低费用多天线GPS变形监测系统的研究

简要介绍多天线 GPS监测系统的设计思想 ,并着重介绍和讨论一个使用低质量 (低费用 ) GPS天线及接收机的变形监测系统 ,包括此系统的设计、资料处理方法以及一些初步测试结果。     

不同天线类型对 GAMIT 基线解算的影响

在GPS外业测量中测到的位置,通常是测到GPS接收机天线相位中心的位置。天线的相位中心在实际意义中看不到,是无线电信号接收的瞬时位置,它随着卫星信号输入的强度和角度而改变。本文针对不同的GPS天线,通过实际观测到的数据,利用高精度数据处理软件GAMIT进行处理,分析了不同的GPS天线对解算坐标及解算精度的影响。     

A New Approach for Health Monitoring of Structures: Terrestrial Laser Scanning

Abstract:   A new approach is presented for health monitoring of structures using terrestrial laser scanning (TLS). Three-dimensional (3D) coordinates of a target structure acquired using TLS can have maximum errors of about 10 mm, which is insufficient for the purpose of health monitoring of structures. A displacement measurement model is presented to improve the accuracy of the measurement. The model is tested experimentally on a simply supported steel beam. Measurements were made using three different techniques: (1) linear variable displacement transducers (LVDTs), (2) electric strain gages, and (3) a long gage fiber optic sensor. The maximum deflections estimated by the TLS model are less than 1 mm and within 1.6% of those measured directly by LVDT. Although GPS methods allow measurement of displacements only at the GPS receiver antenna location, the proposed TLS method allows measurement of the entire building's or bridge's deformed shape, and thus a realistic solution for monitoring structures at both structure and member level. Furthermore, it can be used to create a 3D finite element model of a structural member or the entire structure at any instance of time automatically. Through periodic measurements of deformations of a structure or a structural member and performing inverse structural analyses with the measured 3D displacements, the health of the structure can be monitored continuously.     

Simulation of Accuracy Performance for Wireless Sensor-Based Construction Asset Tracking

Abstract:   Today's mobile and remote construction applications, such as tracking of materials, equipment, and workers, demand high reliability and scalability of wireless sensor networks for a large-scale construction site. In particular, identifying the location of distributed mobile entities throughout wireless communications becomes the primary task to realize the remote tracking and monitoring of the construction assets. Even though several alternative solutions have been introduced by utilizing recent technologies, such as radio frequency identification (RFID) and the global positioning system (GPS), they could not provide a solid direction to accurate and scalable tracking frameworks in large-scale construction domains due to limited capability and inflexible networking architectures. This article introduces a new tracking architecture using wireless sensor modules and shows an accuracy performance using a numerical simulation approach based on the time-of-flight method. By combining radio frequency (RF) and ultrasound (US) signals, the simulation results showed an enhanced accuracy performance over the utilization of an RF signal only. The proposed approach can provide potential guidelines for further exploration of hardware/software design and for experimental analysis to implement the framework of tracking construction assets.     

GPS振动变形监测中单一衍射或反射信号误差处理研究

当卫星被测站周围的障碍物遮挡,接收机仅接收到该卫星经过衍射或反射信号,而没有接收到直射信号时,GPS测量结果将含有较大的误差,本文称之为单一衍射或反射误差。经分析,这种误差对载波相位测量最大可达1个波长。为了消除这种误差的影响,本文提出了基于测站环境建模的卫星剔除法,通过野外实际测量的结果表明,该方法能有效地消除单一衍射或反射信号误差的影响。     

GPS天线阵列变形监测系统设计

GPS是监测大坝以及滑坡安全的有效手段。但是成本过高和传输监测数据困难都是限制其发展的关键问题。文中提出的GPS天线阵列变形监测系统很好的解决了这些问题,该系统利用GPS多天线共享器,降低了设备成本;并且利用WLAN(无线局域网)进行数据传输.通过实践证明GPS天线阵列监测系统拥有与常规GPS监测方法相当的精度,但大大降低了监测系统的成本。     

CSRS-PPP在线定位服务系统精度分析

2003年10月,加拿大自然资源部大地测量司开发了一套在线定位服务系统CSRS-PPP.GPs用户可以通过网络向该系统提交单点GPS观测文件,之后就能得到高精度的单点定位结果.本文首先对PPP技术的发展历程作了回顾,并详细介绍了CSRS-PPP系统以及IGS精密产品,最后分析讨论了该系统的静态和动态定位精度,取得了一些有益的结论.相对于传统的使用广播星历的单点定位方法,CSRS-PPP可以使单点定位精度提高2～100倍,其单点定位结果与相位差分GPS定位精度相当,并且不需要基准站同步观测.研究结果对控制点的建立、GPS基准站的建立和线路测量等工作有一定的实际价值.     

