Abstract
Abstract. We recently proposed a method to establish an optimal ionospheric shell height model based on the international GNSS service (IGS) station data and the differential code bias (DCB) provided by the Center for Orbit Determination in Europe (CODE) during the time from 2003 to 2013. This method is very promising for DCB and accurate total electron content (TEC) estimation by comparing to the traditional fixed shell height method. However, this method is basically feasible only for IGS stations. In this study, we investigate how to apply the optimal ionospheric shell height derived from IGS station to non-IGS stations or isolated GNSS receivers. The intuitive and practical method to estimate TEC of non-IGS stations is based on optimal ionospheric shell height derived from nearby IGS stations. To validate this method, we selected two dense networks of IGS stations located in regions in the US and Europe. Two optimal ionospheric shell height models are established by two reference stations, namely GOLD and PTBB, which are located at the approximate center of two selected regions. The predicted daily optimal ionospheric shell heights by the two models are applied to other IGS stations around these two reference stations. Daily DCBs are calculated according to these two optimal shell heights and compared to respective DCBs released by CODE. The validation results of this method are as follows. (1) Optimal ionospheric shell height calculated by IGS stations can be applied to its nearby non-IGS stations or isolated GNSS receivers for accurate TEC estimation. (2) As the distance away from the reference IGS station becomes larger, the DCB estimation error becomes larger. The relation between the DCB estimation error and the distance is generally linear.
Highlights
Dual-frequency GPS signal propagation is affected effectively by ionospheric dispersive characteristics
For the five selected international GNSS service (IGS) stations, the results have shown that the optimal ionospheric shell height models improve the accuracies of differential code bias (DCB) and total electron content (TEC) estimation compared to a fixed ionospheric shell height of 400 km in a statistical sense
We implement and validate a method to transfer the optimal ionospheric shell height derived for IGS stations to non-IGS stations or isolated GNSS receivers
Summary
Dual-frequency GPS signal propagation is affected effectively by ionospheric dispersive characteristics Taking advantage of this property, ionospheric total electron content (TEC) along the path of signal can be estimated by differencing the pseudorange or carrier phase observations from dual-frequency GPS signals. Sovers and Fanselow (1987) firstly simplified the ionosphere to a spherical shell They set the bottom and the top side of the ionospheric shell as h−35 and h + 75 km, where h is taken to be 350 km above the surface of the earth and allowed to be adjusted. In this model, the electron density was evenly distributed in the vertical direction. Based on this model, Sardón et al (1994) introduced the Kalman filter method for real-time ionospheric vertical TEC (VTEC) estimation, which can be a promising prediction of DCBs under adverse conditions (antispoofing, ionospheric disturbances). Klobuchar (1987) assumed that STEC equals VTEC multiplied by the approximation of the standard geometric mapping function at the mean vertical height of 350 km along the path of STEC. Lanyi and Roth (1988)
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