Abstract
In [1-3], we have preliminary developed a method of estimating the local models of an ionosphere VTEC (Vertical Total Electron Content) based on GNSS regression models (abbreviated by GR models) and have shown the ionospheric delay (or advance) in the sky over Japan using the Gps Earth Observation NETwork (GEONET) data provided from the Geographical Survey Institute (GSI) of Japan [4]. In this paper, we try to refine the local models based on the orthogonal polynomials for VTEC at the ionospheric pierce points in the ionospheric single layer model with by comparing with the Taylor series expansion. Furthermore from the aspect of model fitting, we discuss the best number of orthogonal polynomials for the local model of VTEC from informational theoretical points of views such as AIC [5] and BIC [6].
