Behavior of Broadcast Ionospheric-Delay Models from GPS, Beidou, and Galileo Systems

AbstractThe GNSS observations suffer from different types of errors that could affect the achieved positioning accuracy based on the receiver type used. Single-frequency receivers are widely used worldwide because of its low cost. The ionospheric delay considers the most challenging error for single-frequency GNSS observations. All satellite navigation systems, except GLONASS, are advising their users to correct for the ionospheric delay using a certain model. Those models’ coefficients are sent to users in the system’s navigation message. These models are different in their accuracy and behavior based on its foundation theory as well as the updating rate of their coefficients. The GPS uses Klobuchar model for mitigating the ionospheric delay. BeiDou system (BDS-2) adopts a slightly modified Klobuchar model that resembles GPS ICA (Ionospheric Correction Algorithm) with eight correction parameters but is formulated in a geographic coordinate system with different coefficients in origin and updating rate. Galileo system uses a different model (NeQuick model). This article investigates the behavior of the three models in correcting the ionospheric delay for three stations at different latitudes during 3 months of different states of ionospheric activity, comparing with International GNSS Service-Global Ionospheric Maps (IGS-GIMs). It is advised from this research’s outputs to use the GPS model for mitigating the ionospheric delay in low-latitude regions during the state of low-and medium-activity ionosphere. It is advised to use the BeiDou model for mitigating the ionospheric delay in mid-latitude regions during different states of ionospheric activity. It is advised to use the Galileo model for mitigating the ionospheric delay in high-latitude regions during different states of ionospheric activity. Also, the Galileo model is recommended for mitigating the ionospheric delay for low-latitude regions during the state of high-activity ionosphere.

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High accuracy positioning with low-cost single-frequency GPS system in multipath environments

10.32920/ryerson.14654085.v1 ◽

2021 ◽

Author(s):

Abdulla Al-Naqbi

Keyword(s):

Low Cost ◽

Low Frequency ◽

Ionospheric Delay ◽

Measurement Noise ◽

Single Frequency ◽

International Gnss Service ◽

Phase Measurements ◽

Differential Positioning ◽

The Difference ◽

Gps System

Positioning using low-cost, single-frequency GPS receivers provides an economical solution, but these receivers are subject to biases leading to degradation of the accuracy required. Factors contributing to degradation in the accuracy of low-cost systems are ionospheric delay, multipath, and measurement noise. Unless carefully addressed, these errors distort the ambiguity resolution process, and result in less accurate positioning solutions. However, with the modern hardware improvements, measurement noise is now almost neglibible. Ionospheric delay has been dramatically reduced with the availablity of global or local ionospheric maps produced by various organizations (e.g., International GNSS Service (IGS), and National Oceanic and Atmospheric Administraion (NOAA). The major remaining constraint and challenging problem is multipath. This is because mulitpath is environmentally dependant, difficult to model mathematically, and cannot be reduced through differential positioning. The research proposes a new approach to identify multipath-contaminated L1 measurements. The approach is based on wavelet analysis using Daubechies family wavelets. First, the difference between the code and carrier phase measurements was estimated, leaving essentially twice the ionospheric delay, multipath and system noise. The ionospheric delay is largely removed by using high resolution ionospheric delay maps produced by NOAA. The remaining residuals contain mainly low-frequency multipath, if existed, and high-frequency part of the residual component described above. The L1 measurements obtaines from the staellites with lowest multipath were used to compute the final positions using Trimble Total Control (TTC) and Bernese scientific processing software packages. The AC12 single-frequency GPS receiver was extensively tested in static and kinematic modes. Accuracies within 5 cm was demostrated for baselines up to 65 km under various multipath environments.

