Abstract
Global ionospheric total electron content (TEC) is generally derived with ground-based Global Navigation Satellite System (GNSS) observations based on mathematical models in a solar-geomagnetic reference frame. However, ground-based observations are not well-distributed. There is a lack of observations over sparsely populated areas and vast oceans, where the accuracy of TEC derivation is reduced. Additionally, the modified dip (modip) latitude is more suitable than geomagnetic latitude for the ionosphere. This paper investigates the improvement of global TEC with multi-source data and modip latitude, and a simulation with International Reference Ionosphere (IRI) model is developed. Compared with using ground-based observations in geomagnetic latitude, the mean improvement was about 10.88% after the addition of space-based observations and the adoption of modip latitude. Nevertheless, the data from JASON-2 satellite altimetry and COSMIC occultation are sparsely-sampled, which makes the IRI TEC a reasonable estimation for the areas without observation. By using multi-source data from ground-based, satellite-based and IRI-produced observations, global TEC was derived in both geomagnetic and modip latitudes for 12 days of four seasons in 2014 under geomagnetic quiet conditions. The average root-mean-square error (RMSE) of the fitting was reduced by 7.02% in modip latitude. The improvement was largest in March and smallest in June.
Highlights
The ionosphere is the ionized part of Earth’s upper atmosphere, in the range of 60~1000 km above the ground
Alizadeh et al [13] obtained global ionospheric maps (GIMs) in geomagnetic latitude through combining observations from Global Navigation Satellite System (GNSS), satellite altimetry and occultation measurements, and the results show that the root-mean-square error (RMSE) of the combined GIMs is decreased when compared with the results of fitting with ground-based GNSS data
It can be seen from the GIMs that the phenomenon of equatorial ionospheric anomaly (EIA) is clear near the magnetic equator, and there is no obvious unreasonable value due to the use of multi-source data
Summary
The ionosphere is the ionized part of Earth’s upper atmosphere, in the range of 60~1000 km above the ground. Radio signals of satellite systems, such as Global Navigation Satellite Systems (GNSSs), traveling through the ionosphere are delayed in time and advanced in phase, which are proportional to the integration of electron density along the signal propagation path and referred to as total electron content (TEC). This provides a means to obtain TEC from the differences in time delays or phase advances of dual-frequency satellite observations. With the rapid development of GNSS applications, global TEC has been effectively measured at low-cost with ground-based GNSS receivers. In TEC derivation from GNSSs, the task of assessing differential code biases (DCBs), which originate in the hardware of the satellite and the receiver, and obtaining absolute
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