河北坝上地区草地退化指示种的高光谱特征波段识别

Identification of Hyperspectra Characteristic Bands of Grassland Degradation Indicator Plant Species in Bashang Region of Hebei Province

草地生态系统对发展畜牧业、保持水土和维持生态平衡有重要作用,实时、准确地监测草地的退化具有重要意义.高光谱遥感能够大幅度提高草地退化进程中植被结构退化的识别精度,为草原退化研究开辟新领域.利用高光谱遥感技术进行植被结构退化鉴别时,特征波段的选择和提取至关重要.根据地面实测高光谱数据,对河北坝上地区3种退化指示种和2种优势物种光谱反射曲线进行对数变换处理,采用均值置信区间对原始光谱和变换处理后的对数光谱进行波段选择,提取了退化指示种的光谱特性,并利用Manhattan距离对所选择的波段进行识别检验.结果表明：（1）与2种优势物种苔草（Carexpediormis）和羊草（Leymusc Ainensis）相比,退化指示种狼毒（Stellerac Aamaeiasme）的特征波段为402-412nm,冷嵩（Artemis iairigid）的特征波段为627？689、715-929和929-1033nm,星毛委陵菜（Potentilla acaulis）的特征波段为705？721nm;（2）在上述特征波段内,同种植被的Manhattan距离值显著小于异种植被的Manhattan距离值,狼毒、冷蒿和星毛委陵菜的Manhattan距离值分别为0.0066、0.3101和0.3855;（3）在可见光范围内,退化植被与主要优势植被的光谱差异不明显,经对数变换后,其差异被放大,易于提取特征波段,且基于均值置信区间的植被原始光谱曲线与对数光谱曲线相结合方法的特征提取结果更精细,最终确定狼毒的特征波段为402-412nm,冷蒿的特征波段为627-689、758-924和940-1033nm,星毛委陵菜的特征波段为705-721nm.

Grassland ecosystem plays an important role in the development of animal husbandry,soil and water conservation,and maintenance of the ecological balance. Therefore,it is of great significance to perform real-time monitoring of degradation of grasslands. The technology of hyperspectral remote sensing can greatly improve precision of the identification of degraded vegetation structure in the process of grassland degeneration,and opens up a new field in the study of grassland degradation. In using the technology to identify degraded vegetation structure,it is very important to choose and extract characteristic bands. To that end,based on the hyperspectral data measured in field,spectral reflection curves of three species of degradation indicator plants and two dominant species in Bashang Region were processed with the logarithmic transformation method. Then bands were selected out of the original spectra and transformed logarithmic spectra with the confidence interval of mean for extraction of spectral characteristics of the degradation indicator species. And the selected bands were identified and validated with the Manhattan distance method. Results of the study show as follows:( 1)Compared with the two dominant species,namely Carex pediformis and Leymus chinensis,the degradation indicator species Stellera chamaejasme featured at 402-412 nm,Artemisia frigid at 627- 689,715- 929 and 929- 1 033 nm and Potentilla acaulis at 705-721 nm;( 2) In the above characteristic bands,the Manhattan distance of the vegetation homogeneous inplant species was obviously smaller than that of the vegetation heterogeneous in plant species. And the Manhattan distance of Stellera chamaejasme,Artemisia frigida and Potentilla acaulis was 0.006 6,0.310 1 and 0.385 5,respectively;( 3) No big difference was found,in the visible band between degraded vegetation and vegetation of dominant species. After logarithmic transformation,the difference was amplified and made easy the extraction of characteristic bands. The use of the original spectral curve in combination with its logarithmic spectral curve based on the confidence interval of mean made the extraction of characteristic bands more accurate. The eventually defined characteristics band for Stellera chamaejasme is402-412 nm,for Artemisia frigid 627-689,758-924 and 940-1 033 nm and for Potentilla acaulis 705-721 nm.