Low Earth orbit satellite navigation errors and vertical total electron content in single-frequency GPS tracking

The prevalence of real-time, low-cost, single-frequency, decimeter-level positioning has increased with the development of global navigation satellite systems (GNSSs). Ionospheric delay accounts for most errors in real-time single-frequency GNSS positioning. To eliminate ionospheric interference in real-time single-frequency precise point positioning (RT-SF-PPP), global ionospheric vertical total electron content (VTEC) product is designed in the next stage of the International GNSS Service (IGS) real-time service (RTS). In this study, real-time generation of a global ionospheric map (GIM) based on IGS RTS is proposed and assessed. There are three crucial steps in the process of generating a real-time global ionospheric map (RTGIM): estimating station differential code bias (DCB) using the precise point positioning (PPP) method, deriving slant total electron content (STEC) from PPP with raw observations, and modeling global vertical total electron content (VTEC). Experiments were carried out to validate the algorithm’s effectiveness. First, one month’s data from 16 globally distributed IGS stations were used to validate the performance of DCB estimation with the PPP method. Second, 30 IGS stations were used to verify the accuracy of static PPP with raw observations. Third, the modeling of residuals was assessed in high and quiet ionospheric activity periods. Afterwards, the quality of RTGIM products was assessed from two aspects: (1) comparison with the Center for Orbit Determination in Europe (CODE) global ionospheric map (GIM) products and (2) determination of the performance of RT-SF-PPP with the RTGIM. Experimental results show that DCB estimation using the PPP method can realize an average accuracy of 0.2 ns; static PPP with raw observations can achieve an accuracy of 0.7, 1.2, and 2.1 cm in the north, east, and up components, respectively. The average standard deviations (STDs) of the model residuals are 2.07 and 2.17 TEC units (TECU) for moderate and high ionospheric activity periods. Moreover, the average root-mean-square (RMS) error of RTGIM products is 2.4 TECU for the one-month moderate ionospheric period. Nevertheless, for the high ionospheric period, the RMS is greater than the RMS in the moderate period. A sub-meter-level horizontal accuracy and meter-level vertical accuracy can be achieved when the RTGIM is employed in RT-SF-PPP.

Download Full-text

Single-frequency GNSS retrieval of vertical total electron content (VTEC) with GPS L1 and Galileo E5 measurements

Journal of Space Weather and Space Climate ◽

10.1051/swsc/2013033 ◽

2013 ◽

Vol 3 ◽

pp. A11 ◽

Cited By ~ 3

Author(s):

Torben Schüler ◽

Olushola Abel Oladipo

Keyword(s):

Total Electron Content ◽

Single Frequency ◽

Electron Content ◽

Vertical Total Electron Content ◽

Total Electron ◽

Galileo E5

Download Full-text

A Refinement Method of Real-Time Ionospheric Model for China

Remote Sensing ◽

10.3390/rs12203354 ◽

2020 ◽

Vol 12 (20) ◽

pp. 3354

Author(s):

Yang Wang ◽

Yibin Yao ◽

Liang Zhang ◽

Mingshan Fang

Keyword(s):

Real Time ◽

Total Electron Content ◽

Global Navigation Satellite Systems ◽

Single Frequency ◽

Electron Content ◽

Vertical Total Electron Content ◽

Ionospheric Model ◽

Total Electron ◽

Satellite Systems ◽

Refinement Method

Ionospheric delay is a crucial error source and determines the source of single-frequency precise point positioning (SF-PPP) accuracy. To meet the demands of real-time SF-PPP (RT-SF-PPP), several international global navigation satellite systems (GNSS) service (IGS) analysis centers provide real-time global ionospheric vertical total electron content (VTEC) products. However, the accuracy distribution of VTEC products is nonuniform. Proposing a refinement method is a convenient means to obtain a more accuracy and consistent VTEC product. In this study, we proposed a refinement method of a real-time ionospheric VTEC model for China and carried out experiments to validate the model effectiveness. First, based on the refinement method and the Centre National d’Études Spatiales (CNES) VTEC products, three refined real-time global ionospheric models (RRTGIMs) with one, three, and six stations in China were built via GNSS observations. Second, the slant total electron content (STEC) and Jason-3 VTEC were used as references to evaluate VTEC accuracy. Third, RT-SF-PPP was used to evaluate the accuracy in the positioning domain. Results showed that even if using only one station to refine the global ionospheric model, the refined model achieved a better performance than CNES and the Center for Orbit Determination in Europe (CODE). The refinement model with six stations was found to be the best of the three refinement models.

Download Full-text

NeQuick-G performance assessment for space applications

GPS Solutions ◽

10.1007/s10291-019-0931-2 ◽

2019 ◽

Vol 24 (1) ◽

Cited By ~ 6

Author(s):

Oliver Montenbruck ◽

Belén González Rodríguez

Keyword(s):

Electron Density ◽

Total Electron Content ◽

Thick Layer ◽

Computational Effort ◽

Low Earth Orbit ◽

Single Frequency ◽

Electron Content ◽

Path Delay ◽

Space Applications ◽

Total Electron

AbstractOther than traditional single-layer ionosphere models for global navigation satellite system (GNSS) receivers, the NeQuick-G model of Galileo provides a fully three-dimensional description of the electron density and obtains the ionospheric path delay by integration along the line of sight. While optimized for users on or near the surface of the earth, NeQuick-G can thus as well be used for ionospheric correction of single-frequency observations from spaceborne platforms. Based on slant and total electron content measurements obtained in the Swarm mission, the performance of NeQuick-G for users in low earth orbit is assessed for periods of high and low solar activity as well as different orientations of the orbital plane with respect to the sun and the region of high total electron content. A slant range correction performance of better than 70% is achieved in more than 85% of the examined epochs in good accord with the performance reported for terrestrial users. Likewise, the positioning errors can be notably reduced when applying the NeQuick-G corrections in single-frequency navigation solutions. For users at orbital altitudes, it is furthermore shown that vertical total electron predictions from NeQuick-G may be favorably combined with an elevation-dependent thick-layer mapping function to reduce the high computational effort associated with the integration of the electron density along the ray path for each tracked GNSS satellite.

