Study On Key Techniques Of Remote Sensing In Earthquake-induced Geohazard Evaluation

The damages and influences caused by earthquake-induced geohazards are very severe, even outnumbering the direct losses from earthquakes sometimes. Therefore, a better understanding and prevention of impacts from earthquake-induced geohazards plays a very important role in mitigating geohazards. Some effective means to avoid or reduce geohazard losses may include accurate and quick determination of geohazard resource, reasonable evaluation of possible induction of geohazards and corresponding measurements.Remote sensing (RS) has shown some outstanding characteristics in information acquisition of geohazard areas such as real time, wide coverage, rich data types and high resolution. Thus, it can rapidly gain information related to landslides, avalanches, debris flows and dammed lakes after earthquakes, and provide scientific decision-making references for geohazard relief, geohazard evaluation and geohazard mitigation. There are many successful cases and valuable experiences of RS applications in geohazards and relevant fields, especially in information acquisition and macroscopic measurements of geohazard regions. However, there has been little studied in high-resolution RS interpretation, refined interpretation of geohazard units, information acquisition of inside structure, analysis of geohazard emerging procedure and integrated management of above-mentioned information.The research object in this thesis is5.12Wenchuan earthquake areas and its incident region. Based on field investigations, several key techniques such as RS image preprocessing, geohazard RS interpretation and geohazard database setting up are studied. Main research contents and contributions are as follows,(1) An improved RS image enhancement method is presented Russo proposed a fuzzy image enhancement method which shows more advantages than other traditional methods. A shortcoming of the method is that the parameters are fixed which leads to unsatisfied results sometimes. Some auto-adjust parameter methods are presented, but not always feasible. In this thesis, A new self-adaption parameter adjusting approach is presented. The simulation results have shown that the proposed approach has several characteristics such as simple, fast and better enhancement effects, compared to other traditional methods. This approach has been applied to image processing in this geohazard research region and has exhibited effectiveness and practical applicability.(2) According to characteristics of the geohazards induced by Wenchuan earthquake, e.g., multiple types, large-scale distributions and complex inside structures, based on the property analysis of geohazard images, relevant feature extraction and spot investigations, the author proposed a method to well explain geohazards and analyze its inside structures, interpreted geogazard bodies of the research zone in details, found out its spatial features and distributions roughly, and provided scientific references for risk controls of geohazards.(3) Considering that debris flows are very active after earthquakes and it is very different for traditional exploration means to obtain basic data for hazardous assessment of debris flows, the author presented a method to dynamically investigate, analyze, evaluate and predict typical debris flows by applying3S technology. Taking Niumiangou, near the quake center of Wenchuan, as an example, the author studied geohazard body features and statistical information of debris flows in details by applying RS and GIS. This method can help effectively ascertain the geological and water source conditions, dynamics and size, damage levels and dangerous situations of debris flows. Combining GIS technique, relevant parameters of debris flows are abstracted; computations of total fluxes and transporting sand fluxes are performed; occurrence degrees, developing trends and danger of debris flows are analyzed.(4) Designing and realizing information database of earthquake-induced geohazard based on WebGIS. In the aspect of quick searching and sharing geohazard data, an element data theory is used as a guide to design an element data model of earthquake-induced geohazards which is applied in practice. This information database mainly provides three core functions:data query, data output and database management. This information system covers comprehensive geology information including basic geographic spatial data, RS image data, special subject data and evaluation model data of geohazard. The practical applications have shown that (1) from the viewpoint of sharing integration, this information database can meet the demands of managing present data, visualizing results and providing network sharing services for users;(2) from the viewpoint of function realization, this system can complete data classification, organization and management, increasing integration and applicability of geohazard data. In general, this work can provide decision-making guidance for related research and management, and can be served as a paradigm for the similar research topics.