National GPS Network Research Articles

Exploring the role of PPP–RTK network configuration: a balance of server budget and user performance

With atmospheric corrections generated from the server, precise point positioning real-time kinematic (PPP–RTK) can achieve high-precision solutions in a fast convergence. PPP–RTK users are concerned about how to use the corrections and the level of performance that can be achieved; thus, our research has focused on correction methods, a priori stochastic modeling, and positioning performance evaluation. Conversely, it is crucial for the server to improve the precision of corrections provided and to consider the balance between cost, computation burden and user performance, especially for commercial applications. We use different scales of the national GPS network of France to generate ionospheric and tropospheric corrections, and corresponding uncertainty information is generated by establishing error functions with respect to an inter-station distance. The quality of corrections and corresponding user performance are analyzed with inter-station distances varying from 22 to 251 km. The results show that the precision of atmospheric corrections can be improved with an increasing number of stations in the network, but the improvement is not significant when the inter-station distances are smaller than 50 km. Regarding user performance, compared to conventional PPP solutions with ambiguity resolution, the convergence time can be reduced by a maximum of 93% and 85% in the horizontal and vertical components, respectively, when the inter-station distance is about 23 km. However, a station spacing within 100 km can still support a 3-min convergence; thus, a balance of server budget and user performance should be considered instead of a dense network.

Practical Application of a Horizontal Intraplate Velocity Field Model for the Territory of Bulgaria

The Republic of Bulgaria is situated on the edge of the Eurasian tectonic plate. This is defined by active tectonic and seismic activity, which is an issue in the implementation of the official coordinate reference system in the country - the ETRS89, as far as precise solutions are concerned. The reason is that the intraplate, relative to Eurasia, tectonic movements south of Stara Planina are about 5 times larger than those north of it. Over a period of time (about 10 years), the coordinate errors of the points from a static network become bigger than the uncertainties of GNSS measurements and thus limit their potential. Thanks to the presence of networks of continuously operating reference GNSS stations (CORS networks), and advanced methods of processing and analysis of the results, it is possible to monitor the crustal deformations with sufficient precision. A model of horizontal intraplate velocities was developed based on measurements from different epochs of the CORS networks operating on the territory of Bulgaria. Precise coordinates and velocities of the stations were estimated using the Bernese GNSS Software v5.2, and the deformation modeling was performed using a method of determining parameters of local deformation and Euler poles of distinctive tectonic blocks to which the country is divided according to the authors. This paper presents the practical applicability of this model for interpolation the velocities of stations from static networks and verification of the official results for the points of the National GPS Network. The results are encouraging for the practical realization of ETRS89 on the territory of Bulgaria.

A Combined Velocity Field of the Mediterranean Region

We present a full 3-D velocity field of the Earth's surface in the Euro-Mediterranean area obtained from a combination of three different velocity solutions computed at the Centro Nazionale Terremoti (CNT) of the Istituto Nazionale di Geofisica e Vulcanologia (INGV). All the publicly available GPS data since 1993, have been fully reprocessed by three different software tools and the final velocity field is estimated combining three independent velocity solutions in a least squares sense. The input velocity solutions are treated as stochastic samples of the true velocity field by loosening the reference frame constraints in the associated variance-covariance matrix. The proposed approach allows for a fast and efficient combination of multi velocity solutions, taking into account the full network covariance, if available. The velocity map for the Euro-Mediterranean region will be updated and released regularly on the web portal of the National GPS Network (http://ring.gm.ingv.it) and made available to the scientific community. Here we show and discuss the data analysis and the combination schemes, and the results of the combined velocity field.

The Italian National Seismic Network and the earthquake and tsunami monitoring and surveillance systems

