scholarly journals Vertical Ionosphere Delay Estimation using Zero Difference GPS Phase Observation

2018 ◽  
Author(s):  
Ahmed Elsayed ◽  
Ahmed Sedeek ◽  
Mohamed Doma ◽  
Mostafa Rabah
Keyword(s):  
Carrier Phase ◽  
Free Carrier ◽  
Error Modeling ◽  
Ionospheric Delay ◽  
Electron Content ◽  
Gps Receiver ◽  
Dual Frequency ◽  
Total Electron ◽  
Longitudinal Gradients ◽  
Least Squares Adjustment

Abstract. An apparent delay is occurred in GPS signal due to both refraction and diffraction caused by the atmosphere. The second region of the atmosphere is the ionosphere. The ionosphere is significantly related to GPS and the refraction it causes in GPS signal is considered one of the main source of errors which must be eliminated to determine accurate positions. GPS receiver networks have been used for monitoring the ionosphere for a long time. The ionospheric delay is the most predominant of all the error sources. This delay is a function of the total electron content (TEC). Because of the dispersive nature of the ionosphere, one can estimate the ionospheric delay using the dual frequency GPS. In the current research our primary goal is applying Precise Point Positioning (PPP) observation for accurate ionosphere error modeling, by estimating Ionosphere delay using carrier phase observations from dual frequency GPS receiver. The proposed algorithm was written using MATLAB. The proposed Algorithm depends on the geometry-free carrier-phase observations after detecting cycle slip to estimates the ionospheric delay using a spherical ionospheric shell model, in which the vertical delays are described by means of a zenith delay at the station position and latitudinal and longitudinal gradients. Geometry-free carrier-phase observations were applied to avoid unwanted effects of pseudorange measurements, such as code multipath. The ionospheric estimation in this algorithm is performed by means of sequential least-squares adjustment. Finally, an adaptable user interface MATLAB software are capable of estimating ionosphere delay, ambiguity term and ionosphere gradient accurately.

Vertical ionospheric delay estimation for single-receiver operation

2019 ◽  
Vol 13 (2) ◽  
pp. 81-91 ◽  
Author(s):  
Ahmed Elsayed ◽  
Ahmed Sedeek ◽  
Mohamed Doma ◽  
Mostafa Rabah
Keyword(s):  
Carrier Phase ◽  
Free Carrier ◽  
Error Modeling ◽  
Ionospheric Delay ◽  
Electron Content ◽  
Gps Receiver ◽  
Dual Frequency ◽  
Total Electron ◽  
Longitudinal Gradients ◽  
Least Squares Adjustment

Abstract An apparent delay is occurred in GPS signal due to both refraction and diffraction caused by the atmosphere. The second region of the atmosphere is the ionosphere. The ionosphere is significantly related to GPS and the refraction it causes in GPS signal is considered one of the main source of errors which must be eliminated to determine accurate positions. GPS receiver networks have been used for monitoring the ionosphere for a long time. The ionospheric delay is the most predominant of all the error sources. This delay is a function of the total electron content (TEC). Because of the dispersive nature of the ionosphere, one can estimate the ionospheric delay using the dual frequency GPS. In the current research our primary goal is applying Precise Point Positioning (PPP) observation for accurate ionosphere error modeling, by estimating Ionosphere delay using carrier phase observations from dual frequency GPS receiver. The proposed algorithm was written using MATLAB and was named VIDE program. The proposed Algorithm depends on the geometry-free carrier-phase observations after detecting cycle slip to estimates the ionospheric delay using a spherical ionospheric shell model, in which the vertical delays are described by means of a zenith delay at the station position and latitudinal and longitudinal gradients. Geometry-free carrier-phase observations were applied to avoid unwanted effects of pseudorange measurements, such as code multipath. The ionospheric estimation in this algorithm is performed by means of sequential least-squares adjustment. Finally, an adaptable user interface MATLAB software are capable of estimating ionosphere delay, ambiguity term and ionosphere gradient accurately.

scholarly journals Evaluation of Seasonal Variability of First-order Ionospheric Delay Correction at L5 and S1 Frequencies Using Dual-frequency Navic System

2021 ◽  
Author(s):  
Sharat chandra Bhardwaj ◽  
Anurag Vidyarthi ◽  
Bhajan Singh Jassal ◽  
Ashish kumar Shukla
Keyword(s):  
Seasonal Variability ◽  
Ionospheric Delay ◽  
Electron Content ◽  
Dual Frequency ◽  
Satellite Constellations ◽  
Total Electron ◽  
First Order ◽  
Seasonal Characteristics ◽  
Geosynchronous Satellites ◽  
Delay Correction

