Engineering › Aerospace Engineering

GNSS positioning and interference

Works Count: 51512

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Description

This cluster of papers focuses on the advancements and applications of Global Navigation Satellite Systems (GNSS), including topics such as precise point positioning, reference frame modeling, atmospheric effects, orbit determination, tropospheric delay modeling, ambiguity resolution, multi-GNSS experiments, and receiver antennas.

Keywords

Global Navigation Satellite Systems; GNSS; Precise Point Positioning; Reference Frame; Atmospheric Effects; Orbit Determination; Tropospheric Delay; Ambiguity Resolution; Multi-GNSS Experiment; Receiver Antennas

GPS Satellite Surveying

2015-03-02

Alfred Leick , Lev Rapoport , Dmitry Tatarnikov

INTROOUCTION 2 LEAST-SQUARES AOJUSTMENTS 2.1 Elementary Considerations / 12 2 INTROOUCTION 2 LEAST-SQUARES AOJUSTMENTS 2.1 Elementary Considerations / 12 2

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GPS Sounding of the Atmosphere from Low Earth Orbit: Preliminary Results

1996-01-01

Robert S. Ware , C. Rocken , Fredrick Solheim +7 more

This paper provides an overview of the methodology of and describes preliminary results from an experiment called GPS/MET (Global Positioning System/Meteorology), in which temperature soundings are obtained from a low … This paper provides an overview of the methodology of and describes preliminary results from an experiment called GPS/MET (Global Positioning System/Meteorology), in which temperature soundings are obtained from a low Earth-orbiting satellite using the radio occultation technique. Launched into a circular orbit of about 750-km altitude and 70° inclination on 3 April 1995, a small research satellite, MicroLab 1, carried a laptop-sized radio receiver. Each time this receiver rises and sets relative to the 24 operational GPS satellites, the GPS radio waves transect successive layers of the atmosphere and are bent (refracted) by the atmosphere before they reach the receiver, causing a delay in the dual-frequency carrier phase observations sensed by the receiver. During this occultation, GPS limb sounding measurements are obtained from which vertical profiles of atmospheric refractivity can be computed. The refractivity is a function of pressure, temperature, and water vapor and thus provides information on these variables that has the potential to be useful in weather prediction and weather and climate research. Because of the dependence of refractivity on both temperature and water vapor, it is generally impossible to compute both variables from a refractivity sounding. However, if either temperature or water vapor is known from independent measurements or from model predictions, the other variable may be calculated. In portions of the atmosphere where moisture effects are negligible (typically above 5–7 km), temperature may be estimated directly from refractivity. This paper compares a representative sample of 11 temperature profiles derived from GPS/MET soundings (assuming a dry atmosphere) with nearby radiosonde and high-resolution balloon soundings and the operational gridded analysis of the National Centers for Environmental Prediction (formerly the National Meteorological Center). One GPS/MET profile was obtained at a location where a temperature profile from the Halogen Occultation Experiment was available for comparison. These comparisons show that accurate vertical temperature profiles may be obtained using the GPS limb sounding technique from approximately 40 km to about 5–7 km in altitude where moisture effects are negligible. Temperatures in this region usually agree within 2°C with the independent sources of data. The GPS/MET temperature profiles show vertical resolution of about 1 km and resolve the location and minimum temperature of the tropopause very well. Theoretical temperature accuracy is better than 0.5°C at the tropopause, degrading to about 1°C at 40-km altitude. Above 40 km and below 5 km, these preliminary temperature retrievals show difficulties. In the upper atmosphere, the errors result from initial temperature and pressure assumptions in this region and initial ionospheric refraction assumptions. In the lower troposphere, the errors appear to be associated with multipath effects caused by large gradients in refractivity primarily due to water vapor distribution.

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Global mapping functions for the atmosphere delay at radio wavelengths

1996-02-10

A. E. Niell

I have developed expressions for calculating the ratios (mapping functions) of the “line of sight” hydrostatic and wet atmospheric path delays to their corresponding zenith delays at radio wavelengths for … I have developed expressions for calculating the ratios (mapping functions) of the “line of sight” hydrostatic and wet atmospheric path delays to their corresponding zenith delays at radio wavelengths for elevation angles down to 3°. The coefficients of the continued fraction representation of the hydrostatic mapping function depend on the latitude and height above sea level of the observing site and on the day of the year; the dependence of the wet mapping function is only on the site latitude. By comparing with mapping functions calculated from radiosonde profiles for sites at latitudes between 43°S and 75°N, the hydrostatic mapping function is seen to be more accurate than, and of comparable precision to, mapping functions currently in use, which are parameterized in terms of local surface meteorology. When the new mapping functions are used in the analysis of geodetic very long baseline interferometry (VLBI) data, the estimated lengths of baselines up to 10,400 km long change by less than 5 mm as the minimum elevation of included data is reduced from 12° to 3°. The independence of the new mapping functions from surface meteorology, while having comparable accuracy and precision to those that require such input, makes them particularly valuable for those situations where surface meteorology data are not available.

Attaining Doppler Precision of 3 M s-1

1996-06-01

R. P. Butler , G. W. Marcy , Eric Williams +3 more

Current spectroscopic techniques yield Doppler-shift errors of 10 to 50 m s-1, barely adequate to detect reflex velocities caused by Jupiter-like and lower-mass planets. We describe a technique which yields … Current spectroscopic techniques yield Doppler-shift errors of 10 to 50 m s-1, barely adequate to detect reflex velocities caused by Jupiter-like and lower-mass planets. We describe a technique which yields relative radial velocity errors of 3 m s-1. This technique makes use of a fast echelle spectrograph at resolution of R=62,000 and a large format CCD which acquires the entire visible and near IR spectrum in each exposure. Starlight is sent through an iodine absorption cell placed at the spectrometer entrance slit. The resulting superimposed iodine lines provide a fiducial wavelength scale against which to measure radial velocity shifts. The shapes of iodine lines convey the PSF of the spectrometer to account for changes in spectrometer optics and illumination on all times scales. We construct a model of each observed spectrum by multiplying a stellar spectrum with an iodine spectrum and convolving the result with the spectrometer PSF. The free parameters of the model include the wavelength scale, spectrometer PSF, and stellar Doppler shift. All model parameters are derived anew for each exposure and the synthesis is done on a grid of CCD sub-pixels, using spline functions as interpolation predictors. We present Doppler tests of the Sun, Tau Ceti, and 107 Psc, observed with the Lick and Keck echelles. All exhibit apparent errors of about 3 m s-1, maintained on time scales of minutes to a year. This precision agrees with the theoretically predicted errors that stem primarily from photon statistics.

Global positioning system : theory and applications

1996-01-01

Bradford W. Parkinson , James J. Spilker

Differential GPS and Integrity Monitoring Differential GPS Pseudolites Wide Area Differential GPS Wide Area Augmentation System Receiver Autonomous Integrity Monitoring Integrated Navigation Systems Integration of GPS and Loran-C GPS and … Differential GPS and Integrity Monitoring Differential GPS Pseudolites Wide Area Differential GPS Wide Area Augmentation System Receiver Autonomous Integrity Monitoring Integrated Navigation Systems Integration of GPS and Loran-C GPS and Inertial Integration Receiver Autonomous Integrity Monitoring Availability for GPS Augmented with Barometric Altimeter Aiding and Clock Coasting GPS and Global Navigation Satellite System (GLONASS) GPS Navigation Applications Land Vehicle Navigation and Tracking Marine Applications Applications of the GPS to Air Traffic Control GPS Applications in General Aviation Aircraft Automatic Approach and Landing Using GPS Precision Landing of Aircraft Using Integrity Beacons Spacecraft Attitude Control Using GPS Carrier Phase Special Applications GPS for Precise Time and Time Interval Measurement Surveying with the Global Position System Attitude Determination Geodesy Orbit Determination Test Range Instrumentation.

Resolution of GPS carrier-phase ambiguities in Precise Point Positioning (PPP) with daily observations

2008-01-07

Maorong Ge , G. Gendt , Markus Rothacher +2 more

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The International Celestial Reference Frame as Realized by Very Long Baseline Interferometry

1998-07-01

Chao Ma , E. F. Arias , T. M. Eubanks +6 more

A quasi-inertial reference frame is defined based on the radio positions of 212 extragalactic sources distributed over the entire sky. The positional accuracy of these sources is better than about … A quasi-inertial reference frame is defined based on the radio positions of 212 extragalactic sources distributed over the entire sky. The positional accuracy of these sources is better than about 1 mas in both coordinates. The radio positions are based upon a general solution for all applicable dual-frequency 2.3 and 8.4 GHz Mark III very long baseline interferometry data available through the middle of 1995, consisting of 1.6 million pairs of group delay and phase delay rate observations. Positions and details are also given for an additional 396 objects that either need further observation or are currently unsuitable for the definition of a high-accuracy reference frame. The final orientation of the frame axes has been obtained by a rotation of the positions into the system of the International Celestial Reference System and is consistent with the FK5 J2000.0 optical system, within the limits of the link accuracy. The resulting International Celestial Reference Frame has been adopted by the International Astronomical Union as the fundamental celestial reference frame, replacing the FK5 optical frame as of 1998 January 1.

