EGU General Assembly 2013, 7 – 12 April 2013, Vienna, Austria

This study:

• is pioneer in modeling the upper atmosphere, using space geodetic techniques,• includes geophysical parameters, i.e. F2-peak electron density and its

corresponding height,• provides information about the ionosphere at different altitudes.

Our further steps are:• Applying real GNSS observations,• Integrating data from different space geodetic techniques,• Taking curvature effect and higher-order ionospheric effects into account, using ray-

tracing technique,• Estimating plasmaspheric parameters as well as characteristic parameters of other

layers as individual unknowns,• 4D modeling of electron density applying Fourier series expansion.

References• Alizadeh M. Multi-dimensional modeling of the ionospheric parameters, using space geodetic

techniques, Ph.D. thesis, Vienna University of Technology, February 2013, in press.• Feltens J., Chapman Profile Approach for 3-D Global TEC Representation., Proceedings of the

1998 IGS Analysis Workshop, ESOC, Darmstadt, Germany, February 1998.

1. Introduction

Three-dimensional Reconstruction of Ionosphere/Plasmasphere using GNSS measurementsAlizadeh M.M. (1), 2, Schuh H.1, 2, Schmidt M.3

1. Research Group Advanced Geodesy, Department of Geodesy and Geoinformation, Vienna University of Technology, Austria

2. Department of Geodesy and Geoinformation Science, Technical University of Berlin, Berlin, Germany

3. Deutsches Geodätisches Forschungsinstitut (DGFI), Munich, Germany

alizadeh@mail.tuwien.ac.at

6. Results

7. Conclusions and Outlook

The project MDION (P22203-N22) is funded by the Austrian Science Fund (FWF)

Acknowledgement

The dispersion of the ionosphere pertaining to the microwave signals allows gaining information about this medium. Among different systems observing the ionosphere, space geodetic techniques have turned into a promising tool for monitoring and modeling the ionospheric parameters in terms of Total Electron Content (TEC) or electron density along the ray path. The relevant input data for modeling ionospheric parameters is the ionospheric observable (L4) and is formed from the phase-smoothed code pseudorange obtained from dual-frequency GNSS measurements. L4 is related to the ionospheric electron density using adequate profile function. Within this study, we apply a combination of the multi-layer Chapman profile function for the bottom-side and topside ionosphere, and a separate profile function for the plasmasphere. As a first step of this study, we assume the plasmaspheric contribution to be known, and concentrate only on the ionospheric part. To model the ionospheric electron density in globe, the parameters of electron density, i.e. the maximum electron density, and its corresponding height are modeled using two sets of spherical harmonics expansion. The coefficients of two sets of spherical harmonics expansions are obtained through recursive parameter stimation technique applying appropriate constraints.

2. TEC observable and Chapman function

The main observable is the GNSS geometry-free linear combination of phase leveled to code (TEC observable)

STEC is the integral of ionospheric electron density along the signal path:

In this study we combine two models to represent electron density:

Multi-layer Chapman function (Feltens et.al 2010) for bottomside ionosphere, and TIP model (Jakowski et.al 2011) for top-side ionosphere/plasmasphere

(1)

(2)

4. Simulating input data

As an experimental step, we simulate the input data. Since STEC in Eq. (1) is related to VTEC using a mapping function F(z’)

where z‘ is the satellite zenith angle at the Ionosphere Pierce Point (IPP). The additional terms in Eq. (5) could be neglected when using simulated data, so the relation would be simplified to

(6)

5. Estimation Procedure

Figures below depict estimated results for the snap-shot at [0,2] UT, day 182, 2010.

Fig. 5(a) Estimated maximum electron density ( ×1011 elec/m3) and (b) estimated maximum electron density height (km) GNSS estimated model, doy 182, 2010 – [0,2]UT

(3)

(4)

3. Ray-tracing technique

To solve the integral in Eq. (4) numerically, a ray-tracing technique is deployed. Using this technique the values for satellite zenith angle, solar zenith angle, height increment at each layer, and height of layer above the Earth’s surface can be determined. So the integration in Eq. (4) will turn into a simple summation: Fig.2 – Curved and straight ray-paths

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Fig.1 – Expressing electron density with Chapman function

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VTEC values for all IPP of GNSS observations are extracted from IGS VTEC maps.

Fig. 3 – input data with true GNSS ray-path, but simulated values from IGS GIM

In Eq. (5) plasmaspheric contribution is neglected and only bottom-side ionosphere is presented.

where

Substituting electron density from Eq. (3) into TEC observable Eq. (2) and Eq.(1), we obtain the relation between TEC observable and electron density:

• Calculating a priori values

Simulated using IGS VTEC Calculated using IRI-2012 Calculated using ray-tracing

Figure 4 – (a) Maximum electron density (elec/m3), and (b) maximum electron density height (km) from IRI background model, doy 182, 2010 – [0,2] UT

• Representing unknown parameters with spherical harmonics

• Applying constraints

o Global mean constraint (for estimating Nm and hm)

o Surface function (for estimating Nm) (Feltens et al. 2010)

zero-degree SH coefficients and

predefined height range

small numerical constant

geomagnetic latitude

local time

To illustrate a better understanding of the estimated parameters, the related Nm and hm values are depicted in a 3D conjunction plot:

Fig. 6 – 3D model of F2-peak electron density for day 182, 2010 - [0,2]UT; color bar indicates the maximum electron density (x1011 elec/m3) and the Z-axis indicates maximum electron density height in km

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