Abstract For the precise positioning application it is important to determine and eliminate the positioning error introduced by various sources such as the ionosphere. To develop a standalone precise navigation system, India has launched the seven satellite constellations of NavIC (Navigation with Indian Constellation) system to provide precision positioning over India and surrounded landmass. Since the ionospheric delay depends on the frequency of the satellite signal and NavIC systems work at different frequencies (L5 and S1) than GPS systems (L1 and L2), it is not possible to use the GPS data-driven study for NavIC based location calculations directly. Thus there is a need for a specialized ionospheric study for NavIC systems. In addition, the ionospheric delay is directly proportional to Slant Total Electron Content (STEC) which is dependent upon diurnal and seasonal solar activity. To achieve accurate positioning facilities, there is also a need for evaluation for seasonal variability of ionospheric delay correction for NavIC receivers. This paper deals with the STEC estimation; its smoothing, and removal of instrumental biases from STEC. The determined true STEC has been used to determine first-order ionospheric delay at L5 and S1 frequencies. The delay at S1 has been found less (2 to 7m) as compared to L5 (10 to 30m). Furthermore, the seasonal variability of ionospheric delay has been analyzed using about 19 months of data (from June 2017 to December 2018) and found that the ionospheric delay follows unique seasonal characteristics which can be utilized for delay modeling. It has been also observed that the geostationary satellites of the NavIC system are more appropriate than geosynchronous satellites for ionospheric related studies.

Performance Evaluation of USTEC Product for Single-Frequency Precise Point Positioning

GEOMATICA ◽  
2013 ◽  
Vol 67 (4) ◽  
pp. 253-257 ◽  
Author(s):  
Mahmoud Abd El-Rahman ◽  
Ahmed El-Rabbany
Keyword(s):  
Total Electron Content ◽  
Precise Point Positioning ◽  
Ionospheric Delay ◽  
Single Frequency ◽  
Electron Content ◽  
Dual Frequency ◽  
Total Electron ◽  
Gps Receivers ◽  
Mitigation Techniques ◽  
Point Positioning

Geodetic-grade dual-frequency GPS receivers are typically used for precise point positioning (PPP). Unfortunately, these receiver systems are expensive and may not provide a cost-effective solution in many instances. The use of low-cost single-frequency GPS receivers, on the other hand, are limited by the effect of ionospheric delay. A number of mitigation techniques have been proposed to account for the effect of ionospheric delay for single-frequency GPS users. Unfortunately, however, those mitigation techniques are not suitable for PPP. More recently, the U.S. Total Electron Content (USTEC) product has been developed by the National Oceanic and Atmospheric Administration (NOAA), which describes the ionospheric total electron content in high resolution over most of North America. This paper investigates the performance of USTEC and studies its effect on single-frequency PPP solution. A performance comparison with two widely-used ionospheric mitigation models is also presented.

scholarly journals Analysis of Tec Variations over Nepal Obtained from GPS Data on Geo-Magnetically Quiet and Disturbed Days of the Year 2015

2021 ◽  
Vol 7 (2) ◽  
pp. 102-109
Author(s):  
B. D. Ghimire ◽  
N. P. Chapagain ◽  
V. Basnet ◽  
B. Khadka
Keyword(s):  
Weather Prediction ◽  
Vapor Concentration ◽  
Gps Data ◽  
Electron Content ◽  
Gps Receiver ◽  
Dual Frequency ◽  
Total Electron ◽  
Gps Tec ◽  
Global Positioning ◽  
The Difference

