重金属铜污染植被光谱响应特征研究

重金属铜污染植被的反射光谱特性会发生明显改变。在本研究中,采用不同程度的铜污染土壤作为培养基质,选择春小麦、上海青两种农作物进行铜胁迫实验,获取了4个不同生育期、10个不同铜污染强度下的植被叶片的反射光谱,并采用铜污染叶片7个特征波段和光谱角的方法研究了铜污染叶片的光谱特征。结果表明,铜污染叶片光谱差异与作物时期和作物类型有关,可以采用叶片光谱角描述铜污染叶片与健康叶片的光谱差异。该方法只需与阈值做简单的比较,方法简便易行,而且对轻度及重度铜污染十分敏感。叶片光谱辐射传输模型反演结果表明铜污染叶片内部结构参数N明显变大,这也证明了铜污染使叶片内部结构更加散乱无序。在此基础上进一步建立了N与红肩处反射率值的线性关系,相关系数为0.978。本文为铜污染叶片光谱反射模型的建立提供了初步的数据基础与理论支持。     

嫦娥3号巡视探测器桅杆的转动角度误差检校

嫦娥3号巡视探测器桅杆的展开机构、偏航机构和俯仰机构在转动过程中存在系统性的偏差,这些误差影响了巡视探测器导航定位、地形恢复和路径规划的精度.针对这一问题,文章提出了一种间接平差模型,通过真实数据试验证明该方法能够用于对嫦娥3号巡视探测器桅杆的转动角度误差进行检校,并且具有很高的精度和稳定性.     

GPS/BDS组合系统伪距单点定位模型精度分析

合理确定观测值权阵对于应用GPS/BDS组合系统提高单点定位的精度和稳定性十分重要.文章对GPS/BDS常用的几种定权模型等权模型、高度角随机模型、基于Helmert验后方差估计模型、顾及PDOP值的定权模型等进行了实验与分析.结果表明:基于Helmert的定权方法精度最高,进一步对其观测值的分类根据高度角进行改进并利用PDOP值的选星思想后,模型精度再次提高.研究结果可以为提高GPS/BDS组合系统伪距单点定位的精度提供参考.     

面向端元提取的光谱角特征空间图像分块方法

传统的高光谱端元提取算法一般是在高维的光谱特征空间中进行运算,并且图像的全部像元都参与算法,因此运算量偏大,运算效率较低。提出了一种光谱角特征空间的概念,利用图像的空间信息辅助端元提取。图像的全部像元都可以映射到8维的光谱角特征空间中,样本点在特征空间中距离原点的远近表征了其在图像中的位置是否为地物区块的边缘,利用这点可以对高光谱图像进行空间分割。在分割后的每个子块图像内部只选取少数"最纯"像元参与端元提取算法,从而大大降低了端元提取的计算复杂度。     

Chaotic scattering in the restricted three-body problem I. The Copenhagen problem

We consider the scattering motion of the planar restricted three-body problem with two equal masses on a circular orbit. Using the methods of chaotic scattering we present results on the structure of scattering functions. Their connection with primitive periodic orbits and the underlying chaotic saddle are studied. Numerical evidence is presented which suggests that in some intervals of the Jacobi integral the system is hyperbolic. The Smale horseshoe found there is built from a countable infinite number of primitive periodic orbits, where the parabolic orbits play a fundamental role.     

Characterization of the mesospheric sodium layer at La Palma

We present the results of a mesospheric sodium monitoring programme at La Palma carried out through five campaigns of one week each, from 1999 September to 2000 August. The yearly averaged parameters of the layer (the sodium column density and the width) are given. We show that the short time-scale dynamics of the layer are governed by the sporadic layers with an average frequency of one event per night. The influence of the short time-scale dynamics of the layer on an adaptive optics system working on the William Herschel Telescope is quantified. It appears that it is a small effect in terms of defocus error. Finally, we present data obtained during the Perseid meteor shower and show that the dynamics of the sodium layer undergoes a transition with the meteoric activity.     

Intrinsic intraday variability in the gravitational lens system B0218+357

Radio monitoring of the gravitational lens system B0218+357 reveals it to be a highly variable source with variations on time-scales of a few days correlated in both images. This shows that the variability is intrinsic to the background lensed source and suggests that similar variations in other intraday variable sources can also be intrinsic in origin.     

SCATTERING PHASE MATRICES OF ICE CRYSTALS WITH HEXAGONAL PRISM AND TRIANGULAR PYRAMID FORM—A VECTOR RAY TRACING METHOD

The work presented previously by the authors(Cai and Liou,1982)has been extended in this paper.By making use of our improved model the calculations on scattering phase matrices of hexagonal prismice crystals(HPIC)have been conducted for monodisperse and polydisperse systems.Compared with themodel of Cai and Liou,the required computational quantity is decreased by about two orders of magni-tude and the errors of results are less for the new model.Meanwhile,the scattering phase matrices of triangularpyramid ice crystals(TPIC)are also computed in the paper,and the comparison between the scatterings of thetwo forms of ice crystals is performed.     

双基地激光测风雷达回波信号仿真研究

本文针对传统的体散射模型并未考虑大气不均匀性对信号传输的影响等问题,通过引入垂直非均匀的大气参数改进了模型,并利用其建立了体目标的双基地激光测风雷达方程,仿真了侧向散射回波信号,并与单基地雷达进行了对比分析。研究表明:水平方向上,双基地激光测风雷达的回波信号分布特征与单基地雷达差异较大,其回波信号等值线在近地面为卵形线,随着探测高度的增加,回波信号等值线逐渐变为以主、被动雷达为焦点的椭圆形,并最终趋近于圆形;垂直方向上,双基地激光测风雷达的回波信号随高度衰减剧烈,近地面的回波能量约为10^-10 J,4 km高度的回波能量约为10^-15J,在中低层大气(0~10 km),回波信号中气溶胶散射占比大,在高层大气(10 km以上),分子散射占比大。     

Scattering of elastic wave by a partially sealed cylindrical shell embedded in poroelastic medium

Scattering of an elastic wave by a cylindrical shell embedded in poroelastic medium is investigated theoretically with the assumption that the shell material is also a porous elastic medium. The porous medium is modellized via Biot's theory and the scattering by cylindrical shell is expressed by the definition of scattering matrix. The normal mode expansion technique is employed for analysing the scattering field, and the asymptotic solutions of displacements, stresses and pore pressure are derived. Two limiting cases‐scattering by a poroelastic cylinder in Biot medium and a elastic cylindrical shell in elastic medium are obtained from the general solutions. The dispersion curves of displacement amplitude at the interface of shell and medium is compared with the case of elastic shell. The scattering amplitude associated with the fast, slow and transverse waves are identified by numerical simulation. Furthermore, the influence of the poroelastic property of shell material on scattering amplitude is analysed. Copyright © 2005 John Wiley & Sons, Ltd.