GPS载波相位时间频率传递的研究

构建了GPS载波相位时间频率传递系统,初步实现了GPS载波相位时间频率传递.使用GPS载波相位进行了两种不同类型的实验,包括零基线和长基线实验.在数据处理中,使用了专业GPS测地软件包结合自主开发的软件处理30 s间隔GPS载波相位观测数据,分析了1 min间隔的相对时钟估计结果.零基线实验结果表明,GPS载波相位时间频率传递在1d内的数据有约100 ps的时间稳定度,即在采样间隔为1 d时,与之对应的频率不确定度约为2×10~(-15);通过计算其阿伦方差可以看出,其具备远程测量某些原子钟(包括一些铯钟)频率稳定度的能力.在长基线实验中,GPS载波相位时间频率传递在一天的数据中具有约900 ps的时间稳定度,即在采样间隔为1 d时,与之对应的频率不确定度约为2×10~(-14).     

建筑材料特性对GPS监测信号影响规律的试验研究

为了研究常用建筑材料对GPS监测信号的影响规律,进行了多路径误差的试验研究。建立了一套GPS多路径信号模拟与监测系统,通过在流动站天线不同高度、不同距离处安置具有不同介电常数的木板、PVC板和瓷砖,分别获取了三种材料连续两天的GPS监测数据;将改进的粒子滤波算法用于GPS数据后处理中,通过比较发现,试验结果与GPS多路径信号的仿真结果吻合较好,同一种反射材料在不同距离时引起的多路径误差随着距离的增加而逐渐减小,且在增加相同距离的情况下减小的幅度越来越小;具有不同介电常数的反射材料在相同的距离时引起的多路径误差随着介电常数的增大而增大。     

Zinc adsorption on goethite as affected by glyphosate

Cosorption of metals with herbicides on minerals affects their mobility and their environmental effect. Batch experiments were conducted to evaluate the interaction between Zn and glyphosate [N-(phosphonomethyl)glycine (GPS; H3L)] with regard to the effect of GPS on Zn adsorption on goethite. The herbicide GPS markedly affected Zn adsorption on goethite when they coexisted in a goethite suspension. When solution pH was not intentionally adjusted, addition of GPS decreased Zn adsorption on goethite, since the equilibrium solution pH was significantly decreased in the presence of GPS and correspondingly the negative surface charges of goethite decreased. Zinc adsorption on goethite in the presence and absence of GPS at different pH of the equilibrium solution was studied in order to know if pH was the only variable for Zn adsorption with coexisting GPS. At lower pH (pH<5), the presence of GPS increased the adsorption of Zn, because Zn adsorbed on the sites of goethite via GPS bridge. However, at higher pH (pH>5), the presence of GPS decreased the adsorption of Zn on goethite, because GPS reacted with solution Zn to form water-soluble complexes that had lower affinity to the goethite surface in comparison with Zn itself. Zeta potential of goethite significantly decreased after adsorption of GPS, suggesting a chemical bond occurred between GPS and the mineral. FTIRs also show that GPS adsorbs on goethite by coordinating through caboxylate group.     

Set of Standards and Measuring Instruments for Testing the Equipment of Users of the GLONASS and GPS Satellite-Based Navigation Systems

The set of standards and measuring instruments used to test and certify the equipment of users of GLONASS and GPS satellite-based navigation systems is examined. This set enables users to determine the errors of measurements of time, location (during motion or at rest), and velocity for various types of equipment.     

Carrier-phase time transfer

We have conducted several time-transfer experiments using the phase of the GPS carrier rather than the code, as is done in current GPS-based time-transfer systems. Atomic clocks were connected to geodetic GPS receivers; we then used the GPS carrier-phase observations to estimate relative clock behavior at 6-minute intervals. GPS carrier-phase time transfer is more than an order of magnitude more precise than GPS common view time transfer and agrees, within the experimental uncertainty, with two-way satellite time-transfer measurements for a 2400 km baseline. GPS carrier-phase time transfer has a stability of 100 ps, which translates into a frequency uncertainty of about two parts in 10(-15) for an average time of 1 day.     

