Search

In 1997, the National Geodetic Survey (NGS) published static global positioning system (GPS) surveying guidelines for determining ellipsoidal heights on marks. These guidelines, commonly referred to as NGS-58, are used today in the United States for modernizing heights on marks. Later, in 2013, the NGS released OPUS-Projects, a web-based tool for processing GPS surveys. To evaluate OPUS-Projects and compare it with NGS-58, a static GPS survey was conducted in Oregon. The data were used to develop four different networks. For the most part, the recommendations in NGS-58 worked well, but the 1-h observations did not always produce accurate ellipsoidal heights for baselines longer than 7 km. For the other networks that consisted of 5-h observations or greater, the resulting ellipsoidal heights on all of the marks agreed within±1 cm. For these networks, the estimated network accuracy of the ellipsoidal height for each mark was less than 1.2 cm at 95% confidence. Such consistent results indicate that OPUS-Projects can be used for height modernization surveys. [ABSTRACT FROM AUTHOR]

A comprehensive quality-control approach is presented when monitoring motion of tectonic plates using Global Navigation Satellite System (GNSS) measurements of Continuously Operating Reference Station (CORS) networks. The approach was used in a case study in which changes of coordinates with time in a dynamic datum of the newly established CORS network in Western Australia were used to determine the rate of horizontalmotion of this part of the Australian Plate. Biweekly data spanning 3 years were used. Quality control started in the preprocessing stage by multipath analysis of all sites and screening of data for outliers, cycle slips, and clock jumps. Possible error sources in the observations were addressed in the processing software. The stability of CORS networks was evaluated by checking changes of their coordinates in a static datum. The computed positions were checked for their consistency, precision, and repeatability. The few problematic data were replaced by better neighboring data sets. The final positions that passed the quality-control process were used for assessment of the Australian Plate movement. Results showed that this plate had a rate of motion in a grid Universal Transverse Mercator (UTM) projection of International Terrestrial Reference Frame ITRF2008 that was 6.84 cm/year with a precision of 2 mm/year and an azimuth of 29.6° on average. [ABSTRACT FROM AUTHOR]

The authors investigated the possibility of expanding the application of global navigation satellite systems (GNSS) into the monitoring of stiff civil-engineering structures from the current limit of dominant frequencies of 3-4 Hz to a new limit of 6-7 Hz. On the basis of experience from previous supervised learning experiments, the authors analyzed 100-Hz GNSS data collected with an optimal phase-locked loop and collocated accelerometer data, both describing the attenuation of forced excitations of a timber pedestrian bridge. Computed vertical apparent deflections were masked by noise, but it was still possible to accurately identify the natural frequency of the bridge, equal to 6.5 Hz, and weak fusion with accelerometer data led to accurate oscillation waveforms. The quality of the latter was assessed by structural constraints and by comparison of waveforms of acceleration and of damping ratios derived from GNSS and from accelerometers. These results made it possible to (1) assess the quality of 100-Hz data in monitoring real structures, (2) propose methods for deriving highly dynamic deflections on the order of a few millimeters, and (3) expand the application of GNSS into the measurement of three-dimensional dynamic deflections of stiffer structures, i.e., with natural frequencies of up to 6-7 Hz and vertical deflections of a few millimeters only-an important contribution to structural-health monitoring and structural identification. [ABSTRACT FROM AUTHOR]

This study investigated long-term land subsidence derived from borehole extensometer and Global Positioning System (GPS) observations from Addicks, a suburb located in West Houston, Texas. The Addicks borehole extensometer was built in 1974 by the USGS. Two GPS stations were installed at this site in 1993 and 1996, respectively. One GPS antenna (ADKS) is mounted on the inner pipe of the extensometer borehole, which is firmly anchored 549 m below the land surface. Another GPS antenna (PA05) is mounted on a permanent antenna pole anchored 6 m below the land surface. The horizontal distance between these two GPS antennas is 50 m. Continuous GPS data collected from the deeply anchored GPS antenna indicate that the bottom of the borehole has been stable over the past 20 years (1993-2012). Hence the compaction derived from the borehole extensometer data represents the total subsidence at this site, which should be approximately equivalent to the vertical displacement (subsidence) recorded by the shallowly anchored GPS antenna (PA05). In this study, the vertical displacement time series recorded by the shallowly anchored GPS antenna are regarded as the true values to assess the accuracy of the subsidence time series recorded by the extensometer. The authors' analysis indicates that the difference between the cumulative subsidence measured by the extensometer and the GPS antenna (PA05) is less than 5 mm for a 17-year span (1996-2012). The RMS of the residuals of the monthly subsidence time series derived from the extensometer and GPS antenna (PA05) data over 13 years (2000-2012) is 2 mm. [ABSTRACT FROM AUTHOR]

