A study on environmental change analysis in Sand Hill of Nebraska using remote sensing
美国中西部沙山地区环境变化的遥感研究

In this paper, the Sand Hill of Nebraska, a typical semi arid area located in mid west part of US and recognized as the largest 'sand sea' in the western hemisphere, is selected as the study area The study is focused on extraction of thematic information referring to sands, wetlands, waters, and grassland, which relatvely inicate e?vironmetal changes in the region Four temporal Landsat TM and MSS data from 1972 to 1993 are collected for analysis In the study, LSMM (Linear Spectral Mixture Model) is applied to pixel decomposition for classification of sands, and TC transformation is used for separation of vegetation and soil Besides, thematic information on sands, wetlands, waters, and grassland with different coverages is extracted through synthetic analysis of NDVI (Normalized Difference Vegetation Index), NDWI (Normalized Difference Water Index) and NDMI (Normalized Difference Moisture Index) Remote sensing images in 1972, 1979, 1987 and 1993 are classified respectively and compared to obtain the changes in corresponding land types The features of environmental changes for the last 20 years in the study area are finally discussed The result shows that there has been the trend towards increasing in the areal extent of sands and towards decreasing in coverage and green degree of grassland in the study area and that, changes of areal extent of wetlands and waters are controlled by annual precipitation Through analysis on temperature and precipitation of summer for more than 40 years, which is understood as the most important season for energy exchange and changes of ecological environment in a year of this region, we can infer that the upwards trend of temperature, the downwards trend of precipitation and the desiccation trend of climate are the main causes for the increase of sandy area and decrease of vegetation coverage and green degree For the study area, which belongs to the sparcsely populated prairie landscape, even there is less human interference and slight environmental change, the impact of climatic factor on environmental change should not be ignored The relation between climate and environmental change will be further studied