Correlation between antenna radiation pattern and field performance for global positioning systems in telematics as a function of antenna placement

The effect of antenna placement on the global positioning system (GPS) performance in telematics is investigated. Two sets of measurements were conducted. The first set consisted of measuring the vehicle-level antenna radiation pattern at three distinct antenna locations on a sedan vehicle. The second set consisted of a series of drive tests in three distinct driving environments. The field data were collected in parallel for each antenna location in all driving environments. GPS availability and accuracy results from the field testing are correlated to the vehicle-level antenna radiation pattern measurements. Results are presented to show the impact of the antenna placement on the GPS system performance and to demonstrate the good correlation between the vehicle-level radiation pattern measurements and the performance in the field.     

Developing an IGS time scale

Currently, the International GPS Service (IGS) provides a set of clock products for both satellites and tracking receivers, tabulated at 5-min intervals. These products allow users to determine consistent coordinates and clock values for an isolated GPS receiver with an internal accuracy at the few-cm level. However, because the underlying time scale for the IGS combined clocks is based on a linear alignment to broadcast GPS Time for each day separately, the day-to-day stability of this reference is poor. We show the results of a new filter package written to automate the production of an integrated IGS frequency scale based on a dynamically weighted ensemble of the included frequency standards. The new scale is loosely steered to GPS Time.     

基于动态差分GPS的滑坡位移监测系统

针对目前滑坡位移监测中的难点以及野外应用中的高度自动化、全天候、不受天气影响等要求,综合比较了各类滑坡位移监测方法和已有的监测系统,基于动态差分GPS算法,结合GPRS无线传输网络,设计了一种低成本的滑坡位移实时监测系统.将安置在滑坡监测现场的两台GPS接收机通过无线网络把观测到的原始数据传输至监控中心,然后在计算机上作差分解算,并实时显示出基线长度的变化曲线.实验结果表明该系统的测量精度能够满足滑坡位移监测的要求.     

Further Characterization of the Time Transfer Capabilities of Precise Point Positioning (PPP): The Sliding Batch Procedure

In recent years, many national timing laboratories have installed geodetic Global Positioning System receivers together with their traditional GPS/GLONASS Common View receivers and Two Way Satellite Time and Frequency Transfer equipment. Many of these geodetic receivers operate continuously within the International GNSS Service (IGS), and their data are regularly processed by IGS Analysis Centers. From its global network of over 350 stations and its Analysis Centers, the IGS generates precise combined GPS ephemeredes and station and satellite clock time series referred to the IGS Time Scale. A processing method called Precise Point Positioning (PPP) is in use in the geodetic community allowing precise recovery of GPS antenna position, clock phase, and atmospheric delays by taking advantage of these IGS precise products. Previous assessments, carried out at Istituto Nazionale di Ricerca Metrologica (INRiM; formerly IEN) with a PPP implementation developed at Natural Resources Canada (NRCan), showed PPP clock solutions have better stability over short/medium term than GPS CV and GPS P3 methods and significantly reduce the day-boundary discontinuities when used in multi-day continuous processing, allowing time-limited, campaign-style time-transfer experiments. This paper reports on follow-on work performed at INRiM and NRCan to further characterize and develop the PPP method for time transfer applications, using data from some of the National Metrology Institutes. We develop a processing procedure that takes advantage of the improved stability of the phase-connected multiday PPP solutions while allowing the generation of continuous clock time series, more applicable to continuous operation/ monitoring of timing equipment.     

移动式机动车现场标准测速仪溯源技术的研究

介绍了当前广泛使用的两种基于光电和GPS原理的非接触移动式机动车现场标准测速仪的溯源技术,对光电式机动车速度仪和高精度机动车GPS测速仪进行了实验室模拟测速误差的检测和机动车道路速度实测值的对比试验。在10～180km/h范围内特定速度点,采用同步齿形带式台架校准装置对光电式机动车速度仪进行校准;采用机动车GPS信号模拟器对高精度机动车GPS测速仪在相同速度点进行模拟测速误差检测。使用机动车道路速度实测方法对两类测速仪器在20～150km/h速度范围内的测速性能进行对比,结果表明,两类测速仪器在速度波动较小时,不同速度点的测速偏差在±0.3%范围内;速度变化较快时,高精度机动车GPS测速仪的速度测量值响应速度较快,而光电式机动车速度仪的速度响应与之相比有一定的延时滞后,两者的最大测速偏差在±8%范围内。因此,在能够搜到6颗以上卫星信号时,使用高精度机动车GPS测速仪具有更好的测速性能。     