Abstract. The Istituto Nazionale di Geofisica e Vulcanologia (INGV) is an Italian research institution, with focus on Earth Sciences. INGV runs the Italian National Seismic Network (Rete Sismica Nazionale, RSN) and other networks at national scale for monitoring earthquakes and tsunami as a part of the National Civil Protection System coordinated by the Italian Department of Civil Protection (Dipartimento di Protezione Civile, DPC). RSN is composed of about 400 stations, mainly broadband, installed in the Country and in the surrounding regions; about 110 stations feature also co-located strong motion instruments, and about 180 have GPS receivers and belong to the National GPS network (Rete Integrata Nazionale GPS, RING). The data acquisition system was designed to accomplish, in near-real-time, automatic earthquake detection, hypocenter and magnitude determination, moment tensors, shake maps and other products of interest for DPC. Database archiving of all parametric results are closely linked to the existing procedures of the INGV seismic monitoring environment and surveillance procedures. INGV is one of the primary nodes of ORFEUS (Observatories & Research Facilities for European Seismology) EIDA (European Integrated Data Archive) for the archiving and distribution of continuous, quality checked seismic data. The strong motion network data are archived and distributed both in EIDA and in event based archives; GPS data, from the RING network are also archived, analyzed and distributed at INGV. Overall, the Italian earthquake surveillance service provides, in quasi real-time, hypocenter parameters to the DPC. These are then revised routinely by the analysts of the Italian Seismic Bulletin (Bollettino Sismico Italiano, BSI). The results are published on the web, these are available to both the scientific community and the general public. The INGV surveillance includes a pre-operational tsunami alert service since INGV is one of the Tsunami Service providers of the North-eastern Atlantic and Mediterranean Tsunami warning System (NEAMTWS).

Results from a comprehensive GPS Network: natural gas pipeline GPS Network

Developing the Nabucco engineering infrastructure was the most challenging task imaginable and required state-of-the-art technologies. For this purpose, a Nabucco-Global Positioning System (GPS) Network was established. It is 762 km long. Nine-hundred and two ground control unit points were established. In order to provide the relationship with ITRF96 datum, it was surrounded by TFNGN (Turkish Fundamental National GPS Network) and TNVCN (Turkish National Vertical Control Network) checkpoints. GPS observations were evaluated in the form of a unique network. After being reduced to projection segments, coordinates in ED50 datum were provided between datums by 2D-Helmert Transformation. Orthometric heights related to the GPS Network were obtained by the improvement of TG-03 data based on a GPS/leveling procedure. The objective of the study is to present the results of a comprehensive engineering project which involved many geodetic considerations including GPS, orthometric heights, and geoid undulations and gives insight into the accuracy and precision of such large projects in terms of recent geodetic practice. In this study, a Global Navigation Satellite System (GNSS)-based geodetic infrastructure is presented, methods to obtain the necessary precision requirements are provided, and experience is shared in order to provide an example of a large-scale pipeline project, and to provide insight into the planning necessary for future similar engineering projects.

A back-propagation artificial neural network approach for three-dimensional coordinate transformation

The European Datum 1950 (ED50) of the Turkish national geodetic network (TNGN) and the World Geodetic System 1984 (WGS84) of the Turkish national fundamental GPS network (TNFGN) are in use as geodetic reference frames in Turkey. According to the use of two reference systems, it is necessary to transform the three-dimensional (3D) coordinate data from ED50 to WGS84 or vice versa. The seven-parameter similarity transformation method is frequently used for 3D coordinate transformation in geodesy. In this study, a back propagation artificial neural network (BPANN) that has been more widely applied in engineering among all other neural network models is evaluated as an alternative 3D coordinate transformation method. BPANN is compared with a popular seven-parameter similarity transformation (Molodensky-Badekas) method over a test area, in terms of root mean square error (RMSE). The results indicated that the employment of BPANN transformed 3D coordinates (X, Y, Z) more accurate than Molodensky-Badekas method and can be useful for 3D coordinate transformation between ED50 and WGS84. Key words: 3D coordinate transformation, back propagation artificial neural network, seven-parameter similarity transformation, BPANN, Molodensky-Badekas.

Chinese geodetic coordinate system 2000

The basic strategies in establishing the Chinese geodetic coordinate system 2000 have been summarized, including the definition of the coordinate system, the structure of the terrestrial reference frame, the functional and stochastic models involved in the realization of the reference frame as well as the improvements of the adjustment procedures. First, the fundamental frame of the coordinate system is composed of the permanent GPS tracking network in China which is integrated into the international GPS service stations by combined adjustment, in order to guarantee the consistence between the international terrestrial reference system and the Chinese geodetic coordinate system. Second, the extended frame of the coordinate system is composed of the unified 2000’ national GPS network which is integrated by 6 nationwide GPS networks with more than 2500 stations under the controlling of the fundamental frame. Third, the densified frame is composed of national astronomical geodetic network with nearly 50 thousand stations which was updated by the combined adjustment with the 2000’ national GPS network, thus the datum of the national astronomical geodetic network has been unified and the precision greatly improved. By the optimal data fusion method the influences of the datum errors, systematic errors and the outliers in the separated geodetic networks are weakened in the unified Chinese geodetic coordinate frame. The significance in application of the new geodetic coordinate system and the existing problems in the reference frame are described and analyzed.