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High accuracy positioning with low-cost single-frequency GPS system in multipath environments

10.32920/ryerson.14654085 ◽

2021 ◽

Author(s):

Abdulla Al-Naqbi

Keyword(s):

Low Cost ◽

Low Frequency ◽

Ionospheric Delay ◽

Measurement Noise ◽

Single Frequency ◽

International Gnss Service ◽

Phase Measurements ◽

Differential Positioning ◽

The Difference ◽

Gps System

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Gauss process regression for real-time ionospheric delay estimation from GNSS observations

Acta Geodaetica et Geophysica ◽

10.1007/s40328-021-00368-y ◽

2022 ◽

Author(s):

Balazs Lupsic ◽

Bence Takacs

Keyword(s):

Real Time ◽

Low Cost ◽

Autonomous Vehicle ◽

Satellite System ◽

Ionospheric Delay ◽

Single Frequency ◽

Gauss Process ◽

Global Navigation Satellite ◽

Autonomous Vehicle Navigation ◽

Gnss Observations

AbstractThe number of devices equipped with global satellite positioning has exceeded seven billion recently. There are a wide variety of receivers regarding their accuracy and reliability. Low cost, multi-frequency units have been released on the market latterly; however, the number of single-frequency receivers is still significant. Since their measurements are influenced by ionospheric delay, accurate ionosphere models are of utmost importance to reduce the effect. This paper summarizes how Gauss process regression (GPR) can be applied to derive near real-time regional ionosphere models using raw Global Navigation Satellite System (GNSS) observations of permanent stations. While Gauss process is widely used in machine learning, GPR is a nonparametric, Bayesian approach to regression. GPR has several benefits for ionosphere monitoring since it is quite robust and efficient to derive a grid model from data available in irregular set of ionospheric pierce points. The corresponding instrumental delays are estimated by a parallel Kalman filter. The presented algorithm can be applied near real-time, however the results are offline calculated and are compared to two high quality TEC map products. Based on the analysis, the accuracy of the GPR modell is in 2 TECu range. The developed methods could be efficiently applied in the field of autonomous vehicle navigation with meeting both accuracy and integrity requirements.

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Single-Frequency Ionospheric-Delay Correction from BeiDou & GPS Systems for Northern Hemisphere

Artificial Satellites ◽

10.2478/arsa-2019-0002 ◽

2019 ◽

Vol 54 (1) ◽

pp. 1-15

Author(s):

Ashraf Farah

Keyword(s):

Northern Hemisphere ◽

Current Source ◽

Single Frequency ◽

International Gnss Service ◽

Low Latitude ◽

Klobuchar Model ◽

Beidou System ◽

Latitude Region ◽

Geographic Regions ◽

Activity State

Abstract The range delay caused by the ionosphere layer is the major current source of error for GNSS users with single-frequency receivers. GNSS advice users to correct this type of error using ionospheric models whose coefficients are sent in their navigation messages. GPS-users use the Klobuchar model to correct this type of error. GPS navigation message contains the model’s eight coefficients which vary on the basis of seasonal ionospheric variations and average solar flux. The correction accuracy of Klobuchar model is about 50% (rms) of the ionospheric range delay. Beidou system calculates and broadcast 8 parameters of Klobuchar model based on continuous monitoring stations. BeiDou system updates the ionospheric coefficients every two hours. GPS-Klobuchar model uses completely different coefficients than BeiDou-Klobuchar model. This research demonstrates a comparison study between the Klobuchar model using the GPS broadcast coefficients and the same model using BeiDou-coefficients. The correction accuracy offered by the two models has been judged using the most accurate International GNSS Service-Global Ionospheric Maps (IGS-GIMs) for three different-latitude stations along northern hemisphere, one station in low-latitude region, the second station is in mid-latitude region and the third station is in high-latiude region to reflect models’ behaviour in different geographic regions. The study was applied over three different months of the year 2017 that each of them reflects a different activity state for the ionosphere layer. The study proves that BeiDou model is able to show the ionosphere’s day-to-day fluctuations while GPS model can’t. It can be concluded that GPS model offers better behaviour than BeiDou model in correcting range delay in low-latitude and high-latitude geographic regions under any activity state for the ionosphere. BeiDou model offers better correction accuracy than GPS model in mid-latitude under any activity state for the ionosphere.

