垄行结构玉米冠层方向亮温模型研究

基于热红外成像仪获取的玉米冠层图像，对垄行结构玉米的方向亮温（DBT）进行模型化描述并开展了初步验证工作。模型中假设某一方向上的冠层DBT是组分亮温及各组分在视场中所占面积权重的函数，它们在视场中的比例依赖太阳与传感器的几何位置关系，以及在作物行内，作物行与行之间孔隙的分布。对于玉米冠层的几何特征，简化为横截面是矩形的、其中有空隙透光的一组无限长的平行立方体；立方体内双向孔隙率的方向变化由Kuusk函数来描述。模型模拟表明，玉米亮温组分在视场中的权重具有垄行特性。中午前后，通过对中等密度的冠层DBT模拟，在DBT极坐标图形上发现了一个明显位于垄行方向的热条带的出现，热点出现在太阳位置的周围。最后，利用实地观测的结果与模型模拟结果作对比，对该模型的不足和以后的改进作了初步分析。

Modeling Directional Brightness Temperature over a Maize Canopy in Row Structure

A modeling study on the variations of directional brightness temperature(DBT) for row-structure crops was carried out with the help of the images captured by a large aperture thermal infrared camera over a maize canopy.The model assumes that the DBT is a function of component brightness temperatures and their directional fractions.Component fractions in the scene of view depend on sun-view geometry and the distributions of gaps within and between plant rows.To describe canopy geometrical features,a system of porous hedgerows with rectangle cross-section has been used;the directional variations of gap fraction are described by Kuusk function.The model demonstrates directional variations of DBT as a function of sun-viewing geometry and canopy geometrical structure as well as component brightness temperatures.In the simulation of DBT over a middle dense canopy near the noontime,the results reveal an evident row-direction-oriented hot stripe in DBT polar map,where appeared the hot spot along the sun direction.Further validation analysis has also been conducted which demonstrates modeled DBT agreeing closely with field observations.