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| Titel |
Higher order ionospheric effects in GNSS positioning in the European region |
| VerfasserIn |
Z. G. Elmas, M. Aquino, H. A. Marques, J. F. G. Monico |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 29, no. 8 ; Nr. 29, no. 8 (2011-08-22), S.1383-1399 |
| Datensatznummer |
250017073
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| Publikation (Nr.) |
 copernicus.org/angeo-29-1383-2011.pdf |
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| Zusammenfassung |
After removal of the Selective Availability in 2000, the ionosphere became
the dominant error source for Global Navigation Satellite Systems (GNSS),
especially for the high-accuracy (cm-mm) demanding applications like the
Precise Point Positioning (PPP) and Real Time Kinematic (RTK) positioning.
The common practice of eliminating the ionospheric error, e.g. by the
ionosphere free (IF) observable, which is a linear combination of
observables on two frequencies such as GPS L1 and L2, accounts for about
99 % of the total ionospheric effect, known as the first order ionospheric
effect (Ion1). The remaining 1 % residual range errors (RREs) in the IF
observable are due to the higher – second and third, order ionospheric
effects, Ion2 and Ion3, respectively. Both terms are related with the
electron content along the signal path; moreover Ion2 term is associated
with the influence of the geomagnetic field on the ionospheric refractive
index and Ion3 with the ray bending effect of the ionosphere, which can
cause significant deviation in the ray trajectory (due to strong electron
density gradients in the ionosphere) such that the error contribution of
Ion3 can exceed that of Ion2 (Kim and Tinin, 2007).
The higher order error terms do not cancel out in the (first order)
ionospherically corrected observable and as such, when not accounted for,
they can degrade the accuracy of GNSS positioning, depending on the level of
the solar activity and geomagnetic and ionospheric conditions (Hoque and
Jakowski, 2007). Simulation results from early 1990s show that Ion2 and Ion3
would contribute to the ionospheric error budget by less than 1 % of the
Ion1 term at GPS frequencies (Datta-Barua et al., 2008). Although the IF
observable may provide sufficient accuracy for most GNSS applications, Ion2
and Ion3 need to be considered for higher accuracy demanding applications
especially at times of higher solar activity.
This paper investigates the higher order ionospheric effects (Ion2 and Ion3,
however excluding the ray bending effects associated with Ion3) in the
European region in the GNSS positioning considering the precise point
positioning (PPP) method. For this purpose observations from four
European stations were considered. These observations were taken in four
time intervals corresponding to various geophysical conditions: the active
and quiet periods of the solar cycle, 2001 and 2006, respectively, excluding
the effects of disturbances in the geomagnetic field (i.e. geomagnetic
storms), as well as the years of 2001 and 2003, this time including the
impact of geomagnetic disturbances. The program RINEX_HO (Marques et al., 2011) was
used to calculate the magnitudes of Ion2 and Ion3 on the range measurements
as well as the total electron content (TEC) observed on each
receiver-satellite link. The program also corrects the GPS observation files
for Ion2 and Ion3; thereafter it is possible to perform PPP with both the
original and corrected GPS observation files to analyze the impact of the
higher order ionospheric error terms excluding the ray bending effect which
may become significant especially at low elevation angles (Ioannides and
Strangeways, 2002) on the estimated station coordinates. |
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