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On Global Ionospheric Maps based winter-time GPS ionospheric delay with reference to the Klobuchar model

Pomorstvo ◽

10.31217/p.33.2.11 ◽

2019 ◽

Vol 33 (2) ◽

pp. 210-221

Author(s):

David Brčić ◽

Renato Filjar ◽

Serdjo Kos ◽

Marko Valčić

Keyword(s):

Ionospheric Delay ◽

Single Frequency ◽

Electron Content ◽

Ground Truth Data ◽

Local Pattern ◽

Satellite Positioning ◽

Klobuchar Model ◽

Global Ionospheric Maps ◽

Winter Time ◽

Delay Correction

Modelling of the ionospheric Total Electron Content (TEC) represents a challenging and demanding task in Global Navigation Satellite Systems (GNSS) positioning performance. In terms of satellite Positioning, Navigation and Timing (PNT), TEC represents a significant cause of the satellite signal ionospheric delay. There are several approaches to TEC estimation. The Standard (Klobuchar) ionospheric delay correction model is the most common model for Global Positioning System (GPS) single-frequency (L1) receivers. The development of International GNSS Service (IGS) Global Ionospheric Maps (GIM) has enabled the insight into global TEC dynamics. GIM analyses in the Northern Adriatic area have shown that, under specific conditions, local ionospheric delay patterns differ from the one defined in the Klobuchar model. This has been the motivation for the presented research, with the aim to develop a rudimentary model of the TEC estimation, with emphasis on areas where ground truth data are not available. The local pattern of the ionospheric delay has been modelled with wave functions based on the similarity of waveforms, considering diurnal differences in TEC behavior from defined TEC patterns. The model represents a spatiotemporal winter-time ionospheric delay correction with the Klobuchar model as a basis. The evaluation results have shown accurate approximation of the local pattern of the ionospheric delay. The model was verified in the same seasonal period in 2007, revealing it successfulness under pre-defined conditions. The presented approach represents a basis for the further work on the local ionospheric delay modelling, considering local ionospheric and space weather conditions, thus improving the satellite positioning performance for single-frequency GNSS receivers.

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TWIGA project activities for the enhancement of heavy rainfall predictions in Africa: low-cost GNSS network deployment and NWP model parameterization.

10.5194/egusphere-egu2020-16122 ◽

2020 ◽

Author(s):

Alessandra Mascitelli ◽

Agostino Niyonkuru Meroni ◽

Stefano Barindelli ◽

Marco Manzoni ◽

Giulio Tagliaferro ◽

...

Keyword(s):

South Africa ◽

Time Series ◽

Water Vapor ◽

Heavy Rainfall ◽

Low Cost ◽

Sustainable Growth ◽

Single Frequency ◽

Sar Images ◽

Nwp Model ◽

Gnss Observations

One of the objectives of the H2020 project TWIGA - Transforming Weather Water data into value-added Information services for sustainable Growth in Africa - is the improvement of heavy rainfall prediction in Africa. In this area, the scarcity of data to support such predictions makes it fundamental to enhance the monitoring of atmospheric parameters.In this project, GNSS observations and SAR images from Sentinel missions are used to produce water vapor products to be assimilated into Numerical Weather Prediction Models (NWPs).GNSS observations, collected by ad-hoc networks of geodetic and low-cost stations, are processed to obtain near real-time (NRT) Zenith Total Delay (ZTD) time series, while Sentinel-1 SAR images are used to derive Atmospheric Phase Screens, APSs. The free and open source GNSS software goGPS, developed by the Politecnico di Milano spin-off Geomatics Research and Development (GReD), is used for the retrieval of ZTDs time series.After proper calibration and validation procedures, the delay maps from SAR and the delay time series from GNSS will be finally assimilated into NWP models to improve the prediction of heavy rainfall.The GNSS-related activities will be presented in terms of network deployment and processing settings evaluation. A network of 5 single-frequency low-cost GNSS stations was installed in Uganda, and a new network of dual-frequency low-cost stations is going to be installed in Kenya. To improve the outputs provided by these networks, preliminary tests on ionospheric delay corrections at various distances were performed. Different methods, focused on the reconstruction of a synthetic L2 observation for the single-frequency receivers, were employed and evaluated with the aim to define the optimal approach.In order to demonstrate the capability to achieve GNSS NRT processing within TWIGA, an automated procedure was set up to estimate hourly ZTDs from two geodetic permanent stations located in South Africa (Cape Town and Southerland) and to upload them to the TWIGA project web portal.Meanwhile, first sets of WRF NWP model parameterizations have been defined for both South Africa and Kenya. A cooperation has been established with the Kenya Meteorological Department on the exploitation of 3DVAR tool for water vapor data assimilation into WRF. Studies to define a strategy for ZTD maps retrieval from InSAR APS have been performed on Italian datasets and further investigations on TWIGA-collected African datasets will follow.&#160;&#160;&#160;&#160;