Navigation of gun-launched precision munitions using affordable technologies is investigated. Estimation algorithms were developed to blend flight dynamic models with measurements from inertial sensors. The launch and flight characteristics of the unique, gun-launched environment were exploited both in the state estimator and for novel heuristic parameter identification. Using the heuristic parameter, the inertial navigation system was calibrated without a global positioning system (GPS), and its performance was compared with a similar calibration performed with a GPS. The experimental results from guided mortar flights indicate that the algorithm with only inertial sensor measurements yields position errors of less than 40 m over a 30-s flight. Trade studies were conducted in simulation to assess algorithm performance over a wider range of conditions such as variation in the flight dynamic model parameters. These results demonstrate that position errors are less than tens of meters for flight times of interest to munitions. Estimation is tolerant to inertial sensor errors because of the novel manner in which known flight dynamics are used to compensate measurements. Overall, this effort shows that navigation error resulting from a low-throughput algorithm using affordable inertial sensors is sufficient to increase system accuracy for munitions in GPS-denied environments. [ABSTRACT FROM AUTHOR]

This paper describes a new model for precise point positioning (PPP), which overcomes the drawbacks of existing PPP models. This model is based on between-satellite single-difference (BSSD), which cancels out the receiver clock error, receiver initial phase bias, and receiver hardware delay. The decoupled clock (DC) corrections, which were provided by Natural Resources Canada (NRCan), were applied to account for code and carrier-phase satellite clock corrections, satellite hardware delay, and satellite initial phase bias. The results from three PPP models (namely, undifferenced-DC, BSSD, and BSSD-DC) were compared with the traditional (i.e., undifferenced) PPP solution. It is shown that the proposed BSSD models improves the PPP convergence time by up to 50% and improves the solution precision by more than 60% in comparison with the traditional PPP model. [ABSTRACT FROM AUTHOR]

This paper presents a method of designing railway sections located in horizontal arcs. The adopted procedure is universal, i.e., it creates the possibility of varying both the type and the length of the assumed transition curves. This means that the applied analytical formulas apply to the boundary conditions of the transition curves and all of the simplifications widely existing in common algorithms have been eliminated. The presented approach is especially useful in the case of analyzing data obtained from continuous satellite measurements. To create the horizontal arc, a calculation algorithm has been implemented in an original computer program that is under the authors' development. The main features and the results obtained by the use of the program have been described in the paper on the basis of the existing geometrical layout. The authors show the process of designing a particular arc as a sequence of characteristic steps that highlight the problem of assessment. It is shown that the proposed design method allows the generation of the following alternative variants instantaneously, without any restrictions. The program also includes quality indicators to help assess the practical suitability of particular geometrical layouts. [ABSTRACT FROM AUTHOR]

Methods based on integer ambiguity determination, such as the least-squares ambiguity decorrelation adjustment (LAMBDA) method, are currently used for precise global navigation satellite system (GNSS) differential positioning. In the present paper, the author proposes an ambiguity-free method based on a dedicated mixed (stochastic/deterministic) optimization algorithm that, unlike the LAMBDA method, is capable of providing reliable and accurate results using few observation epochs (e.g., 1-cm accuracy with just two epochs), having the additional advantages of insensitivity to cycle slips and impossibility of wrong ambiguity fixation. In addition, it is demonstrated that the application of the linear (deterministic) part of this algorithm yields the correct baseline results much more easily and quickly than methods requiring integer ambiguity determination, provided the initial approximate coordinates are accurate to a few centimeters. However, the use of ambiguity-free methods requires that the integer character of the ambiguities be preserved so that they can be eliminated; therefore no ionosphere-free combination can be computed and the methods are valid only for short baselines (e.g., less than 10 km). [ABSTRACT FROM AUTHOR]

Various corrector surface models are proposed to mitigate systematic height errors to fit the orthometric heights determined by combining the Tainan City real-time kinematic (RTK) global positioning system (GPS) network and the local geoid model data to the published orthometric heights. Several data sets for Tainan City were tested and analyzed. Two geometric geoid models and one gravimetric-geometric geoid model were generated using the GPS and leveling data. Consequently, three types of orthometric heights were determined (Models I, II, and III). The selection of the optimal corrector surface model for different models was based on a series of statistical tests. The test results show that (1) the selection of the optimal corrector surface model is highly related to the geoid model generating method, hence the optimal corrector surface models are a fifth-degree polynomial for Models I and II and a seven-parameter similarity transformation for Model III; and (2) the determined orthometric height is accurate to 2-4 cm after applying an optimal corrector surface model. [ABSTRACT FROM AUTHOR]

Among the main factors affecting road crash injuries, speed is considered as a leading cause and contributing factor. There are numerous studies linking travel speeds and road crashes. Hence, an essential part of road safety plans and interventions is devoted to speed management. However, to manage speed, actual travel speeds have to be systematically and consistently monitored and analyzed. In this study, a system for the collection and analysis of free-flow travel speeds on the road network is presented, enabling speed monitoring at the nationwide level. The paper focuses on the collection and analysis of travel speeds on different road sections. Using the information gathered through advanced technologies combined with geographical information systems, a comprehensive speed database in space and time is provided allowing visual presentation and comparison of the results. This analysis can identify the road sections with significant excesses of travel speeds relative to the speed limits. It can also serve as a baseline to evaluate the impact of various counter-measures employed to reduce speeds. [ABSTRACT FROM AUTHOR]

