Remote Sensing Application
Study on Environmental Hazards in Shaanxi, China Yang Minjun Shaanx Remote Sensing Center Xian. Chian It is a very important subject for the protection of environment and development of economy in the present world to make reasonable exploration and good use of natural resources, take precautions against natural hazards and try every means to lessen the aftermath of each disaster. Shaanxi Province is situated in the center of China, enjoying natural landsenes of the North and the South, The west and the East Shaaxi is rich in datural resources by suffers serious natural hazards. Shaanxi Remote Sensing Center has made application of remote sensing technology in the survey and intergraded evaluation study on geology, mineral resources, land use, ecological environment and natural nazards is Shaaanxi Province, providing scientific basis for reasonable exploration and use of natural resources and for the protection of environment for the protection of environment for the province. The major natural hazrtds hitting Shaanxi are land desertization, land erosion, landslide, debris flow, earthquakes. Active structures, ground figures, surface subsidence, ground water pollution, air pollution and storms, hails, droughts and so on. Most of the hazards are local, though, the damages are quite great. Remote sensed survey of environmental bazards are various natural or rectificial evolution and events of variations which happen on surface of the earth and bring disasters to human society. These evolutions and events often leave director or indirect marks or records of the events on the surface of the earth. Remote sensing images are true portraitures of the natural landscene of the earth’s surface and they show various marks, prints, or hints of the environmental disasters directly through interpretation of the images. And these are the main basis for remote sensing study on environmental hazards and also the essential information for the study of distribution of environmental hazards. I. llazards of Land Descrtization Land desertization hazards mainly occur along the Great all in the Northern part of the province. Some are in the joining area of the Weihe River and the Yellow River in the east of Guanzhong. Land desertification are marked clearly on images and can be circumscribed accurately. And according to the distribution, the areas and the development of the moving dunes. Stable and semi-stable dunes, and forestry, grass clusters, four kinds of damaging intensities, or say seriousness, of serious, strong, developing and potential can be classification for the land desertization of the hazards hit areas. Evaluation can also be carried out for the achievements in plantation and in battles against desertification. Through studies of comparison of images of different period of time, it is concluded that local land desertification hazards are still going on inside the province. II. Liazaros Soil Errosion The loess plateau in the Northern Shaanxi is one of the most serious areas of soil erosion along the Yellow River. The intensity of damage is indicated by the structure features of loess geomorphology and formation of river system. The classification of soil erosion intensities of certain accuracy and various degrees scan be obtained. Through statistics study of loess dones and valleys shown in the large scaled remote sensing images, and by classification of developing types of these valleys, and the evaluation of the features of geomorphology, and then through necessary processes. It is concluded in the study that soil erosion in the north of the Yanhe River is quite serious and in some parts of the belly areas in Southern Shaanxi, soil erosions have become clearly damaging hazards. III. Landslide and Debris Flow Hazards As the geomorphic features remain and effects of human activities continuo, landslide and debris flow hazards are always in a developing tendency and they are the main forms of hazards of debris flows happening all over the province. Since each of these hazards is in a small scale, it is not easy to be recognized in the images. So the images were enlarged to 1:50,000, no matter satellite or airborne images, the signs are relatively much clear, the stable and active landslide and debris flows can be defined. In Northern Shaanxi, these hazards are in large areas but concentrated in several regions. They appear to be developing along deep loess valleys in Guanzhong, and can be divided into 8 dense concentrated areas and 4 concentrated areas. While in the south of the province, they appear to be in separate distributions, and some of them in zones, forming heavy disastered areas. IV. Active Structures, Ground Fissures and surface subsidence Hazards Active rifting is concentrated mainly along the boundaries of Guanzhong areas in the center of Shaanxi, and it is clearly shown in the remote sensing images, spreading in light grey line shape. And secondarily it appears in the mountain areas in the South of the province. Such active structures often cause landslide, debris flow hazards to happen. And in the center and the east parts of Guanzhong Basin, especially in Xian, concentrated are serious damaging ground fissures. Through interpretation of remote sensing images, most of them shown are to be in certa9in directions and zones, making a hint that they are controlled by structures, at the same time, indicating that the controlling structures are still in activities. On the surface, their formations are normally in conformity with regional tectonic lines, their development is in relation with excessive pumping of underground V. Ground Water Pollution Remote sensing image captured in dry season and computer processed bear certain image features for water pollutions, of which the normal bear certain image features for water pollutions, of which the normal colour has changed ( such as the waste water from iron and steel works, from chemical works. Power plants using coal) and water polluted with sand and soil, water additionally polluted. These features are sometimes even very clear. Clear water is in deep blue, water with much sand and soil is in light grey or grey. And when clear water is joined with