Local Ionospheric Modeling Using the Localized Global Ionospheric Map and Terrestrial GPS

Mohammad Ali Sharifi,Saeed Farzaneh

doi:10.1515/acgeo-2015-0065

Abstract

global ionosphere maps are generated on a daily basis at CODE using data from about 200 GPS/GLONASS sites of the IGS and other institutions. The vertical total electron content is modeled in a solargeomagnetic reference frame using a spherical harmonics expansion up to degree and order 15. The spherical Slepian basis is a set of bandlimited functions which have the majority of their energy concentrated by optimization inside an arbitrarily defined region, yet remain orthogonal within the spatial region of interest. Hence, they are suitable for decomposing the spherical harmonic models into the portions that have significant strength only in the selected areas. In this study, the converted spherical harmonics to the Slepian bases were updated by the terrestrial GPS observations by use of the least-squares estimation with weighted parameters for local ionospheric modeling. Validations show that the approach adopted in this study is highly capable of yielding reliable results.

Highlights

A layer of atmosphere between the altitudes of about 60 to 2000 km above the Earth’s surface is called ionosphere, where the solar radiation produces partially ionized plasma of different gas components
Ionospheric models are divided into three main categories: one group includes physical models, in which ionospheric changes are simulated based on the physical laws or the assumptions concerning the structure and variations of the ionosphere, e.g., the Global Assimilative Ionospheric Model (GAIM) (Schunk et al 2004); another group is known as empirical models, including the International Reference Ionosphere (IRI; Bilitza et al 2011) or the NeQuick (Angrisano et al 2013, Radicella et al 2008); and the third group consists of mathematical models, which are mainly based on the observations of the ionosphere
The 3-D modeling is based on latitude, longitude, and height, in which the slant total electron content (STEC; i.e., the number of electrons which are present in a column of 1 m2 cross-section and extend along the ray-path of the signal between global positioning system (GPS) satellites and the ground receiver) measurements are inverted into electron density distribution using tomographic approaches

Summary

Introduction

A layer of atmosphere between the altitudes of about 60 to 2000 km above the Earth’s surface is called ionosphere, where the solar radiation produces partially ionized plasma of different gas components. Mainly two approaches are applied to model the spatial distribution of ionospheric density using GPS observations, i.e., twodimensional (2-D) or three-dimensional (3-D) models of the electron density. The 3-D modeling is based on latitude, longitude, and height, in which the slant total electron content (STEC; i.e., the number of electrons which are present in a column of 1 m2 cross-section and extend along the ray-path of the signal between global positioning system (GPS) satellites and the ground receiver) measurements are inverted into electron density distribution using tomographic approaches (for a comprehensive overview about various techniques of ionospheric density modeling, see, e.g., García-Fernández 2004). In 2-D approaches, a single-layer model (SLM) tends to be adopted for ionospheric density changes. Since GPS basically provides the measurements of slant total electron content, an elevation-dependent mapping function is required to describe the ratio between the STEC and VTEC

Methods

Results

Conclusion