Abstract
The Ionosphere Working Group of the International GNSS Service (IGS) has been a reliable source of global ionospheric maps (GIMs) since 1998. Modeling of the global ionospheric total electron content (TEC) is performed daily by several Ionosphere Associate Analysis Centers (IAACs). Four IAACs (CODE, ESA, CAS and WHU) use the spherical harmonic (SH) expansion as their primary method for modeling GIMs. The IAACs generally solve a normal equation to obtain the SH coefficients and Differential Code Biases (DCBs) of satellites and receivers by traditional least-squares estimation (LSE) without any prior knowledge. In this contribution, an improved method is proposed and developed for global ionospheric modeling based on utilizing prior knowledge. Prior values of SH coefficients and DCBs of satellites and receivers, as well as the variance factor and covariance matrix, could be obtained from the ionospheric modeling on the previous day. The parameters can subsequently be updated through GNSS measurements to achieve higher accuracy. Comparisons are carried out between WHU products based either on priori information or original LSE and IGS final products, other IAAC products, and JASON data for the year 2014. The results indicate that there is improved consistency between WHU GIMs and IGS final GIMs, other IAAC products, and JASON data, particularly in comparison with ESA and UPC products, with the probabilities of achieving better consistency with these products exceeding 95%. Moreover, WHU-produced DCBs of satellites also have slightly improved consistency with IGS final GIMs and IAAC products.
Highlights
The ionosphere plays an important role in the Earth’s upper atmosphere
It should be noted that the denominator in Equation (5) is n − t if the equation is solved by least-squares estimation (LSE)
root mean square (RMS) decrease of differences in vertical TEC (VTEC) maps between Wuhan University (WHU) global ionospheric maps (GIMs) based on Bayesian estimation estimation and Ionosphere Associate Analysis Centers (IAACs) GIMs compared to those between GIMs based on original LSE and the International global navigation satellite system (GNSS) Service (IGS) final and IAAC
Summary
The ionosphere plays an important role in the Earth’s upper atmosphere. The ionospheric total electron content (TEC) is a significant parameter for satellite navigation and for scientific studies of the ionosphere and space weather. The further improvement of global vertical TEC (VTEC) maps remains as an important goal. Ionospheric empirical model IRI 2012 was used to provide VTEC values as virtual measurements for global ionospheric modeling and the release of improved GIMs [10]. Additional a priori information could be available before the daily modeling of global ionospheric VTEC values, such as the coefficients of the model, DCBs of satellites and receivers, and the standard deviation of and information about the normal equation from the ionospheric modeling on the previous day. The study’s conclusions are presented in the last section
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