Comparison of the Hungarian first order triangulation network with the national GPS network using scale and azimuth differences

While the cadastral and topographic maps tie to the classical reference systems and frames, there will be need to know the relation between the classical and GPS-based networks in a particular country. In this study we discuss the scale factor and azimuth discrepancies between the Hungarian first order triangulation and the national GPS network emphasising their practical significance.The comparison of traditional and GPS derived slope and geodesic distances as well as the comparison of the different azimuths make possible the estimation of the scale and orientation differences of the two systems without the knowledge of height and geoid information which may contain additional errors, too.The estimated −4.34 mm/km mean value reflects the significant scale difference, which is similar to the values derived in neighbour countries. The −2.51 arcsec mean azimuth difference reflects the orientation of the two system.

National 2000' GPS control network of China

Abstract An accurately unified national GPS network with more than 2500 stations, named “National 2000' GPS Control Netweork”, signed the epoch 2000.0, has been established by integrating the existing six nationwide GPS networks of China set up by different departments with different objectives. this paper presents the characteristics of the exciting GPS networks, summarizes the strategies in the integrated adjustment of the GPS network, including functional model, stochastic model as well as the adjustment principle modification. By modifying the adjustment strategies according to the characteristics of the existing GPS networks and under the support of the IGS stations, the accuracy of the integrated national GPS network is greatly improved. The datum differences among the sub networks disappear, the systematic error influences are weakened, and the effects of the outliers on the estimated coordinates and their variances are controlled. It is shown that the average standard deviation for the horizontal ...

Tomographic determination of the spatial distribution of water vapor using GPS observations

With the advent of the GPS navigation system, a promising ground based technique has been introduced which makes it possible to estimate the amount of water vapor in the troposphere from operational GPS networks at relatively low additional costs. While the estimation of the integrated amount is currently well established, the determination of the spatial water vapor distribution and its temporal variation are still a major challenge. To account for the vertical resolution, several tomographic approaches were pursued. We developed the software package AWATOS (atmospheric water vapor tomography software) which is based on the assimilation of double differenced GPS observations. Applying a least-squares inversion, the inhomogeneous spatial distribution of water vapor is determined. An extensive investigation has been carried out in Switzerland. GPS measurements are performed by the dense permanent Swiss national GPS network AGNES of the Swiss Federal Office of Topography (swisstopo). A total of 40 equally distributed water vapor profiles have been estimated on an hourly basis. For the purpose of validation, 22 radiosonde profiles were used at the GPS and meteorological station Payerne. Furthermore, data of the numerical weather model aLMo (alpine model in Switzerland, MeteoSwiss) were compared with the tomographic results. An overall good agreement of the three methods with an rms of better than 1.6 g/m 3 absolute humidity was achieved. The results show that AGNES can be used as a dedicated network for the purpose of GPS-tomography, using a horizontal resolution of approximately 50 km and height layers of 300–500 m thickness in the lower troposphere.

ON SOME IMPROVEMENTS IN THE GEODETIC FRAMEWORK OF TRINIDAD AND TOBAGO

Geodetic Services was contracted by the Lands and Surveys Division and the Ministry of Energy of Trinidad and Tobago to adjust the recent precise national GPS network on the International Terrestrial Reference Frame, compute optimal transformation parameters between the six horizontal datums used in this region and compute a precise geoid for the country. This paper summarizes the work done on this project, including a related academic research on regional tectonic deformation, and suggests some further geodetic improvements.

UTILISING THE ORDNANCE SURVEY NATIONAL GPS NETWORK FOR DIGITAL SURFACE MODELLING

High accuracy Digital Surface Models can be created quickly and efficiently using GPS survey techniques. However, survey grade GPS receivers are not renowned for their affordability. The positioning requirements of many GIS and environmental survey applications can be met with cheaper receivers, but many of the high-end requirements are not achievable unless two survey grade receivers are purchased. The advent of the National GPS network may provide a means of reducing the cost of hardware for users by the removing the requirement of two receivers. GPS data is processed using the Ordnance Survey stations as base stations for relative positioning. The results are used to create DSMs and a comparison of the outputs computed from three different stations is presented.

