三江源中东部地区1990-2008草地覆盖度变化遥感估算与分析

Analysis Grassland Degradation of the Region of the Sources of the Yangtze River,the Yellow River,and the Lancang River Based on Vegetation Coverage Estimated by TM Imagery

以中国三江源称多、玛多、玉树、曲麻莱、治多、杂多、囊谦、达日等县部分地区为草地变化研究区,利用20世纪90年代初期、2008年两个时期TM影像,结合实地测量盖度、地面光谱信息以及GPS技术,建立了监测草地植被变化的重要指标——植被盖度的定量反演模型。将两期影像进行比较,监测研究区草地植被变化的时空变化规律。将模型预测的植被盖度与2008年实地调查的结果进行相关性检验与精度验证,相关性达到0.84,平均精度为80.18%。用光谱分解分析法得到的盖度分布结果与本文结果做精度验证,精度为77.46%。分析研究结果,较符合已有研究成果和草地保护区建设规律,表明了方法的有效性。两个时期三江源部分县的草地监测结果表明:该研究区部分地区草地是退化的,但也有部分地区草地正在恢复。研究区0.16%严重退化,11.40%中度退化,31.89%轻度退化,56.55%处于不同程度的草地恢复中。草地恢复区与轻度退化区位于三江源自然保护区内,国家自然保护区建设起到了一定效果。

The severity of grassland degradation was assessed between two periods of 1990 s and 2008 for the sources region of the Yangtze River,the Yellow River,and the Lancang River in west China,which includes counties of Chenduo,Maduo,Yushu,and part of Qumalai,Zhiduo,Zaduo,Nangqian,and Dari.TM images,spectral reflectance and the percentage of grassland coverage obtained by field surveying,as well as GPS technology are employed.Grassland coverage,which is one of the most important indicators for evaluating grassland vegetation dynamic change,was estimated by a quantitative model.The grassland coverage indicators of two period images were compared with pixel by pixel.The change of grassland vegetation in temporal and spatial was discovered.The paper compared the correlation between NDVI and grassland coverage,which were both surveyed by samples,and the correlation between NDVI of TM image and the coverage of grassland samples.And the paper calibrated TM image NDVI by model of NDVI and grassland coverage surveyed by samples.The quantitative model was made by calibrated TM image NDVI and surveyed grassland coverage.The correlation between the coverage of grassland samples surveyed in 2008 and the one estimated by TM image was 0.84,and average assessing accuracy was 80.18%.The assessing accuracy was 77.46%,by comparing results of grassland coverage distribution between methods of the paper and spectral mixture analysis.Method of the paper is verified effectively by analyzing and comparing results of the paper and grassland change regularity of nature reserves.The result indicates that part of the research region grassland is degraded,while part is recovered.0.16% of the study area is highly degraded,11.40% is moderate degraded,and 31.89% is slight degraded,while 56.55% of the region grassland is recovered in some degree.The regions of recovered and slight degraded are located in nature reserves of the sources region of the Yangtze River,the Yellow River,and the Lancang River.It indicates that country nature reserve construction has taken effective measures to solve grassland degradation problem.