Wetlands are special ecosystem lying between the terrestrial and open-water areas. Similar to forest, grass, and ocean ecosystems, wetlands take parts in protecting environments and exploring resources. In China, wetlands are undergoing significant degradation that is caused by both natural processes and human activities. In order to know the
details of wetlands change so as to take suitable actions to protect wetlands, Landsat TM/ETM images are used as main data sets. Accessorial data such as topography map and China mire map are also used. In this paper, wetlands are defined as swamplands, potholes, wet meadow, riverine, lacurtrine. Three periods (1990a, 1995a, 2000a) data of wetlands in china are extracted from TM through the interactive interpretation. Applying spatial analysis function of
GIS technology and statistics methods, the spatial distribution pattern and temporal changes are studied. The research results show that, during the 10 years from 1990 to 2000, wetlands area decreased largely, and spatial difference is notable. Finally, the driving forces resulting in mires changes are analyzed.
Distributed optical fiber temperature sensor system can sense the temperature changes along the optical fiber by the continuous form of distance. For the characteristics of insulation and resistance to electromagnetic interference, it has a wide using prospect in the field of petroleum and gas pipeline, tunnel and mine. The distributed temperature measurement is realized by using single channel anti-Stokes light, and the temperature and space resolution of the system can be assured. But the anti-Stokes signal will be submerged by noise because of the weakness of anti-Stokes light signal, the loss of scattering light and the system noise. In order to reduce the influence of various noises in distributed temperature measurement, the method of increasing the times of signal accumulating is used to increase temperature resolution. But this will lengthen the period of temperature measurement and influence the practical application of the system. By using the multi-resolution analysis of Wavelet to handle the distributed temperature signal, we can shorten the period of temperature measurement and enhance the response speed of system on the basis of the assurance of time and space resolutions.
This paper described the distributed optical fiber temperature sensing system based on Brillouin amplifier structure, which combined Brillouin amplifier effect with optical time domain reflection(OTDR). With the relationship of temperature and stimulated Brillouin frequency shift, we can obtain the temperature on each point. Based on this principle, some experiments were taken, then the linear relationship and experimental data were given, which provided powerful foundation for future research.
Distributed optical fiber temperature sensor use the principle of temperature effect of spontaneous Raman scattering in fiber and optical domain time reflection (OTDR) to detect the temperature field in space and its changing with time. It can sense the temperature changes along the fiber length by the continuous form of distance in a fiber of several kilometers length. Theoretically, the minimal discernible space length of fiber in the distributed optical fiber temperature sensor system is proportional to the width of incident light pulse, that is, the narrower the width of incident light pulse, the higher the space resolution of fiber. The width, power and edge quality of incident light pulse can directly influence the space and temperature resolution of distributed optical fiber temperature sensing system. This paper focused on the optimum design of light pulse producing based on the use of LD light source. A high power light pulse of narrower width is produced by designing reasonable circuit of increasing voltage, discharging control and making full use of LD, which makes sure to improve the space and temperature resolution of the system.