基于光谱分析的生物结皮提取研究——以毛乌素沙地为例

利用典型地物高光谱数据和TM遥感影像,对毛乌素沙地处于旺盛生长期(7-9 月)的由苔藓结皮主导的生物结皮进行了提取研究.结果表明:① 苔藓结皮在生长期具有与绿色植物相似的光谱曲线变化趋势;红边参数显示,二者除红边位置非常接近外,红边振幅、红边宽度和红边面积差异均较大;在近红外区域,苔藓结皮比绿色植物的反射率低很多;苔藓结皮无明显的553 nm反射峰;低盖度苔藓结皮(33%)、藻类结皮和植被枯落物在整个波段光谱曲线比较接近,与裸沙相比,三者反射率均较低.② 基于TM影像,用生物结皮指数(BSCI)、归一化植被指数(NDVI)、监督分类和坡度分级相结合的方法提取生物结皮,发现苔藓结皮的像元面积为0.72×10⁴ km²,占研究区总面积的6.43%.

Research on Biological Soil Crust Extraction by Spectral Analysis in Mu Us Desert,China

Using the hyperspectral reflectance data of typical objects and TM remote sensing images, the paper extracts the moss-dominated biological soil crusts at vigorous growth stage (from July to August) in Mu Us Desert. We collected the reflectance spectra of six typical ground features including bare sand, algae crust, dry vegetation, green vegetation, the moss crusts of 33% coverage and 100% coverage. Remote sensing data include twelve Landsat TM images acquired from July to August in 2010 and 2011. The results are as follows: 1) Moss crust in vigorous growth stage has similar spectral reflectance curves with green plants. There are obvious reflection peak and“red edge”phenomenon in visible light band. However, in the red band (680-760 nm), they have differences in all“red edge”parameters including red edge amplitude, red edge width and red edge area, except red edge position. In the near- infrared shortwave bands(760-900 nm), the reflectance of moss crust is much lower than that of green plants. Their average reflectance is 0.198 and 0.424 respectively. Moss crust has no reflection peak at the wavelength of 550 nm, but at the wavelength of 625 nm. The moss crust of 33% coverage, algae crust and dry vegetation have similar spectral curves between the wavelength of 400 nm and 900 nm. Their spectral reflectance is lower than that of bare sand which is 48%. 2) Based on the Landsat TM images, the method extracts biological crust by combing biological soil crust index (BSCI), normalized difference vegetation index (NDVI), supervised classification and slope classification. 3) The pixel area of moss crusts is 7200 km², which takes 6.43% of the total study area.