Multi-layer ionosphere mapping function for ground and LEO GNSS data and its performance analysis

Abstract

When estimating ionospheric total electron content (TEC) using Global Navigation Satellite System (GNSS) observations, one of the significant error sources is the mapping error introduced by slant to vertical TEC conversion and vice versa. A single-layer mapping function (MF) based on a thin-shell assumption of the Earth’s ionosphere is commonly used for TEC conversion. However, the accuracy of single-layer MF is susceptible to the inaccurate fixing of the ionospheric single-layer height. In order to find a mapping approach less sensitive to the choice of ionospheric effective height we defined a multi-layer ionosphere mapping function and investigated its performance in comparison with the single-layer model. We found that the multi-layer MF outperforms the single-layer MF when computing GNSS receiver differential code biases (DCBs) especially at low latitude and equatorial regions where ionosphere is highly dynamic and difficult to model. When compared with the International GNSS Services (IGS) products, we found that the mean receiver DCB estimation is improved (closer to benchmark) by about 0.14 – 0.27 ns and 0.30 – 0.78 ns during days in 2019 and 2023, respectively. We found that the receiver DCB estimation improves for about 66-87% receivers. This is also reflected in Global Ionosphere Maps (GIMs) showing better performance for the multi-layer MF when comparing with IGS GIMs. Our investigation using GNSS observations onboard Low Earth Orbiting (LEO) satellites shows that the multi-layer MF can be successfully applied in computing satellite and receiver DCBs accurately.