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GNSS-R with Low-Cost Receivers for Retrieval of Antenna Height from Snow Surfaces Using Single-Frequency Observations

Sensors ◽

10.3390/s19245536 ◽

2019 ◽

Vol 19 (24) ◽

pp. 5536 ◽

Cited By ~ 1

Author(s):

Simone Rover ◽

Alfonso Vitti

Keyword(s):

Low Cost ◽

Test Site ◽

Global Navigation Satellite Systems ◽

Single Frequency ◽

Satellite Systems ◽

Management Plans ◽

Gnss Reflectometry ◽

Application Fields ◽

Global Navigation Satellite ◽

Gnss Observations

Snowpack is an important fresh water storage; the retrieval of snow water equivalents from satellite data permits to estimate potentially available water amounts which is an essential parameter in water management plans running in several application fields (e.g., basic needs, hydroelectric, agriculture, hazard and risk monitoring, climate change studies). The possibility to assess snowpack height from Global Navigation Satellite Systems (GNSS) observations by means of the GNSS reflectometry technique (GNSS-R) has been shown by several studies. However, in general, studies are being conducted using observations collected by continuously operating reference stations (CORS) built for geodetic purposes and equipped with geodetic-grade instruments. Moreover, CORS are located on sites selected according to criteria different from those more suitable for snowpack studies. In this work, beside an overview of key elements of GNSS reflectometry, single-frequency GNSS observations collected by u-blox M8T GNSS receivers and patch antennas from u-blox and Tallysman have been considered for the determination of antenna height from the snowpack surface on a selected test site. Results demonstrate the feasibility of GNSS-R even with non-geodetic-grade instruments, opening the way towards diffuse GNSS-R targeted applications.

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Precise GPS Positioning with Low-Cost Single-Frequency System in Multipath Environment

Journal of Navigation ◽

10.1017/s0373463309990373 ◽

2010 ◽

Vol 63 (2) ◽

pp. 301-312 ◽

Cited By ~ 2

Author(s):

Abdulla Alnaqbi ◽

Ahmed El-Rabbany

Keyword(s):

High Resolution ◽

Low Cost ◽

Low Frequency ◽

Ionospheric Delay ◽

Single Frequency ◽

Static Mode ◽

Phase Measurements ◽

System Noise ◽

Differential Positioning ◽

The Difference

Low-cost, single-frequency GPS systems provide economical positioning solutions to many geomatics applications, including GIS and low-accuracy surveying applications. Unfortunately however, the positioning accuracy obtained with those systems is not sufficient for many surveying applications. This is mainly due to the presence of ionospheric delay and multipath. In this research ionospheric delay is accounted for using regional high-resolution ionospheric maps produced by the US National Oceanic and Atmospheric Administration (NOAA). The major remaining constraint and challenging problem is multipath. This is because multipath is environmentally-dependent, difficult to model mathematically and cannot be reduced through differential positioning. This research proposes a new approach to identify multipath-contaminated L1 measurements through wavelet analysis. First, the difference between the code and carrier-phase measurements is estimated, leaving essentially twice the ionospheric delay, multipath and system noise. The ionospheric delay is largely removed by using high-resolution ionospheric delay maps produced by NOAA. The remaining residuals contain mainly low-frequency multipath, if it exists, and high-frequency system noise, which are decomposed using Daubechies family wavelets (db8). A satellite signal is identified as contaminated by multipath based on the standard deviation of the low-frequency part of the residual component. The L1 measurements obtained from the satellites with the lowest multipath are used to compute the final positions using two software packages, namely Trimble Total Control (TTC) and Bernese scientific processing software. The Magellan AC12 low-cost single-frequency GPS receiver was extensively tested in static mode. It is shown that accuracies within 5 cm are routinely obtained for baselines up to 65 km under various multipath environments.

