【摘要】 文章对风导致的苜蓿冠层光谱反射率的变化进行了较细致的分析。分析所用的光谱反射率的取样速度平均为1.5赫。观测表明,大多数情况下苜蓿冠层的光谱反射率有风时比静稳条件下低。偏离的大小依波段而异。相对偏离大于3%的概率分别为:TMA和TMB波段80%;TMC波段100%;TMD波段60%。风影响冠层反射率的机制是复杂的,不能用简单的统计方法如求平均值或中值消除。常用的亮度、绿度、红度和黄度等植被指数对风敏感,不宜在多风地区使用。因此建议在多风地区使用标准差植被指数。更多还原

【Abstract】 The influence of alfalfa canopy spectral reflectance caused by wind are analyzed in detail, the spectral reflectance averaging 1.5Hz. Obser. tion indicates that generally the spectral reflectance is much smaller under windy conditions than under calm conditions. Deviations of the reflectance vary with wavelengths. Probabilities of relative deviations greater than 3% are. 80% in TMA and TMB bands, 100% in TMC band and 60% in TMD band. The effects of wind on spectral reflectance of flexible canopy are so complicated that the errors caused by wind cannot be eliminated by using simple methods for determining the mean or medium values. Some vegetation indexes, such as brightness, greenness, redness and yellowness, are sensitive to wind and are not suitable when used under windy conditions. So the standard deviation vegetation indexes are recommended for windy areas.更多还原