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Carrier phase ambiguity resolution for the Global Positioning System applied to geodetic baselines up to 2000 km

1989-08-10

Geoffrey Blewitt

The Global Positioning System (GPS) carrier phase data are biased by an integer number of cycles. A successful strategy has been developed and demonstrated for resolving these integer ambiguities for … The Global Positioning System (GPS) carrier phase data are biased by an integer number of cycles. A successful strategy has been developed and demonstrated for resolving these integer ambiguities for geodetic baselines of up to 2000 km in length, resulting in a factor of 3 improvement in baseline accuracy, and giving centimeter‐level agreement with coordinates inferred by very long baseline interferometry in the western United States. For this experiment, a method using pseudorange data is shown to be more reliable than one using ionospheric constraints for baselines longer than 200 km. An automated algorithm exploits the correlations between the many phase biases of a GPS receiver network to enable the resolution of ambiguities for very long baselines. A method called bias optimizing has been developed, which, unlike traditional bias fixing, does not require an arbitrary confidence test. Bias optimizing is expected to be preferable to bias fixing for poorly configured networks. In order to enable ambiguity resolution for long baselines, it is recommended that future GPS networks have a wide spectrum of baseline lengths ranging from <100 to >1000 km and that GPS receivers be used which can acquire dual‐frequency P code data.

Effect of annual signals on geodetic velocity

2002-07-01

Geoffrey Blewitt , David Lavallée

Our analysis of Global Positioning System (GPS) site coordinates in a global reference frame shows annual variation with typical amplitudes of 2 mm for horizontal and 4 mm for vertical, … Our analysis of Global Positioning System (GPS) site coordinates in a global reference frame shows annual variation with typical amplitudes of 2 mm for horizontal and 4 mm for vertical, with some sites at twice these amplitudes. Power spectrum analysis confirms that GPS time series also contain significant power at annual harmonic frequencies (with spectral indices 1 < α < 2), which indicates the presence of repeating signals. Van Dam et al. [2001] showed that a major annual component is induced by hydrological and atmospheric loading. Unless accounted for, we show that annual signals can significantly bias estimation of site velocities intended for high accuracy purposes such as plate tectonics and reference frames. For such applications, annual and semiannual sinusoidal signals should be estimated simultaneously with site velocity and initial position. We have developed a model to calculate the level of bias in published velocities that do not account for annual signals. Simultaneous estimation might not be necessary beyond 4.5 years, as the velocity bias rapidly becomes negligible. Minimum velocity bias is theoretically predicted at integer‐plus‐half years, as confirmed by tests with real data. Below 2.5 years, the velocity bias can become unacceptably large, and simultaneous estimation does not necessarily improve velocity estimates, which rapidly become unstable due to correlated parameters. We recommend that 2.5 years be adopted as a standard minimum data span for velocity solutions intended for tectonic interpretation or reference frame production and that we be skeptical of geophysical interpretations of velocities derived using shorter data spans.

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The International Laser Ranging Service

2002-07-01

M. R. Pearlman , John J. Degnan , John M. Bosworth

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Confidence limits for small numbers of events in astrophysical data

1986-04-01

N. Gehrels

view Abstract Citations (1952) References (1) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Confidence Limits for Small Numbers of Events in Astrophysical Data Gehrels, N. Abstract The … view Abstract Citations (1952) References (1) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Confidence Limits for Small Numbers of Events in Astrophysical Data Gehrels, N. Abstract The calculation of limits for small numbers of astronomical counts is based on standard equations derived from Poisson and binomial statistics; although the equations are straightforward, their direct use is cumbersome and involves both table-interpolations and several mathematical operations. Convenient tables and approximate formulae are here presented for confidence limits which are based on such Poisson and binomial statistics. The limits in the tables are given for all confidence levels commonly used in astrophysics. Publication: The Astrophysical Journal Pub Date: April 1986 DOI: 10.1086/164079 Bibcode: 1986ApJ...303..336G Keywords: Astrophysics; Binomial Theorem; Confidence Limits; Data Processing; Poisson Density Functions; Approximation; Tables (Data); Astrophysics; NUMERICAL METHODS full text sources ADS |

Ionospheric Time-Delay Algorithm for Single-Frequency GPS Users

1987-05-01

J. A. Klobuchar

The goal in designing an ionospheric time-delay correctionalgorithm for the single-frequency global positioning system userwas to include the main features of the complex behavior of theionosphere, yet require a minimum … The goal in designing an ionospheric time-delay correctionalgorithm for the single-frequency global positioning system userwas to include the main features of the complex behavior of theionosphere, yet require a minimum of coefficients and usercomputational time, while still yielding an rms correction of at least50 percent. The algorithm designed for this purpose, andimplemented in the GPS satellites, requires only eight coefficientssent as part of the satellite message, contains numerousapproximations designed to reduce user computationalrequirements, yet preserves the essential elements required to obtaingroup delay values along multiple satellite viewing directions.

Precise point positioning for the efficient and robust analysis of GPS data from large networks

1997-03-10

J. Zumberge , M. B. Heflin , D. Jefferson +2 more

Networks of dozens to hundreds of permanently operating precision Global Positioning System (GPS) receivers are emerging at spatial scales that range from 10 0 to 10 3 km. To keep … Networks of dozens to hundreds of permanently operating precision Global Positioning System (GPS) receivers are emerging at spatial scales that range from 10 0 to 10 3 km. To keep the computational burden associated with the analysis of such data economically feasible, one approach is to first determine precise GPS satellite positions and clock corrections from a globally distributed network of GPS receivers. Then, data from the local network are analyzed by estimating receiver‐specific parameters with receiver‐specific data; satellite parameters are held fixed at their values determined in the global solution. This “precise point positioning” allows analysis of data from hundreds to thousands of sites every day with 40‐Mflop computers, with results comparable in quality to the simultaneous analysis of all data. The reference frames for the global and network solutions can be free of distortion imposed by erroneous fiducial constraints on any sites.

Error analysis of continuous GPS position time series

2004-03-01

Simon Williams , Yehuda Bock , Peng Fang +5 more

A total of 954 continuous GPS position time series from 414 individual sites in nine different GPS solutions were analyzed for noise content using maximum likelihood estimation (MLE). The lengths … A total of 954 continuous GPS position time series from 414 individual sites in nine different GPS solutions were analyzed for noise content using maximum likelihood estimation (MLE). The lengths of the series varied from around 16 months to over 10 years. MLE was used to analyze the data in two ways. In the first analysis the noise was assumed to be white noise only, a combination of white noise plus flicker noise, or a combination of white noise plus random walk noise. For the second analysis the spectral index and amplitude of the power law noise were estimated simultaneously with the white noise. In solutions where the sites were globally distributed, the noise can be best described by a combination of white noise plus flicker noise. Both noise components show latitude dependence in their amplitudes (higher at equatorial sites) together with a bias to larger values in the Southern Hemisphere. In the regional solutions, where a spatially correlated (common mode) signal has been removed, the noise is significantly lower. The spectral index of the power law in regional solutions is more varied than in the global solutions and probably reflects a mixture of local effects. A significant reduction in noise can be seen since the first continuous GPS networks began recording in the early 1990s. A comparison of the noise amplitudes to the different monument types in the Southern California Integrated GPS Network suggests that the deep drill braced monument is preferred for maximum stability.

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ITRF2008: an improved solution of the international terrestrial reference frame

2011-02-02

Z. Altamimi , Xavier Collilieux , Laurent Métivier

ITRF2008 is a refined version of the International Terrestrial Reference Frame based on reprocessed solutions of the four space geodetic techniques: VLBI, SLR, GPS and DORIS, spanning 29, 26, 12.5 … ITRF2008 is a refined version of the International Terrestrial Reference Frame based on reprocessed solutions of the four space geodetic techniques: VLBI, SLR, GPS and DORIS, spanning 29, 26, 12.5 and 16 years of observations, respectively. The input data used in its elaboration are time series (weekly from satellite techniques and 24-h session-wise from VLBI) of station positions and daily Earth Orientation Parameters (EOPs). The ITRF2008 origin is defined in such a way that it has zero translations and translation rates with respect to the mean Earth center of mass, averaged by the SLR time series. Its scale is defined by nullifying the scale factor and its rate with respect to the mean of VLBI and SLR long-term solutions as obtained by stacking their respective time series. The scale agreement between these two technique solutions is estimated to be 1.05 ± 0.13 ppb at epoch 2005.0 and 0.049 ± 0.010 ppb/yr. The ITRF2008 orientation (at epoch 2005.0) and its rate are aligned to the ITRF2005 using 179 stations of high geodetic quality. An estimate of the origin components from ITRF2008 to ITRF2005 (both origins are defined by SLR) indicates differences at epoch 2005.0, namely: −0.5, −0.9 and −4.7 mm along X, Y and Z-axis, respectively. The translation rate differences between the two frames are zero for Y and Z, while we observe an X-translation rate of 0.3 mm/yr. The estimated formal errors of these parameters are 0.2 mm and 0.2 mm/yr, respectively. The high level of origin agreement between ITRF2008 and ITRF2005 is an indication of an imprecise ITRF2000 origin that exhibits a Z-translation drift of 1.8 mm/yr with respect to ITRF2005. An evaluation of the ITRF2008 origin accuracy based on the level of its agreement with ITRF2005 is believed to be at the level of 1 cm over the time-span of the SLR observations. Considering the level of scale consistency between VLBI and SLR, the ITRF2008 scale accuracy is evaluated to be at the level of 1.2 ppb (8 mm at the equator) over the common time-span of the observations of both techniques. Although the performance of the ITRF2008 is demonstrated to be higher than ITRF2005, future ITRF improvement resides in improving the consistency between local ties in co-location sites and space geodesy estimates.

