Global Positioning System System Research Articles

The protonospheric contribution to GPS total electron content: Two‐station measurements

Results are presented from an experiment to estimate the contribution of plasma on ray paths through the protonosphere to measurements of total electron content (TEC) using Global Positioning System (GPS) signals. Simulations using the Sheffield University plasmasphere ionosphere model show that observations of GPS satellites made at two stations separated by a few degrees of latitude could involve a common ionospheric volume but very different intersection geometries of the ray paths with protonospheric flux tubes. Experimental results demonstrate that, on average, higher equivalent vertical TECs are measured on ray paths to the south than those to the north of the European midlatitude stations considered here. The observations are discussed in terms of the known asymmetries of the protonospheric flux tubes, and caution is advised in the use of thin‐shell ionospheric models for precise determination of TEC or correction for its effects on GPS systems.

A New GPS Data Processing Algorithm for the Positioning of Oceanographic Experiments

Abstract In this paper, the authors present a Global Positioning System (GPS) algorithm for medium accuracy (1-m rms) positioning of ocean buoys. The application addressed in this paper is that of the Fast Pegasus experiments that require the positioning of surface buoys used in collecting subsurface acoustic data for ocean current profiling. The current GPS system designed for the Fast Pegasus experiments requires a land-based single-frequency GPS receiver for differential GPS positioning. In contrast, the technique presented here is designed for the point positioning of a stand-alone single-frequency GPS receiver (which is in motion) and does not require the use of a land-based reference receiver. The precise point positioning algorithm developed here uses postprocessed GPS satellite ephemerides and clock corrections to compute the position of a single GPS receiver. A square root information filter/smoother uses the GPS pseudorange and carrier phase measurements to estimate the position and clock offset...

Applications of differential GPS in upland fluvial geomorphology

Recent technological developments in the application of the Global Positioning System (GPS) offer the prospect of rapidly mapping difficult terrain and quantifying temporal and spatial dynamics of erosion and sedimentation. While many developments in GPS have been considered from the viewpoint of geodesy, their versatility in geomorphological situations has had limited attention. In particular, the improved accuracy and reduced costs of some GPS systems makes them attractive for many mapping applications. Differential GPS allows the logging of position of a mobile receiver relative to a control station. In difficult terrain, such as uplands, the location and distribution of survey points by GPS is much more efficient than conventional survey techniques. However, it should be emphasised that GPS is not simply an alternative to existing techniques but has advantages and disadvantages which need to be evaluated. Three case studies in the uplands of Northern England demonstrate the trade-off between the advantage of speed and disadvantage of reduced accuracy afforded by GPS. The studies are concerned with the rapid mapping of flood extent based on ephemeral flow limit indicators; detailed mapping of alluvial fan surfaces and associated sediment sources; and the spatial distribution of colluvial sediment supply and downstream movement of bedload slugs. The extent to which approaches based on differential GPS, in combination with more traditional survey techniques, can provide information on sediment dynamics or validation of distributed models is evaluated.

The influence of the protonosphere on GPS observations: Model simulations

The accuracy of the Global Positioning System (GPS) satellite navigation system can be degraded by propagation effects on ray paths through the ionized atmosphere. The bulk of the plasma resides in the F layer, and models of total electron content have been developed to compensate for the effects of this ionization. However, use of the GPS system involves long ray paths through the tenuous hydrogen‐based plasma of the protonosphere, and little is known about the electron content in this region. In the present study, the Sheffield University plasmasphere ionosphere model has been used to determine the electron content on the protonospheric section of GPS ray paths. Results are presented for stations at midlatitudes in the European and American sectors at both extremes of the solar cycle. The results are discussed in terms of the geometry of the flux tubes and the known behavior of the plasma.

A future vehicle positioning system for data capture in the urban canyon

Rapid data acquisition from a moving vehicle using positions given by the Global Positioning System (GPS) allows fast and reliable data collection for digital mapping and Geographic Information Systems (CIS). However, built-up city ‘urban canyons’ offer an environment which challenges the physical limitations of modern GPS positioning and, yet, is perhaps the one environment where the successful application of GPS technology could benefit most GIS users. With a view to the next generation of vehicle positioning system to be used for rapid data collection purposes, this paper highlights the limitations imposed on current GPS systems operating in the urban canyon. The capabilities of a future vehicle-based positioning system operating in this type of environment are discussed. Such a system would comprise receivers capable of integrating the Global Positioning System and the Russian equivalent, the Global Navigation Satellite System (GLONASS), and relatively cheap dead-reckoning sensors.