The regulatory requirements limiting the physical dimensions of heavy vehicles and driving skills do not guarantee the feasibility of negotiating the tightest curves of compact roundabouts. The specific evaluations needed for the intersection and the assumed design vehicle are often achieved by setting vehicle movement trajectories via computer programs, given the possibility of changing the design parameters both quickly and economically. The basic requirement for using these programs is their reliability, but they do have some weaknesses and flaws because of necessary simplifications, without which running the simulations would not be workable. A field test based on global positioning system instrumentation was conducted to define the area covered by a heavy vehicle turning in a real compact roundabout, successively compared with the simulated swept path. The preparation and the results of the experiment are described in the present study. [ABSTRACT FROM AUTHOR]

To achieve the best linear unbiased estimation of unknown parameters in geodetic data processing a realistic stochastic model for observables is required. This work is a follow-up to work carried out recently in which the geometry-free observation model (GFOM) was used. Here, least-squares variance component estimation is applied to global positioning system (GPS) observables using the geometry-based observation model (GBOM). The benefit of using GBOM, rather than GFOM, is highlighted in the present contribution. An appropriate stochastic model for GPS observables should include different variances for each observation type, the correlation between different observables, the satellite elevation dependence of the observables' precision, and the temporal correlation of the GPS observables. Unlike the GFOM, in the GBOM two separate variances along with their corresponding covariances are simultaneously estimated for the phase observations of the L1 and L2 frequencies. The numerical results for two receivers-namely, Trimble 4000 SSi (Trimble Navigation, Sunnyvale, California) and Leica SR530 (Leica Geosystems, Aarau, Switzerland)-indicate a significant correlation between the observation types. The results show positive correlations of 0.55 and 0.51 between the CA and P2 code observations for Trimble 4000 SSi and Leica SR530, respectively. In addition, the satellites' elevation dependence of the GPS observables' precision is remarkable. Also, a temporal correlation of about 10 s exists in the L2 GPS observables for the Trimble 4000 SSi receiver. [ABSTRACT FROM AUTHOR]

In the road geometric design process, speed variation along the road segment is one of the most popular criteria to evaluate road consistency, hence the importance of estimating operating speed and its variations. Most of the estimation models are based on speed spot data collection, usually assuming some hypotheses like operating speed remains constant at curves and speed variations take place entirely at preceding tangent. This paper presents the results of the study of the deceleration phenomenon using a new methodology based on data collection by global positioning system devices. By means of this new methodology, not only new and more accurate models can be developed, but also the previous hypotheses can be checked and new studies can be carried out. Tangent-to-curve speed variations have been evaluated, comparing the 85th percentile speed differential () and the differential of the 85th percentile operating speed (), analyzing the percentage of deceleration length that takes place at curves, and developing two deceleration models with radius of horizontal curve and parameter of transition curve as explanatory variables. [ABSTRACT FROM AUTHOR]

Providing real-time bus arrival information can help to improve the service quality of a transit system and enhance its competitiveness among other transportation modes. Taking the city of Jinan, China, as an example, this study proposes two artificial neural network (ANN) models to predict the real-time bus arrivals, based on historical global positioning system (GPS) data and automatic fare collection (AFC) system data. Also, to contend with the difficulty in capturing the traffic fluctuations over different time periods and account for the impact of signalized intersections, this study also subdivides the collected dataset into a bunch of clusters. Sub-ANN models are then developed for each cluster and further integrated into a hierarchical ANN model. To validate the proposed models, six scenarios with respect to different time periods and route lengths are tested. The results reveal that both proposed ANN models can outperform the Kalman filter model. Particularly, with several selected performance indices, it has been found that the hierarchical ANN model clearly outperforms the other two models in most scenarios. [ABSTRACT FROM AUTHOR]

The Houston area has been suffering from subsidence for several decades. Therefore, continuously operating reference stations (CORS) in this area may have experienced considerable vertical displacements. The Online Positioning User Service (OPUS), provided by the National Geodetic Survey (NGS), uses CORS as references in its data processing. This study investigated what effects, if any, the subsidence experienced by these CORS around Houston contributes to the accuracy of OPUS vertical results. Our OPUS results were determined from three long-term (over 10-year) blocks of continuous data using Global Positioning System (GPS) stations located in different parts of the Houston area. The OPUS results were compared with the vertical measurements from the precise point positioning with single receiver phase ambiguity (PPP-SRPA) solution implicit in the GIPSY/OASIS 6.1.2 software. This particular study indicates that OPUS achieves 1.0-cm vertical accuracy for daily sessions (24 h) in the region around Houston, which is comparable to the OPUS accuracy previously reported in other investigations. Subsidence as slow as can be detected by analyzing OPUS results spanning 5 or more years of data. Our main conclusion is that the subsidence experienced by NGS CORS in the Houston area does not considerably affect the accuracy of OPUS vertical results. For those users who require a few centimeters of vertical accuracy for daily sessions, OPUS is a good choice, because users do not need to establish any control stations and do not need to install any GPS software packages on their local computers. [ABSTRACT FROM AUTHOR]