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Troposphere mapping functions for GPS and very long baseline interferometry from European Centre for Medium‐Range Weather Forecasts operational analysis data

2006-02-01

J. Boehm , Birgit Werl , Harald Schuh

In the analyses of geodetic very long baseline interferometry (VLBI) and GPS data the analytic form used for mapping of the atmosphere delay from zenith to the line of site … In the analyses of geodetic very long baseline interferometry (VLBI) and GPS data the analytic form used for mapping of the atmosphere delay from zenith to the line of site is most often a three‐parameter continued fraction in 1/sin(elevation). Using the 40 years reanalysis (ERA‐40) data of the European Centre for Medium‐Range Weather Forecasts for the year 2001, the b and c coefficients of the continued fraction form for the hydrostatic mapping functions have been redetermined. Unlike previous mapping functions based on data from numerical weather models (isobaric mapping functions (Niell, 2000) and Vienna mapping functions (VMF) (Boehm and Schuh, 2004)), the new c coefficients are dependent on the day of the year, and unlike the Niell mapping functions (Niell, 1996) they are no longer symmetric with respect to the equator (apart from the opposite phase for the two hemispheres). Compared to VMF, this causes an effect on the VLBI or GPS station heights that is constant and as large as 2 mm at the equator and that varies seasonally between 4 mm and 0 mm at the poles. The updated VMF, based on these new coefficients and called VMF1 hereinafter, yields slightly better baseline length repeatabilities for VLBI data. The hydrostatic and wet mapping functions are applied in various combinations with different kinds of a priori zenith delays in the analyses of all VLBI International VLBI Service for Geodesy and Astrometry (IVS)‐R1 and IVS‐R4 24‐hour sessions of 2002 and 2003; the investigations concentrate on baseline length repeatabilities, as well as on absolute changes of station heights.

Precise Point Positioning Using IGS Orbit and Clock Products

2001-10-01

J. Kouba , Pierre Héroux

Single receiver phase ambiguity resolution with GPS data

2010-03-19

Willy Bertiger , S. D. Desai , Bruce Haines +4 more

Accuracy and reliability of multi-GNSS real-time precise positioning: GPS, GLONASS, BeiDou, and Galileo

2015-03-13

Xingxing Li , Maorong Ge , Xiaolei Dai +4 more

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The least-squares ambiguity decorrelation adjustment: a method for fast GPS integer ambiguity estimation

1995-11-01

P. J. G. Teunissen

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Effects of antenna orientation on GPS carrier phase

1993-04-01

Jui‐Hsien Wu , Siyu Wu , G. A. Hajj +2 more

In-Car Positioning and Navigation Technologies—A Survey

2009-02-09

Isaac Skog , Peter Händel

In-car positioning and navigation has been a killer application for Global Positioning System (GPS) receivers, and a variety of electronics for consumers and professionals have been launched on a large … In-car positioning and navigation has been a killer application for Global Positioning System (GPS) receivers, and a variety of electronics for consumers and professionals have been launched on a large scale. Positioning technologies based on stand-alone GPS receivers are vulnerable and, thus, have to be supported by additional information sources to obtain the desired accuracy, integrity, availability, and continuity of service. A survey of the information sources and information fusion technologies used in current in-car navigation systems is presented. The pros and cons of the four commonly used information sources, namely, 1) receivers for radio-based positioning using satellites, 2) vehicle motion sensors, 3) vehicle models, and 4) digital map information, are described. Common filters to combine the information from the various sources are discussed. The expansion of the number of satellites and the number of satellite systems, with their usage of available radio spectrum, is an enabler for further development, in combination with the rapid development of microelectromechanical inertial sensors and refined digital maps.

ITRF2005: A new release of the International Terrestrial Reference Frame based on time series of station positions and Earth Orientation Parameters

2007-09-01

Z. Altamimi , Xavier Collilieux , Juliette Legrand +2 more

Unlike the past International Terrestrial Reference Frame (ITRF) versions where global long‐term solutions were combined, the ITRF2005 uses as input data time series (weekly from satellite techniques and 24‐h session‐wise … Unlike the past International Terrestrial Reference Frame (ITRF) versions where global long‐term solutions were combined, the ITRF2005 uses as input data time series (weekly from satellite techniques and 24‐h session‐wise from Very Long Baseline Interferometry) of station positions and daily Earth Orientation Parameters (EOPs). The advantage of using time series of station positions is that it allows to monitor station non‐linear motion and discontinuities and to examine the temporal behavior of the frame physical parameters, namely the origin and the scale. The ITRF2005 origin is defined in such a way that it has zero translations and translation rates with respect to the Earth center of mass, averaged by the Satellite Laser Ranging (SLR) time series spanning 13 years of observations. Its scale is defined by nullifying the scale and its rate with respect to the Very Long Baseline Interferometry (VLBI) time series spanning 26 years of observations. The ITRF2005 orientation (at epoch 2000.0) and its rate are aligned to the ITRF2000 using 70 stations of high geodetic quality. The estimated level of consistency of the ITRF2005 origin (at epoch 2000.0) and its rate with respect to the ITRF2000 is respectively 0.1, 0.8, 5.8 mm and 0.2, 0.1, 1.8 mm/yr along the X , Y and Z ‐axis. We estimate the formal errors on these components to be 0.3 mm and 0.3 mm/yr. We believe that this low level of agreement between the two frame origins is most probably due to the poor SLR network geometry and its degradation over time. The ITRF2005 combination involving 84 co‐location sites revealed a scale inconsistency of 1 ppb (6.3 mm at the equator), at epoch 2000.0, and 0.08 ppb/yr between the SLR and VLBI long‐term solutions as obtained by the stacking of their respective time series. Possible causes of this inconsistency may include the poor SLR and VLBI networks and their co‐locations, local tie uncertainties, systematic effects and possible inconsistent model corrections used in the data analysis of both techniques. For the first time of the ITRF history, the ITRF2005 rigorous combination provides self‐consistent series of EOPs, including Polar Motion from VLBI and satellite techniques and Universal Time and Length of Day from VLBI only. A velocity field of 152 sites with an error less than 1.5 mm/yr is used to estimate absolute rotation poles of 15 tectonic plates that are consistent with the ITRF2005 frame. This new absolute plate motion model supersedes and significantly improves that of the ITRF2000 which involved six major tectonic plates.

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Velocity field of GPS stations in the Taiwan area

1997-06-01

Shui-Beih Yu , Horng‐Yue Chen , Long‐Chen Kuo

GPS meteorology: Remote sensing of atmospheric water vapor using the global positioning system

1992-10-20

Michael Bevis , Steven Businger , T. A. Herring +3 more

We present a new approach to remote sensing of water vapor based on the global positioning system (GPS). Geodesists and geophysicists have devised methods for estimating the extent to which … We present a new approach to remote sensing of water vapor based on the global positioning system (GPS). Geodesists and geophysicists have devised methods for estimating the extent to which signals propagating from GPS satellites to ground‐based GPS receivers are delayed by atmospheric water vapor. This delay is parameterized in terms of a time‐varying zenith wet delay (ZWD) which is retrieved by stochastic filtering of the GPS data. Given surface temperature and pressure readings at the GPS receiver, the retrieved ZWD can be transformed with very little additional uncertainty into an estimate of the integrated water vapor (IWV) overlying that receiver. Networks of continuously operating GPS receivers are being constructed by geodesists, geophysicists, government and military agencies, and others in order to implement a wide range of positioning capabilities. These emerging GPS networks offer the possibility of observing the horizontal distribution of IWV or, equivalently, precipitable water with unprecedented coverage and a temporal resolution of the order of 10 min. These measurements could be utilized in operational weather forecasting and in fundamental research into atmospheric storm systems, the hydrologic cycle, atmospheric chemistry, and global climate change. Specially designed, dense GPS networks could be used to sense the vertical distribution of water vapor in their immediate vicinity. Data from ground‐based GPS networks could be analyzed in concert with observations of GPS satellite occultations by GPS receivers in low Earth orbit to characterize the atmosphere at planetary scale.

Geodesy by radio interferometry: Effects of atmospheric modeling errors on estimates of baseline length

1985-11-01

J. L. Davis , T. A. Herring , I. I. Shapiro +2 more

Analysis of very long baseline interferometry data indicates that systematic errors in prior estimates of baseline length, of order 5 cm for ∼ 8000‐km baselines, were due primarily to mismodeling … Analysis of very long baseline interferometry data indicates that systematic errors in prior estimates of baseline length, of order 5 cm for ∼ 8000‐km baselines, were due primarily to mismodeling of the electrical path length of the troposphere and mesosphere (“atmospheric delay”). Here we discuss observational evidence for the existence of such errors in the previously used models for the atmospheric delay and develop a new “mapping” function for the elevation angle dependence of this delay. The delay predicted by this new mapping function differs from ray trace results by less than ∼ 5 mm, at all elevations down to 5° elevation, and introduces errors into the estimates of baseline length of ≲ 1 cm, for the multistation intercontinental experiment analyzed here.