森林消防车无网络通信定位及参数采集系统设计

为了实现在无信号林区对森林消防车的定位及参数采集,采用传感技术、北斗短报文技术,研发了一种基于北斗短报文的通信定位及参数采集系统,该系统包括数据采集系统、北斗短报文通信系统。参数采集系统采用STM32 芯片采集传感器数据,同时利用三防平板电脑的GPS 定位功能获取森林消防车的位置,在原始林区弱信号甚至是无信号情况下利用北斗短报文技术上报消防车的传感器参数和位置信息,指挥车车载终端收到报文信息,在本地存储并上传到云端,支持APP 实时显示。经测试,系统定位的精度可克服环境空旷程度的影响,整体运行情况良好,符合林区无网环境下消防车参数和位置信息采集需求,能够作为提高无信号林区救援的有效手段,从而提高无信号林区消防救援的安全性和高效性。     

GPS一机多天线变形监测系统前期试验网的精度研究

介绍了东江大坝GPS一机多天线变形监测系统前期试验网的试验背景、试验目的以及建立情况 ,讨论了试验过程中遇到的问题及解决方法 ,详细分析了试验精度情况及周围环境对监测质量的影响。得出了一些有益的结论。     

GAMIT基线解算中天线高处理方法的探讨

天线高的计算是GPS数据处理过程中一个重要的环节,GAMIT软件提供了一系列函数和内部文件进行天线高的处理,这些函数根据内部文件中包含的接收机/天线信息进行天线相位中心改正,要保证基线解算过程顺利进行,需要明确GAMIT软件中与天线高有关的各文件之间的关系。该文在探讨了GAMIT中与天线高有关的各个文件之间的关系的基础上,总结出GAMIT处理天线高的大致流程,可为相关的工程实践提供一定的参考。     

Experimental Assessment of the Accuracy of GPS and RTS for the Determination of the Parameters of Oscillation of Major Structures

Abstract:   Based on experimental evidence we explore the possibility of using GPS and robotic total stations (RTS) for measurements of oscillations of relatively rigid structures (modal frequencies up to 3–4 Hz). Our strategy was to compare uni-axial oscillations of known characteristics with simultaneous recordings of both GPS and RTS, and analyze obtained time series to determine amplitude and frequency of oscillations. The conclusion of this study is that GPS can record oscillations up to 4 Hz with a minimum amplitude of 5–10 mm with an accuracy of a few millimeters, and that RTS can record peaks of oscillations with submillimeters to a few millimeters accuracy, but at high frequencies some cycles were lost. Based on recordings of both the instruments frequencies of oscillations were also accurately determined, though noise seems to increase with increasing frequency. Spectral analysis was based on the least-square-based software which permits one to analyze discontinuous, short, and non-equispaced time series. The latter derive either from GPS signal outages/imperfections and hardware/software imperfections, or from a non-constant rate of sampling for RTS. The overall conclusion is that the adopted computational approaches permit us to overcome some main disadvantages of these instruments and to use conventional GPS and RTS instrumentation for a wide range of cases of structural monitoring, especially if displacements relative to an independent coordinate system are required.     

Wireless sensor networks as part of a web-based building environmental monitoring system

The presented research shows how advanced wireless sensor technology can be used by engineers to monitor conditions in and around buildings. The objective is split into three different tasks. First, wireless sensor hardware is programmed to process signals from sensors and transmit the data in a suitable format. This task was accomplished through an open-source operating system and a programming language designed specifically for wireless sensor hardware. The second task involved the processing of signals sent by the wireless sensor nodes. In this application, a Java program was written that deciphered messages transmitted from a wireless receiver over a computer's serial port and then placed the data in a database. The structure of that database is discussed to help identify the key pieces of information that are needed to make use of the data. The third piece of the proposed monitoring system is an interface to review the data. A Web-based system was developed that allows a user to mine the database using parameters such as the type of data, location of sensor, and the time of data acquisition. It is anticipated that this research will demonstrate the potential of using wireless sensor networks for monitoring buildings.     

