光谱混合机制研究对混合像元解算具有一定指导意义。 利用全波段光谱仪累积期和消融期对规则和非规则分布模式下积雪-荒漠植被混合像元及纯净积雪和荒漠植被像元控制式采集反射光谱。 K-均值法计算采集影像积雪和荒漠植被面积比并分析其对应混合像元光谱变化特征以获取更加精细的光谱特征信息, 准同步Tetracam ADC3(Agricultural Digital Camera 3)采集图像并计算典型指数, 从微观尺度上证实了混合像元主要出现在地类边界处。 结果发现, 1 456～1 697 nm粗粒径冻结雪反射光谱高于新雪反射光谱, 新雪反射光谱明显高于陈雪; 因冻结覆冰, 荒漠植被光谱为积雪、 冰晶和植被枝干混合光谱信息, 新降积雪覆盖植被光谱特征为积雪和植被枝干的混合光谱信息, 不存在常规绿色植被“红边”效应; 采集角度为5°和10°时光谱低于垂直角度采集光谱, 角度大于10°随角度增加荒漠植被光谱逐渐增大。 像元内各个组成物质的面积比及所处像元的位置、 采集角度和方向都会影响混合像元的光谱组合信息。

The study on spectral mixing mechanism has a certain instructive significance to unmixing. With a full-wavelength spectrometer, the research made a controlled acquisition of the spectral reflectivity of pure snow pixels, pure desert-vegetation pixels and snow-desert vegetation mixed pixels in the mode of rule and irregular distribution during the accumulation period and ablation period. The ratio of snow area to desert vegetation area of images was calculated by K-means clustering algorithm and spectral variation characteristics of mixed pixels were analyzed; to obtain more precise spectral characteristic information, the absorption characteristic parameters to the response bands were calculated; the images were collected by quasi-synchronous Tetracam ADC3 and the typical indices were calculated. It’s verified at the micro-scale that the mixed pixels are mainly located at the boundary between one category to another. The results are seen as follows: the spectral reflectivity of coarse-grained frozen snow is obviously higher than that of new snow which is obviously higher than that of aged snow in the ranges of 1 456～1 697 nm. Because of the ice cover, the collected desert vegetation spectra is actually a mixture of spectral information of snow, ice crystals and vegetation branches; the spectral properties of vegetation covered with new snow are actually the mixed spectral information of snow and vegetation branches; there is no “red edge” effect like conventional green vegetation. When the acquisition angles are 5° and 10°, the spectral reflectivity is lower than that at a vertical angle. When the acquisition angle is bigger than 10°, the spectral reflectivity increases if the angle becomes bigger.