基于北斗卫星导航系统的飞行物轨迹标记法

为了实时准确地掌握和了解导航系统飞行物的位置和空间关系,以提高北斗系统的运行准确性,该文根据北斗卫星导航系统不间断授时服务特点,提出一种利用北斗卫星授时信号估计空间飞行物轨迹的方法。卫星下发的授时信号到达用户终端的过程中,受到空间飞行物的遮挡而产生扰动。用户终端将接收的扰动信号的变化量通过各种网络汇聚到数据中心,如果用户终端、空间星座和地面数据中心的时钟同步,在多个用户终端存在的条件下,将数据中心计算出的飞行物的时空参量等信息标注到空间地理信息系统上,连接这些空间点,就可以绘制出空间飞行物的运动轨迹。     

Visualizing spatiotemporal trajectories of mobile social media users using space–time cube

The implementation of social network applications on mobile platforms has significantly elevated the activity of mobile social networking. Mobile social networking offers a channel for recording an individual’s spatiotemporal behaviors when location-detecting capabilities of devices are enabled. It also facilitates the study of time geography on an individual level, which has previously suffered from a scarcity of georeferenced movement data. In this paper, we report on the use of georeferenced tweets to display and analyze the spatiotemporal patterns of daily user trajectories. For georeferenced tweets having both location information in longitude and latitude values and recorded creation time, we apply a space–time cube approach for visualization. Compared to the traditional methodologies for time geography studies such as the travel diary-based approach, the analytics using social media data present challenges broadly associated with those of Big Data, including the characteristics of high velocity, large volume, and heterogeneity. For this study, a batch processing system has been developed for extracting spatiotemporal information from each tweet and then creating trajectories of each individual mobile Twitter user. Using social media data in time geographic research has the benefits of study area flexibility, continuous observation and non-involvement with contributors. For example, during every 30-minute cycle, we collected tweets created by about 50,000 Twitter users living in a geographic region covering New York City to Washington, DC. Each tweet can indicate the exact location of its creator when the tweet was posted. Thus, the linked tweets show a Twitter users’ movement trajectory in space and time. This study explores using data intensive computing for processing Twitter data to generate spatiotemporal information that can recreate the space–time trajectories of their creators.     

人工增雨防雹火箭弹道跟踪系统的研制及初步试验

由于受到高空风场的影响,人工增雨防雹火箭真实的弹道轨迹和射程与理论弹道值具有不一致性。为增强实施增雨防雹作业的科学性、精准性及其作业效果评估准确性,研制了一套人工增雨防雹火箭播撒作业跟踪系统。该系统分为火箭定位系统和数据传输系统两部分,利用卫星定位模块加上数据传输电台模式将火箭飞行轨迹实时传输至地面。并开展了一次人工增雨防雹火箭弹道跟踪实弹发射试验,发射两发人工增雨防雹测试火箭,除初始阶段4～5 s卫星定位失锁而没有数据外,其余时间所有数据均接收完整。结合高空风场数据对人工增雨防雹测试火箭进行风偏修正后的实际弹道更接近于理论弹道,风偏修正意义明显,有利于增雨防雹火箭精准作业。     

Study on stability and reinforcement of a landslide on Ji＇an-Dandong highway

This study clarified the failure mechanism of a landslide on Ji＇ an-Dandong highway, through the detailed analysis of its geological condition. Then based on the back analysis of the broken landslide, take limit equilibrium method to evaluate the stability of the potential landslide. The result shows that the landslide is lack of safety stock, so anchor rope is designed to reinforce the landslide.     

Evaluation and forecasting of daily groundwater outflow in a small chalky watershed

The purpose of this research is to include expert knowledge as one part of the modelling system and therefore offer the chance to create a productive interaction system between expert, mathematical model (MMO8) and artificial neural networks (ANNs). In the present project, the first objective is to determine some parameters by the MMO8 model, introduced as ANN input parameters to forecast spring outflow. The second objective is first to investigate the effect of temporal information by taking current and past data sets and then to forecast spring outflow. The good results obtained reveal the merit of the ANNs–MMO8 combination, and specifically multilayer perceptron (MLP) models. This methodology, for a network with lower, lag and number hidden layer, consistently produced better performance. Copyright © 2003 John Wiley & Sons, Ltd.     