Pavement performance assessment using a cost‐effective wireless accelerometer system

Pavement condition monitoring is required to identify pavements in need of maintenance or rehabilitation. Early identification of reduction in pavement's structural resistance and improving the structural resistance by minor repairs can lead to significantly lower maintenance costs for transportation agencies. In this study, a cost‐effective wireless sensor that can be embedded in the road to measure the transient vibrations due to different applied loads was tested to determine its effectiveness in terms of pavement displacement measurements. Test results show that the vibration sensor, combined with the algorithms, can be embedded in new or existing pavements and used as an accurate wireless displacement sensor. The low cost of the sensor system allows the use of these sensors at high densities for monitoring the performance of an entire road network. Outputs from the developed system can be directly used to evaluate the condition and performance of pavement structure (increasing displacement over time indicating increasing pavement damage). In addition, displacement data from the system can be used to backcalculate pavement layer stiffnesses, which can be used to predict long‐term performance of the pavement structure. Reduction in pavement layer stiffness over time can be used to determine long‐term damage accumulation.     

支撑杆节点极限承载力有限元分析

本文应用有限元法,考虑材料非线性和几何非线性,分析了现代常用的天线载体支撑杆节点的应力和塑性区分布规律、节点变形等重要受力性能,提出了满足工程精度的节点承载力计算的简易等效方法和节点的加强措施,方便工程实际应用。     

两种典型电离层延迟改正模型的效果研究

针对单频GPS接收机受电离层影响较大的特点,分析讨论了Klobuchar模型和IONEX模型的使用特点及其改正精度,讨论了两种不同的电离层延迟改正模型的改正效果,研究结果可以为单频GPS用户有效修正电离层延迟影响提供好的建议。     

Road Infrastructure Data Acquisition Using a Vehicle-Based Mobile Mapping System

Abstract:   This study presents the technology of a vehicle-based mobile mapping system to maintain an updated transportation database. The mobile mapping system that integrates the global positioning system (GPS), the inertial navigation system (INS), and digital cameras has been developed to collect data on position and attributes of road infrastructure. The vehicle-based mobile mapping system works by having the GPS and INS record the position and attitude data, and digital cameras take road images. The stereovision system can determine the position of objects that are visible on the image pair in the global coordinate system with GPS and INS data. As field data acquisition is a very expensive task, a mobile mapping system offers a greatly improved solution. In this study, we successfully created a road infrastructure map with mobile mapping technology and proposed automatic algorithms for detecting and identifying road signs from road images. The proposed detection algorithm includes line and color region extraction processes and uses the Hopfield neural networks. The identification algorithm uses seven invariant moments and parameters that present geometric characteristics. With this combined method, we could successfully detect and identify road signs.     

An Unmanned Aerial Vehicle‐Based Imaging System for 3D Measurement of Unpaved Road Surface Distresses1

Abstract: Road condition data are important in transportation management systems. Over the last decades, significant progress has been made and new approaches have been proposed for efficient collection of pavement condition data. However, the assessment of unpaved road conditions has been rarely addressed in transportation research. Unpaved roads constitute approximately 40% of the U.S. road network, and are the lifeline in rural areas. Thus, it is important for timely identification and rectification of deformation on such roads. This article introduces an innovative Unmanned Aerial Vehicle (UAV)‐based digital imaging system focusing on efficient collection of surface condition data over rural roads. In contrast to other approaches, aerial assessment is proposed by exploring aerial imagery acquired from an unpiloted platform to derive a three‐dimensional (3D) surface model over a road distress area for distress measurement. The system consists of a low‐cost model helicopter equipped with a digital camera, a Global Positioning System (GPS) receiver and an Inertial Navigation System (INS), and a geomagnetic sensor. A set of image processing algorithms has been developed for precise orientation of the acquired images, and generation of 3D road surface models and orthoimages, which allows for accurate measurement of the size and the dimension of the road surface distresses. The developed system has been tested over several test sites with roads of various surface distresses. The experiments show that the system is capable for providing 3D information of surface distresses for road condition assessment. Experiment results demonstrate that the system is very promising and provides high accuracy and reliable results. Evaluation of the system using 2D and 3D models with known dimensions shows that subcentimeter measurement accuracy is readily achieved. The comparison of the derived 3D information with the onsite manual measurements of the road distresses reveals differences of 0.50 cm, demonstrating the potential of the presented system for future practice.     