Real-world vehicle fuel use and emission rates are sensitive to road grade. There is a need for a practical method for measuring road grade in combination with on-board measurement of vehicle activity, energy use, and emissions using portable emissions measurement systems (PEMS). This paper focuses on quantification of the accuracy and precision of a low-cost method using a stand-alone global positioning system (GPS) receiver with an in-built barometric altimeter. Approximately 100 one-way runs were made on each of several study routes. The sensitivity of average grade estimates to the averaging distance over which grade is estimated is quantified. The repeatability of vehicle location and distance traveled is quantified. The run-to-run variability and confidence intervals for average estimates of grade are quantified. The accuracy of the grade estimates is evaluated in comparison to LIDAR-based estimates. The low-cost method is shown to be accurate, but imprecision in the measurements leads to a need for typically at least 10 or more repeated runs, depending on the desired precision of the average estimate of grade. [ABSTRACT FROM AUTHOR]

A surveying-engineering procedure is presented for gravimetric geoid model verification along selected railway traverse lines using collocated ellipsoid and orthometric heights. The proposed method relies on (1) a tactical-grade, multisensor [Global Navigation Satellite System (GNSS)/inertial navigation system (INS)] kinematic-surveying system used to measure the ellipsoid heights along the traveled section and (2) the orthometric heights derived from the railway-line construction and/or maintenance works. Compared with the standard static GPS/leveling technique, the proposed approach produces geoid height profiles in a very short acquisition time, with dense point spacing, and in a considerably inexpensive manner. The quality of the final results reflects the accuracy of modern GNSS/INS systems and available rail-track orthometric height information. The method was applied to a long (101-km) railway traverse in central Greece using a custom-built mobile mapping system. Gravimetric geoid model verification was undertaken in an absolute and relative manner for the Earth Gravitational Model 2008 (EGM08) and 1996 (EGM96) geopotential models. Analysis of the results has demonstrated the potential of the method both in terms of efficiency and in terms of the evaluation checks performed. Based on the absolute- and relative-quality tests undertaken, the superiority of EGM08 over EGM96 is clearly evident for the tested line. Also, these results are cross compared and evaluated with the findings obtained from previous studies in Greece. [ABSTRACT FROM AUTHOR]

Pile positioning, for driving piles below the surface of water in a marine pier construction project, is typically a time-consuming task owing to the fact that the pile wharf is affected significantly by environmental limitation and marine meteorology. As a result, it is always a goal to minimize the positioning time while maintaining a desired level of accuracy. This study developed a global positioning system (GPS)-based information system, which integrated six major modules. This system was designed to provide a real-time positioning and guidance solution for pile-driving barge control in a marine pier construction project. In a case study, the developed system has been implemented successfully in a real project and proved this system can improve the horizontal accuracy of real-time pile positions by less than 1 cm. It also contributed to a 42% reduction in the construction time and thus an 11% reduction in the final budget. Consequently, the efficiency of a piling construction project could be improved significantly by incorporating such a system. [ABSTRACT FROM AUTHOR]

Precise point positioning (PPP) involves observations from a single global navigation satellite system (GNSS) receiver and benefits of satellite orbit and clock products obtained from the global infrastructure of permanent stations. PPP avoids the expense and logistic difficulties of deploying a network of GNSS receivers around survey areas in isolated places, such as the arctic or less populated areas. Potential accuracies are at the centimeter level for static applications and at the subdecimeter level for kinematic applications. Static and kinematic PPP based on the processing of global positioning system (GPS) observations is limited by the number of visible satellites, which is often insufficient for urban or mountain applications, or it can be partially obstructed or present multipath effects. Even if a number of GPS satellites are available, the accuracy and reliability can still be affected by poor satellite geometry. One possible way of increasing satellite signal availability and positioning reliability is to integrate GPS and GLONASS observations. This case study deals with the possibilities of combining GPS and GLONASS dual-frequency measurements on the static and kinematic PPP solution to reduce the convergence time and improve the accuracy of the solution. The results show that the addition of the GLONASS constellation does not always improve the convergence of static PPP; the kinematic results (car and walk trajectories) present better accuracy from the GPS + GLONASS solution rather than the GPS-only solution. The MagicGNSS software was used in processing of all observations. [ABSTRACT FROM AUTHOR]

