Real-time Differential GPS Research Articles

RTDGPS Accuracy Improvement Using PSO-LSWSVM and Low-Cost GPS Receivers

The position of mobile devices is determined by Real Time Differential Global Positioning System (RTDGPS). This system is composed of fixed and mobile station. The accuracy of this system depends on the speed of updating the correction data. Yet, this system often faces the problem of the reference GPS receiver’s signal cut off and internal or non- internal delays which increase the latency time and decrease the updating speed. The prediction models are used to compensate these delays. In this paper, the Particle Swarm Optimization Least Square Wavelet Support Vector Machine (PSO-LSWSVM) is used for predicting the DGPS correction. An experimental setup is designed in order to carry out the operations of reference and user stations. Low-cost receivers were used in both stations. The accuracy of PSO-LSWSVM was evaluated through various simulations and experimental. The practical tests showed that the accuracy of the designed RTDGPS is 0.42 m with PSO-LSWSVM and is equal to 0.73 m without it. In comparing with other method that recently is introduced; it has a higher positioning accuracy.

Utilizing hybrid recurrent neural network and genetic algorithm for predicting the pseudo-range correction factors to improve the accuracy of RTDGPS

Positioning in real time with high precision is realized through implementing a Real-time Differential GPS (RTDGPS). Amccuracy of the system depends on sequential and uninterruptible transmission of Pseudo-Range Correction (PRC) codes from Reference Station (RS) to the user station. This transmission takes place in RTCM protocol. In order to compensate the signal absence and transmission delay of differential corrections, future values of the PRC should somehow be estimated. To this end a combination of Recurrent Neural Network (RNN) and Genetic Algorithm (GA) has been used. Addition of this algorithm not only improved the efficiency and consistency of the RTDGPS service, but also increased the accuracy of the positioning system. In this research RTDGPS system has been implemented using two inexpensive receivers in reference and user stations. Simulation and experimental results indicate that RTDGPS accuracy improved by predicting the future values of PRC. Time step of the prediction algorithm is considered to be 5 s. RMS value of the positioning error for a fixed point after addition of the RNN-GA algorithm to RTDGPS system has decreased.

Improving RTDGPS accuracy using hybrid PSOSVM prediction model

Users of Global Positioning System (GPS) require more accuracy from positioning service of this system. Accurate and real time positioning is realized through implementing Real Time Differential GPS (RTDGPS). Accuracy of this system depends on successive and punctual transmission of Pseudo Range Corrections (PRCs) from Reference Station (RS) to user station. Corrections are transmitted using Radio Technical Commission for Maritime services (RTCM) protocol. To compensate signal absence and transmission delay of differential corrections which is created while transferring, processing and reception, a hybrid prediction algorithm combined of Support Vector Machine (SVM) and Particle Swarm Optimization (PSO) has been implemented in RS. Corrections are predicted using SVM while, PSO is used for determination and optimization of the basic parameters in SVM algorithm. A Low Cost GPS receiver is used in RS. Prediction time step was five seconds. Simulation results show that the total Root Mean Square (RMS) prediction error for PSOSVM is less than 0.126 m for one step ahead and 0.46 m for 10 step ahead predictions. Experimental results indicate that by employing PSOSVM, accuracy of RTDGPS has been improved.

A Wide Area Real-Time Differential GPS Prototype System in China and Result Analysis

This paper introduces the Wide Area Real-Time Differential GPS Prototype System on the basis of the PANDA software platform which is independently developed by Wuhan University. The system is a suite of algorithmic, infrastructure elements to enable the processing, distribution and archiving of Real-Time and Near Real-time GNSS data and results. Currently, it adopts observation data from nearly 100 real-time stations, including IGS global stations and regional stations of China, to continuously estimate real-time satellite clock offset second by second and to provide a Global Ionospheric Map product updated every 5 minutes. 1 HZ corrections to the GPS spacecraft position and clock to Broadcast Ephemeris and grid VTEC with 30 sec' interval are provided to users through a wireless communication network. In this research, real-time orbit and clock product, as well as single frequency and double frequency point positioning accuracy are investigated. Results of tests show the SISRE of real-time orbit and clock by the system is about 5cm; real-time double frequency positioning RMS are respectively better than 10cm and 20cm in the horizontal and vertical direction; single frequency positioning RMS(3D) is better than 1m .