Filtration methods for recovery of Bacillus anthracis spores spiked into source and finished water

Spores of Bacillus anthracis Sterne strain were recovered from 100 ml and 1 L volumes of tap and source waters using filtration through a 0.45 um filter, followed by overnight culture on agar plates. In a set of experiments comparing sheep red blood cell (SRBC) plates with a chromogenic agar formulation designed by R & F Laboratories, with a spiking dose of 47 plate-enumerated spores in 100 ml tap water, the mean spore recoveries were 34.0 and 30.8 spores, respectively. When a spiking dose of 100 fluorescence activated cell sorter(FACS)-enumerated spores was used in 100 ml potable water, the average recovery with SRBC plates was 48 spores. Detection efforts with spiking doses of 35 and 10 spores in 1 L tap water were successful, but recovery efforts from spiked 1 L volumes of source water were problematic due to the concomitant growth of normal spore-forming flora. Recoveries were also attempted on 10 L volumes of tap water. For a spiking dose of 100 spores, mean recovery from six replicates was 11 spores (±6.8, range 2–20), and for a spiking dose of 10 spores, mean recovery from six replicates was 2.3 spores (±3.5, range 0–9). Efforts were also made to “direct detect” spores via polymerase chain reaction (PCR) on washes from filters. When spiking 534 spores in 100 ml, 9/9 replicates of spiked tap water, 6/6 source water replicates, and 0/3 unspiked controls were positive by lef PCR. When 534 spores were spiked into 1 L tap water, the lef PCR was unsuccessful; however, using the nested vrrA PCR resulted in 4/9 spiked samples, and 0/3 unspiked controls, testing positive. Our results indicate that an inexpensive and user-friendly method, utilizing filtration apparatus commonly present in many water quality testing labs, can readily be adapted for use in detecting this potential threat agent.     

Development and performance of a small relative humidity sensor for indoor microclimate measurements

The development and performance of a small relative humidity sensor is described, capable of distinguishing humidities over distances only millimetres apart, allowing humidities to be measured in the microenvironments of biocontaminants such as dust mites and mould. The sensor can, for example, distinguish between humidities at the bottom of a carpet pile from humidities at the top, or between closely spaced locations in bedding such as below a sheet and on top of a mattress. Calibration showed that the device was accurate to 1% humidity, had a time constant of the order of 10 seconds, and had low drift. Being cheap it can be used in large numbers.     

A Synchronized Wireless Sensor Network for Experimental Modal Analysis in Structural Health Monitoring

Abstract: Structural health monitoring aims to provide an accurate diagnosis of the condition of civil infrastructures during their life span using data acquired by sensors. Wireless sensor networks represent a suitable monitoring technology to collect reliable information about the structure's condition, replacing visual inspections, and reducing installation and maintenance time and costs. This article introduces a time synchronized and configurable wireless sensor network for structural health monitoring enabling a highly accurate identification of the modal properties of the monitored structure. The wireless sensor nodes forming the network are equipped with a 3‐axis digital accelerometer and a temperature and humidity sensor. The implemented Medium Access Control layer time synchronization protocol (μ‐Sync) ensures a highly accurate synchronicity among the samples collected by the nodes, the absolute error being constantly below 10 μs, also when high sampling frequency (up to 1 kHz) and extended sampling periods (up to 10 minutes) are applied. The experimental results obtained on a wooden model bridge, compared with those derived from acceleration signals acquired by high‐quality wired sensors, show that the so synchronized wireless sensor nodes allow a precise identification of the natural frequencies of vibration of the monitored structure (1% maximum relative difference).