The role of GPs in the WEGENER project

In recent years, the Global Positioning System (GPS) has become a major tool for high precision geodesy. The precision is now better than 1 ppb. In this paper, the importance of GPS for the WEGENER project is highlighted. First, an overview of the GPS system is presented including a description of the development of its capabilities. One of the most significant developments of the past few years has been the establishment of the International GPS Service for Geodynamics (IGS). Thanks to its standards and products, the state-of-the-art in high precision GPS has been advanced considerably. Therefore, a summary of the goals and principles of IGS is presented next. This is followed by a compilation of the major GPS projects in Europe and its surrounding areas, since 1988. Most of these are not related to the WEGENER project, but it shows how much work has already been done. It also indicates the possible future role of GPS in WEGENER. Since all these projects are usually quite independent, they might benefit from the existence of a consistent, dense, accurate regional reference frame. This is exemplified by the success of IGS, which is based on an expanding global network of continuously operating permanent GPS stations. It provides a stable global reference frame, which makes it feasible to combine the results from independent field campaigns. In certain regions of the world the coverage is not yet optimal, however, and it is planned to further densify the IGS network. Therefore, it might be interesting to establish a dense regional GPS network in the general research area of WEGENER, which extends from Greenland to mid-Asia. This idea is promoted in Section 5 of the paper, where it is proposed to create such a network under the name of WEGNET, for WEGENER GPS Network. It would seek to establish new sites where none exist yet and to include existing stations that may already have been established for other purposes. Apart from providing a regional densification of IGS and a reference frame for WEGENER, the network may also yield valuable contributions to the monitoring of tectonic motions in the area and for studies concerning ocean and atmospheric loading.

The future of RTK GPS/GLONASS positioning in the urban canyon

Abstract Built-up city ‘urban canyons’ offer an environment which challenges the physical limitations of modem real-time GPS positioning systems and, yet, is perhaps the one environment where the successful application of GPS technology could benefit most users. With a view to the next generation of Real Time Kinematic (RTK) positioning systems, this paper highlights the limitations imposed on current RTK systems operating in the urban canyon using GPS visibility trials conducted in the urban canyon of the Perth Central Business District (CBD). Furthermore, following the recent release of receivers capable of integrating the Global Positioning System (GPS) and the Russian equivalent, the Global Navigation Satellite System (GLONASS), the advantages of integration of both GPS and GLONASS systems are demonstrated using GLONASS visibility simulations at selected points in the Perth CBD.

Continuous monitoring of surface deformation at Long Valley Caldera, California, with GPS

Continuous Global Positioning System (GPS) measurements at Long Valley Caldera, an active volcanic region in east central California, have been made on the south side of the resurgent dome since early 1993. A site on the north side of the dome was added in late 1994. Special adaptations for autonomous operation in remote regions and enhanced vertical precision were made. The data record ongoing volcanic deformation consistent with uplift and expansion of the surface above a shallow magma chamber. Measurement precisions (1 standard error) for “absolute” position coordinates, i.e., relative to a global reference frame, are 3–4 mm (north), 5–6 mm (east), and 10–12 mm (vertical) using 24 hour solutions. Corresponding velocity uncertainties for a 12 month period are about 2 mm/yr in the horizontal components and 3–4 mm/yr in the vertical component. High precision can also be achieved for relative position coordinates on short (<10 km) baselines using broadcast ephemerides and observing times as short as 3 hours, even when data are processed rapidly on site. Comparison of baseline length changes across the resurgent dome between the two GPS sites and corresponding two‐color electronic distance measurements indicates similar extension rates within error (∼2 mm/yr) once we account for a random walk noise component in both systems that may reflect spurious monument motion. Both data sets suggest a pause in deformation for a 3.5 month period in mid‐1995, when the extension rate across the dome decreased essentially to zero. Three dimensional positioning data from the two GPS stations suggest a depth (5.8±1.6 km) and location (west side of the resurgent dome) of a major inflation center, in agreement with other geodetic techniques, near the top of a magma chamber inferred from seismic data. GPS systems similar to those installed at Long Valley can provide a practical method for near real‐time monitoring and hazard assessment on many active volcanoes.