SINGLE RECEIVER HEIGHTING USING THE ACTIVE STATIONS OF THE NATIONAL GPS NETWORK OF GREAT BRITAIN

Precise height determination using a single GPS receiver is now possible, following the establishment of GPS networks that include active stations with typical separations of about 100km. A method is described to determine precise heights when using a single GPS receiver and active stations of the National GPS Network of Great Britain. From the computation of the heights of 188 GPS stations distributed across the British mainland, a precision of 1.5cm was attained. This was achieved using only 4 hours of dual frequency static GPS data, but with scientific GPS processing soflware to mitigate systematic error effects.

Great Britain's Ordnance Survey National GPS Network

To encourage compatibility of national and global precise positioning of GPS surveys in Great Britain, Ordnance Survey is providing access at no cost to the new National GPS Network, via a website first available in June 2000. By requiring the use of this infrastructure to provide ETRS89 control station coordinates at a stated level of precision, survey clients can be assured that any commissioned survey will be precisely consistent with any other, even if the two are widely spaced in location and time. All such surveys will also be precisely consistent with the Ordnance Survey large-scale base mapping, using the precise National Grid Transformation and National Geoid Model. This is now the Ordnance Survey recommended ‘standard method’ of creating new National Grid coordinate datasets, eventually to replace completely the traditional national control networks of triangulation stations and height bench marks.

Current crustal motion and deformation in the Chinese mainland and its surrounding area determined from GPS data

Based on the geodetic data taken from the National GPS Network established by China Climbing Program “Investigation of Crust Motion and Geodynamics in Modern Time”, we derived the movement velocities of the GPS sites. In terms of the power series expansion of a rotation function for horizontal velocities on a spherical surface proposed by Haines and Holt (1993), we computed the horizontal velocity and strain-rate field. We preliminarily studied the appearances and characteristics of the present-day crustal movement and deformation in the Chinese mainland with the computed results. The researches demonstrated: (1) The present-day crustal movement and deformation in the Chinese mainland are being jointly controlled by Indian, Pacific and Philippines Ocean Plates and Siberia-Mongolia block, and these three large plates and block form a situation of tripartite confrontation, but Indian Plate seems to play a leading role; (2) The North-South Earthquake Zone plays an important adjustment role in the present-day crustal movement and deformation process, displaying clear characteristics of demarcation line of tectonics in large areas; (3) There seems to be another adjustment zone along the latitude line approximate N35°, but its characteristics are less obvious than that of the former; (4) Dynamic actions of these three large plates and block on the Chinese mainland are dynamic stable; appearing in stable push-press velocities. These results are generally accorded with the results determined from geology, geophysics, and seismology. By the contrast with seismicities, it appears preliminarily that there is some corresponding relation between intense shear strain zone and future strong seismicity area, but this problem needs further examination of earthquake examples.

Completion of the nationwide GPS-gravimetric geoid solution for Hungary

The establishment of the Hungarian National GPS Network (OGPSH) had been completed in 1997. It is exclusively settled on the traditional horizontal network sites, no leveling benchmarks were included. The OGPSH network consists more than 1100 GPS points, but less than 30% of the sites have trustful leveled heights. Our task was to supply the remaining points with cm-accuracy heights above the geoid in a uniform system. For this purpose a technique had been developed using the GPS data and the geoid information available. A specialized geoid solution, covering the whole country was computed and used for supporting the GPS-heighting procedure.The OGG98B GPS-gravimetric geoid solution made the GPS-heighting very simple and efficient. The accuracy of the technique was extensively tested and proved to be accurate not worse than ±3 cm. Higher residuals were found only at some points, where the height information was questionable. The improved technique is planned to be used in the 3rd order leveling network in Hungary.This paper shortly summarizes the computational procedure of the GPS-gravimetric geoid and presents some results on the GPS-heighting had been performed in the OGPSH network.

How Accurate is the Australian National GPS Network as a Framework for GPS Heighting?

How Accurate is the Australian National GPS Network as a Framework for GPS Heighting?

How accurate is the Australian National GPS network as a framework for GPS heighting?

The Australian National GPS Network (ANN) is to provide the fundamental framework for the new Geocentric Datum of Australia (GDA 1994.0 ). Whilst the GDA 1994.0 final solution will represent a new horizontal datum for Australia, the Australian Height Datum (AHD) will remain unchanged. This paper demonstrates the suitability of the ANN as one component of a fundamental framework for a new vertical datum by discussing the errors associated with the height component of the ANN GPS solution.