sand and soil bearing water, or to say, polluted, the colour would be changed. This provides direction information for the administrations. VI. Air Pollution Air pollution is one of the most serious environmental hazards and is a kind of hazards still developing and concerning every individual. And this result of concentrations of lots of industrial waste gas, coal smoke and dust . Remote sensing images chosen are those taken after strong wind and they show clear states and ranges of exhausting with dust from chimneys and the polluted area concerned, of the exhaust of high temperature gas from big chemical plants chimneys. And according to the states and ranges shown and circumscribed the degrees of pollution can be define. Integrating with ground survey, the intensities of the pollution can be classified. And with comparison lution development can be studied. VII. Thunderstorms and Hail Hazards Though thunderstorms and hails often occur in relationship with climate changes they happen to be in regions and areas of certain geomorphy of certain features. Such as plain and hilly areas in front of mountain renges, the margin areas of the basins in the mountains. Through geomorphic study of remote sensing images, integrating weather conditions, the features of regularities of these hazards can be found out and the plans for the constructions can thus be made. Regularities of Distributions and Development of Environmental Hazards in Shaanxi Province The remote sensing survey and compilation of series of maps and multidisciplinary study result in the discovery of regularities of main environmental hazards in Shaaxi Province, of their distributions in time-space and their intensities and causes of their damages. I. Regularitie of “Area” Distribution of Hazards Integration The distribution of harzarads integration in the whole province show obviously regional regulations. Different areas suffer different hazards. In the North are mainly draughts, land desertification and soil erosions. In the center, the Guanzhong Basin, ground fissures, ground water pollutions and air pollutions, and in the south, thunderstorms, lands lide and debris flows are the main hazards, Such regional distributions show clear controlling actions of large regional climate ones, geological and geomorphic frames. II. Regulations of “Hazards Chains’ of Their Locations Land desertification and soil arrosioin are the main hazards in northern Shaanxi. The developing and potential developing areas and the arade of which soil are seriously damaged are tending to be in Northe-East Direction and North-East direction. In Guanzhong, earthquakes and active structures occur on the margins of the basin in the direction of west-east. The saturated ground water and saline and water pollution are in zones in the West-East direction. Landslide and debris flows in the South are in West-East arrangement. And the detailed studies show that these hazards are controlled by the surface structures and deep structures of the eruct and such structure field is in conformity with the meteorological field countrolling the distributions of clouds and rains. This conformity shows the controi of hazard distributions by the electro magnetic fields of the space. III. Regulations of Time of the Happering of These Hazards In Shaanxi, landslide, debris flow, soil erosions, thunderstorms and hails often happen in flood season of July to September every year. This period is the period with many hazards happening. Pollutions, draughts and desertification mainly happen in winter and in spring when there are less rains. IV. Distribution Regulations of the Intensity of Hazards The intensity of hazards is often in position correlation with the degrees of hazards development. And the major evaluation criterions are their damaging degrees. Some of the important and thick populated industrial area, towns, lines of communification often suffer stronger damages, or to say, wheel there are more and unhealthy constructive activities, there are more types of hazards happening and the damages are much stronger. Classifications of Environmental Hazards and Integrated Prevention Through the remote sensed survey on the environmental hazards in Shaanxi and the strudies on the distribution and developing regularities, integrated classifications were carried out for the types of hazards in Shaanxi according to the features of remote sensing images and hazards chins and various factors of human activities. Five First Types areas classified as hazardous areas of heavy draught and land desertification along the Great Wall Hazardous areas of draught and soil erosion in Northern Shaanx Hazadous areas of thunderstorm, hail, landslide and active structure areas in Guanzhong and hazardous arcas of thunderstorm, landslide and debris flow in the South of Shaanxi. And 98 secondary hazardous areas in the above areas are classified according to major hazards and their intensities and to the integrating degrees of the Shenfucoal fields coal minig areas in Tongehuan, Huangling and Weibei coal fields, Xian area, Fengxian and Lueyang regions are these keys areas of integrated prevention and administration for the major hazseds. In order to make prevention and administration of environmental hazards to lessen the damages on used, the first important thing is to make reasonable use and exploration of natural resources, and to make clear the hazards that may happen during and after exploration, and the time when they will happen, the frequency, the intensity and regularities. Secondly, every means of techniques be adopted including remote sensing technology to strengthen the monitoring and recasting Special attentions be paid for the development of the hazards during the highly happening period and information be exchanged taxingly so as to make precasting judgment. Thirdly popularization of the knowledge of prevention and lessening of hazards must often be carried out so to make people realize the importance and responsibilities of preventing and lessening nazaras and raise their own ability of self-protection. The situation will be much better if all the people take actions against hazards and for the protection of our environment. |