An Automated Cost-effective System for Real-time Slope Mapping in Commercial Wild Blueberry Fields

The development of site-specific agriculture has increased the need for knowledge regarding within-field variability in factors such as soil/plant characteristics and topography that influence wild blueberry (Vaccinium angustifolium) production. Surface soil properties are the first type of information most frequently used by blueberry producers in developing management plans. Topographic features are not yet routinely used to guide within-field management. The majority of blueberry fields in eastern Canada have gentle to severe topography. An automated slope measurement and mapping system (SMMS) consisting of low-cost accelerometers used as tilt sensors, differential global positioning system (DGPS), and laptop and custom software was developed. The SMMS was mounted on an all-terrain vehicle for real-time slope measurement and mapping. Six commercial wild blueberry fields were surveyed in central Nova Scotia to evaluate the performance of SMMS. The automatically sensed slopes (SS) were also compared with manually measured slopes (MS) at 20 randomly selected points in each field to examine the accuracy of SMMS. The SMMS measured slope reliably in the selected fields with root mean square error ranging from 0.12 to 0.56 degrees and correlations of SS with MS of R2 = 0.95 to 0.99. The selected fields had substantial variation in slope (ranging from 0.8 to 31.0 degrees). Therefore, the use of low-cost and reliable accelerometers with a DGPS is a better option than expensive real-time kinematic DGPS for developing cost-effective SMMS to quantify and map slopes (real-time) for planning site-specific management practices in commercial fields. The SS maps or real-time SMMS could also be used to adjust vehicle speed at particularly steep slopes.

Monitoring morphological and vegetation changes and flow events in dryland river channels

Monitoring of impacts of floods in river valleys of dryland regions has become important with the onset and threats of desertification and is likely to become even more vital with predictions of increased effects of climate and land use change. It is also needed in order to conform to requirements of the EU Water Framework Directive. Monitoring in such regions sets particular challenges. This paper explains a system of low-cost monitoring of changes in morphology, vegetation and sediment cover in channels and valley floors of ephemerally flowing streams. It has been applied in SE Spain for 10 years and has proved very effective. In particular, the use of simple crest-stage recorders for measuring flow height and the use of real-time differential GPS for rapid and accurate survey and for relocating points have proved very valuable. Part of the monitoring is focused on the interaction of plants and channel processes. Small changes in and around vegetation associated with flow events have been detected by a combination of quadrat surveys and cross-profiling of the channel. A range of flow events has been measured over the period of monitoring, demonstrating their differing effects and the varying sensitivity and responsiveness of different sites. The sporadic occurrence of flood events in such an environment means that a strategy of monitoring several sites and of continuation over many years has great benefits.

Efficient interpolations to GPS orbits for precise wide area applications

For precise real time or near real time differential GPS positioning in a wide or global area, precise GPS orbits or, alternatively, precise orbital corrections with respect to a reference orbit, such as GPS broadcast ephemerides, must be used. This work tests orbit interpolation methods, in order to represent the GPS orbits and orbital corrections accurately and efficiently for these and other GPS applications. For precise GPS orbits given in the SP3 format at the 15 min interval, numerical tests were conducted using Lagrange and Chebyshev as well as trigonometric polynomial functions. The results have demonstrated that the 19- or 20-term trigonometric function is apparently the most efficient interpolator for a 12 h GPS orbital arc, achieving 1 cm level 3D interpolation accuracy that can meet the requirements of most precise applications. The test results also demonstrated that the 9-term trigonometric function always yields optimal interpolation for a 2 h GPS orbit arc, in terms of interpolation errors, compared to the results when using a different number of terms for the same function or one of the other tested polynomial functions. This is evident from the minimal performance degradation when using the 9-term trigonometric function to interpolate near or at the end of a data interval. By limiting interpolation to the center 15 min to 1.5 h of a 2 h orbit arc, thereby eliminating the need to interpolate near the ends of that interval, users can opt for more terms (11 and 13) or different interpolators to further improve interpolation accuracy. When interpolating the orbital corrections with respect to the GPS broadcast ephemeris, all the tested interpolation functions of 3- to 9-term yield the same suitably accurate results. Therefore, a 3- to 5-term trigonometric function is arguably sufficiently accurate and more efficient for GPS orbital correction messaging in wide area and real time positioning.