A hybrid Bayesian back‐propagation neural network approach to multivariate modelling

There is growing interest in the use of back‐propagation neural networks to model non‐linear multivariate problems in geotehnical engineering. To overcome the shortcomings of the conventional back‐propagation neural network, such as overfitting, where the neural network learns the spurious details and noise in the training examples, a hybrid back‐propagation algorithm has been developed. The method utilizes the genetic algorithms search technique and the Bayesian neural network methodology. The genetic algorithms enhance the stochastic search to locate the global minima for the neural network model. The Bayesian inference procedures essentially provide better generalization and a statistical approach to deal with data uncertainty in comparison with the conventional back‐propagation. The uncertainty of data can be indicated using error bars. Two examples are presented to demonstrate the convergence and generalization capabilities of this hybrid algorithm. Copyright © 2003 John Wiley & Sons, Ltd.     

大型射电望远镜背架精密安装技术

对65 m射电望远镜的背架安装做了尝试,取得较满意的结果.针对天线背架尺寸大、质量重、焊接变形大、几何精度要求高等特性,采用全站仪工业测量系统实现背架的快速、无接触、高精度定位测量,点位测量精度优于1 mm;采用独特的施工工艺和焊接技术,最大限度控制焊接变形,最终点位偏差优于1.5 cm.提出基于设计坐标系建立安装测量...     

Aerosol optical depths at Mohal-Kullu in the northwestern Indian Himalayan high altitude station during ICARB

First time observations of spectral aerosol optical depths (AODs) at Mohal (31.9°N, 77.11°E; altitude 1154 m amsl) in the Kullu valley, located in the northwestern Indian Himalayan region, have been carried out during Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB), as a part of the Indian Space Research Organisation-Geosphere Biosphere Program (ISRO-GBP). AODs at six wavelengths are obtained using Microtops-II Sunphotometer and Ozonometer. The monthly mean values of AOD at 500 nm are found to be 0.27 ± 0.04 and 0.24 ± 0.02 during March and April, 2006 respectively. However, their monthly mean values are 0.33 ± 0.04 at 380 nm and 0.20 ± 0.03 nm at 870 nm during March 2006 and 0.31 ± 0.3 at 380 nm and 0.17 ± 0.2 at 870 nm during April 2006, showing a gradual decrease in AOD with wavelength. The Ångstrom wavelength exponent ‘α’ had a mean value of 0.72 ± 0.05, implying reduced dominance of fine particles. Further, the afternoon AOD values are higher as compared to forenoon values by ～ 33.0% during March and by ～ 9.0% during April 2006 and are attributed to the pollutant lifted up from the valley by the evolving boundary layer. Besides the long-range transportation of aerosol particles by airmass from the Great Sahara and the Thar Desert regions to the observing site, the high values of AODs have also been influenced by biomass burning and frequent incidents of forest fire at local levels.     

济南典型地层HSS参数选取及适用性研究

针对济南地区典型地层上的基坑工程,土体采用PLAXIS 3D中的硬化土小应变（HSS）模型,建立了有限元模型,并根据实际监测数据结合位移反分析技术,得到了该典型地层下土体HSS模型参数的一般选取方法。之后简化模型,分别采用土体的HSS模型与Mohr-Coulomb（M-C）模型进行有限元分析,对比基坑开挖至不同深度时,应用两种模型模拟所得挡土墙变形与墙后地表沉降的差异。结果表明：基坑数值分析中,土体采用M-C模型与HSS模型所得结果的差异随基坑挖深增加而增加,且采用HSS模型所得结果更符合深基坑的实际变形。综合考虑采用HSS模型与M-C模型建模时的参数选取难易程度、经济性以及两种模型数值分析的工程适用性,建议基坑开挖超过15 m时,土体采用HSS模型进行数值分析,反之可采用M-C模型。研究结果对指导深基坑支护设计及岩土工程参数的勘察、选取,具有重要参考价值。     

港珠澳大桥沉管隧道基槽异常回淤分析与数值模拟

港珠澳大桥沉管隧道E15管节基槽发生异常回淤,海底隧道沉管安装被迫中止。为查明E15管节基槽发生异常回淤的原因,先后开展了现场水文泥沙观测、遥感影像资料分析和数值模拟等多种技术手段。采用水沙数学模型反演了内伶仃岛上游采砂活动形成的浑水团在潮流作用下的扩散输移过程,沙源在数学模型中以面源形式模拟。模拟结果表明,采砂活动形成的浑水团在一个大潮期间的落潮过程中可输移扩散至基槽水域,其中E15—E27管节基槽日淤厚在采砂活动影响下将增加43.8%。数值模拟结果为查明E15管节基槽异常回淤的泥沙来源提供了佐证。E15管节以东基槽水域水沙环境复杂,天然淤积已经接近临界回淤允许值,基槽上游水域的采砂活动对沉管基槽回淤将带来不可控因素,采砂活动对周边水域产生的泥沙回淤影响应引起足够重视。