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Observing Earth's atmosphere with radio occultation measurements using the Global Positioning System

1997-10-01

E. R. Kursinski , G. A. Hajj , J. T. Schofield +2 more

The implementation of the Global Positioning System (GPS) network of satellites and the development of small, high‐performance instrumentation to receive GPS signals have created an opportunity for active remote sounding … The implementation of the Global Positioning System (GPS) network of satellites and the development of small, high‐performance instrumentation to receive GPS signals have created an opportunity for active remote sounding of the Earth's atmosphere by radio occultation at comparatively low cost. A prototype demonstration of this capability has now been provided by the GPS/MET investigation. Despite using relatively immature technology, GPS/MET has been extremely successful [ Ware et al. , 1996; Kursinski et al. , 1996], although there is still room for improvement. The aim of this paper is to develop a theoretical estimate of the spatial coverage, resolution, and accuracy that can be expected for atmospheric profiles derived from GPS occultations. We consider observational geometry, attenuation, and diffraction in defining the vertical range of the observations and their resolution. We present the first systematic, extensive error analysis of the spacecraft radio occultation technique using a combination of analytical and simulation methods to establish a baseline accuracy for retrieved profiles of refractivity, geopotential, and temperature. Typically, the vertical resolution of the observations ranges from 0.5 km in the lower troposphere to 1.4 km in the middle atmosphere. Results indicate that useful profiles of refractivity can be derived from ∼60 km altitude to the surface with the exception of regions less than 250 m in vertical extent associated with high vertical humidity gradients. Above the 250 K altitude level in the troposphere, where the effects of water are negligible, sub‐Kelvin temperature accuracy is predicted up to ∼40 km depending on the phase of the solar cycle. Geopotential heights of constant pressure levels are expected to be accurate to ∼10 m or better between 10 and 20 km altitudes. Below the 250 K level, the ambiguity between water and dry atmosphere refractivity becomes significant, and temperature accuracy is degraded. Deep in the warm troposphere the contribution of water to refractivity becomes sufficiently large for the accurate retrieval of water vapor given independent temperatures from weather analyses [ Kursinski et al. , 1995]. The radio occultation technique possesses a unique combination of global coverage, high precision, high vertical resolution, insensitivity to atmospheric particulates, and long‐term stability. We show here how these properties are well suited for several applications including numerical weather prediction and long‐term monitoring of the Earth's climate.

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Understanding GPS : principles and applications

1996-01-01

Elliott Kaplan

Fundamentals of Satellite Navigation. GPS Systems Segments. GPS Satellite Signal Characteristics and Message Formats. Satellite Signal Acquisitions and Tracking. Effects of RF Interference on GPS Satellite Signal Receiver Tracking. Performance … Fundamentals of Satellite Navigation. GPS Systems Segments. GPS Satellite Signal Characteristics and Message Formats. Satellite Signal Acquisitions and Tracking. Effects of RF Interference on GPS Satellite Signal Receiver Tracking. Performance of Standalone GPS. Differential GPS. Integration of GPS with other Sensors. Galileo. The Russian GLONASS, Chinese Bediou, and Japanese QZSS Systems. GNSS Markets and Applications.

The Westerbork Northern Sky Survey (WENSS)

1997-08-01

R. Rengelink , Yuan Tang , A. G. de Bruyn +4 more

The Westerbork Northern Sky Survey (WENSS) is a low-frequency radio survey that will cover the whole sky north of at a wavelength of 92 cm to a limiting flux density … The Westerbork Northern Sky Survey (WENSS) is a low-frequency radio survey that will cover the whole sky north of at a wavelength of 92 cm to a limiting flux density of approximately 18 mJy (). This survey has a resolution of and a positional accuracy for strong sources of . Here we present a source list comprising 11 299 sources and maps of 120 extended sources for a 570 square degree region around the north ecliptic pole, the so-called mini-survey. We discuss the errors and reliability of the source parameters and the completeness of the survey.

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The International GNSS Service in a changing landscape of Global Navigation Satellite Systems

2009-02-18

J. Dow , R. E. Neilan , Chris Rizos

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Noise in GPS coordinate time series

1999-02-10

Ailin Mao , C. G. A. Harrison , Timothy H. Dixon

We assess the noise characteristics in time series of daily position estimates for 23 globally distributed Global Positioning System (GPS) stations with 3 years of data, using spectral analysis and … We assess the noise characteristics in time series of daily position estimates for 23 globally distributed Global Positioning System (GPS) stations with 3 years of data, using spectral analysis and Maximum Likelihood Estimation. A combination of white noise and flicker noise appears to be the best model for the noise characteristics of all three position components. Both white and flicker noise amplitudes are smallest in the north component and largest in the vertical component. The white noise part of the vertical component is higher for tropical stations (±23° latitude) compared to midlatitude stations. Velocity error in a GPS coordinate time series may be underestimated by factors of 5–11 if a pure white noise model is assumed.

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An Automatic Editing Algorithm for GPS data

1990-03-01

Geoffrey Blewitt

An algorithm has been developed to edit automatically Global Positioning System data such that outlier deletion, cycle slip identification and correction are independent of clock instability, selective availability, receiver–satellite kinematics, … An algorithm has been developed to edit automatically Global Positioning System data such that outlier deletion, cycle slip identification and correction are independent of clock instability, selective availability, receiver–satellite kinematics, and tropospheric conditions. This algorithm, called TurboEdit, operates on undifferenced, dual frequency carrier phase data, and requires (1) the use of P code pseudorange data and (2) a smoothly varying ionospheric electron content. The latter requirement can be relaxed if the analysis software incorporates ambiguity resolution techniques to estimate unresolved cycle slip parameters. TurboEdit was tested on the large data set from the CASA Uno experiment, which contained over 2500 cycle slips. Analyst intervention was required on 1% of the station–satellite passes, almost all of these problems being due to difficulties in extrapolating variations in the ionospheric delay. The algorithm is presently being adapted for real time data editing in the Rogue receiver for continuous monitoring applications.

GPS Meteorology: Mapping Zenith Wet Delays onto Precipitable Water

1994-03-01

Michael Bevis , Steven Businger , Steven Chiswell +4 more

Emerging networks of Global Positioning System (GPS) receivers can be used in the remote sensing of atmospheric water vapor. The time-varying zenith wet delay observed at each GPS receiver in … Emerging networks of Global Positioning System (GPS) receivers can be used in the remote sensing of atmospheric water vapor. The time-varying zenith wet delay observed at each GPS receiver in a network can be transformed into an estimate of the precipitable water overlying that receiver. This transformation is achieved by multiplying the zenith wet delay by a factor whose magnitude is a function of certain constants related to the refractivity of moist air and of the weighted mean temperature of the atmosphere. The mean temperature varies in space and time and must be estimated a priori in order to transform an observed zenith wet delay into an estimate of precipitable water. We show that the relative error introduced during this transformation closely approximates the relative error in the predicted mean temperature. Numerical weather models can be used to predict the mean temperature with an rms relative error of less than 1%.

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ITRF2014: A new release of the International Terrestrial Reference Frame modeling nonlinear station motions

2016-07-18

Z. Altamimi , Paul Rebischung , Laurent Métivier +1 more

Abstract For the first time in the International Terrestrial Reference Frame (ITRF) history, the ITRF2014 is generated with an enhanced modeling of nonlinear station motions, including seasonal (annual and semiannual) … Abstract For the first time in the International Terrestrial Reference Frame (ITRF) history, the ITRF2014 is generated with an enhanced modeling of nonlinear station motions, including seasonal (annual and semiannual) signals of station positions and postseismic deformation for sites that were subject to major earthquakes. Using the full observation history of the four space geodetic techniques (very long baseline interferometry (VLBI), satellite laser ranging (SLR), Global Navigation Satellite Systems (GNSS), and Doppler orbitography and radiopositioning integrated by satellite (DORIS)), the corresponding international services provided reprocessed time series (weekly from SLR and DORIS, daily from GNSS, and 24 h session‐wise from VLBI) of station positions and daily Earth Orientation Parameters. ITRF2014 is demonstrated to be superior to past ITRF releases, as it precisely models the actual station trajectories leading to a more robust secular frame and site velocities. The ITRF2014 long‐term origin coincides with the Earth system center of mass as sensed by SLR observations collected on the two LAGEOS satellites over the time span between 1993.0 and 2015.0. The estimated accuracy of the ITRF2014 origin, as reflected by the level of agreement with the ITRF2008 (both origins are defined by SLR), is at the level of less than 3 mm at epoch 2010.0 and less than 0.2 mm/yr in time evolution. The ITRF2014 scale is defined by the arithmetic average of the implicit scales of SLR and VLBI solutions as obtained by the stacking of their respective time series. The resulting scale and scale rate differences between the two solutions are 1.37 (±0.10) ppb at epoch 2010.0 and 0.02 (±0.02) ppb/yr. While the postseismic deformation models were estimated using GNSS/GPS data, the resulting parametric models at earthquake colocation sites were applied to the station position time series of the three other techniques, showing a very high level of consistency which enforces more the link between techniques within the ITRF2014 frame. The users should be aware that the postseismic deformation models are part of the ITRF2014 products, unlike the annual and semiannual signals, which were estimated internally with the only purpose of enhancing the velocity field estimation of the secular frame.