Augmentation of Low?Cost GPS Receivers via Web Services and Wireless Mobile Devices

Low-cost GPS receivers can produce positions almost instantly, however they have a limited use and application due to the impact of random and systematic errors associated with real time autonomous positioning. To achieve higher levels of accuracy and precision, some other form of correction or augmentation information must be applied. There are various real time augmentation alternatives, such as WAAS/LAAS, integrated sensors and systems, receiver based optimal estimation algorithms, and potentially, combined GNSS. To improve the accuracy of low-cost GPS receivers, a feasible option is Differential GPS (DGPS). A popular means for transferring real time DGPS corrections is via the RTCM SC-104 protocol over radio transmission. In recent times, the Internet has been shown to be an efficient and reliable form of data communication. In this paper, the Web services architecture is examined as a viable protocol and communication alternative for disseminating DGPS augmentation information over the Internet. Preliminary results from a simple prototype indicate that Web services offers a practical, efficient and secure method for exchanging CORS network data, and augmenting GPS enabled mobile devices capable of wirelessly reaching the internet. Web services are further shown to provide advantages for disseminating other GPS related data, such as IGS satellite orbit data, carrier- phase data for location-centric augmentation, and a host of other LBS information.

An Application of LiDAR in a Double-Sample Forest Inventory

Abstract Multireturn LiDAR data (2-m posting) were used in a double-sample forest inventory in central Idaho. Twenty-four 15-plot (0.2 ac) strips were established with a real-time Differential Global Positioning System. Tree dbh and height were measured on every 5th plot. Volume and basal area were computed for eight encountered species. LiDAR trees were selected with a focal max filter and height computed as the z-difference between interpolated canopy and DEM surfaces. LiDAR-derived trees/ac, height, and dbh had mean differences of −4.4 trees, −10.7 ft, and −1.01 in. from ground values. Four dbh-height models were fitted. Predicted dbh was used to compute LiDAR estimates of basal area and volume on 360 Phase 1 plots. Phase 2 LiDAR estimates on 60 plots were computed by randomly assigning heights to species classes using a 500-iteration Monte Carlo simulation. Regression estimators for Phase 2 ground and LiDAR ft3 and ft2 were computed by single and composite species. Phase 1 estimates were partitioned to obtain species volumes. The regression estimate of composite volume was partitioned by percent species distribution of trees, basal area, and volume. There was no statistical difference between individual and partitioned composite species estimates. Sampling error was ±11.5% on a mean volume estimate of 1,246 ft3/ac with standard error ±72.98 ft3/ac. West. J. Appl. For. 19(2):95–101.

An Integrated Navigation System For Suez Canal (SCINS)

This paper offers a designed Integrated Navigation System that will permit vessels to transit safely through the Suez Canal avoiding collision and grounding in all weather environments instead of being directed to anchor, thus keeping the Canal open at all times for ship transits. The Suez Canal Integrated Navigation System (SCINS) includes Differential Global Positioning System (DGPS), Suez Canal LORAN-C system, and Vessel Traffic Management System (VTMS). The combination of DGPS and LORAN-C systems would provide real-time DGPS corrections that could be used to calibrate the Loran fix; this can be achieved by means of portable integrated DGPS/LORAN-C sets installed aboard the vessels. The addition of VTMS provides significant capability for preserving system accuracy during periods of GPS outages. Due to the interface between LORAN-C and VTMS systems, the SCINS will be able to solve the problem of targets that cannot be tracked by VTMS radars in the shadow areas behind the new bridges along the Canal. The SCINS automates position fixing in real-time, offers a designed algorithm to return the ship to the middle of the Canal and computes the cross-track error (XTE) and the ship squat. Kalman Filter design and system level performance predictions for the SCINS are briefly described. Simulation results show that the SCINS offers superior performance and better position accuracy than current integrated systems.