As of this writing, there are two popular methods to perform precise surveying using the single dual-frequency Global Positioning System (GPS) receiver. One is the Real-Time Kinematic (RTK) technique. The other is the Precise Point Positioning (PPP) technique. The RTK technique requires GPS surveyors to have at least one GPS base station while the PPP technique needs a long observation period to resolve the carrier-phase ambiguities. This paper proposes a new, fast method that can conduct precise kinematic surveying using a single dual-frequency GPS receiver, overcoming the aforementioned problems. This new method, Absolute Plus Loop-based Accumulated-solution Time-relative (APLAT), combines the GPS absolute-positioning method and a loop-based accumulated-solution time-relative positioning method. In this APLAT method, the kinematic surveying trajectory must form a loop. The coordinates of the start-point of the loop can be precisely determined using the absolute positioning function of APLAT by making two short sessions of static observations. This function is useful if no control-point is available in the kinematic surveying. The relative positions of other kinematic surveying points in the loop are determined using the function of loop-based accumulated-solution time-relative GPS positioning. The integration of the absolute and the relative positioning functions allows kinematic surveying to precisely determine the absolute coordinates of each surveyed point in the loop. To determine the absolute coordinates of the start-point of a loop, only two short sessions (5 min each in this study) of static GPS observations (prior to starting and after completing the loop surveying) are required. The results of extensive absolute-positioning tests show that 3D-positioning standard deviation about 7 cm and root-mean-square (RMS) error about 13.4 cm can be achieved when the loop-duration is in the range of 40-80 min. Too short or long a loop-duration may degrade the absolute-positioning accuracy. Results from various relative positioning tests using the loop-based accumulated-solution time-relative method indicate that relative-positioning RMS errors of 1.3 cm, 2.6 cm, and 8.8 cm can be obtained for loop durations of 20 min, 40 min, and 60 min, respectively. This new APLAT method offers a new, fast, and precise (RMS error of 12 cm for absolute and RMS error of 8.8-cm relative positioning for 60-min loop duration) kinematic surveying method that is able to meet many GPS surveying and mapping requirements. This is particularly useful for postmission data processing in circumstances where single-base-station RTK or network RTK service is not available. In this study, the final precise-orbit and precise-satellite-clock data from the International GNSS Service are used to mitigate these errors. At present, this method is useful just for postmission applications, but it offers the flexibility of using absolute-positioning or relative-positioning function only, depending upon the specific surveying and mapping conditions and requirements. This method is a good complement to the PPP and RTK precise-positioning techniques currently in use. Due to the increasing spatial decorrelation of error sources, the positioning accuracy may degrade as the maximum spatial distance (approximately between the loop start-point and the loop middle-point) increases. [ABSTRACT FROM AUTHOR]

Real-time precise point positioning (PPP) is possible through the availability of the real-time satellite orbit and clock corrections to broadcast ephemeris, the real-time broadcast corrections (BCs). The real-time BCs are currently available in global as well as in regional reference frames. In this contribution, PPP usage and the performance of these global and regional BCs are analyzed for the North American Datum of 1983 (NAD83). The limitations of the current regional BC approach for NAD83 are identified and the coordinate differences it leads to compared with the traditional global BC approach are shown. Although the biases as a result of the different reference frame usage are shown to be subcentimeter, it is also shown how they can be reduced or eliminated by modifying either the PPP algorithm or the regional BC approach. Analyses were performed for three different PPP variants, a single-frequency ionosphere-free variant, a dual-frequency ionosphere-free variant, and a single-frequency ionosphere-corrected variant. [ABSTRACT FROM AUTHOR]

In this paper, the network real-time kinematic (NRTK) positioning method based on undifferenced (UD) observation corrections (abbreviated as URTK) are described, in which instantaneous ambiguity resolution can be carried out within rover's precise point positioning (PPP) software, thus achieving position solutions equivalent to NRTK. The URTK method transforms the fixed double-differenced (DD) ambiguities of the reference network into UD ambiguities. With the transformed ambiguities, the residuals of the UD observation are used for interpolating the corrections at the user side. This approach breaks down the connections between the stations and satellites of the DD corrections in the current NRTK methods, such that corrections can be broadcast by the base station and automatically selected and optimized by a rover during the real-time kinematic (RTK) processing when the rover is transitioning into a more favorable subnetwork configuration, thus avoiding ambiguity reinitialization as a result of the change of reference. More importantly, this proposed approach provides a seamless integration of regional NRTK (PPP with regional augmentation) and global PPP-assisted kinematic surveying, which should be very useful for a wide range of applications. The key for realizing the improvements over standard NRTK is the development of a logical scheme that has the capability of rapid fixing of the single-differenced ionosphere-free ambiguity of the rover. Case studies at sea and on land demonstrate the advantages of this approach in terms of improvement in positioning accuracy, elimination of subsequent ambiguity reinitialization, and wider applications in the future. [ABSTRACT FROM AUTHOR]