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The Multi-GNSS Experiment (MGEX) of the International GNSS Service (IGS) – Achievements, prospects and challenges

2017-01-17

Oliver Montenbruck , Peter Steigenberger , Lars Prange +7 more

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Springer Handbook of Global Navigation Satellite Systems

2017-01-01

P. J. G. Teunissen , Oliver Montenbruck

Resolution of GPS carrier-phase ambiguities in Precise Point Positioning (PPP) with daily observations

2007-10-22

Maorong Ge , G. Gendt , Markus Rothacher +2 more

GNSS-Global Navigation Satellite Systems: GPS, GLONASS, Galileo, and more

2008-07-01

Bernhard Hofmann-Wellenhof , Herbert Lichtenegger , Elmar Wasle

Reference systems.- Satellite orbits.- Satellite signals.- Observables.- Mathematical models for positioning.- Data processing.- Data transformation.- GPS.- Glonass.- Galileo.- More on GNSS.- Applications.- Conclusion and outlook. Reference systems.- Satellite orbits.- Satellite signals.- Observables.- Mathematical models for positioning.- Data processing.- Data transformation.- GPS.- Glonass.- Galileo.- More on GNSS.- Applications.- Conclusion and outlook.

A survey of GNSS receiver autonomous integrity monitoring: Research status and opportunities

2025-06-25

Zhen Huang , Weihua Mou , Hui Sun +3 more | Frontiers in Physics

Integrity monitoring is crucial in applications closely related to the safety of human life and property, such as aviation, maritime navigation, autonomous driving, and rail transportation. Receiver autonomous integrity monitoring … Integrity monitoring is crucial in applications closely related to the safety of human life and property, such as aviation, maritime navigation, autonomous driving, and rail transportation. Receiver autonomous integrity monitoring (RAIM) has attracted significant attention due to its comprehensive monitoring coverage and fast alerting capability. The paper provides a comprehensive review of RAIM algorithms for global navigation satellite system (GNSS) positioning applications. The parameters related to integrity assessment and typical fault detection and exclusion methods are reviewed, and RAIM is categorized into three types of methods: error probability distribution model-based, set representation-based, and machine learning-based. The latest state-of-the-art research, along with the strengths and shortcomings of each type of method, is presented for each type. The opportunities for the future development of RAIM are analyzed in the light of current challenges and existing results, aiming to promote further research and provide effective assurance for GNSS integrity.

High-precision deformation monitoring and intelligent early warning for wellbore based on BDS/GNSS

2025-06-23

Li Jiang , Lei Dai , Keke Xu +4 more | PLoS ONE

To address the complex deformation of wellbores influenced by surrounding coal mining operations, this study employed an improved modified least-squares ambiguity decorrelation (MLAMBDA) algorithm based on the double-difference model for … To address the complex deformation of wellbores influenced by surrounding coal mining operations, this study employed an improved modified least-squares ambiguity decorrelation (MLAMBDA) algorithm based on the double-difference model for high-frequency dynamic computation of Bei Dou System and Global Navigation Satellite System (BDS/GNSS) observation data. A quantitative analysis was conducted on the performance of various combinations of BDS/GNSS in wellbore deformation monitoring, and the effects of different baseline lengths on the monitoring results were evaluated. Based on the high-precision deformation monitoring sequences, an intelligent early warning model for wellbore deformation was established using the deep learning Bi-LSTM algorithm. The results indicate that the monitoring accuracy of the BDS/GNSS multi-system combination in the E, N and U directions is within 2 mm, with all three directions outperforming the results obtained from a single Global Position System (GPS) system. As the baseline length increased from 1 km to 6 km, the accuracy in the E, N, and U directions decreased by 15.8%, 16.0%, and 5.6%, respectively. Within a 6 km range, the horizontal accuracy remains better than 3 mm, while the vertical accuracy is better than 6 mm, meeting the requirements for wellbore deformation monitoring. The early warning model can flexibly adapt to the deformation conditions at different sites and the various disturbances encountered, effectively capturing the complex nonlinear time-varying characteristics of the observation time series. The prediction of future results for one month based on one year of observation sequences achieves an accuracy better than mm, providing a safeguard for safe production in mines. This research method can also be extended to use BDS/GNSS for hourly level high-precision deformation monitoring and early warning of major engineering infrastructure such as bridges, dams, and high-speed railway systems.

Automated monitoring of road surfaces taking into account the correction of tropospheric delays of satellite navigation signals

2025-06-22

K. Badanis | Vestnik of Samara State Technical University Technical Sciences Series

The article considers the development of an automated road surface monitoring subsystem taking into account the correction of tropospheric delays of satellite navigation signals. Global and regional tropospheric models recommended … The article considers the development of an automated road surface monitoring subsystem taking into account the correction of tropospheric delays of satellite navigation signals. Global and regional tropospheric models recommended by ICAO SARPS and their application to improve the accuracy of navigation measurements are presented. The block diagram of the hardware of the subsystem, including the MSP432P401R microcontroller, acceleration sensors and a GPS module, is described, and the process of developing a prototype is detailed. The results of the work demonstrate the possibility of integrating complex tropospheric delay models into the monitoring subsystem to improve the accuracy of data and the efficiency of road surface assessment. The proposed approach to tropospheric delay correction allows to increase the stability and reliability of coordinate determinations in a changing environment. The developed hardware platform ensures reliable data collection and processing in real time, which makes it suitable for use in road monitoring systems in various climatic conditions, as well as for integration into a smart city system. Particular attention is paid to the adaptation of tropospheric delay models to specific regional conditions, which allows for increasing the reliability and accuracy of the data obtained.

ML-test: validating machine learning for GNSS integer ambiguity resolution in quad-constellation dual-frequency observations of Hong Kong

2025-06-22

Yanqing Hou , Yining Shi , Xuan Chen +1 more | GPS Solutions

Joint Spoofing Detection Algorithm Based on Dual Control Charts and Robust Estimation

2025-06-20

Lunlong Zhong , Yuan Xu , Wenjing Yue | Electronics

To address the issue that existing GNSS spoofing detection methods are not suitable for intermittent minor spoofing detection and spoofing duration identification, this paper theoretically analyzes the shortcomings of existing … To address the issue that existing GNSS spoofing detection methods are not suitable for intermittent minor spoofing detection and spoofing duration identification, this paper theoretically analyzes the shortcomings of existing detection algorithms in terms of minor spoofing termination detection performance, and proposes comprehensively utilizing two types of control charts and robust estimation to detect the spoofing end moment, laying a foundation for spoofing duration identification and intermittent minor spoofing detection. The Shewhart control chart-based spoofing detection algorithm (M1) is proposed to achieve rapid spoofing termination detection, serving as one of the baseline algorithms for the joint algorithm. The strengths and weaknesses of the two baseline algorithms (M1 and existing EWMA control chart and robust estimation-based detection algorithm (M2)) in minor spoofing detection are analyzed. Under the robust estimation mechanism, a joint spoofing detection metric that can effectively indicate spoofing termination is constructed by combining their respective spoofing test statistics; then, anomaly detection on the joint detection metric is performed based on sample quantiles to identify the spoofing end moment. The experimental results under various typical abrupt spoofing and slowly varying spoofing scenarios demonstrate that the proposed joint spoofing detection algorithm based on dual control charts and robust estimation satisfies the spoofing alert time requirements specified by the International Civil Aviation Organization (ICAO) for the cruise phase. Compared with existing detection algorithms, the joint algorithm maintains excellent spoofing initiation detection performance while significantly improving both the speed and accuracy of spoofing termination detection. This effectively integrates the advantages of the two baseline algorithms and compensates for their individual limitations when operating independently. Upon timely and effective detection of the start and end moments of minor spoofing, it becomes possible to achieve spoofing duration identification and intermittent minor spoofing detection.

Evaluating stochastic models for estimating site velocity from daily and weekly GNSS time series in the stable region of the South American plate

2025-06-20

Haroldo Antonio Marques , Lucas Gonzales Lima Pereira Calado , João Francisco Galera Monico +3 more | Journal of Applied Geodesy

Abstract Accurate estimation of GNSS station velocities requires a precise characterization of stochastic noise in coordinate time series. This study evaluates stochastic models for estimating site velocities using weekly network … Abstract Accurate estimation of GNSS station velocities requires a precise characterization of stochastic noise in coordinate time series. This study evaluates stochastic models for estimating site velocities using weekly network and daily PPP GNSS solutions from 74 stations in the stable South American mid-plate. The functional model incorporated seasonal components, while the stochastic model was based on noise variance estimates. The Non-Negative Least Squares Variance Component Estimation method was applied to estimate noise amplitudes, classifying noise as a combination of white and colored components. Additionally, the spectral index was refined using Maximum Likelihood Estimation. Results show that most time series are best described by a combination of white and flicker noise, with differences in spectral properties between weekly and daily solutions. The impact of these models on velocity uncertainties was assessed, showing that neglecting an appropriate noise model can lead to overestimated uncertainties. These findings contribute to improving GNSS-based velocity estimations for geodynamic studies.

Breaking the Cyclic Prefix Barrier: Zero-Padding Correlation Enables Centimeter-Accurate LEO Navigation via 5G NR Signals

2025-06-20

Lingyu Deng , Yikang Yang , Jiangang Ma +3 more | Remote Sensing

Low Earth orbit (LEO) satellites offer a revolutionary potential for positioning, navigation, and timing (PNT) services due to their stronger signal power and rapid geometric changes compared to traditional global … Low Earth orbit (LEO) satellites offer a revolutionary potential for positioning, navigation, and timing (PNT) services due to their stronger signal power and rapid geometric changes compared to traditional global navigation satellite systems (GNSS). However, dedicated LEO navigation systems face high costs, so opportunity navigation based on LEO satellites is a potential solution. This paper presents an orthogonal frequency division multiplexing (OFDM)-based LEO navigation system and analyzes its navigation performance. We use 5G new radio (NR) as the satellite transmitting signal and introduce the NR signal components that can be used for navigation services. The LEO NR system and a novel zero-padding correlation (ZPC) are introduced. This ZPC receiver can eliminate cyclic prefix (CP) and inter-carrier interference, thereby improving tracking accuracy. The power spectral density (PSD) for the NR navigation signal is derived, followed by a comprehensive analysis of tracking accuracy under different NR configurations (bandwidth, spectral allocation, and signal components). An extended Kalman filter (EKF) is proposed to fuse pseudorange and pseudorange rate measurements for real-time positioning. The simulations demonstrate an 80% improvement in ranging precision (3.0–4.5 cm) and 88.3% enhancement in positioning accuracy (5.61 cm) compared to conventional receivers. The proposed ZPC receiver can achieve centimeter-level navigation accuracy. This work comprehensively analyzes the navigation performance of the LEO NR system and provides a reference for LEO PNT design.