97/01696 A year of GPS at Fording Coal Limited, Green-hills operations

Fording Greenhills first acquired GPS (Global Positioning System) technology with the commissioning of a GPS-based dispatch system in December 1994. The second exposure to satellite technology came with the conversion of the conventional optical survey system to a high-resolution GPS system in June 1995. In September 1995, a GPS-based grade control system was tested on the largest shovel (Marion 301 - 58 cubic yard). In January 1996, the system was added to all of the cable shovels (2 P&H 2800s). All three applications of GPS at Greenhills are fully operational and producing positive results. This paper will focus on the practical application of GPS in a mining environment and the effect that GPS technology has had on the Greenhills Mine.

A dual-band circularly polarized aperture-coupled stacked microstrip antenna for global positioning satellite

This paper describes the design and testing of an aperture-coupled circularly polarized antenna for Global Positioning System (GPS) applications. The antenna operates at both the L1 and L2 frequencies of 1575 and 1227 MHz, which is required for differential GPS systems in order to provide maximum positioning accuracy. Electrical performance, low-profile, and cost were equally important requirements for this antenna. The design procedure is discussed, and measured results are presented. Results from a manufacturing sensitivity analysis are also included.

The Global Positioning System and Its Integration into College Geography Curricula

Abstract This paper introduces global positioning system (GPS) technology to nonspecialist geographers and recommends a framework for implementing GPS instructional modules in college geography courses. The GPS system was developed as a worldwide satellite-based system by the U.S. Department of Defense (DoD) to simplify and improve military and civilian navigation and positioning. By presenting GPS in several courses, the approach outlined can expose large numbers of students to GPS and may help to demonstrate the utility of GPS for several geographic subdisciplines.

Real-time APL prototype of a GPS system

The Global Positioning System (GPS) consists of a constellation of 24 high-altitude satellites with very accurate atomic clocks, along with a global network of satellite tracking stations and sophisticated ground processing stations, that together provide precise navigation coordinates to any user who possesses a small, readily available GPS receiver.The precision that is achieved depends on[1] the number of GPS satellites in view of the user and the geometries involved;[2] the design of the user's receiver (e.g., military or civilian);[3] the presence of nearby objects that may interfere with or degrade the reception of signals from one or more satellites;[4] and other factors.In most cases civilian users (whose receivers can read only unencrypted, intentionally corrupted GPS signals) can expect navigation accuracy on the order of 50-100 meters. The advertised accuracy for users with military receivers, which read the encrypted GPS signals, is 16 meters. Coalition forces in Desert Shield / Desert Storm relied heavily on GPS, and U.S. military authorities praised GPS effusively for its effectiveness as a force multiplier in that conflict.Loral Federal Systems (formerly IBM Federal Systems Division) in Gaithersburg, Maryland has been intimately involved with GPS from its concept validation phase through operations and maintenance. People in this group analyzed the physical dynamics, designed the mathematical algorithms and associated software, and performed the system integration work that culminated in the GPS ground control segment.APL was used over the years in most major aspects of GPS design and analysis. Early in the full-scale development phase, APL was used to model the initial GPS system design, to perform design tradeoffs, to model and test candidate algorithms, and to perform error analyses to estimate future system performance. In later phases APL was used to monitor and analyze actual GPS system performance, to compare it with theoretically achievable performance, and to analyze and isolate anomalies [Allan].

Resolving cycle slips with redundant satellites for kinematic global positioning system

AbstractThe kinematic global positioning system (GPS) is a system that successively executes the positioning of a mobile user with the accuracy of several centimeters by measuring the phase of the radio wave (carrier) from the GPS satellite while moving. A problem in the kinematic GPS system, however, is that the phase‐shift corresponding to the integer multiple of the wavelength (cycle slip) produced during the phase measurement must be eleminated to realize a highly accurate positioning.For this problem, this paper presents a method that can detect and eliminate the cycle slip with a high accuracy and lobustness by more than four GPS satellite signals which is needed in the positioning. The detection/elimination of the cycle slip based on the update residual error of the Kalman filter and the detection/elimination of the cycle slip based on the redundant GPS signal are integrated and a method to determine the cycle slip with a high accuracy is realized.

