Global Navigation Satellite System

... The 1 Eric Benson, ebenson@udel.edu, 242 Townsend Hall, Newark, DE 19716. Copyright, 2001. Page 2. Benson, Eric. 2001. ... and multiple satellites. The standard satellite position model is a measurement-state Page 3. Benson, Eric. 2001. Global Navigation Satellite Systems. ...

Les GNSS (global navigation satellite system) parmi lesquels le système américain GPS (global positioning system) ont tous  pour principal objectif de donner la position et la vitesse d’un mobile à tout instant, en tout lieu et dans un référentiel global. Comme tout système basé sur des satellites, il est structuré en trois composantes qui seront détaillées afin de mieux appréhender les principes de la géolocalisation : le segment
spatial (les satellites), le segment de contrôle (les stations au sol) et le segment utilisateur (le récepteur mobile).
Le calcul du géopositionnement peut être basé sur deux mesures : (1) soit la mesure du temps qu’ont mis les
signaux émis par au moins quatre satellites pour parcourir la distance les séparant du mobile, (2) soit le décalage
de phase des signaux auquel cas un appareillage très sophistiqué doit lever des ambiguïtés (nombre des oscillations
entre l’émission du signal par le satellite et la réception par le mobile). Théoriquement (1) doit donner une précision
décimétrique et (2) millimétrique mais des sources d’erreur viennent la parasiter. Pour améliorer la qualité du
géopositionnement il existe d’autres systèmes satellitaires (SBAS - satellite based augmentation system) et
également des réseaux de stations au sol (GBAS - ground based augmentation system) pour transmettre des
corrections de positionnement. les algorithmes de repositionnement peuvent être utilisés en direct (correction
différentielle en temps réel « DGPS ») ou en différé (post-traitement) pour atteindre une précision centimétrique à
condition d’avoir le matériel approprié. Sur la base des principes de la géolocalisation il sera présenté les bonnes
pratiques à adopter sur le terrain : bien choisir son matériel, préparer ses levées et bien mesurer les géopositionnements.

In environmental monitoring, environmental impact assessments and environmental audits, topographical maps play an essential role in providing a means by which the locations of sampling sites may be selected, in assisting with the interpretation of physical features, and in indicating the impact or potential impact on an area due to changes in the system being monitored (e.g., spatially changing features such as wetlands). Global Navigation Satellite Systems (GNSS) are hereby presented as a rapid method for monitoring spatial changes to support environmental monitoring decisions and policies. To validate the GNSS-based method, a comparison is made of results from a small-scale topographic survey using radio-based real-time kinematic GNSS (GNSS-RTK) and total station survey methods at Jack Finnery Lake, Perth, Australia. The accuracies achieved by the total station in this study were 2 cm horizontally and 6 cm vertically, while the GNSS-RTK also achieved an accuracy of 2 cm horizontally, but only 28 cm vertically. While the GNSS-RTK measurements were less accurate in the height component compared to those from the total station method, it is still capable of achieving accuracies sufficient for a topographic map at a scale of 1:1,750 that could support environmental monitoring tasks such as identifying spatial changes in small water bodies or wetlands. The time taken to perform the survey using GNSS-RTK, however, was much shorter compared to the total station method, thereby making it quite suitable for monitoring spatial changes within an environmental context, e.g., dynamic mining activities that require rapid surveys and the updating of the monitored data at regular intervals.

The latest innovation of the global navigation satellite systems (GNSS) technologies plays an important role in improving the quality and safety of modern life. Most of the applications evolved from the integration between GNSS, geographical information systems (GIS) and wireless communications and networking (WCN) systems. The wide spread applications that are using these technologies include: the automatic vehicle location (AVL), tracking systems, navigation systems, pedestrian navigation systems, intelligent transportation systems, precise positioning, and emergency callers, among others. The location-based services (LBS) are possible only by the combination of GNSS, GIS and WCN. The growing need for commercial LBS has forced cellular-phone and network manufacturers to concentrate on positioning solutions, which are even more precise than the regulatory mandates for positioning of emergency callers and other user services and applications. In this paper, we will present a literature review of the GNSS, the three satellite systems GPS, GLONASS and Galileo, which are aimed to support GNSS services, and a comparison between them and their role in creating a GIS. Copyright © 2006 John Wiley & Sons, Ltd.

