Abstract
The reparameterization of the geometry-free and geometry-based approaches to derive single-site ionospheric delays using Global Navigation Satellite System (GNSS) measurements is described. Kalman filtering is used to compute the geometry-free and geometry-based ionospheric delays in a forward computation procedure, aiming for a real-time application case. The numerical similarity and differences between the geometry-free and geometry-based ionospheric delays are assessed in terms of both formal and experimental errors (precision). The differences between geometry-free and geometry-based ionospheric delays are derived using two types of precise orbit and clock products. The effects of the precise orbit and clock residual errors are analyzed. The correlation coefficients between the L1 and L2 wide-lane ambiguities with the ionospheric delay are derived and analyzed. It is discovered that the geometry-based ionospheric delay is negatively correlated with geometry-based wide-lane ambiguities, while the geometry-free ionospheric delay and wide-lane ambiguities are much less correlated. A simulation analysis indicates that the impacts on geometry-based ionospheric delay estimates are partly coincided with the actual time-variant errors of the used orbit and clock in the line-of-sight direction.
Highlights
Published: 30 May 2021The ionosphere is defined as the ionized part of the Earth’s upper atmosphere, consisting of abundant ions and free electrons
The geometry-free approach has the advantage of simplicity without the need for a precise orbit and clock (OC)
The geometry-free ionospheric delay estimates are often derived on the basis of an entire arc in order to have more precise ambiguity levelling [15,16,19,23,24,25] and, in this case, they cannot be computed in real-time
Summary
The ionosphere is defined as the ionized part of the Earth’s upper atmosphere, consisting of abundant ions and free electrons. The geometry-free approach has the advantage of simplicity without the need for a precise orbit and clock (OC) It is widely used for global ionosphere modelling (GIM) [2,17,18]. The geometry-free ionospheric delay estimates are often derived on the basis of an entire arc in order to have more precise ambiguity levelling [15,16,19,23,24,25] and, in this case, they cannot be computed in real-time. The comparison and assessment of the ionospheric delays should be based on filtering solutions derived from current and past data, rather than smoothed solutions from the entire and continuous arc [26] This contribution is an extension of our previous studies [20,21], aimed at the analysis of single-site ionospheric delays derived from both geometry-free and geometry-based approaches.
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