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Reduction of GPS Noise for Precision Control of Robot Navigation in Confined Areas

Volume 4A: Dynamics, Vibration, and Control ◽

10.1115/imece2014-38548 ◽

2014 ◽

Cited By ~ 1

Author(s):

Andrew Narvesen ◽

Majura Selekwa

Keyword(s):

Low Cost ◽

Single Frequency ◽

Gps Data ◽

Navigation Systems ◽

Differential Gps ◽

Positioning Errors ◽

Home Service ◽

The Cost ◽

Gps Noise ◽

Robotic Applications

Most modern navigation systems solve the localization problem by extensively using global positioning system (GPS) data. Unfortunately the GPS data quality depends on several factors, which can lead to large positioning errors. Known GPS errors fall in two groups: either atmospheric errors, or multipath errors. Because of these errors, differential GPS systems have been developed using both ground based and satellite based reference systems. The cost of a differential GPS unit such as a Novatel range from a little over $2000 to over $9000, which can be prohibitive for use on certain home service robotic vehicles such as autonomous snow plows or autonomous lawn mowers. This paper discusses ways of mitigating GPS errors on low cost single frequency GPS units such as Copernicus II, Skytraq and U-Blox, which cost far less than $100 each, and hence are attractive for use in many robotic applications such as those mentioned above. The paper will present a model of GPS noise and use that model to process GPS data for use in navigation of an autonomous snow plow designed for use in residential driveways and side-walks; it will be supported by experimental results only.

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Estimation and Analysis of BDS2 and BDS3 Differential Code Biases and Global Ionospheric Maps Using BDS Observations

Remote Sensing ◽

10.3390/rs13030370 ◽

2021 ◽

Vol 13 (3) ◽

pp. 370

Author(s):

Min Li ◽

Yunbin Yuan

Keyword(s):

Assessment System ◽

Ionospheric Delay ◽

Single Frequency ◽

International Gnss Service ◽

Efficient Manner ◽

Frequency Bands ◽

Measurement Science ◽

Receiver Dcb ◽

Global Ionospheric Maps ◽

German Aerospace

Following the continuous and stable regional service of BDS2, the BDS3 officially announced its global service in July 2020. To fully take advantage of the new multi-frequency BDS3 signals in ionosphere sensing and positioning, it is essential to understand the characteristics of the differential code bias (DCB) of new BDS3 signals and BDS performance in global ionospheric maps (GIMs) estimation. This article presents an evaluation of the characteristics of 13 types of BDS DCBs and the accuracy of BDS-based GIM based on the data provided by the International GNSS Service (IGS) and International GNSS Monitoring and Assessment System (iGMAS) for the first time. The GIMs and DCBs are estimated by the APM (Innovation Academy for Precision Measurement Science and Technology) method in a time efficient manner, which can be divided into two main steps. The first step is to produce GIMs based on BDS observations at the B1I, B2I and B3I signals, and the second step is to estimate DCBs among the other frequency bands by removing the ionospheric delay using the precomputed GIMs. Good agreement is found between the APM-based satellite DCB estimates and those from the Chinese Academy of Sciences (CAS) and the German Aerospace Center (DLR) at levels of 0.26 ns and 0.18 ns, respectively. The results, spanning one month, show that the stability of BDS DCB estimates among different frequency bands are related to the contributed observations, and the receiver DCB estimates represent larger STD values than the satellite DCB estimates. The differences in receiver DCB estimates between BDS2 and BDS3 are found to be related to the types of receivers and antennas and firmware version, and the bias of the JAVAD receivers reaches 1.03 ns. The results also indicate that the difference in the single-frequency standpoint positioning (SPP) accuracy using GPS-based and BDS-based GIMs for ionospheric delay corrections is less than 0.03 m in both the horizontal and vertical directions.

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