Accuracy analysis of BDS-3 PPP-B2b precise point positioning over Sri Lanka

2025-06-20

Achila D.G.R. Achila , Prasanna H.M.I. Prasanna | Research Square (Research Square)

<title>Abstract</title> The BeiDou Navigation Satellite System (BDS-3) provides a real-time precise point positioning (PPP) solution with its BDS PPP-B2b signal, which does not rely on local base stations, and therefore … <title>Abstract</title> The BeiDou Navigation Satellite System (BDS-3) provides a real-time precise point positioning (PPP) solution with its BDS PPP-B2b signal, which does not rely on local base stations, and therefore has become a promising solution for GNSS-based surveying applications in real-time. The present study assesses the accuracy, convergence duration and environmental impact of PPP-B2b in the case of Sri Lanka in comparison with traditional post-processed GNSS approaches such as Differential Global Navigation Satellite System (DGNSS), Single Point Positioning (SPP), and PPP-Static. The study was carried out in three different sites Maharagama (open field), Thalangama (semi-urban, adjacent to a body of water) and Diyagama (dense urban area) to evaluate PPP-B2b’s performance on varying terrain-different environmental conditions. The results demonstrate that PPP-B2b allows sub-meter positioning with an average horizontal accuracy of 0.4 m and vertical accuracy of 2.3 m, and the open-field site (Maharagama) experiences the best accuracy due to geomorphological factors and complete satellite visibility, whereas Thalangama gave moderate deviations due to multipath generated from reflections on the water. Diyagama site had the least accuracy, because of signal obstruction, urban canyon and increasing the convergence time. Even though PPP-B2b is a low-cost and independent solution that does not require terrestrial infrastructure, it is limited by several factors that result in high convergence time (typically up to 10-15 minutes) and errors generated through multipath and ionospheric delay. These limitations notwithstanding, satellite-based PPP services such as PPP-B2b are still viable options for real-time positioning and atmospheric applications that do not require internet connectivity.

Simulation of GNSS Dilution of Precision for Automated Mobility Along the MODI Project Road Corridor Using High-Resolution Digital Surface Models

2025-06-19

Kristian Breili , Carl William Lund | Geomatics

Horizontal dilution of precision (HDOP) is a widely used quality indicator of Global Navigation Satellite System (GNSS) positioning, considering only satellite geometry. In this study, HDOP was simulated using GNSS … Horizontal dilution of precision (HDOP) is a widely used quality indicator of Global Navigation Satellite System (GNSS) positioning, considering only satellite geometry. In this study, HDOP was simulated using GNSS almanacs and high-resolution digital surface models (DSMs) along three European road sections: Oslo— Svinesund Bridge (Norway); Hamburg city center (Germany); and Rotterdam—Dutch–German border (Netherlands). This study was accomplished as part of the MODI project, which is a cross-border initiative to accelerate Cooperative, Connected, and Automated Mobility (CCAM). Our analysis revealed excellent or good overall GNSS performance in the study areas, particularly on highway sections with 99–100% of study points having a median HDOP that is categorized as excellent (HDOP < 2) or good (HDOP < 5). However, the road section in Hamburg’s city center presents challenges. When GPS is used alone, 8% of the study points experience weak or poor HDOP, and there are study points where the system is available (HDOP < 5) less than 50% of the time. Combining GNSS constellations significantly improved system availability, reaching 95% for 99% of the study points in Hamburg. To validate our simulations, we compared results with GNSS observations from a survey vehicle in Hamburg. Initial low correlation was attributed to the reception of signals from non-line-of-sight satellites. By excluding satellites with low signal-to-noise ratios, the correlation increased significantly, and reasonable agreement was obtained. We also examined the impact of using a 10 m DSM instead of a 1 m DSM in Hamburg. While the coarser spatial resolution offers computational benefits, it may miss critical details for accurate assessment of satellite visibility.

An Investigation into the Correlation Between Signal Path Variation and Structural Deformation in Large Radio Telescopes

2025-06-18

Lingling Wang , Jinqing Wang , Linfeng Yu +2 more | Research Square (Research Square)

<title>Abstract</title> Signal path variation in radio telescopes is a critical factor affecting observational accuracy, with structural deformation-induced path changes representing a primary error source. In Very Long Baseline Interferometry (VLBI) … <title>Abstract</title> Signal path variation in radio telescopes is a critical factor affecting observational accuracy, with structural deformation-induced path changes representing a primary error source. In Very Long Baseline Interferometry (VLBI) observations using large telescopes, such deformations introduce signal delays that compromise measurement precision, especially in high-accuracy applications like geodesy and spacecraft tracking. This study systematically investigates signal path variation patterns induced by structural deformations through theoretical analysis and experimental validation, focusing on four key mechanisms: gravitational deformation of main/sub-reflectors, thermal expansion/contraction of the main reflector, offset-axis structural configurations, and antenna pointing errors.

An Investigation of GNSS Radio Occultation Data Pattern for Temperature Monitoring and Analysis over Africa

2025-06-18

Usman Sa’i Ibrahim , Kamorudeen Aleem , Tajul Ariffin Musa +4 more | NDT

Climate change monitoring and analysis is a critical task that involves the consideration of both spatial and temporal dimensions. Theimproved spatial distribution of the global navigation satellite system (GNSS) ground-based … Climate change monitoring and analysis is a critical task that involves the consideration of both spatial and temporal dimensions. Theimproved spatial distribution of the global navigation satellite system (GNSS) ground-based Continuous Operating Reference (COR) stations can lead to enhanced results when coupled with a continuous flow of data over time. In Africa, a significant number of COR stations do not operate continuously and lack collocation with meteorological sensors essential for climate studies. Consequently, Africa faces challenges related to inadequate spatial distribution and temporal data flow from GNSS ground-based stations, impacting climate change monitoring and analysis. This research delves into the pattern of GNSS radio occultation (RO) data across Africa, addressing the limitations of the GNSS ground-based data for climate change research. The spatial analysis employed Ripley’s F-, G-, K-, and L-functions, along with calculations of nearest neighbour and Kernel density. The analysis yielded a Moran’s p-value of 0.001 and a Moran’s I-value approaching 1.0. For temporal analysis, the study investigated the data availability period of selected GNSS RO missions. Additionally, it examined seasonal temperature variations from May 2001 to May 2023, showcasing alignment with findings from other researchers worldwide. Hence, this study suggests the utilisation of GNSS RO missions/campaigns like METOP and COSMIC owing to their superior spatial and temporal resolution.

GPS Precise Point Position Technique’s Usability for Improving Geodesy Applications

2025-06-17

Somnath Mahato , Aravindh Subramanian Subramanian , Debipriya Dutta | National Academy Science Letters

LSTM-based comprehensive evaluation method of GNSS observation quality for robust RTK positioning

2025-06-17

Yuying Li , Jinguang Jiang , Jiaji Wu +5 more | Measurement Science and Technology

Abstract Real-time and accurate GNSS signal quality analysis is a prerequisite for improving the performance of GNSS RTK positioning in complex scenarios. Its core lies in ensuring the reliability and … Abstract Real-time and accurate GNSS signal quality analysis is a prerequisite for improving the performance of GNSS RTK positioning in complex scenarios. Its core lies in ensuring the reliability and stability of high-precision positioning through a multi-dimensional signal characteristic evaluation system and RTK robust technology. In view of the fact that the evaluation of GNSS data quality in dynamic and complex scenarios depends mostly on regular threshold determination or independent index analysis, which leads to problems such as static modeling defects, isolated analysis misjudgment, and insufficient real-time, a multi-index fusion evaluation method of GNSS satellite observation quality in urban dynamic and complex environments based on LSTM is proposed. On the basis of adaptive unsupervised clustering, the labels of each cluster data are reordered according to the RTK positioning accuracy, and the LSTM neural network is used to accurately classify the unmodeled data to achieve a comprehensive evaluation and classification of GNSS satellite observation quality. When compared with other machine learning algorithms, LSTM's performance in GPS and BDS data quality classification is stable at the best, and the accuracy of GPS and BDS in the test set is 96.97% and 98.51%, respectively. The advantages and disadvantages of the classification are introduced into the execution judgment of the robust Kalman filter. The experimental results show that the RTK positioning accuracy that takes into account the LSTM data quality classification is better than that is not taken into account.&#xD;

GPS and Galileo Precise Point Positioning Performance with Tropospheric Estimation Using Different Products: BRDM, RTS, HAS, and MGEX