The GNSS modernization provides new signal frequencies and satellites which can allow for more accurate methods of monitoring, modeling and mitigating the ionospheric effects on the GNSS applications. In this work, part of the Innovative Navigation using new GNSS SIGnals with Hybridized Technologies (iNsight) project funded by the UK Engineering and Physical Sciences Research Council (EPSRC), the ionospheric scintillation effects (abrupt power fades and phase variations in the received signals) are investigated regarding the GNSS modernization. Analysis of the scintillation effects is done through a simulation-based approach using the Spirent GSS8000 GNSS signal simulator where the signals are perturbed using the Cornell Scintillation Model (CSM). The receiver signal tracking performance is evaluated based on the variance of the code and carrier tracking loop errors using the scintillation-sensitive tracking models [1, 2]. Preliminary results on the User Equivalent Range Error (UERE) on particular receiver-satellite links are investigated to understand the effect of scintillation on the (code-based) range measurements.

SUMMARY It is well recognized today that a reference network comprised of permanent stations operating Global Navigation Satellite System (GNSS) receivers on a continuous basis provides the fundamental infrastructure required to meet the needs not only of geodesy and the geosciences, but also of professional GNSS users in areas of surveying, mapping and navigation. These high accuracy applications can only

Linear variable differential transformers (LVDTs) and inclinometers are widely used in many industrial establishments, particularly in the metrology area. These sensors are used by many engineering disciplines because of their high-precision characteristics. In addition, Global Navigation Satellite System (GNSS) receivers and total stations are widely used in geodesy. Using GNSS receivers is very popular, particularly for navigational purposes. In this paper, a new railway track geometry surveying system, which is designed by integrating the LVDT, inclinometer, GNSS receiver, and total station, is introduced. This new surveying system is an alternative to classical geodetic measurement methods that are often used for controlling the railway track geometry. Track gauge, super-elevation, gradient, and track axis coordinates, which are railway geometrical parameters, can be instantly determined while making measurements by using the new surveying system.

Recently, direct position estimation (DPE) has arisen as a potential approach to deal with the positioning problem in global navigation satellite system receivers. The conventional navigation solution is obtained in two steps: synchronization parameters are estimated and then a trilateration procedure is in charge of computing user's position, based on those parameters. In contrast, DPE estimates receiver's position directly from digitized signal. DPE was seen to provide GNSS receivers with appealing capabilities, such as multipath mitigation. However, a theoretical bound for those estimates is still missing and the answer to ldquohow better can DPE perform compared to the conventional approach?rdquo has not been addressed in the literature. Aiming at clarifying those issues, this paper presents the derivation of the CramEacuter-Rao bound (CRB) of position for both conventional and DPE approaches. We present the derivation for a multiantenna receiver as a general case. In addition, a number of realistic scenarios are tested in order to compare the theoretical performance bounds of both alternatives and the actual root mean squared error performance of the corresponding maximum likelihood estimator.

