Towards a high spatial resolution limit for pixel-based interpretations of optical remote sensing data

The divergence of horizontal radiation in vegetation canopies is generally considered to be of negligible consequence in algorithms designed for the physically-based interpretation of space borne observations. However, non-zero horizontal radiation balances are likely to occur if the internal variability of a vegetation target and the typical distances that photons may travel horizontally within such three-dimensional (3-D) media extend to spatial scales that are similar to or larger than those of the nominal footprint of the measuring sensor. Detailed radiative transfer simulations in 3-D coniferous forest environments are presented to document the typical distances that photons may travel in such media, and to quantify the impact that the resulting net horizontal fluxes may have with respect to the local and domain-averaged canopy reflectance. Based on these simulations it is possible to identify a fine spatial resolution limit beyond which pixel-based interpretations of remote sensing data over tall forested areas should be avoided because the horizontal radiation transport at the surface may contribute to 10% or more of the measured reflectance signature of the target pixel.     

大型翼伞的三维气动性能分析

随着回收物质量的增加和回收物可控定点回收要求的提出,大型翼伞的设计研究迫在眉睫。文章采用有限体积法求解K-epsilon二方程湍流模型下的Navier-Stokes(N-S)方程,对某大型翼伞进行三维定常数值模拟,研究考虑伞衣鼓包下翼伞的气动性能,同时对翼伞单侧后缘下拉情况下(翼伞转弯过程)的气动性能进行初步分析。结果表明,翼伞的升力系数随迎角的增大而增加,达到失速迎角后缓慢降低。翼伞阻力系数在负迎角时随迎角增大而缓慢降低,而在正迎角时随迎角增大而增加。翼伞升阻比开始时随迎角增大而增加,在迎角等于8°时达到最大值后随迎角增大而逐渐降低。同时,单侧后缘下拉翼伞相比普通翼伞升力与阻力系数均有所增加,但其最大升阻比却有所减小。     

新、老大豆品种冠层产量和光合作用的比较

对10个新、老大豆品种冠层产量和光合作用的研究表明,新品种的产量显著高于老品种(P<0.01),新品种产量主要集中在冠层的中上部,而老品种的产量则以冠层中部最大,冠层上部、下部产量较低且相差不大.新品种植株叶面积和叶面积指数高于老品种,但差异不显著.新品种叶片的光合速率高于老品种,同时,新品种冠层不同部位叶片光合速率差异较小,老品种冠层不同部位叶片光合差异较大,特别是下层叶片净光合速率下降较大;由于新品种的叶面积指数和单位叶面积的净光合速率高于老品种,新品种的光合能力显著高于老品种,特别是冠层下部的光合能力得到了显著改善.