高寒草地植被盖度估算及其与冻土的关系

植被覆盖度（盖度）是水文、生态、气象等研究中的一个重要因子，目前目估是野外获取盖度的传统方法。本研究利用多光谱相机拍摄的相片，分析每一个像元的归一化指数，区分植被和土壤，以获取盖度，并与目估法进行对比，评估两种方法的优缺点。结果表明，目估盖度具有较大的主观性，而多人平均值具有一定的参考性；利用多光谱相片能够快捷准确地获取盖度；归一化植被指数取0.4作为阈值较理想；利用阈值的方法区分植被和土壤需要像元所代表的空间尺度不能超过0.2 cm。分析疏勒河上游地区盖度和多年冻土分布的关系发现，多年冻土区盖度显著高于季节冻土区和过渡区(P<0.01)。

Estimation of fractional vegetation cover and its relation with permafrost in the upstream regions of Shule River Basin

Fractional vegetation cover(FVC) is an important factor in researches of hydrology,ecology,and meteorology.Nevertheless,the principal way of getting FVC is to estimate visually in situ or from digital picture.In this study,we applied multi-spectral camera to take pictures of alpine grassland,and then analyzed normalized difference vegetation index(NDVI) of each pixel of pictures to distinguish vegetation and bare land,and calculated the FVC.We compared the FVCs from multi-spectral camera and those from visual estimation,and found:(1) the visual estimation of FVC was subjective,however,the average of these estimates was reasonable;(2) the estimation using multi-spectral pictures was accurate and rapid;(3) the value of 0.4 for NDVI could be used as a threshold to distinguish vegetation and bare land;(4) to apply the threshold of NDVI for estimating FVC,the spatial scale of a pixel in a multi-spectral picture should not be more than 0.2 cm.We also studied the relations between FVC and permafrost distribution,and found that the FVCs in the permafrost area were significantly higher than those in the seasonal frost and transitional areas.