Crop Coefficients Derived from Reflected Canopy Radiation: A Concept
Crop Coefficients Derived from Reflected Canopy Radiation: A Concept
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由冠层反射辐射得出的作物系数：一个概念
DOI：
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发表时间：
1987
期刊：
影响因子：
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通讯作者：
C. Neale
中科院分区：
文献类型：
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作者：
W. Bausch;C. Neale
摘要作物系数曲线和植被指数之间的相似性显示了将植被指数建模为作物系数的潜力。因此，研究了从测量的作物/土壤场景的反射特性直接估计作物系数的可能性。在0.63~0.69 JWM和0.76~0.90 jim波段测量了玉米(Zea Mays L.)垂直方向和上方2米处的冠层反射辐射，并计算了归一化植被指数(ND)。季节ND曲线为曲线，与玉米的基本作物系数(K^b)曲线相似。当ND达到最大值时，叶面积指数和冠层遮盖度分别为3.2%和77.6%。通过将试验点的有效覆盖和干裸土的ND分别等同于有效覆盖的K^b和干土壤蒸发的K^b，建立了ND的线性变换。这种转换产生了与基本作物系数曲线非常相似的季节曲线，并被命名为基本光谱作物系数(K^J)。从光谱测量得出的作物系数与与传统作物系数相关的通常的时基参数、种植日期和有效覆盖日期无关。因此，基本光谱作物系数是允许作物表达其对天气、管理措施和压力的反应的实时作物系数。
ABSTRACT SIMILARITIES between the crop coefficient curve and a vegetation index showed potential for modeling a vegetation index into a crop coefficient. Therefore, the possibility of directly estimating the crop coefficient from measured reflectance properties of a crop/soil scene was investigated. Reflected canopy radiation in the 0.63 to 0.69 jwm and 0.76 to 0.90 jjim band widths was measured normal to and two meters above corn (Zea mays L.), and the normalized difference (ND) vegetation index was computed. The seasonal ND curve was curvilinear and resembled the basal crop coefficient (K^b) curve for corn. Leaf area index and canopy shading were 3.2 and 77.6%, respectively, when the ND reached its maximum valvue. A linear transformation of the ND was developed by equating the ND at effective cover and for dry, bare soil at the experimental site to the K^b at effective cover and for dry soil evaporation, respectively. This transformation produced a seasonal curve very similar to the basal crop coefficient curve and was named the basal spectral crop coefficient (K^J. Crop coefficients derived from spectral measurements are independent of the usual time base parameters, planting date and effective cover date, associated with traditional crop coefficients. Thus, the basal spectral crop coefficient is a real-time crop coefficient that permits the crop to express its response to weather, management practices, and stresses.