2025-06-17

Damian Kiliszek | Remote Sensing

The performance of Precise Point Positioning (PPP) using different Global Navigation Satellite System (GNSS) product sets, including broadcast ephemerides, International GNSS Service Real-Time Service (IGS-RTS) corrections, Galileo High Accuracy Service … The performance of Precise Point Positioning (PPP) using different Global Navigation Satellite System (GNSS) product sets, including broadcast ephemerides, International GNSS Service Real-Time Service (IGS-RTS) corrections, Galileo High Accuracy Service (HAS) corrections, and precise products from the Center for Orbit Determination in Europe (CODE) Multi-GNSS Experiment (MGEX), has been evaluated. The availability of solutions, convergence time, position accuracy and Zenith Tropospheric Delay (ZTD) estimation across these products were analyzed using simulated real-time and postprocessing static modes, using data from globally distributed stations with a 1 s observation interval. The results indicate that precise products from the MGEX provide the highest accuracy, achieving centimeter-level precision in post-processed mode. Real-time simulated solutions, such as HAS and IGS-RTS, deliver promising results, with Galileo HAS meeting its target accuracy of 20 cm horizontally and 40 cm vertically and a convergence time under 5 min. However, Global Positioning System (GPS) performance within HAS is limited by a significantly lower correction availability—around 67% on average compared to over 95% for Galileo—which negatively impacts PPP performance. ZTD estimation results show that real-time services (HAS, IGS-RTS) achieved errors within 1–3 cm, sufficient for meteorological applications. This study highlights the growing importance of HAS in real-time positioning applications and suggests further improvements in GPS for enhanced performance.

Global Navigation Satellite System Spoofing Attack Detection Using Receiver Independent Exchange Format Data and Long Short-Term Memory Algorithm

2025-06-17

Alexandru-Gabriel Romaniuc , Vlad-Cosmin Vasile , Monica-Elena Borda | Information

Global Navigation Satellite Systems (GNSS) are widely used for positioning, navigation, and timing (PNT) applications, making them a critical infrastructure component. However, GNSS signals and receivers are vulnerable to several … Global Navigation Satellite Systems (GNSS) are widely used for positioning, navigation, and timing (PNT) applications, making them a critical infrastructure component. However, GNSS signals and receivers are vulnerable to several attacks that can expose the users to serious threats. The GNSS spoofing attack, for example, is one of the most widespread in this domain and is used to manipulate positioning and timing data by transmitting counterfeit signals. Thus, in this study, we propose a method for analyzing and detecting anomalies in RINEX observation data that is associated with spoofing attacks. The proposed method is based on Long Short-Term Memory (LSTM) networks and focuses on the observation parameters defined by the RINEX standard, which are computed in the Measurements block and subsequently used in the Navigation block of a GNSS receiver architecture. Attack detection involves processing GNSS observation codes and learning the temporal dependencies necessary to identify anomalies associated with GNSS signal spoofing. During the testing phase, the proposed method was applied to GNSS observation codes affected by spoofing, using an LSTM-based reconstruction approach. An ensemble strategy across grouped observation codes was used to identify temporal inconsistencies indicative of anomalies.

Enhancing PPP-RTK performance at low latitudes through mitigation of ionospheric scintillation effects

2025-06-17

Xin Li , Bo Wang , Xingxing Li +2 more | GPS Solutions

Basis Recovery Method for Ionospheric Delay Corrections in PPP-RTK Model with Recommendations for Interpolation Reference Station Number Selection

2025-06-16

Siyao Wang , Runzhi Zhang , Rui Tu +2 more | Remote Sensing

Precise point positioning–real-time kinematic (PPP-RTK) enables users to achieve rapid centimeter-level absolute positioning accuracy within a few epochs. The interpolation of ionospheric delay corrections at the user end, extracted from … Precise point positioning–real-time kinematic (PPP-RTK) enables users to achieve rapid centimeter-level absolute positioning accuracy within a few epochs. The interpolation of ionospheric delay corrections at the user end, extracted from reference stations, constitutes a key aspect of the process, which depends not solely on the precision of the interpolation model. This study investigates the recommended number of selected reference stations and proposes a method to mitigate the potential loss of observations due to missing ionospheric corrections. According to the experimental results, the number of reference stations should be determined based on the reference network size. Under normal conditions (terrain is relatively flat and the atmospheric conditions are inactive) where reference stations are approximately evenly distributed in all directions, and using low-order surface interpolation model, for networks with 50 km spacing, four or five reference stations are recommended, while for 100 km networks, six or seven stations are enough to calculate precise corrections. Adding more stations beyond these thresholds provides limited improvement in interpolation accuracy and increases the communication load. In addition, an interpolation basis recovery algorithm is proposed to preserve otherwise excluded satellite observations through intelligent handling of correction data gaps at individual reference stations. Experimental validation demonstrates that the recovered ionospheric delay corrections obtained through the algorithm deviate from the ground-truth interpolated values of no more than ±1 cm, an accuracy level deemed adequate for PPP-RTK applications. Furthermore, approximately 3% of the observations, which would otherwise have been discarded due to the missing corrections from a specific reference station, are retained by the algorithm.

Düşük Maliyetli GNSS ve IMU Verilerinin Entegrasyonu: Uygulama Örneği

2025-06-16

Ramazan Alper Kuçak , Aysan Şahin | International Journal of Advances in Engineering and Pure Sciences

Günümüz teknolojik gelişmeleri, konum belirleme sistemlerinin mühendislik uygulamaları ve disiplinler arası alanlardaki kritik rolünü vurgulamaktadır. Light Detection and Ranging (LiDAR), Inertial Measurement Unit (IMU) ve Global Navigation Satellite System (GNSS) … Günümüz teknolojik gelişmeleri, konum belirleme sistemlerinin mühendislik uygulamaları ve disiplinler arası alanlardaki kritik rolünü vurgulamaktadır. Light Detection and Ranging (LiDAR), Inertial Measurement Unit (IMU) ve Global Navigation Satellite System (GNSS) tabanlı sistemler, geomatik mühendisliği, akıllı şehir uygulamaları, insansız hava araçları, otonom araçlar ve robotik sistemler gibi alanlarda yaygın olarak kullanılmaktadır. Ancak, yüksek hassasiyet gereksinimleri ve bütçe kısıtları, düşük maliyetli sistemlerin yeterli doğrulukla veri sağlayamaması nedeniyle kullanımını zorlaştırmaktadır. Bu bağlamda, GNSS ve IMU verilerinin entegrasyonu, maliyet etkin bir çözüm sunarken doğruluğun artırılmasına katkı sağlamaktadır. Bu çalışma, IPhone 13 Pro cihazından elde edilen GNSS ve IMU verilerinin entegrasyonu ile İstanbul’un Bebek semtinde yaklaşık 330 metrelik bir yürüyüş rotası boyunca bir yol haritası oluşturulmasını incelemiştir. MATLAB ortamında gerçekleştirilen analizde, önce Butterworth ve Kalman filtreleme teknikleri uygulanarak veriler işlenmiş, GNSS verilerine %95, IMU verilerine %5 ağırlık verilerek sapmalar minimize edilmiştir. Kalman filtresinin parametreleri optimize edilerek daha doğru sonuçlar elde edilmiştir. Daha sonra, GNSS ağırlığı %98’e çıkarılıp IMU ağırlığı %2’ye düşürülerek farklı bir senaryo uygulanmış, böylece entegre verilerin doğruluğu artırılmıştır. Bu süreçte, GNSS verilerinin yüksek hassasiyeti ile IMU’nun sinyal kaybı durumlarındaki katkısı optimize edilmiştir. Çalışma, düşük maliyetli cihazlardan elde edilen GNSS ve IMU verilerinin uygun algoritmalarla işlenmesiyle yüksek doğrulukta konum belirleme sağlanabileceğini göstermektedir. Ayrıca, bu çalışma IPhone 13 Pro ile elde edilen GNSS ve IMU verilerinin birleştirilmesi açısından ilk defa uygulanmasının yanı sıra, IPhone 13 Pro GNSS verilerine herhangi bir ek anten ya da post-process işlemi ile doğruluk artırma çalışması yapılmadan iki verinin birleştirilmesi açısından literatüre yenilikler katmaktadır. Bu yöntem, düşük bütçeli projeler için maliyet etkin çözümler sunarak mühendislik projelerine önemli bir katkı sağlamaktadır.