Assessment of GPS carrier-phase stability for time-transfer applications

We have conducted global positioning system (GPS) carrier-phase time-transfer experiments between the master clock (MC) at the U.S. Naval Observatory (USNO) in Washington, DC and the alternate master clock (AMC) at Schriever Air Force Base near Colorado Springs, Colorado. These clocks are also monitored on an hourly basis with two-way satellite time-transfer (TWSTT) measurements. We compared the performance of the GPS carrier phase and TWSTT systems over a 236-d period. Because of power problems and data outages during the carrier-phase experiment, the longest continuous time span is 96 d. The data from this period show agreement with TWSTT within +/-1 ns, apart from an overall constant time offset (caused by unknown delays in the GPS hardware at both ends). For averaging times of a day, the carrier-phase and TWSTT systems have a frequency uncertainty of 2.5 and 5.5 parts in 10(15), respectively.     

GPS在交通道路测量中的应用

1：500000量级的基础地理信息是我国最重要和最基本的基础空间数据集，对我国的各方面的发展都有着不可忽视的作用。交通道路的测量和数据采集是建立1：50000基础空间数据库的关键之一。将GSP应用于交通道路的测量，可以充分发挥GPS全球性、全天候、高精度、三维定位等优点；快速实现交通道路的测量和相关数据采集，通过研究和现场试验证明，采用差分GPS技术不仅可行，而且有着其它方法无法比拟的优点。     

GPS接收机检定中测量误差超限处理方法的研究

在GPS接收机检定中,面对"测量误差超限"应如何处理,应怎样确定引起误差超限的原因,能否由此判定仪器不合格或者精度达不到指标要求?该文提出了一套处理测量误差超差的方法,对GPS接收机的检定和测量人员具有重要意义。     

A simple spatial integration scheme for solving Cauchy problems of non-linear evolution equations

In this study, we address a new and simple non-iterative method to solve Cauchy problems of non-linear evolution equations without initial data. To start with, these ill-posed problems are analysed by utilizing a semi-discretization numerical scheme. Then, the resulting ordinary differential equations at the discretized times are numerically integrated towards the spatial direction by the group-preserving scheme (GPS). After that, we apply a two-stage GPS to integrate the semi-discretized equations. We reveal that the accuracy and stability of the new approach is very good from several numerical experiments even under a large random noisy effect and a very large time span.     

Decision rules for determining terrestrial movement and the consequences for filtering high-resolution global positioning system tracks: a case study using the African lion (Panthera leo)

The combined use of global positioning system (GPS) technology and motion sensors within the discipline of movement ecology has increased over recent years. This is particularly the case for instrumented wildlife, with many studies now opting to record parameters at high (infra-second) sampling frequencies. However, the detail with which GPS loggers can elucidate fine-scale movement depends on the precision and accuracy of fixes, with accuracy being affected by signal reception. We hypothesized that animal behaviour was the main factor affecting fix inaccuracy, with inherent GPS positional noise (jitter) being most apparent during GPS fixes for non-moving locations, thereby producing disproportionate error during rest periods. A movement-verified filtering (MVF) protocol was constructed to compare GPS-derived speed data with dynamic body acceleration, to provide a computationally quick method for identifying genuine travelling movement. This method was tested on 11 free-ranging lions (Panthera leo) fitted with collar-mounted GPS units and tri-axial motion sensors recording at 1 and 40 Hz, respectively. The findings support the hypothesis and show that distance moved estimates were, on average, overestimated by greater than 80% prior to GPS screening. We present the conceptual and mathematical protocols for screening fix inaccuracy within high-resolution GPS datasets and demonstrate the importance that MVF has for avoiding inaccurate and biased estimates of movement.     

Time transfer using multi-channel GPS receivers

This report is on time transfer experiments using a Global Positioning System (GPS) receiver constructed using a commercial GPS "engine" and a standard PC. The receiver measures the time difference between the local clock and a 1 pps signal synchronized to GPS time using data from up to 8 satellites. The receiver also reports the difference between GPS time as estimated using each of the satellites being tracked and the composite output pulses that have a rate of 1 Hz (1 pps signal). These data can be used to construct the standard 13-minute tracks as defined in the BIPM standard; the same data also can be averaged in other ways that make better use of the multi-channel capabilities of the hardware. The 13-minute averages can be directly compared with standard time-transfer receivers using common-view analysis. The results of the tests suggest that the methods currently used for national and international time and frequency coordination should be re-examined, and an alternative approach based on multi-channel receivers is suggested that should be more flexible, simpler, and easier to operate than the current system.     