Airborne gravimetry – a new gravimeter system and test results

Success of airborne gravity surveys mainly depends on determining the three-dimensional (3D) position of the moving platform. Recent advances in technology, especially the Global Positioning System (GPS), have made it possible to determine the velocity and position of the moving platform more frequently and with greater accuracy. Taking advantage of these advances in GPS technology, and using a newly developed system, helicopter-borne gravity measurements were successfully carried out over the Kanto and Tokai districts of Japan. This new gravimeter system is composed of servo accelerometer sensors, a stabilised platform, an optical-fibre gyroscope to control the stabilised platform, GPS receivers, and a data processor.The 3D position of the helicopter at every second was accurately determined by the interferometric GPS method. These GPS data were also used to compute various correction factors which are applied to the measured gravity acceleration. Real-time differential GPS positioning was also conducted using a separate receiver mounted on the helicopter. These real-time positioning data were used for controlling the optical-fibre gyroscope. The gravity acceleration data were processed and all necessary corrections were applied. Numerical filtering was carried out to remove high-frequency noise in the data. The observed free-air gravity anomalies were then compared with upward continuation of the ground gravity data to the flight altitude. We also compiled an airborne gravity anomaly map from the airborne data, which was compared with upward-continued ground gravity data.

Discussion of "Evaluation of the potential for power-line noise to degrade real-time differential GPS messages broadcast at 283.5-325 kHz"

Discussion of "Evaluation of the potential for power-line noise to degrade real-time differential GPS messages broadcast at 283.5-325 kHz"

Closure to "Evaluation of the potential for power-line noise to degrade real-time differential GPS messages broadcast at 283.5-325 kHz"

The author replies to the comments made on the original paper ("Evaluation of the potential for power-line noise to degrade real-time differential GPS messages broadcast at 283.5-325 kHz", J.M. Silva, see ibid., vol.17, p.326-33, 2002) by V.L. Chartier (see ibid., vol.18, no.1, p.343, Jan. 2003).

Evaluation of the potential for power line noise to degrade real time differential GPS messages broadcast at 283.5-325 kHz

Evaluation of the potential for power line noise to degrade real time differential GPS messages broadcast at 283.5-325 kHz

Evaluation of the Potential for Power Line Noise to Degrade Real Time Differential GPS Messages Broadcast at 283.5-325 kHz

The new nationwide differential global positioning system network uses the 283.5-325 kHz hand to broadcast differential GPS (DOPS) correction messages. Concem has been expressed that power line corona and gap discharge noise could degrade the performance of DGPS receivers using this band. Previous work on power lines and the AM broadcast band identified corona and gap discharges as broadband noise sources in the LFIMF bands. The potential to locally degrade performance of DGPS receivers relatively close to some power facilities appears possible for certain situations. The extent of any DGPS interference problem will depend on receiver/antenna design and placement, signal strength, power line design, weather conditions, and characteristics of the noise source. Also affecting DGPS receiver performance can be the presence of any nearby non-power line RF noise sources such as electronic devices or equipment internal to the user's vehicle.

Real time differential GPS and GLONASS vehicle positioning in urban areas

This paper describes a research programme carried out by the Institute of Satellite Navigation (ISN) and Racal Survey Ltd. to examine the performance of differential positioning using both the GPS ...