This paper describes the development of a systematic methodology for identifying and ranking bottlenecks using probe data collected by commercial global positioning system fleet management devices mounted on trucks. These data are processed in a geographic information system and assigned to a roadway network to provide performance measures for individual segments. The authors hypothesized that truck speed distributions on these segments can be represented by either a unimodal or bimodal probability density function and proposed a new reliability measure for evaluating roadway performance. Travel performance was classified into three categories: unreliable, reliably fast, and reliably slow. A mixture of two Gaussian distributions was identified as the best fit for the overall distribution of truck speed data. Roadway bottlenecks were ranked on the basis of both the reliability and congestion measurements. The method was used to evaluate the performance of Washington state roadway segments, and proved efficient at identifying and ranking truck bottlenecks. [ABSTRACT FROM AUTHOR]

People, industries, and public agencies all face the possibility of sudden events that disrupt their normal activities. Disasters on the transportation network, whether attributable to nature, human error, or human intent, raise awareness of the need for plans of action to quickly restore mobility. Resilience of the transportation network is the capacity to absorb the effects of a disruption and to quickly return to normal operating levels. Resilience measures are useful to evaluate and predict disruptions and recovery and to guide infrastructure investments that protect against those disruptions or that accelerate recovery after a disruption. This paper presents a methodology for estimating two composite resilience measures-reduction and recovery. The method is illustrated by using resilience triangles derived from sampled truck speeds and counts along the Interstate corridor from Hudson to Beloit, Wisconsin during two significant weather events in 2008. This paper presents a set of criteria, on the basis of observed effects on various sections of the highway corridor, to qualify the computed resilience measures. In this paper, the focus is on generalizing the characteristics of the resilience response rather than characteristics of the corridor sections that lead to patterns of the response for each section. The criteria and the measures together are a useful tool to evaluate resilience. [ABSTRACT FROM AUTHOR]

High-precision (centimeter-level) real-time kinematic precise point positioning (PPP-RTK) becomes feasible when using precise corrections, as received from a regional Continuously Operating Reference Station network. These network corrections comprise (biased) satellite clocks, (biased) satellite phase biases, and ionospheric delays, where the latter ones are interpolated to the approximate location of the PPP-RTK receiver. Thus far, very fast PPP-RTK integer ambiguity resolution performance has been reported based on dual-frequency Global Positioning System (GPS) data. The availability of ionospheric corrections enables one to carry out PPP-RTK using a single-frequency receiver. Despite that single-frequency integer ambiguity resolution based on a single epoch of data cannot often be successful, fast integer ambiguity resolution is possible when accumulating a short time span of data, assuming that the ambiguities are time constant. In this paper, results of the performance of single-frequency PPP-RTK for both a high-grade geodetic receiver and a low-grade mass-market receiver are presented. The experiments have been conducted based on corrections determined from the GPS Network Perth. The conclusion reads that single-frequency PPP-RTK integer ambiguity resolution is feasible, even using a low-cost receiver: following an initialization time of about 4 min on average, the correct integers can be resolved in real-time, thus providing centimeter-level positioning. [ABSTRACT FROM AUTHOR]

This research provides a performance test of terrestrial light detection and ranging (LIDAR) and multibeam echo sounder scanners integrated with Global Navigation Satellite System/Inertial Navigation System positioning and orientation on a survey vessel platform. To measure the accuracy of the data, experiments were designed to allow the LIDAR and sonar scanners to acquire scans of a control target that extended above and below the water surface. The scans were acquired under normal and induced conditions expected in a marine survey environment, such as variations in speed, range, motion, and orientation. SD, root-mean-square error (RMSE), and mean were computed across all data sets for each experiment. Horizontal RMSE values of 0.06 and 0.03 m were achieved for the LIDAR and sonar data, respectively. Vertical RMSE results of 0.04 m were found for both data types. These results were comparable with previous mobile mapping research involving similar systems. Contributing uncertainty and error sources were analyzed and discussed. [ABSTRACT FROM AUTHOR]

Vision-based unmanned aerial vehicle (UAV) control is a core technology in global positioning system (GPS)-denied environments. However, small UAVs have difficulty processing image data in real time because of their limited payload capacity and relatively weak processor. Development of an image-processing system that is suitable for small UAVs is therefore needed. In this paper, an approach for a vision-based simultaneous localization and mapping (SLAM) system for small UAVs is suggested. For real-time localization, a method wherein Kanade-Lucas-Tomasi-based localization and tracking are performed within small UAVs in real time is adopted. At the same time, scale-invariant feature transform-based mapping and more accurate localization are performed at the ground-control station. A vision-based three-dimensional map-building method for small UAVs using a monocular camera is also proposed. The proposed method first extracts straight-line information from images and calculates their equations in three-dimensional space. It then constructs plane information from line information. [ABSTRACT FROM AUTHOR]