After removal of the Selective Availability in 2000, the ionosphere became the dominant error source for Global Navigation Satellite Systems (GNSS), especially for the high-accuracy (cm-mm) demanding applications like the Precise Point Positioning (PPP) and Real Time Kinematic (RTK) positioning. The common practice of eliminating the ionospheric error, e.g. by the ionosphere free (IF) observable, which is a linear combination of observables on two frequencies such as GPS L1 and L2, accounts for about 99 % of the total ionospheric effect, known as the first order ionospheric effect (Ion1). The remaining 1 % residual range errors (RREs) in the IF observable are due to the higher - second and third, order ionospheric effects, Ion2 and Ion3, respectively. Both terms are related with the electron content along the signal path; moreover Ion2 term is associated with the influence of the geomagnetic field on the ionospheric refractive index and Ion3 with the ray bending effect of the ionosphere, which can cause significant deviation in the ray trajectory (due to strong electron density gradients in the ionosphere) such that the error contribution of Ion3 can exceed that of Ion2 (Kim and Tinin, 2007). The higher order error terms do not cancel out in the (first order) ionospherically corrected observable and as such, when not accounted for, they can degrade the accuracy of GNSS positioning, depending on the level of the solar activity and geomagnetic and ionospheric conditions (Hoque and Jakowski, 2007). Simulation results from early 1990s show that Ion2 and Ion3 would contribute to the ionospheric error budget by less than 1 % of the Ion1 term at GPS frequencies (Datta-Barua et al., 2008). Although the IF observable may provide sufficient accuracy for most GNSS applications, Ion2 and Ion3 need to be considered for higher accuracy demanding applications especially at times of higher solar activity. This paper investigates the higher order ionospheric effects (Ion2 and Ion3, however excluding the ray bending effects associated with Ion3) in the European region in the GNSS positioning considering the precise point positioning (PPP) method. For this purpose observations from four European stations were considered. These observations were taken in four time intervals corresponding to various geophysical conditions: the active and quiet periods of the solar cycle, 2001 and 2006, respectively, excluding the effects of disturbances in the geomagnetic field (i.e. geomagnetic storms), as well as the years of 2001 and 2003, this time including the impact of geomagnetic disturbances. The program RINEX_HO (Marques et al., 2011) was used to calculate the magnitudes of Ion2 and Ion3 on the range measurements as well as the total electron content (TEC) observed on each receiver-satellite link. The program also corrects the GPS observation files for Ion2 and Ion3; thereafter it is possible to perform PPP with both the original and corrected GPS observation files to analyze the impact of the higher order ionospheric error terms excluding the ray bending effect which may become significant especially at low elevation angles (Ioannides and Strangeways, 2002) on the estimated station coordinates.

The application of Global Positioning System (GPS) technology to the Geostationary Earth Orbit (GEO) determination has been constrained by the poor satellite visibility and weak signal power. This situation is expected to improve when multi-constellation Global Navigation Satellite Systems (GNSS) are available in the future. This paper aims to investigate a navigation algorithm to determine the GEO state vector in real time, using multi-constellation GNSS measurements. The navigation algorithm is based on a Kalman filter where the estimated state includes position and velocity corrections to the nominal reference trajectory and clock biases. The simulation results are presented in the paper. It is concluded that this algorithm meets the requirement for autonomous GEO satellite navigation.

The European Tripartite Group (ETG)1, (ESA - EC - EUROCONTROL) is implementing, via the EGNOS project (1), the European contribution to the Global Navigation Satellite System (GNSS-1) which will provide and guarantee navigation signals for aeronautical, maritime and land mobile Trans- European network applications. On behalf of this Tripartite group, the European Space Agency is responsible for the system design,

The Global Positioning System (GPS) has become a powerful tool for ionospheric studies. In addition, ionospheric corrections are necessary for the augmentation systems required for Global Navigation Satellite Systems (GNSS) use. Dual-frequency carrier-phase and code-delay GPS observations are combined to obtain ionospheric observables related to the slant total electron content (sTEC) along the satellite-receiver line-of-sight (LoS). This observable is affected by inter-frequency biases [IFB; often called differential code biases (DCB)] due to the transmitting and the receiving hardware. These biases must be estimated and eliminated from the data in order to calibrate the experimental sTEC obtained from GPS observations. Based on the analysis of single differences of the ionospheric observations obtained from pairs of co-located dual-frequency GPS receivers, this research addresses two major issues: (1) assessing the errors translated from the code-delay to the carrier-phase ionospheric observable by the so-called levelling process, applied to reduce carrier-phase ambiguities from the data; and (2) assessing the short-term stability of receiver IFB. The conclusions achieved are: (1) the levelled carrier-phase ionospheric observable is affected by a systematic error, produced by code-delay multi-path through the levelling procedure; and (2) receiver IFB may experience significant changes during 1 day. The magnitude of both effects depends on the receiver/antenna configuration. Levelling errors found in this research vary from 1.4 total electron content units (TECU) to 5.3 TECU. In addition, intra-day vaiations of code-delay receiver IFB ranging from 1.4 to 8.8 TECU were detected.