Dual frequency Global Positioning System (GPS) receiver in two nearby stations i.e. BESI (28.228 °N, 84.739 °E) and GHER (28.375 °N, 84.739 °E) located at almost same latitude and longitude are used to measure ionospheric total electron content (TEC) for the year 2015. Since Year of 2014- 2016 have been known as most active years in terms of geomagnetic events, the year 2015 shows some abnormal results. Diurnal, monthly and seasonal variations of GPS TEC have been studied. The difference in the value of TEC is observed between quiet and disturbed days. Moreover, the correlation between GPS-data of each month with solar activities parameters such as Kp index, disturbance storm time (Dst) index, and Solar Flux index (F10.7 cm) have been studied, separately for quiet and disturbed days for each station. In case of diurnal variation, mean TEC varies from 0100 UT (LT= UT+5:45) to maximum from 0900 UT to 1100UT. The value of TEC is observed higher on quiet days than disturbed days. For seasonal variation, local seasons i.e. autumn, Spring, Summer and Winter is taken and, the value of TEC is found to be higher in Spring (March, April and May) in both stations in quiet and disturbed days. The difference in value of quiet and disturbed days of GPS-TEC explained the geomagnetic phenomena difference in these days in ionosphere. This study can be useful to calculate the water vapor concentration in the atmosphere which is useful for weather prediction and meteorological department.

scholarly journals Variation of Total Electron Content (TEC) in the Quite and Disturbed days and their correlation with Geomagnetic Parameters of Lamjung Station in the year of 2015

BIBECHANA ◽  
2020 ◽  
Vol 17 ◽  
pp. 123-132
Author(s):  
Basu Dev Ghimire ◽  
Narayan Prasad Chapagain ◽  
Vardhan Basnet ◽  
Karan Bhatta ◽  
Balaram Khadka
Keyword(s):  
Lower Bound ◽  
Total Electron Content ◽  
Negative Correlation ◽  
Solar Flux ◽  
Electron Content ◽  
Gps Receiver ◽  
Dual Frequency ◽  
Total Electron ◽  
Positive Correlation ◽  
Dst Index

Total Electron content is measured using a dual frequency GPS receiver in Lamgung (LMJG) Station located at 84.57° longitude and 28.17° latitude of the year 2015 as it is considered as geo-magnetically active year. In this study, diurnal variation of VTEC has been studied separately for quiet and disturbed days and, for the effective study of the case the PRN wise data of VTEC have been also used. The maximum VTEC is seen from 0700 LT to 1100 LT (LT=UT+5.45). PRN wise VTEC is studied taking the lower bound (LB) and upper bound (UB). The correlation of VTEC with Dst index, Kp index and Solar flux have been studied. Positive correlation has been found in disturbed days with Kp index and solar flux but negative correlation with Dst index. Dst index shows positive correlation in quiet days but Kp index shows negative correlation. BIBECHANA 17(2020) 123-132

scholarly journals Regional Ionosphere Mapping Using Zero Difference GPS Carrier Phase

2018 ◽  
Author(s):  
Heba Tawfeek ◽  
Ahmed Sedeek ◽  
Mostafa Rabah ◽  
Gamal El-Fiky
Keyword(s):  
Carrier Phase ◽  
Nile Delta ◽  
Mean Difference ◽  
Least Square ◽  
Electron Content ◽  
Dual Frequency ◽  
Total Electron ◽  
Phase Measurements ◽  
Total Electron Contents ◽  
The Mean

Abstract. Ionospheric delay, can be derived from dual frequency GNSS signals, and then converted into the Vertical Total Electron Contents (VTEC) along the signal path. Various models were devised to calculate VTEC. Examples of such models are the polynomial function model and spherical harmonics model. A common hypothesis of these models is that they are constructed based on the assumption that the entire electron content in the ionosphere is concentrated in a single thin shell at a selected height above Earth. The primary goal of the current research to develop an algorithm capable of producing VTEC maps on an hourly basis, using carrier phase observations from dual frequency GPS receiver. The developed algorithm uses a single GPS station (Zero-difference) to map VTEC over a regional area. The carrier phase measurements are much more precise than the code pseudorange measurements, but they contain an ambiguous term. If such ambiguities are fixed, thence the carrier phase measurements become as unambiguous pseudoranges, but accurate at the level of few millimeters. In current research Sequential Least Square Adjustment (SLSA) was considered to fix ambiguity term in carrier phase observations. The proposed algorithm was written using MATLAB and Called (ZDPID). Two GPS stations (ANKR and BSHM) were used from IGS network to evaluate the developed code, VTEC values were estimated over these two stations. Results of the proposed algorithm were compared with the Global Ionosphere Maps (GIMs), which is generally used as a reference. The results show that the mean difference between VTEC from GIM and estimated VTEC at ANKR station is ranging from −2.1 to 3.67 TECU and its RMS is 0.44. The mean difference between VTEC from GIM and estimated VTEC at BSHM station is ranging from −0.29 to 3.65 TECU and its RMS is 0.38. Another three GPS stations in Egypt were used to generate regional ionosphere maps over Nile Delta, Egypt. The mean differences between VTEC from GIM and estimated VTEC at SAID station is ranging from −1.1 to 3.69 TECU and its RMS is 0.37, from −1.29 to 3.27 TECU for HELW station with RMS equal 0.39, and from 0.2 to 4.2 TECU for BORG station with RMS equal 0.46. Therefore, the proposed algorithm can be used to estimate VTEC efficiently.

