.

  2. Assisted analysis of Geo-data

    coastal changes have greatly influenced human living environment. These changes are often remained in certain cultural records and recorded in profile of stratigraphic sequence through

    continental transition sea facies sediments. The analysis of lithologic, microfossil, sporopollen and C14 again data from known drill holes in petrofacies and paleogeogrpahic environment have provided direct evidence of the existence of the paleo-coastal lines. For example, in the Holocene Epoch stratum in Geijian, Xiangxian areas of the Hebei Plain contain euryhaline foraminifera and many semi salt water lived ostracoda have demonstrated the paleo-environment of sea land transition, and reflected the transgression spread to these areas.

    Historical and archaeological data are used to determine time of paleo-coastal line. For example, in the west coastal area of Bohai Bay the cultural ruins and grave of Sui-Tang, Chun-Qiou and Zhan Guo time (2500-1300y B.P.) are distributed along shell ridge II and III; several ruins of the New Stone Age have been found in outer ring along the coastal line (about 7000by B.P)

    Nine paleo-coastal lines o different ages since the Holocene Epoch in the China Plain have been found through remote sensing processing and geoscience integrated anlyses (fig. 2). The coastal liens of historical time (Qin, song, Sui-Tang, Xi-Han, Chun-Qiou, Zhan Guo and Yin-Shang Dynasteis) are determined mainly by direct geomorphologic evidence (especially, well as the coastal lines of archaeological time (4700-4000y.B.P., 5000y.B.P., 7000-6000y.b.P.) are inferred according to ground water features and trace of paelo-coastal lines, and by using geosciences assisted analysis.

Figure 2. Paleo-littoral depressions

Coastal change and environment
Coastal change is a reflection of change in sea level and global climate. The paleo-coastal liens determined here are corresponding to relatively higher sea levels and the warm humid time of paleo-climate since Holocene Epoch. During the warm humid time of the paleo climate (Atlantic time, warm Qin Han time, Warm Tang Time) with higher temperature and rich rainfall, ice and snow melt, sea level rose and the coastal line drawed back. When the sea level remained relatively stable, sand ridges and shell ridges developed along the coastal zone, such as the I=IV shell ridges near Tianjin.

The rate of shore lien forward movement in uneven, for example, during the sea invasion of Holocene Epoch (7000y.B.P.) the horizontal speed of sea water invasion was bout 70-75 km/1000y, the extent of invasion towards west was upto 150-160km. During the dry-cool time of paleo-climate (e.g. 7800y B.P., 5300y. B.P. 200y B.P.), sea levels dropped down, rivers brought a great amount of silt and sand, which were deposited insitive to climate change. Climate sealevel change has direct effect on atmospheric and water circulation, and then results in ecological environment change, such as swamiplization and desertification, and will influence greatly human activities, especially in distribution of industry and agriculture in the coastal zone region.

Coastal change is also a reflection of the history of forming and development of the North-China plain. The formation of the North-china plain has been influenced by supply, deposition of sand and silt material from the Yellow River as well as by geotectonic in a long historical time. Since the Later pleistocen, the west part of China has been rising, as well as the east part has been continuously subsiding. The huge losses sediment has become a main source o shelf erogenous classic material. In this connection, the North-China.

Plain is formed and developed under the common action of the Yellow river and paleo-sea transgression-regression in transportation d deposition do sediments.

Study of coastal change is an important part of study on global change. It is obvious that, remote sensing is an effective tool in recognition of paelo-coastal changes.


References
  1. Yang Huiren, et. al Trends of Climate Change and Sea-level, proceedings of Quaternary Glacier and Geology, pp44-48, Geology Press, 1985.

  2. Zhao Yingshi, Application of Remote Sensing Imagery in Coastal Zione Changes of Bohai Bay Region, Proceedings of Environmental Remote Sensing in Tianjing-Bohai Bay Region, pp238-243, Science press, 1985.

  3. Wu Hongyou, Underground Bittern Water in Littoral Plain of Bohai-Laizhou Bay Region, Marine Science, Vol. 3, 1980.