Global positioning systems in the time domain: How useful a tool for intelligent vehicle-highway systems?

Much of the research and development work in intelligent vehicle-highway systems (IVHS) relies on the availability of methods for locating and monitoring vehicles (e.g. “probe vehicles”) in real time across a road network. This paper considers the use of the global positioning system (GPS) as one method for obtaining information on the position, speed and direction of travel of vehicles. It reports the results of a series of field studies, in which real-time GPS data were compared to data collected by an instrumented vehicle, under a range of physical and traffic conditions. The field studies and consequent data analysis provide a picture of the reliability and usefulness of GPS data for traffic monitoring purposes, and hence the possibilities for the use of GPS in IVHS projects. The use of GPS receivers tailored for mobile applications, and able to provide direct observations of vehicle speed and travel direction, coupled with database management using geographic information systems (GIS) software, was found to provide a reliable and efficient system for vehicle monitoring. Field data collection under “ideal” GPS conditions indicated that accurate speed and position data were readily obtained from the GPS. Under less favourable conditions (e.g. in downtown networks), data accuracy decreased but useful information could still be obtained. In addition, the conditions and situations under which GPS data errors could be expected were noted. The finding that it is possible to relate standard GPS signal quality indicators to increased errors in speed and position provides an enhanced degree of confidence in the use of the GPS system for real-time traffic observations.

Effects of multipath and antenna on GPS observables

The authors present the analysis of effects on global positioning system (GPS) observables using the functional modelling and simulation package of a digital baseband processor for the GPS receiver. Three issues are addressed: first, the static observable errors as functions of multipath parameters are derived mathematically in the absence of input noise; secondly, the dynamic code and carrier tracking errors as functions of time due to multipath in the presence of input noise are investigated; and finally the deterioration in the accuracy of the GPS observables due to antenna residual phase and antenna centre movement is studied with different receiver design parameters. It is shown that the functional modelling and simulation package provide an alternative approach to GPS system accuracy research where theoretical analysis and hardware methods are very difficult, inaccurate or prohibitively expensive.

Precise orbit determination for TOPEX/Poseidon using GPS-SST data

The TOPEX/Poseidon (T/P) altimeter satellite launched in August 1992 is equipped with an experimental Global Positioning System (GPS) receiver. The major goal of the GPS experiment is to demonstrate the GPS system for precise orbit determination of low Earth satellites. The GPS-SST data as obtained from the T/P onboard receiver have been processed in a dynamic orbit determination. In addition, the GPS ephemerides and GPS clock parameters as provided by IGS were used as fixed parameters. The orbit accuracy is assessed using a number of tests. These include external comparisons and analysis of data residuals and orbit overlaps. The orbit determination technique has yielded orbits with an estimated accuracy of about 3 cm in the radial component.

Digital baseband processor for the GPS receiver (parts I and II)

A global positioning system (GPS) receiver has been modeled mathematically and implemented in software. The digital baseband processor of the receiver performs the maximum likelihood estimations (MLEs) of the GPS observables. The following issues are discussed: the fundamentals of the digital GPS receiver, the modeling of the digital baseband processor, and the performance of the modeled static and dynamic receivers. The software-based receiver is more flexible, less expensive, and more accurate compared to hardware receivers in receiver designs and GPS system performance analysis.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Laptop Automated Navigation Aid Positioning System with Differential GPS

