Abstract
A new approach is presented to improve the spatial and temporal resolution of the Vertical Total Electron Content (VTEC) estimates for regional positioning applications. The proposed technique utilises a priori information from the Global Ionosphere Maps (GIMs) of the Center for Orbit Determination in Europe (CODE), provided in terms of Spherical Harmonic (SH) coefficients of up to degree and order 15. Then, it updates the VTEC estimates using a new set of base-functions (with better resolution than SHs) while using the measurements of a regional GNSS network. To achieve the highest accuracy possible, our implementation is based on a transformation of the GIM/CODE VTECs to their equivalent coefficients in terms of (spherical) Slepian functions. These functions are band-limited and reflect the majority of signal energy inside an arbitrarily defined region, yet their orthogonal property is remained. Then, new dual-frequency GNSS measurements are introduced to a Least Squares (LS) updating step that modifies the Slepian VTEC coefficients within the region of interest. Numerical application of this study is demonstrated using a synthetic example and ground-based GPS data in South America. The results are also validated against the VTEC estimations derived from independent GPS stations (that are not used in the modelling), and the VTEC products of international centres. Our results indicate that, by using 62 GPS stations in South America, the ionospheric delay estimation can be considerably improved. For example, using the new VTEC estimates in a Precise Point Positioning (PPP) experiment improved the positioning accuracy compared to the usage of GIM/CODE and Klobuchar models. The reductions in the root mean squared of errors were ∼23% and 25% for a day with moderate solar activity while 26% and ∼35% for a day with high solar activity, respectively.
Highlights
The Global Navigation Satellite System (GNSS) technique has become an integral part of all applications, where mobility plays an important role
The regional Vertical Total Electron Content (VTEC) modelling of this study is based on the ground-based GNSS observations collected across South America and few stations in North America
An overview of the input data used for the ionospheric modelling of this study is shown in Figure 2, where one can see that our VTEC modelling domain covers an extended region above the the GNSS network
Summary
The Global Navigation Satellite System (GNSS) technique has become an integral part of all applications, where mobility plays an important role. The signals from GNSS satellites must transit the ionosphere (i.e., the part of atmosphere between 60 and 2000 km containing ionized plasma of different gas components) on their way to receivers. These free electrons add delay on the code-derived pseudo-range and advance the career phase signals. These effects must be eliminated in some way to achieve high accuracy in GNSS positioning, navigation and timing applications. The ionospheric modelling has received ever increasing attention in various fields including radio communication, navigation, satellite positioning and other space technologies [1]
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