利用多时相近地面反射波谱特征对不同退化等级草地的鉴别研究

 草地各退化等级群落反射波谱特征之间的差异性大小与草地类型和生长季节有关，羊草(Leymus chinensis)草原不同退化等级群落反射波谱特征之间的差异在6月底最为显著，在5月底的差异最不明显, 大针茅(Stipa grandis)草原不同退化等级群落反射波谱特征之间在7月底、8月底的差异最为显著，在5月底和6月底的差异最不明显。植被指数(NDVI)在5月底、6月底和9月底在各草地类型的不同退化等级群落中都无显著差异，而在7月底、8月底差异显著程度也小于各波段反射率。主分量分析(PCA)和模式识别分析结果表明：对于羊草草原退化生态系列的不同退化等级群落分类效果最佳的鉴别函数是蓝光、红光和近红外波段反射率的线性组合，最佳分类时间在6月底，平均错误概率仅为0.7%，5月底进行分类效果最差，平均错误概率为12%左右，7月底、8月底、9月底的分类效果居中；对大针茅草原退化生态系列的不同退化等级群落分类效果最佳的鉴别函数是蓝光、绿光和近红外波段3个反射率的线性组合，在7月底和8月底进行分类效果最好，分类的平均错误概率为4％左右，9月底的分类效果最差，平均错误概率达10%左右。

THE USE OF MULTITEMPORAL NEAR_GROUND SPECTRAL REFLECTANCE TO DISCRIMINATE AMONG DEGRADED GRASSLANDS

From May to September 1998, we measured the seasonal near-ground spectral reflectance characteristics and biological parameters of non-degraded, moderately (or lightly) degraded and heavily degraded grassland communities of Leymus chinensis steppe and Stipa grandis steppe in Inner Mongolia, China. The results of Duncan multi-variance analysis indicated that the near-ground spectral reflectance varied with the degree of degradation, growing season and grassland type. For Leymus chinensis steppe grazing gradient, differences in the near-ground spectral reflectance among degraded communities were most distinct when measured at the end of July and were least at the end of May. For the Stipa grandis steppe grazing gradient, the spectral response was most distinct at the end of July and August and was least distinct at the end of May and June. No distinct differences in the Normalized Difference Vegetation Index (NDVI) among degraded community types were observed at the end of May, June and September. At the end of July and August, differences were observed but the degree of difference of the NDVI was less than that of the near-ground spectral reflectance. PCA and Pattern-Recognition Method, used to develop discriminate functions, indicated that the blue, red and near-infrared reflectance captured at the end of June had the greatest ability to discriminate among degrees of degradation along the L. chinensis grazing gradient ( mean probability of error was 0.7%) and had the poorest discriminatory power at the end of May (the mean probability of error was 12%). For S. grandis steppe grazing gradient, the discrimination ability was highest at the end of June and August when composed of blue, green and near-infrared reflectance (mean probability of error was lower than 4%) and lowest at the end of September (mean probability of error was about 10%).