Evaluation On The Ecological Environments Before And After 5.12 Wenchuan Earthquake By Remote Sensing And GIS

Ecological environment is a basic condition for mankind to survive and develop as well as the foundation for economic and social development. Protecting and constructing ecological environment by implementing a sustainable development strategy is a basic state policy must be obeyed in our country's modernization. The primary purpose of evaluation on ecological environment is to monitor and evaluate the change states and laws of system structure of the ecological environment of a special region under the joint action of mankind and natural factors, thus providing references for the decision-making in the protection and planning work about ecological environment. As the seismical centre of the terrible earthquake occurred on May 12, 2008, Wenchuan County has witnessed dramatic changes of its ecological environment. Therefore, timely evaluation on the quality of ecological environment there and the impact of the earthquake on the ecological environment there is of great significance to reasonable reconstruction of the county.According to lots of home and abroad documents and field investigations as well as previous research results, this thesis, in accordance with the geological conditions of the studied region of its location in the mountainous valleys of Southwest China, huge falls of mountainous regions and plentiful river valleys as well as the fact that geological disasters and secondary geological disasters such as landslides and collapses have developed in the studied region and following the three major principles of factor selection in evaluation on ecological environment, i.e. the maximum contribution rate principle, the stability principle and the feasibility principle, selects land utilization/covering, landform and geomorphology, social activities, soil humidity and geological disaster indicators as the influencing factor layer and main detail indicators in the ecological environment evaluation indicator system as the indicator layer and establishes three-layered ecological environment evaluation indicator system for the comprehensive evaluation of the ecological environment of Wenchuan County after the earthquake. In this thesis, the AHP method decided by experts is used to confirm the weightings of various evaluation indicators; quantized grading and standardization are conducted for all evaluation indicators; and comprehensive evaluation number method is used to establish a comprehensive model for the ecological environment evaluation of the studied region.Taking the Landsat remote sensing images of July 2006 as the pre-earthquake evaluation indicator factor data source and such multi-source remote sensing images obtained in the month after the earthquake as LandSat and Aster as post-earthquake evaluation indicator factor data source and depending on the spatial analysis and raster data operation of GIS technology, this thesis evaluates the ecological environment of the studied region and reaches the main conclusions as follows:(1)According to the ecological environment characteristics of the plentiful mountainous valleys and the vast territory with a sparse population of the studied region, this thesis makes use of the AHP decision-making analysis method to establish an indicator system for the evaluation on the quality of the ecological environment of Wenchuan after the earthquake and evaluates seven indicators such as land utilization/soil covering, vegetation coverage, altitude, gradient, population density, soil humidity and geological disasters;(2)The research takes the multi-source and multi temporal satellite remote sensing data as main data sources to get the indexes necessary to the ecological environment equality evaluation;(3)After comparing the ecological environment qualities of Wenchuan County in 2006 and 2008, we find out that the county in 2006 had high vegetation coverage, complete ecological system structure and functions as well as basically undamaged ecological environment while the county in the left time of 2008 after the earthquake occurred has witnessed dramatic changes of ecological environment quality: some areas have suffered from serious damages of mountains, vegetation and mulching materials; the ecological system has been seriously damaged; and the ecological environment qualities of the areas far away from the seismical centre of the earthquake have not been seriously influenced yet. Compared with the situation in 2006, the ecological environment quality in the left time of 2008 after the earthquake got worse; (4)By evaluating the ecological environment qualities before and after the earthquake and analyzing and evaluating the damage degree of the ecological environment of the region, this thesis provides scientific references for the restoring of ecological environment as well as scientific disaster relief after the earthquake.