GLONASS时间频率传递研究

分析了基于GNSS的时间频率传递方法的发展趋势和GLONASS发展现状及趋势。对GLONASS时间频率传递进行了研究,就其原理实现、误差补偿及数据处理进行了阐述,实现了GLONASS时间频率传递的基本方法,实施了GLONASS和GPS时间频率传递实验。将两种时间频率传递结果进行了对比,对GLONASS时间频率传递自身性能进行了分析,结果显示:GLONASS时间频率传递已达到了可与GPS时间频率传递相比较的水平。     

Detection of the Pine Wilt Disease Tree Candidates for Drone Remote Sensing Using Artificial Intelligence Techniques

Pine wilt disease (PWD) has recently caused substantial pine tree losses in Republic of Korea. PWD is considered a severe problem due to the importance of pine trees to Korean people, so this problem must be handled appropriately. Previously, we examined the history of PWD and found that it had already spread to some regions of Republic of Korea; these became our study area. Early detection of PWD is required. We used drone remote sensing techniques to detect trees with similar symptoms to trees infected with PWD. Drone remote sensing was employed because it yields high-quality images and can easily reach the locations of pine trees. To differentiate healthy pine trees from those with PWD, we produced a land cover (LC) map from drone images collected from the villages of Anbi and Wonchang by classifying them using two classifier methods, i.e., artificial neural network (ANN) and support vector machine (SVM). Furthermore, compared the accuracy of two types of Global Positioning System (GPS) data, collected using drone and hand-held devices, for identifying the locations of trees with PWD. We then divided the drone images into six LC classes for each study area and found that the SVM was more accurate than the ANN at classifying trees with PWD. In Anbi, the SVM had an overall accuracy of 94.13%, which is 6.7% higher than the overall accuracy of the ANN, which was 87.43%. We obtained similar results in Wonchang, for which the accuracy of the SVM and ANN was 86.59% and 79.33%, respectively. In terms of the GPS data, we used two type of hand-held GPS device. GPS device 1 is corrected by referring to the benchmarks sited on both locations, while the GPS device 2 is uncorrected device which used the default setting of the GPS only. The data collected from hand-held GPS device 1 was better than those collected using hand-held GPS device 2 in Wonchang. However, in Anbi, we obtained better results from GPS device 2 than from GPS device 1. In Anbi, the error in the data from GPS device 1 was 7.08 m, while that of the GPS device 2 data was 0.14 m. In conclusion, both classifiers can distinguish between healthy trees and those with PWD based on LC data. LC data can also be used for other types of classification. There were some differences between the hand-held and drone GPS datasets from both areas.     

A Methodology for the Evaluation of a GPS Receiver Performance in Telematics Applications

This paper presents a methodology to evaluate the position availability of automotive grade global positioning system (GPS) receivers intended for Telematics applications utilizing a multichannel GPS satellite signal simulator in a controlled laboratory environment. Initially, field testing of two distinct GPS receivers was conducted in an urban canyon environment and a foliage environment to assess each receiver's position availability performance. Test scenarios were then developed on a multichannel GPS satellite signal simulator in order to create controlled and repeatable stimuli to the GPS receivers. The scenarios take into account the actual satellite constellations at the same day, time, and locations of the field data collections. Furthermore, the number of visible satellites and power levels was adjusted in order to stimulate the hardware tracking sensitivity, hardware acquisition sensitivity, dynamic range, and navigation filter design, all of which impact position availability for GPS receivers. Quantitative results demonstrated good correlation between the results obtained using the developed test scenarios and the results from the field testing. The proposed methodology will result in reducing validation cost and time to market for automotive Telematics products     

GPS定位技术在安县航测外业施测中的应用

本文从生产实践出发,阐述了GPS技术在航洲外业测量中控制劂布测、数据采集、像控点联测等工序施测过程的方法和作业依据。特别是针列灾区复杂环境所遇到特殊情况的处置以及GPS高精度定位技术在生产实施过程中的应用价值,对GPS所具有的通用性、稳定性、高精度的优势和特点进行了有益的探讨。