Higher‐order ionospheric effects on the GPS reference frame and velocities

Abstract

[1] We describe how GPS time series are influenced by higher-order ionospheric effects over the last solar cycle (1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008) and examine implications for geophysical studies. Using 14 years of globally reprocessed solutions, we demonstrate the effect on the reference frame. Including second-and third-order ionospheric terms causes up to 10 mm difference in the smoothed transformation to the International Terrestrial Reference Frame (ITRF) 2005, with the Z translation term dominant. Scale is also slightly affected, with a change of up to ∼0.05 ppb. After transformation to ITRF2005, residual effects on vertical site velocities are as high as 0.34 mm yr −1 . We assess the effect of the magnetic field model on the second-order term and find a time-varying difference of 0-2 mm in the Z translation. We also assess the effect of omitting the third-order term. We find that while the second-order term is responsible for almost all the Z translation effects, it is the combination of the second-and third-order terms that causes the effect on scale. Comparison of our GPS reprocessing with ITRF2005 suggests that GPS origin rates may vary with time period. For example, we find Z translation rates of −0.82 ± 0.17 mm yr −1 for 1995-2008 and 0.17 ± 0.24 mm yr −1 for 1995-2005. If GPS were to contribute to origin rate definition for future ITRFs, higher-order ionospheric corrections would need to be applied due to their effect on translation parameters during solar maximum.

Improved Constraints on Models of Glacial Isostatic Adjustment: A Review of the Contribution of Ground-Based Geodetic Observations

“…As shown in Fig. 6, Petrie et al (2010b) demonstrated that neglecting higher order ionospheric terms can bias 3-d site velocities, with up to *0.4 mm/year biases appearing in the vertical component, after transforming to the ITRF, depending on the evolution of electron content throughout the solar cycle, and producing a maximum bias of up to a few millimetres in position after half a solar cycle, i.e. about six years.…”

“…Empty circles show sites processed which did not meet these criteria. Reproduced from Petrie et al (2010b) the product of the zenith (hydrostatic or wet) delay and the corresponding (hydrostatic or wet) mapping function (see, e.g., Davis et al 1985). Whereas the zenith hydrostatic delay may be determined from the pressure at the site (Saastamoinen 1972;Davis et al 1985) (from local measurements or from numerical weather models) and mapped with the hydrostatic mapping function to obtain the delay at a certain elevation angle, the zenith wet delay cannot be accurately modelled and is instead estimated in the least-squares adjustment with the wet mapping function as the corresponding partial derivative.…”

Characterizing the Seasonal Crustal Motion in Tianshan Area Using GPS, GRACE and Surface Loading Models

“…In addition, Finite Element Solutions 2004 (FES2004) ocean tidal loading corrections, diurnal (S1) and semi-diurnal (S2) atmosphere tidal loading corrections and absolute phase-center corrections for satellites and receivers, as issued by International GNSS Service (IGS) [23], were used to correct corresponding errors. The tropospheric delay was modeled using the Global Mapping Function (GMF) [24]; firstorder ionospheric delays were eliminated by means of the ionosphere-free linear combination, and higher-order terms were also modeled [25]. The final coordinates were aligned with the the International Terrestrial Reference Frame 2008 (ITRF2008) with minimum constraint [26].…”

A Study of Rank Defect and Network Effect in Processing the CMONOC Network on Bernese

“…The tropospheric delay was modeled by using the Vienna Mapping Function (VMF) [33], with zenith delay hourly estimated for the wet part and VMF model values assigned for the dry part. First-order ionospheric delays were eliminated by means of the ionosphere-free linear combination, and higher-order terms were modeled as recommended in Petrie et al (2010) [34]. Satellite orbits and Earth rotation parameters are recommended to be fixed in the final least squares estimation of the position parameters, with phase ambiguities resolved as much as possible and geometrical correlations among GPS stations fully considered.…”