scholarly journals Study of GPS derived Total Electron Content and Scintillation Index variations over Indian Arctic and Antarctic stations

2013 ◽  
Vol 5 (2) ◽  
pp. 255-264 ◽  
Author(s):  
P. Bhawre ◽  
A. K. Gwal ◽  
A. A. Mansoori ◽  
P. A. Khan
Keyword(s):  
Total Electron Content ◽  
Winter Season ◽  
Scintillation Index ◽  
Activity Period ◽  
Electron Content ◽  
Gps Receiver ◽  
Dual Frequency ◽  
Total Electron ◽  
Ionospheric Variability ◽  
Solar Activity Period

In the present study we have investigated the monthly and seasonal variability of total electron content (TEC) and amplitude scintillation index (S4) over two Indian polar stations Maitri (Antarctic) and Ny-Alesund (Arctic), during the low solar activity period 2008. We have used the Novatel’s dual frequency GPS receiver GSV4004A to accomplish this study. From our analysis we observed that TEC achieves its highest values during the months of November and December while during the month of May and June the lowest values of TEC were recorded at Maitri station. Similarly during summer season the highest values of TEC are recorded while in winter season lowest values of TEC are observed. The scintillations that occurred during the year 2008 at Maitri as well as at Ny-Alesund were generally found to be of weak type (S4?0.1), although few cases of moderate (S4?0.3) and strong (S4?0.5) scintillation were also observed. The occurrence characteristics of scintillations showed that maximum scintillations at Maitri occur during the month of July and August while least scintillations occur during the month of January and February. This type of ionospheric variability can be explained on the basis of solar irradiance at Polar Regions.Keywords: Total electron content; Scintillation index; Polar ionosphere.© 2013 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved.doi: http://dx.doi.org/10.3329/jsr.v5i2.12724        J. Sci. Res. 5 (2), 255-264 (2013)

scholarly journals Functional model modification of precise point positioning considering the time-varying code biases of a receiver

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Baocheng Zhang ◽  
Chuanbao Zhao ◽  
Robert Odolinski ◽  
Teng Liu
Keyword(s):  
Precise Point Positioning ◽  
Functional Model ◽  
Geodetic Network ◽  
Temporal Variations ◽  
Gps Data ◽  
Electron Content ◽  
Time Varying ◽  
Dual Frequency ◽  
Total Electron ◽  
Point Positioning

AbstractPrecise Point Positioning (PPP), initially developed for the analysis of the Global Positing System (GPS) data from a large geodetic network, gradually becomes an effective tool for positioning, timing, remote sensing of atmospheric water vapor, and monitoring of Earth’s ionospheric Total Electron Content (TEC). The previous studies implicitly assumed that the receiver code biases stay constant over time in formulating the functional model of PPP. In this contribution, it is shown this assumption is not always valid and can lead to the degradation of PPP performance, especially for Slant TEC (STEC) retrieval and timing. For this reason, the PPP functional model is modified by taking into account the time-varying receiver code biases of the two frequencies. It is different from the Modified Carrier-to-Code Leveling (MCCL) method which can only obtain the variations of Receiver Differential Code Biases (RDCBs), i.e., the difference between the two frequencies’ code biases. In the Modified PPP (MPPP) model, the temporal variations of the receiver code biases become estimable and their adverse impacts on PPP parameters, such as ambiguity parameters, receiver clock offsets, and ionospheric delays, are mitigated. This is confirmed by undertaking numerical tests based on the real dual-frequency GPS data from a set of global continuously operating reference stations. The results imply that the variations of receiver code biases exhibit a correlation with the ambient temperature. With the modified functional model, an improvement by 42% to 96% is achieved in the Differences of STEC (DSTEC) compared to the original PPP model with regard to the reference values of those derived from the Geometry-Free (GF) carrier phase observations. The medium and long term (1 × 104 to 1.5 × 104 s) frequency stability of receiver clocks are also significantly improved.

Sign in / Sign up

Export Citation Format

Share Document