冬小麦冠层氮素的垂直分布及光谱响应

The Vertical Distribution Characteristic and Spectral Response of Canopy Nitrogen in Different Layer of Winter Wheat

考察了田间条件下冬小麦主要生育阶段冠层氮素、叶绿素的垂直分布及其光谱响应。不同叶层的叶片含氮量按上 (冠层顶部向下至 1 / 3株高处 )、中、下层的顺序呈明显下降的梯度 ,全生育期不同土壤施氮处理平均 ,上、中层间相差 1 3 3% ,中、下层间相差 2 9 5 %。在生育前期 ,各层叶片的含氮量随土壤供氮水平增高而增加 ,但不同叶层间氮素的梯度相对稳定。到生育中后期 ,中、下层叶片间氮素含量梯度增大 ,且随土壤供氮水平增高而加剧 ,最大时可相差 4 5 3% ;冠层内叶绿素 (a +b)含量的垂直分布规律与氮素含量的垂直分布相类似 ,但对土壤供氮水平的反应上表现出与氮素不尽一致的趋势。不同叶层的光谱特征表现为 ,在土壤低氮水平下 ,不同叶层间在红光波段、短波红外波段 (1 4 0 0nm— 1 80 0nm及 1 95 0nm— 2 30 0nm)的反射率差异显著 ,下部叶层的反射率显著高于上、中叶层 ,但在土壤高氮水平下 ,上述差异消失 ;在近红外平台处 ,不同叶层间反射率按上、中、下顺序降低 ,梯度分布特征明显。

The precision of quantificational remote sensing can be enhanced by tapping the potential of sensor,transfer model and exact describing of the object. We think exactly of describing the object is the base of enhancing inversion precision of remote sensing. For this purpose,the vertical distribution of canopy nitrogen and Chl (a+b) status in winter wheat were studied. The spectral response of nitrogen and Chl(a+b) at different layer in canopy also had been analyzed. There appeared an apparent descending trend of nitrogen content from the upper layer to the lower layer. The nitrogen content of upper layer was higher than that of the middle layer with 13 3% and 29 5% between the middle layer and the lower layer in the growth duration. At early stage,the nitrogen content gradually increased with the increasing of the nitrogen application. But there were stable nitrogen gradient between different layers. There appeared greater nitrogen content gradient at middle and latter growth stage and the gradient sharpening with the nitrogen application amount. The vertical distribution property of Chl(a+b) concentration was similar to that of the nitrogen. But there were greater gradient of Chl(a+b) concentration than that of nitrogen content between upper and middle layer and less between middle and lower layer. The amount of nitrogen application decreased the Chl(a+b) gradient between middle and lower layer,which differ from that of nitrogen. Under the lower nitrogen condition,there existed significant reflectance difference among different layer at the red wavebands,the wavebands from 1400nm to 1800nm and from 1950nm to 2300nm.The reflectance of lower layer was significantly higher than that of upper and middle layer. But there was almost no difference among different layer with affluent nitrogen application. There was apparent gradient distribution in different layer and appeared gradually decreased from upper to lower layer at near infrared platform. But the amount of nitrogen application didn't affect the gradient distribution characteristics of spectral reflectance. Besides,the correlative coefficients between canopy spectra and foliar biochemical contents of different layers were analyzed. The canopy spectral reflectance in different bands for remote sensing of foliar biochemical contents in different layers were found,and the spectral reflectance is significant correlative with foliar Chl(a+b) content of middle and lower layers. Future work should involve giving more attention on the method for multi angle analyzing and establishing inversion model.