Modeling the impact of spectral sensor configurations on the FLD retrieval accuracy of sun-induced chlorophyll fluorescence

Chlorophyll fluorescence is related to photosynthesis and can serve as a remote sensing proxy for estimating photosynthetic energy conversion and carbon uptake. Recent advances in sensor technology allow remote measurements of the sun-induced chlorophyll fluorescence signal (Fs) at leaf and canopy scale. The commonly used Fraunhofer Line Depth (FLD) principle exploits spectrally narrow atmospheric oxygen absorption bands and relates Fs to the difference of the absorption feature depth of a fluorescensing and a non-fluorescensing surface. However, due to the nature of these narrow bands, Fs retrieval results depend not only on vegetation species type or environmental conditions, but also on instrument technology and processing algorithms. Thus, an evaluation of all influencing factors and their separate quantification is required to further improve Fs retrieval and to allow a reproducible interpretation of Fs signals.Here we present a modeling study that isolates and quantifies the impacts of sensor characteristics, such as spectral sampling interval (SSI), spectral resolution (SR), signal to noise ratio (SNR), and spectral shift (SS) on the accuracy of Fs measurements in the oxygen A band centered at 760 nm (O₂-A). Modeled high resolution radiance spectra associated with known Fs were spectrally resampled, taking into consideration the various sensor properties. Fs was retrieved using the three most common FLD retrieval methods, namely the original FLD method (sFLD), the modified FLD (3FLD) and the improved FLD (iFLD). The analysis investigates parameter ranges, which are representative for field and airborne instruments currently used in Fs research (e.g., ASD FieldSpec, OceanOptics HR, AirFLEX, AISA, APEX, CASI, and MERIS).Our results show that the most important parameter affecting the retrieval accuracy is SNR, SR accounts for ≤ 40% of the error, the SSI for ≤ 12%, and SS for ≤ 7% of the error. A trade-off study revealed that high SR can partly compensate for low SNR. There is a strong interrelation between all parameters and the impact of specific parameters can compensate or amplify the influence of others. Hence, the combination of all parameters must be considered by the evaluation of sensors and their potential for Fs retrieval. In general, the standard FLD method strongly overestimates Fs, while 3FLD and iFLD provide a more accurate estimation of Fs. We conclude that technical sensor specifications and the retrieval methods cause a significant variability in retrieved Fs signals. Results are intended to be one relevant component of the total uncertainty budget of Fs retrieval and have to be considered in the interpretation of retrieved Fs signals.     

网络安全策略求精一致性检测和冲突消解机制的研究

通过对基于策略的网络安全管理的研究,分析了现有网络安全策略冲突检测和消解方法存在的不足.基于策略求精的思想和安全策略冲突分类技术,建立基于策略的网络管理安全级模型,并用扩展的XACML语言加以描述.根据策略行为间的关系,采用知识推理技术,动态分层地对相应安全级策略进行一致性自动检测和实时冲突消解,使其具有良好的可重用性...     

基于互信息的颅脑MR影像序列的三维配准

医学图像配准具有重要的临床应用价值,并一直是医学图像处理领域的热点研究问题。基于互信息的配准方法由于自动化程度高和配准精度高的优点而被广泛应用于三维医学图像配准;但是,也存在着数据量大、计算速度慢的问题。采用归一化互信息测度,并将一种新的正交优化技术应用于颅脑MR影像序列的三维配准,旨在缩短处理时间。将该方法与使用传统优化算法的配准方法作了比较,实验结果表明,提出的方法能够显著提高配准速度,且不降低配准精度。     

基于专家系统的并行工程冲突解决的研究

如何解决设计领域中出现的冲突问题一直是并行工程研究的一个重要课题。该文分析了设计领域冲突的特点,提出了面向对象的冲突知识表达形式,以及规则推理机制,实现了基于专家系统的冲突解决方法。该系统得到了实践的检验,有力地支持了并行工程的实施。     

Current manufacturing technologies for TFT‐LCDs

Abstract— TFT‐LCD panels for notebook‐PC applications requires a thin and light form factor, low power consumption, and good display quality, whereas the desktop monitor has different requirements such as large panel size, wide viewing angle, high resolution, brightness, etc. However, for the fifth‐generation of mass production, current panel technologies have to improve in order to cope with these requirements. In this article, various approaches to the manufacturing technologies of next‐generation TFT‐LCDs are discussed.     

An object-oriented organizational model to support dynamic role-based access control in electronic commerce

Role-based access control (RBAC) provides flexibility to security management over the traditional approach of using user and group identifiers. In RBAC, access privileges are given to roles rather than to individual users. Users acquire the corresponding permissions when playing different roles. Roles can be defined simply as a label, but such an approach lacks the support to allow users to automatically change roles under different contexts; using static method also adds administrative overheads in role assignment. In electronic commerce (E-Commerce) and other cooperative computing environments, access to shared resources has to be controlled in the context of the entire business process; it is therefore necessary to model dynamic roles as a function of resource attributes and contextual information.In this paper, an object-oriented organizational model, Organization Modeling and Management (OMM), is presented as an underlying model to support dynamic role definition and role resolution in E-Commerce solution. The paper describes the OMM reference model and shows how it can be applied flexibly to capture the different classes of resources within a corporation, and to maintain the complex and dynamic roles and relationships between the resource objects. Administrative tools use the role model in OMM to define security policies for role definition and role assignment. At runtime, the E-Commerce application and the underlying resource manager queries the OMM system to resolve roles in order to authorize any access attempts. Contrary to traditional approaches, OMM separates the organization model from the applications; thus, it allows independent and flexible role modeling to support realistically the dynamic authorization requirements in a rapidly changing business world.     

多视点平行拼图

提出了一种新的多视点拼图,称之为平行拼图,平行拼图不仅可以应用到基于图像的绘制技术中,而且可以广泛地运用于基于图像的三维重建。该文设计了从真实照片中得到高分辨率平行拼图的算法,建立了从平行拼图得到高精度绘制输出的数学模型,讨论了用照片建立平行拼图的精度上限,并且给出了良好的实验结果。     

超声波六自由度跟踪器设计原理及误差模型研究

位置方位跟踪器是虚拟现实系统和其它人机实时交互系统中不可缺少的人机交互 设备之一.在讨论用超声波测距原理实现运动物体六自由度(6DOF)跟踪器设计原理的基础 上,结合以前关于坐标分辨率及误差的研究结果,深入分析了跟踪器角度分辨率与坐标分辨 率以及跟踪器硬件参数之间的关系,并由此给出了超声波位置方位跟踪器关键物理参数的设 计依据.     

High Order Schemes for Resolving Waves: Number of Points per Wavelength

For energetic flows there are many advantages of high order schemes over low order schemes. Here we examine a previously unknown advantage. It is commonly thought that the number of points per wavelength in order to obtain a given error in a numerical approximation depends only on runtime and the order of the approximation. Using truncation error arguments and examples we will show that it is not a constant and depends also on the wavenumber. This dependence on the numerical order and wavenumber strongly favors high order schemes for use in flows which have significant energy in the high modes such at Rayleigh–Taylor and Richtmyer–Meshkov instabilities.     

浅谈网页制作的经验与技巧

在制作网页的过程中,会发现预想的结果和实际预览网页时的效果有很大的区别,比如说网页在不同分别率预览时发生了改变、网页中的字体大小也在变化、图片上传后不能显示等等。在几年的网页教学中,笔者不断摸索,总结了一些经验和技巧供大家借鉴。