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根据光谱辐射仪对黄土高原冬小麦整个生育期光谱反射率的连续观测数据及CO2通量观测数据,对冬小麦田光谱特征变化及其与CO2日收支的相关性进行了分析.结果表明:冬小麦田不同波长光谱反射率和归一化植被指数(NDVI)呈现明显的日变化和季节变化.同一天内,反射率随太阳高度角的变化而变化,变化最大的波段(550nm左右、700～1050nm)表现为峰.不同生育期同一时刻,可见光波段(350～670nm)反射率变化不大,近红外波段(700～1050nm)出现较大差异,在出苗期、分蘖期和越冬期后红边位置向长波方向“红移”;越冬期前出现向短波方向“蓝移”的现象;但成熟期“蓝移”现象不明显,表现为突变;其他生育时期没有观测到波谱位移.NDVI的日变化呈U型,13:00左右最低,16:00后出现较大波动,与抛物线有较好的拟合效果,小麦生长旺盛时期,对其地面遥感观测应选择在NDVI变化不大的13:00左右进行;整个冬小麦生长季11:00反射率及NDVI以播种后第140天为中心对称,NDVI的季节变化表现为M型,可用四次多项式拟合;在整个小麦生育期中NDVI与CO2的日收支呈极显著负相关,但正午左右的相关性稍差.
According to the spectral radiance data of continuous spectral reflectance and CO2 flux data of winter wheat in the whole Loess Plateau, the spectral characteristics of winter wheat field and its correlation with daily CO2 emission were analyzed.The results showed that: The spectral reflectance at different wavelengths and normalized NDVI showed obvious diurnal and seasonal changes, and the same day the reflectance varied with the solar elevation angle. The most varied band (about 550nm, 700 ~ 1050nm) At the same time, the reflectivity of the visible light band (350-670nm) did not change much at the same growth stage, and the difference appeared in the near infrared band (700-1050nm). At the seedling stage, tillering stage and overwintering stage, Direction “” redshift “. Before winter, the phenomenon of” blue shift “appeared in the direction of shortwave. However, the phenomenon of” blue shift "was not obvious at the mature stage and showed a mutation. No other spectral shift was observed in other growth stages. The diurnal variation of NDVI was U-shaped, the lowest was around 13:00, the larger fluctuation appeared after 16:00, and the fitting effect with parabola was better. During the vigorous growth of NDVI, About 13:00 The reflectance and NDVI of the whole winter wheat growing season were symmetrical around the 140th day after sowing. The seasonal variation of NDVI was M type, which could be fitted by four times polynomial. The daily NDVI and CO2 during the whole wheat growing season There was a significant negative correlation between the two groups, but the correlation was slightly lower at noon.