Abstract
The ionosphere can be modeled and studied using multi-frequency GNSS signals and their geometry-free linear combination. Therefore, a number of GNSS-derived ionospheric models have been developed and applied in a broad range of applications. However, due to the complexity of estimating the carrier phase ambiguities, most of these models are based on low-accuracy carrier phase smoothed pseudorange data. This, in turn, critically limits their accuracy and applicability. Therefore, we present a new methodology of estimating the phase bias of the scaled L1 and L2 carrier phase difference which is a function of the ambiguities, the ionospheric delay, and hardware delays. This methodology is suitable for ionospheric modeling at regional and continental scales. In addition, we present its evaluation under varying ionospheric conditions. The test results show that the carrier phase bias of geometry-free linear combination can be estimated with a very high accuracy, which consequently allows for calculating ionospheric TEC with the uncertainty lower than 1.0 TECU. This high accuracy makes the resulting ionosphere model suitable for improving GNSS positioning for high-precision applications in geosciences.
Highlights
The ionospheric delay is one of the most dominant error sources in global navigation satellite systems (GNSS) positioning
In order to investigate the accuracy of the carrier phase bias estimation, we validated our method by analyzing of the bias differences at the day-to-day boundaries for adjacent
We presented and validated a methodology for accurate bias estimation of the phase function LGF for use in GNSSbased regional ionospheric modeling
Summary
The ionospheric delay is one of the most dominant error sources in global navigation satellite systems (GNSS) positioning. Most of the available global, regional, and local ionosphere models are based on carrier phase smoothed pseudorange data, which presents low accuracy and requires strong smoothing to estimate the total electron content (TEC) (Brunini et al 2004; Krypiak-Gregorczyk et al 2013; Alizadeh et al 2015). One TECU = 1016 el/m2, and it is equivalent to 0.162 m of L1 signal delay. The accurate knowledge of the state of the ionosphere plays a key role in determining a position using GNSS observations. This is due to the important influence of the ionospheric delays on determining carrier phase ambiguities. The development of high-accuracy models with higher spatial
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