The advent of the Global Positioning System (GPS) brought about changes in positioning and surveying that are only now being fully exploited. When GPS is in place, positioning accuracy of 100 m or less will be available worldwide, 24 hr/day, in all weather and visibility conditions. The Coast Guard grasped the significance of the potential of the GPS system and has developed a system to improve the accuracy of GPS from 100 m to 5–10 m; this is the differential GPS system, or DGPS. The Short Range Aids to Navigation Division recognized the potential use of DGPS as a new tool for aid positioning. Our present manual buoy‐positioning methods are tedious, time‐consuming, and error‐prone. For these reasons our units must continually check and recheck their positions with electronic navigation aids, radar information, and horizontal sextant angles to place a buoy on station. Automation of this procedure with DGPS input would allow units to obtain real‐time positioning information for navigation and aid placement. The Coast Guard Research & Development Center was tasked with developing an automated navigation aid positioning system. Their efforts provided us with the Laptop Automated Aid Positioning System, or LAAPS. For the Short Range Aids to Navigation Division, LAAPS is everything it was expected to be. The USCGC Bittersweet, out of Woods Hole, Mass., is testing the system and is finding it can find the position of aids to navigation with 2–3 m accuracy. Plans call for nationwide coverage of DGPS by 1996. By that time all Coast Guard aids‐to‐navigation units will have LAAPS ready for operation.

Satellite Navigation: GPS Inadequacies: Comparative Study into Solutions for Civil Aviation

The Global Positioning System (GPS) will be an extremely high-performance satellite-based navigation system which is expected to provide a sole means air navigation service for most aeronautical flight phases. It will be particularly suitable for ‘en route’, ‘terminal’ and ‘non-precision approach’ phases, thus providing substantial savings on aircraft operating costs.However, GPS has three major disadvantages for civil aviation: (1) Insufficient system integrity, since satellites can transmit erroneous information for two hours before being repaired or neutralized. In such an event, the many simultaneous users of the satellite that has lost its integrity can derive false positions and remain unaware of the problem. (2) Availability constrained by the limited number of satellites. Users are then unable to obtain a position fix or else obtain a result with significantly degraded performance. (3) Deliberate spatio-temporal degradation (selective availability) of system performance, the characteristics of which are not fully known or defined.Many solutions to these problems have been put forward. One concept uses the redundancy of the GPS system itself (receiver autonomous integrity monitoring). Another set of solutions is based on complementary information from autonomous navigation equipment (altimeter, clock, inertial system) or external navigation systems already available or being developed (Omega, Loran-C, GLONASS). A third type of solution is to implement a system by which to monitor the status of the GPS satellites and broadcast the information to users.This paper reports on the different techniques put forward and uses different qualitative criteria (technical feasibility, cost, political independence, etc.) to assess their suitability for civil aviation applications. The comparison leads to the recommendation of a system to monitor the status of the GPS satellites and broadcast the information to users. The characteristics of such messages would be as similar as possible to those of GPS messages.

Interferometric Global Positioning System: Three‐dimensional positioning source for airborne gravimetry

The Naval Research Laboratory (NRL) and the National Geodetic Survey recently collaborated on an experiment to test interferometric mode Global Positioning System (GPS) tracking as a source of altitude and vertical acceleration for airborne gravity measurement reduction. A Texas Instruments TI‐4100 GPS receiver and an extremely precise radar altimeter were installed in an NRL P‐3 Orion aircraft. A second TI‐4100 was located at a fixed base station of known location. Carrier phase data from four GPS satellites were recorded from the fixed and airborne receivers and postprocessed to produce three‐dimensional displacements of the airborne station relative to the base station. Differences in GPS and radar altimeter coordinate systems were modeled and removed: the resulting GPS and radar altitudes were compared. The two unfiltered 1‐Hz data sets differed by an rms of 20 cm when aircraft dynamics were controlled by autopilot in straight and level flight. During hand‐flown maneuvers such as turns, climbs, and descents, rms differences varied from 40 to 80 cm. A significant portion of the differences can be attributed to remaining coordinate system discrepancies and to uncompensated geometric effects due to aircraft motion. We have also examined vertical acceleration time series produced by doubly differencing both data sets. By applying a low‐pass filter which allows resolution of features with wavelengths of 20 km and greater (at nominal aircraft speeds of 100 m/s) the rms difference between the radar and GPS derived vertical accelerations was less than 2 mGal (2×10−5 m/s2) during straight and level flight. It should be possible to improve this accuracy and wavelength resolution with future improvements in measurement and processing techniques. The results of this experiment show that the incorporation of interferometric mode GPS tracking into the airborne gravity measurement system will make possible rapid and relatively inexpensive gravity surveys over any type of terrain while simultaneously providing accurate measurements of ground height profiles beneath the aircraft.