Evaluation of Positioning Accuracy in Real Time Differential GPS

Evaluation of Positioning Accuracy in Real Time Differential GPS

Comparison of Two Multi-site Reference Station Differential GPS Systems

This paper describes the infrastructure and concept of two multi-site reference station differential GPS (DGPS) options being offered to land and marine users by Racal Survey. The infrastructure of the Racal SkyFix system is briefly outlined followed by descriptions of Racal's internetting and network capabilities.The two systems are compared including infrastructure, differential data management, user coverage, datalinks and positioning performance in various parts of the world. The paper describes the design of each of the systems and the tests undertaken to assess their functionality, before going on to compare their performances under a variety of conditions. Emphasis is placed on the technical issues associated with multi-reference station DGPS including error sources, weighting observations and monitoring of the data. The fundamental approach of the systems is shown to achieve high data integrity which is necessary to develop the systems to their next phase.Having described the two options, examples of various combinations of reference stations are used to illustrate the potential of the system and to show the increased performance over ordinary, single-station DGPS. The conclusions summarize the paper's findings and make recommendations for the future development of the system. The object of the developments so far have been to improve the quality of real-time offshore DGPS positioning. The internetting and network options are providing real-time results to illustrate the benefits and, together with SkyFix, offer significant developments in the ability of DGPS to provide accurate and reliable positioning over vast areas of the world.

Hydro‐isostatic deflection and tectonic tilting in the central Andes: Initial results of a GPS survey of Lake Minchin shorelines

Sufficiently large lake loads provide a means of probing rheological stratification of the crust and upper mantle. Lake Minchin was the largest of the late Pleistocene pluvial lakes in the central Andes. Prominent shorelines, which formed during temporary still‐stands in the climatically driven lake level history, preserve records of lateral variations in subsequent net vertical motions. At its maximum extent the lake was 140 m deep and spanned 400 km N‐S and 200 km E‐W. The load of surficial water contained in Lake Minchin was sufficient to depress the crust and underlying mantle by 20–40 m, depending on the subjacent rheology. Any other differential vertical motions will also be recorded as departures from horizontality of the shorelines. We recently conducted a survey of shoreline elevations of Lake Minchin with the express intent of monitoring the hydro‐isostatic deflection and tectonic tilting. Using real‐time differential GPS, we measured topographic profiles across suites of shorelines at 15 widely separated locations throughout the basin. Horizontal and vertical accuracies attained are roughly 30 and 70 cm, respectively. Geomorphic evidence suggests that the highest shoreline was occupied only briefly (probably less than 200 years) and radiocarbon dates on gastropod shells found in association with the shore deposits constrain the age to roughly 17 kyr. The basin‐wide pattern of elevations of the highest shoreline is composed of two distinct signals: (27±1) m of hydro‐isostatic deflection due to the lake load, and a planar tilt with east and north components of (6.8±0.4) 10−5 and (−5.3±0.3) 10−5. This rate of tilting is too high to be plausibly attributed to steady tectonism, and presumably reflects some unresolved combination of tectonism plus the effects of oceanic and lacustrine loads on a laterally heterogeneous substrate. The history of lake level fluctuations is still inadequately known to allow detailed inferences of crust and mantle rheology. However, it is already clear that the effective elastic plate thickness is closer to 40 km than the 60–70 km crustal thickness in the central Andes and the effective viscosity is less than 5 1020 Pa s.

Experimental Measurement and Characterization of Ionospheric and Multipath Errors in Differential GPS

Real-time differential GPS is fundamentally limited by a) signal estimation errors, b) satellite ephemeris errors, c) propagation decorrelation errors, and d) local multipath errors. In this paper we address the latter two error sources. An understanding of these is needed to establish an error budget for any monitor station network that the U.S. Coast Guard would consider for a nationwide system. To estimate these error sources, extensive two-frequency P-code and integrated Doppler data have been collected over 150 kilometer and 1500 kilometer baselines. A processing scheme is developed which employs both code and carrier observations. Applicable to real-time differential systems, as well as to post-collection data analyses, the estimation scheme treats multipath errors and carrier-code offsets as state-variables. The resulting Kalman filter yields the very precise carrier observation, corrected for carrier-code offset. Day-to-day repeatability of multipath errors is illustrated. The decorrelation of ionospheric errors across short and long baselines is evaluated by combining the integrated Doppler estimation scheme with the standard two-frequency ionospheric measurement technique. Also discussed are the impact of multipath and ionospheric error sources on Differential GPS.