Improving smartphone precise positioning based on a new weighting method

2025-06-15

Li Liu , Jun Huang , Xiaopeng Gong +4 more | GPS Solutions

A TDCP-assisted partial ambiguity resolution method for GNSS Real-time kinematic positioning in challenging environment

2025-06-15

Xiaosan Man , Wujiao Dai , Wenkun Yu +3 more | GPS Solutions

Temporal convolutional network based on squeeze-and-excitation module and multi-scale feature fusion for GNSS positioning error correction

2025-06-14

X. Y. Liu , Zuping Tang , Jiaolong Wei | GPS Solutions

Machine learning algorithms for FCB (fractional cycle bias) estimation in PPP ambiguity resolution

2025-06-13

Furkan Karlitepe , Bahattin Erdoğan | Arabian Journal of Geosciences

The potential of observing atmospheric rivers with Global Navigation Satellite System (GNSS) radio occultation

2025-06-12

Bahareh Rahimi , Ulrich Foelsche | Atmospheric measurement techniques

Abstract. Atmospheric rivers (ARs) are comparatively narrow regions in the atmosphere that are responsible for most of the horizontal transport of water vapor in the extratropics, which are responsible for … Abstract. Atmospheric rivers (ARs) are comparatively narrow regions in the atmosphere that are responsible for most of the horizontal transport of water vapor in the extratropics, which are responsible for many extreme precipitation events and flooding at midlatitudes, including Europe and the US. The critical role of ARs in global moisture transport and precipitation dynamics necessitates accurate water vapor measurements for both understanding and forecasting these phenomena. While the integrated water vapor content (IWV) of ARs can be measured well with microwave and infrared sounders, the vertical structure is less well known. In this study, we analyzed whether specific humidity profiles and IWV values from Global Navigation Satellite System Radio Occultation (GNSS-RO) measurements provide additional information for the study of ARs, in particular regarding their vertical structure. The retrieval of water vapor from GNSS-RO data requires background information, which is usually incorporated by the one-dimensional variational method (1D-Var) that combines observations and background in an optimal manner. We compared data from the COSMIC Data Analysis and Archive Center (CDAAC), operated by the University Corporation for Atmospheric Research (UCAR) in Boulder, Colorado, with data from the Wegener Center for Climate and Global Change (WEGC) at the University of Graz, Austria. We found that retrievals from both centers agree very well in the altitude range, where the 1D-Var weights the observations strongly, even if the employed background profiles are very different. This demonstrates that GNSS-RO data indeed provide additional vertically resolved information, which was not already contained in the background or in operational analyses. IWV values from CDAAC and WEGC generally agree very well; however, both tend to underestimate the values obtained by Special Sensor Microwave Imager/Sounder (SSMI/S) data, since GNSS-RO profiles do not always reach the lowermost part of the atmosphere, leading to a systematic bias in the IWV data, which decreases with better penetration characteristics of the GNSS-RO data. The results suggest that it is promising to combine the GNSS-RO data – with very high vertical resolution with SSMI/S data – with high horizontal resolution to get a more compete view of the 3D structure of ARs.

Accurate Rainfall Prediction Using GNSS PWV Based on Pre-Trained Transformer Model

2025-06-12

Wenjie Yin , Chen Zhou , Yuan Tian +7 more | Remote Sensing

With an increase in the intensity and frequency of extreme rainfall events, there is a pressing need for accurate rainfall nowcasting applications. In recent years, precipitable water vapor (PWV) data … With an increase in the intensity and frequency of extreme rainfall events, there is a pressing need for accurate rainfall nowcasting applications. In recent years, precipitable water vapor (PWV) data obtained from GNSS observations have been widely used in rainfall prediction. Unlike previous studies mainly focusing on rainfall occurrences, this study proposes a transformer-based model for hourly rainfall prediction, integrating the GNSS PWV and ERA5 meteorological data. The proposed model employs the ProbSparse self-attention to efficiently capture long-range dependencies in time series data, crucial for correlating historical PWV variations with rainfall events. Additionally, the adoption of the DILATE loss function better captures the structural and timing aspects of rainfall prediction. Furthermore, traditional rainfall prediction models are typically trained on datasets specific to one region, which limits their generalization ability due to regional meteorological differences and the scarcity of data in certain areas. Therefore, we adopt a pre-training and fine-tuning strategy using global datasets to mitigate data scarcity in newly deployed GNSS stations, enhancing model adaptability to local conditions. The evaluation results demonstrate satisfactory performance over other methods, with the fine-tuned model achieving an MSE = 3.954, DTW = 0.232, and TDI = 0.101. This approach shows great potential for real-time rainfall nowcasting in a local area, especially with limited data.

Improving GNSS precise point positioning with tropospheric constraints from data-driven numerical weather prediction model

2025-06-12

Yuanfan Deng , Wu Chen , Junsheng Ding +5 more | Geo-spatial Information Science

Towards Geodetic Datum Modernization: A Comparative Study of GNSS Solutions in KGD2002 Using GAMIT/GLOBK and Bernese

2025-06-08

Seung-Jun Lee , Hong‐Sik Yun | Applied Sciences

This study evaluates coordinate consistency in the static Korean Geodetic Datum 2002 (KGD2002) by comparing GNSS station positions derived independently from GAMIT/GLOBK and Bernese software. Using a nationwide network of … This study evaluates coordinate consistency in the static Korean Geodetic Datum 2002 (KGD2002) by comparing GNSS station positions derived independently from GAMIT/GLOBK and Bernese software. Using a nationwide network of approximately 3000 unified geodetic control points (UGCPs), we analyze horizontal coordinate differences (ΔN, ΔE) to identify regional patterns and potential systematic biases. The results indicate that both solutions are closely aligned with the official KGD2002 coordinates, generally within a few millimeters to sub-centimeter levels. However, small regional discrepancies are evident; for example, some provinces exhibit consistent mean northward or southward offsets on the order of 0.1–0.3 cm, and greater dispersions—up to 2 cm—are observed in peripheral regions such as Jeollanam. Notably, the Bernese solution demonstrates slightly tighter agreement, with lower standard deviations compared to GAMIT/GLOBK. The application of two distinct processing strategies within a unified static reference frame is a novel aspect of this study, revealing subtle differences attributable to network geometry, environmental factors, and software modeling approaches. The findings also underscore the limitations of KGD2002’s static nature, particularly its fixed epoch and lack of motion modeling. In response to these issues, this study discusses the rationale for transitioning to a dynamic geodetic reference frame, such as ITRF2020, to improve compatibility with international systems and account for ongoing crustal motions. Overall, the results provide a foundation for the future modernization of Korea’s spatial reference infrastructure and highlight the importance of adopting time-dependent datums in geodetic applications.

Integer ambiguity validation through machine learning for precise point positioning

2025-06-08

Jiang Guo , Jianghui Geng | Satellite Navigation

Abstract The discrimination test of ambiguity resolution, also known as ambiguity validation, is a vital procedure to quantify the reliability of Global Navigation Satellite System (GNSS) ambiguity-fixed solutions. Several well-known … Abstract The discrimination test of ambiguity resolution, also known as ambiguity validation, is a vital procedure to quantify the reliability of Global Navigation Satellite System (GNSS) ambiguity-fixed solutions. Several well-known tests, including the R-ratio, W-ratio, and Ambiguity Dilution of Precision, usually employ empirical thresholds for the discrimination of integer candidates. We aim at improving the reliability of ambiguity validation by integrating these tests using a machine learning model called the Support Vector Model (SVM). The dataset used consists of simulated real-time Precise Point Positioning Ambiguity Resolution (PPP-AR) solutions in 1-day batch. Specifically, the training dataset is derived using the observations from days 1–31 of year 2023, while the testing dataset is generated using the observations from days 153–159 of years 2022 and 2024. The results reveal that the SVM validates PPP-AR at a success rate of 83% for the independent testing dataset. At the same time, the mean error of the convergence time predicted by the SVM is about 1.0 min, whereas that by the R-ratio test up to 5.0 min. A vehicle-borne experiment conducted on day 362 of year 2020 further demonstrates the improvement of this method in a kinematic scenario, with a success rate of 92% compared to 82% with the conventional R-ratio test.

Enhanced Real-Time Onboard Orbit Determination of LEO Satellites Using GPS Navigation Solutions with Signal Transit Time Correction

2025-06-03

Daero Lee , Soon Sik Hwang | Aerospace

Enhanced real-time onboard orbit determination for low-Earth-orbit satellites is essential for autonomous spacecraft operations. However, the accuracy of such systems is often limited by signal propagation delays between GPS satellites … Enhanced real-time onboard orbit determination for low-Earth-orbit satellites is essential for autonomous spacecraft operations. However, the accuracy of such systems is often limited by signal propagation delays between GPS satellites and the user spacecraft. These delays, primarily due to Earth’s rotation and ionospheric effects become particularly significant in high-dynamic LEO environments, leading to considerable errors in range and range rate measurements, and consequently, in position and velocity estimation. To mitigate these issues, this paper proposes a real-time orbit determination algorithm that applies Earth rotation correction and dual-frequency (L1 and L2) ionospheric compensation to raw GPS measurements. The enhanced orbit determination method is processed directly in the Earth-centered Earth-fixed frame, eliminating repeated coordinate transformations and improving integration with ground-based systems. The proposed method employs a reduced-dynamic orbit determination strategy to balance model fidelity and computational efficiency. A predictive correction model is also incorporated to compensate for GPS signal delays under dynamic motion, thereby enhancing positional accuracy. The overall algorithm is embedded within an extended Kalman filter framework, which assimilates the corrected GPS observations with a stochastic process noise model to account for dynamic modeling uncertainties. Simulation results using synthetic GPS measurements, including pseudoranges and pseudorange rates from a dual-frequency spaceborne receiver, demonstrate that the proposed method provides a significant improvement in orbit determination accuracy compared to conventional techniques that neglect signal propagation effects. These findings highlight the importance of performing orbit estimation directly in the Earth-centered, Earth-fixed reference frame, utilizing pseudoranges that are corrected for ionospheric errors, applying reduced-dynamic filtering methods, and compensating for signal delays. Together, these enhancements contribute to more reliable and precise satellite orbit determination for missions operating in low Earth orbit.

LS-VCE based Relative and Absolute Stochastic Modeling: Methods Comparison, Influential Factors Evaluation, and Positioning Validation

2025-06-01

Zhen Li , Jun Tao , Yihao Jiang +4 more | Advances in Space Research

Performance analysis of BDS-3 single-epoch positioning with BDGIM constraints

2025-06-01

Xiaopeng Fan , Xin Liu , Qiuzhao Zhang +4 more | Measurement