The number of global positioning system (GPS) tracking stations is increasing, primarily because the stations are multifunctional. In civil engineering, they can be used for precision positioning; in the earth sciences, they can be used to monitor faults and earthquakes; and in the atmospheric sciences, they can be applied to predict perceptible water vapor. Currently, there are more than 400 GPS stations in Taiwan; however, the data obtained through such stations are not being assessed carefully. Experienced scientists and engineers examine the data in advance to see if they qualify for research purposes, but inexperienced users can adopt poor quality data that eventually lead to inaccurate research results. Of the observation stations with receivers that were renewed between 2006 and 2008 in the International GNSS Service Network, four stations (ZIMM, BOR1, NRC1, and NICO) were selected to be the subjects of this research. Six indexes of data quality were observed to calculate the quality of data obtained before and after receiver renewal. Then, analyses were conducted to understand the relationship between the quality indexes and positioning precision. The results showed that after receiver renewal, the positioning precision of the four stations was improved by 1-19%. Therefore, positioning precision is positively affected by the six data quality indexes. It was also discovered that receiver clock error was the most critical factor among the six indexes. In conclusion, if data quality control can be applied to GPS tracking stations, the data obtained will be more reliable for research purposes, and the accuracy of subsequent engineering and science measurements will be improved. [ABSTRACT FROM AUTHOR]

The idea of integrated measurements, combining classic field observations and satellite observations, has recently been applied in geodetic work with increasing frequency. To draw an entire set of such observations numerically, it is necessary to reduce them to a common mathematical space (e.g., onto the surface of an ellipsoid WGS84). This paper presents a proposed adjustment of GPS observations in a local reference system without the necessity of transforming and mapping them. The adjustment process is carried out after a GPS vector network is transformed into a spatial angular-distance network. This allows an easy integration with classical observations (joint adjustment of all observations). Detailed formulas are provided and used to develop a mathematical adjustment model. The computational algorithm is verified in practice. [ABSTRACT FROM AUTHOR]

Accurate GPS positioning requires correct modeling of tropospheric refraction, the phenomenon responsible for tropospheric delay (TD). The Niell mapping function, which is used in almost all processing packages to model TD, is being replaced by improved models. This study analyzes the influence of TD models and absolute antenna phase center variation (PCV) models. Solutions computed with the Niell mapping function and global mapping function TD models were compared at several European International Global Navigation Satellite Systems (GNSS) Service (IGS) stations. GPS sessions of 24 hours, observed on five different days in 2008, were used for this investigation. Two independent network-station constraint approaches are considered: a GPS network fixing a single station was implemented and was followed by a second network solution in which several IGS stations were constrained. The elevation-cutoff angle was set to 0° to obtain the maximum influence of the TD model at altitudes close to the horizon. Results of the final solutions depend more on the constrained stations within the study area than on the type of tropospheric model or antenna type. [ABSTRACT FROM AUTHOR]

Handheld navigation global positioning system (GPS) receivers are significantly cheaper and their position determination accuracy is less than their geodetic-grade counterparts. Although the main observable in most low-cost handheld GPS receivers is the coarse acquisition (C/A) code, some receive L1 frequency observations and utilize them to smooth the code measurements. In this technical paper, we examined the use of the C/A code and L1 phase observations captured by two GARMIN eTrex receivers in a postprocessing mode. We used software applications that send low level commands to download and save the receiver data stream and convert the observations into standard RINEX file format. Nineteen baselines with different lengths were observed using the eTrex receivers and dual frequency geodetic-grade receivers. The baseline lengths were derived from the eTrex observations and compared to corresponding ones derived from the higher accuracy geodetic-grade receiver observations. Several tests were conducted to analyze the effect of potential error sources on the achieved accuracy. The results showed that low satellite angles and existing cycle slips contributed to the errors in the processed eTrex data. The implementation of a cycle slip detection algorithm and their subsequent deletion significantly enhanced the obtained baseline relative accuracy to a finally limited range of 1.8-13.4 cm/km. [ABSTRACT FROM AUTHOR]

Global Positioning System (GPS) is widely used for monitoring some natural phenomena and man-made structures. The detection of the deformation epoch in real time is of great importance in these applications. This study is concerned with designing algorithms to detect the deformation epoch in order to improve the quality of GPS measurements for the real-time deformation applications. In this regard, the multiple Kalman filters model based on the idea of model selection is proposed to improve the reliability of the detection of the deformation epoch. For the model selection, the proposed model makes use of the statistical criterion comparison in each case instead of the hypothesis test. The model with the lower value of the statistical criterion is to be preferred. According to the statistical criterion, the optimal Kalman filter model can be selected to describe the time series and to identify the deformation epoch at each epoch. The simulated data and the GPS kinematic time series are used to verify the effectiveness of the multiple Kalman filters model. [ABSTRACT FROM AUTHOR]

This study selected five indexes to determine the relationship between data quality and positioning precision. These indexes are multipath on L1, multipath on L2, observations by cycle slips, clock offset, and clock stability. To reduce the number of common errors, six types of global positioning system (GPS) receivers are selected and set up in an Ultra-Short Distance Network at the National Measurement Laboratory, Taiwan, for 3 days. The first three indicators are calculated with the Teqc software, and the last two indicators are computed using the Bernese software. Moreover, the observations from three GPS tracking stations, namely, short baseline (about 25 km), middle baseline (about 150 km), and long baseline (around 2000 km), were downloaded from the Internet and processed using Bernese software. Analytical results indicate that clock stability and observations divided by cycle slips are found to be very important positioning factors. Clock offset and multipath effects do not significantly affect the GPS results. [ABSTRACT FROM AUTHOR]