Download Full-text

Sodankylä ionospheric tomography dataset 2003–2014

Geoscientific Instrumentation Methods and Data Systems Discussions ◽

10.5194/gid-5-385-2015 ◽

2015 ◽

Vol 5 (2) ◽

pp. 385-404

Author(s):

J. Norberg ◽

L. Roininen ◽

A. Kero ◽

T. Raita ◽

T. Ulich ◽

...

Keyword(s):

Total Electron Content ◽

Low Earth Orbit ◽

Electron Content ◽

Vertical Total Electron Content ◽

Dual Frequency ◽

Total Electron ◽

Ionospheric Tomography ◽

Maximum Elevation ◽

Long Term Performance ◽

Term Performance

Abstract. Sodankylä Geophysical Observatory has been operating a tomographic receiver network and collecting the produced data since 2003. The collected dataset consists of phase difference curves measured from Russian COSMOS dual-frequency (150/400 MHz) low-Earth-orbit satellite signals, and tomographic electron density reconstructions obtained from these measurements. In this study vertical total electron content (VTEC) values are integrated from the reconstructed electron densities to make a qualitative and quantitative analysis to validate the long-term performance of the tomographic system. During the observation period, 2003–2014, there were three-to-five operational stations at the Fenno-Scandinavian sector. Altogether the analysis consists of around 66 000 overflights, but to ensure the quality of the reconstructions, the examination is limited to cases with descending (north to south) overflights and maximum elevation over 60°. These constraints limit the number of overflights to around 10 000. Based on this dataset, one solar cycle of ionospheric vertical total electron content estimates is constructed. The measurements are compared against International Reference Ionosphere IRI-2012 model, F10.7 solar flux index and sunspot number data. Qualitatively the tomographic VTEC estimate corresponds to reference data very well, but the IRI-2012 model are on average 40 % higher of that of the tomographic results.

Download Full-text

Extraction of electron density profiles with geostationary satellite-based GPS side lobe occultation signals

10.5194/egusphere-egu2020-1569 ◽

2020 ◽

Author(s):

Wenwen Li ◽

Min Li ◽

Qile Zhao ◽

Chuang Shi ◽

Rongxin Fang

Keyword(s):

Electron Density ◽

Side Lobe ◽

Low Earth Orbit ◽

Single Frequency ◽

Earth Orbit ◽

Electron Content ◽

Density Profiles ◽

Total Electron ◽

Geo Satellite ◽

Electron Density Profiles

<p>Electron density profiles (EDP) obtained by GNSS radio occultation (RO) technique can improve the primary ionospheric parameters. However, current studies mainly focused on GNSS RO measurements observed by low Earth orbit satellites, which can only estimate EDP at low altitudes typically below 1000 km. We investigated the GPS RO measurements recorded on the geostationary earth orbit (GEO) satellite TJS-2 (telecommunication technology test satellite II). To improve EDP derivation precision, the total electron content derived from TJS-2 single-frequency excess phase is refined by a moving average filter, which can smooth high-frequency errors and indicate higher precision over the single-difference technique. By comparison with the ground-based digisonde, the IRI 2016 model and the Constellation Observing System for Meteorology, Ionosphere, and Climate satellite (COSMIC) EDPs, the TJS-2 ionospheric EDPs show good agreement with correlation coefficients exceeding 0.8. The TJS-2 average NmF2 differences compared to digisondes and COSMIC results are 12.9% and 1.4%, respectively, while the hmF2 differences are 1.65 km and 1.76 km, respectively. With a GEO satellite such as TJS-2, the side lobe GPS RO signals can also be received, and they are employed to estimate electron densities up to several thousand kilometers in height for the first time in this contribution. Our results also reveal that GEO-based RO signals can estimate EDPs at specific locations with daily repeatability, which makes it a very suitable technique for routinely monitoring EDP variations</p>

Download Full-text

Ionospheric Correction for GPS Tracking of LEO Satellites

Journal of Navigation ◽

10.1017/s0373463302001789 ◽

2002 ◽

Vol 55 (2) ◽

pp. 293-304 ◽

Cited By ~ 29

Author(s):

Oliver Montenbruck ◽

Eberhard Gill

Keyword(s):

Scale Factor ◽

Low Earth Orbit ◽

Single Frequency ◽

Gps Tracking ◽

Test Case ◽

Electron Content ◽

Path Delay ◽

Ionospheric Correction ◽

Total Electron ◽

Correction Technique

This paper describes an ionospheric correction technique for single frequency GPS measurements from satellites in low Earth orbit. The fractional total electron content (TEC) above the receiver altitude is obtained from global TEC maps of the International GPS Service network and an altitude dependent scale factor. By choosing a suitable effective height of the residual ionosphere, the resulting path delay for positive elevations is then computed from a thin layer approximation. The scale factor can be predicted from the assumption of a Chapman profile for the altitude variation of the electron density or adjusted as a free parameter in the processing of an extended set of single frequency measurements. The suitability of the proposed model is assessed by comparison with flight data from the Champ satellite that orbits the Earth at an altitude of 450 km. For the given test case, a 90% correction of the ionospheric error is achieved in a reduced dynamic orbit determination based on single frequency C/A-code measurements.

Download Full-text