Bridge inspections are tedious, time consuming, and complex tasks in the field that require highly specific information pertinent to the decisions at hand. The use of a centralized inspection database and bridge inspection reporting software has been explored by several state DOTs in recent years. During an inspection routine, the inspector visually assesses the condition of a particular bridge component. Based on a priori knowledge of the bridge components' taxonomic hierarchy and ontology, the inspector navigates to the form corresponding to the component. The inspector then reports the component's condition to the database. Context-aware computing offers the possibility to make inspections more efficient by reducing the time required to navigate the software and the effort spent by inspectors to learn, remember, and recall the taxonomic hierarchy and ontology of bridge components. Context-aware computing leverages environmental variables, which define the inspector's context, and delivers streamlined information, pertinent to the task at hand, to assist decision making. This paper presents a computing framework that identifies the component of interest to the inspector and automatically queries the inspection database to retrieve information relevant to the component being assessed. The framework's run-time and space complexity are analyzed and presented. The uncertainty in sensing the inspector's location and line of sight are translated into errors in identifying the component of interest. Using a case study bridge, sensitivity analysis is performed to evaluate and characterize the errors in identifying the component of interest due to the errors in tracking technologies through simulation studies and field testing. The sensitivity analysis is used to evaluate the feasibility of employing global positioning systems (GPS) and magnetic compass technologies for location and line-of-sight tracking. Finally, the authors suggest a workflow design for integrating the framework into bridge inspection reporting software. [ABSTRACT FROM AUTHOR]

Although extensive research has investigated how the built environment near people's homes and work places influence automobile travel behavior, little is known about how commuting routes affect travel outcomes. This article presents a methodology that addresses this question by examining the correlation between built environment along commuting routes and vehicle miles traveled (VMT) and fuel consumption for nonwork automobile travel. Using a global positioning systems (GPS) data set collected from automobile trips of 46 drivers from the southeast Michigan area over a 30-day time frame, this study identifies the actual commuting routes for all drivers and derives their fuel consumption for nonwork travel. Although statistically significant relationships are not found between route environments and nonwork VMT and fuel consumption, this study is unique in its focus on the commuting routes and in establishing a methodology for using GPS data in transportation and land-use research, and it offers suggestions for refining the modeling of travel behavior along commuting routes. [ABSTRACT FROM AUTHOR]

A total of 595 real-time kinematic global positioning system (RTK-GPS) water surface elevations (WSE) were measured using georectified and nongeorectified survey systems along a 21-km-long river reach to evaluate vertical coordinate accuracy of a nongeorectified RTK-GPS acoustic Doppler current profiler (ADCP) system. A georectified survey of a series of quality control benchmarks produced a vertical root-mean-square error (RMSE) of 0.033 m, which was considered globally accurate for river survey purposes. The WSE measured simultaneously at the same locations comparing the nongeorectified to the georectified system resulted in a m. Evaluation of intersetup precision of the nongeorectified WSE confirmed relative accuracy to each initialized arbitrary vertical datum but were found not to be globally accurate. Only 7% of the nongeorectified base station setups resulted in RMSE less than the combined manufacturer's tolerances when compared to the georectified system at the same spatial locations. When vertical datum corrections were applied to the nongeorectified system from the globally accurate RTK-DGPS system, 80% of the base station setups demonstrated RMSE within the combined manufacturer's tolerances. Datum corrections varied greatly, ranging from to . This study demonstrates that when using nongeorectified RTK-GPS ADCP systems for purposes other than discharge measurement, such as in the extraction of bathymetry data for use in hydraulic assessments and models, great care must be exercised when verifying WSEs [ABSTRACT FROM AUTHOR]

Localization of sensor nodes is one of the most essential tasks for sensor network applications for infrastructure monitoring. Normally, the accuracy of global positioning system (GPS) positioning installed in wireless sensor network is in the order of meters (which is insufficient for infrastructure monitoring). This paper developed a GPS wireless sensor network with a capability of onboard GPS analysis based on a relative positioning algorithm with the accuracy in the order of centimeters. However, employment of a high-performance and energy-hungry CPU is inevitable for this onboard GPS analysis method. To reduce the energy consumption, a sensor node called hybrid sensor node equipped with dual CPUs has been developed. A high-performance CPU on the hybrid sensor node is used only for onboard GPS analysis and another CPU with low energy consumption is used for other tasks such as controling of a GPS receiver and a wireless transceiver. This paper describes the design concept, the hardware, and the software of the newly developed hybrid sensor node. The overview of the sensor network system, task allocation, and the performance evaluation of the whole system work flow from the view point of energy consumption are also described in detail. [ABSTRACT FROM AUTHOR]