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Spectral investigation of traveling ionospheric disturbances:IONOLAB-FFT

Geodesy and Geodynamics 2017年第5期8卷 297-304页

作者： feza arikan Aysenur Yarici Hacettepe University Department of Electrical and Electronics Engineering

Ionosphere is an important layer of atmosphere which is under constant forcing from both below due to gravitational, geomagnetic and seismic activities, and above due to solar wind and galactic radiation. Spatio-temporal variability of ionosphere is made up of two major components that can be listed as spatio-temporal trends and secondary variabilities that are due to disturbances in the geomagnetic field, gravitational waves and coupling of seismic activities into the upper atmosphere and ionosphere. Some of these second order variabilities generate wave-like oscillations in the ionosphere which propagate at a certain frequency, duration and velocity. These oscillations cause major problems for navigation and guidance systems that utilize GNSS （Global Navigation Satellite Systems）. In this study, the frequency and duration of wave-like oscillations are determined using a DFT （Discrete Fourier Transform） based algo- rithm over the STEC （slant total electron content） values estimated from single GPS （Global Positioning System） station. The performance of the developed method, namely IONOLAB-FFT, is first determined using synthetic oscillations with known frequencies and durations. Then, IONOLAB-FFr is applied to STEC data from various midlatitude GPS stations for detection of frequency and duration of both medium and large scale TIDs （traveling ionospheric disturbances）. It is observed that IONOLAB-FFr can estimate TIDs with more than 80% accuracy for the following cases： frequencies from 0.6 mHz to 2.4 mHz and durations longer than 10 min; frequencies from 0.15 mHz to 0.6 mHz and durations longer than 50 min; fre- quencies higher than 0.29 mHz and durations longer than 50 rain.

关键词： IonosphereTID (traveling ionospheric disturbances)GPS (Global Positioning System)TEC (total electron content)IONOLAB-FFF

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维普期刊数据库

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Dynamo equation solution using Finite Volume Method for midlatitude ionosphere

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Geodesy and Geodynamics 2018年第6期9卷 425-431页

作者： feza arikan Umut Sezen Orhan arikan Department of Electrical and Electronics Engineering Hacettepe University Department of Electrical and Electronics Engineering Bilkent University

Ionosphere is the layer of atmosphere which plays an important role both in space based navigation,positioning and communication systems and HF signals. The structure of the electron density is a function of spatio-temporal variables. The electrodynamic medium is also influenced with earth’s magnetic field, atmospheric chemistry and plasma flow and diffusion under earth’s gravitation. Thus, the unified dynamo equation for the ionosphere is a second order partial differential equation for quasi-static electric potential with variable spatial coefficients. In this study, the inhomogeneous and anisotropic nature of ionosphere that can be formulated as a divergence equation is solved numerically using Finite Volume Method for the first time. The ionosphere and the operators are discretized for the midlatitude region and the solution domain is investigated for Dirichlet type boundary conditions that are built in into the diffusion equation. The analysis indicates that FVM can be a powerful tool in obtaining parametric electrostatic potential distribution in ionosphere.

关键词： Ionosphere Finite volume method(FVM) Dynamo equation Electric potential

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维普期刊数据库

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NVIS HF signal propagation in ionosphere using calculus of variations

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Geodesy and Geodynamics 2019年第1期10卷 72-76页

作者： Umut Sezen feza arikan Orhan arikan Department of Electrical and Electronics Engineering Hacettepe University Department of Electrical and Electronics Engineering Bilkent University

Modeling Near Vertical Incidence Sounding(NVIS) High Frequency(HF) signal propagation in the ionosphere is important. Because, ionosondes which are special types of radars probing the ionosphere with certain HF frequencies(between 2 and 30 MHz), work mostly in NVIS mode(where elevation angle is between 89 and 90°). In this work, we are going to propose a new method for NVIS wave propagation in the ionosphere by discretizing the NVIS wave propagation path into mediums in which the refractive index changes linearly, where we solve the ray propagation in each medium analytically using calculus of variations and use Snell's Law at medium changes. The main advantage of the proposed solution is the reduced computational complexity and time. This algorithm can be used to simulate and compare the behavior of vertical ionosondes together with other ray tracing algorithms.

关键词： Ionosphere HF propagation Calculus of variations

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维普期刊数据库

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Online computation of International Reference Ionosphere Extended to Plasmasphere(IRI-Plas) model for space weather

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Geodesy and Geodynamics 2018年第5期9卷 347-357页

作者： Umut Sezen T.L.Gulyaeva feza arikan Department of Electrical and Electronics Engineering Hacettepe University IZMIRAN

Ionosphere is the most challenging part of Space Weather with its spatio-temporal variability and dispersive nature. Ionospheric models are very important in reducing positioning error in GNSS *** Reference Ionosphere(IRI) is an empirical, deterministic and climatic model of ionosphere up to 2000 km in height. Recently, IRI Extended to Plasmasphere(IRI-Plas) model has been developed to extend the interest region of IRI to the GPS orbital height of 20,000 km. Both IRI and IRI-Plas provide ionospheric parameters such as electron density, electron and ion temperatures according to their height profiles. In order to update the model to current ionospheric conditions, IRI-Plas can input F2 layer critical frequency(foF2), maximum ionization height(hmF2), and also Total Electron Content(TEC).Online IRI-Plas is developed for the ionospheric community to run multiple tasks at various locations,dates and times with optional foF2, hmF2 and TEC inputs in a user-friendly manner. In this paper, we are going to present the capabilities of the Online IRI-Plas service and provide some comparisons between IRI-Plas outputs and ionosonde measurements. The comparison between online IRI-Plas foF2 outputs and ionosonde foF2 measurements indicates that the model with TEC input can significantly improve the representation of the current ionospheric state, which is very successful especially in the geomagnetically disturbed days.

关键词： Ionosphere Space weather IRI-Plas GPS TEC IONOLAB

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维普期刊数据库

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Performance of GPS slant total electron content and IRI-Plas-STEC for days with ionospheric disturbance

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Geodesy and Geodynamics 2016年第1期7卷 1-10页

作者： feza arikan Seymur Shukurov Hakan Tuna Orhan arikan T.L. Gulyaeva Department of Electrical and Electronics Engineering Hacettepe University Beytepe Ankara 06800 Turkey Department of Electrical and Electronics Engineering Bilkent Uniuersity Bilkent Ankara 06800 Turkey IZMIRAN Moscow 142190 Troitsk Russian Federation

Total Electron Content （TEC） is an important observable parameter of the ionosphere which forms the main source of error for space based navigation and positioning systems. Since the deployment of Global Navigation Satellite Systems （GNSS）, cost-effective esti- mation of TEC between the earth based receiver and Global Positioning System （GPS） sat- ellites became the major means of investigation of local and regional disturbance for earthquake precursor and augmentation system studies. International Reference Iono- sphere （IRI） extended to plasmasphere （IRI-Plas） is the most developed ionospheric and plasmaspheric climatic model that provides hourly, monthly median of electron density distribution globally. Recently, IONOLAB group {***） has presented a new online space weather service that can compute slant TEC （STEC） on a desired ray path for a given date and time using IRI-Plas model （IRI-Plas-STEC）. In this study, the performance of the model based STEC is compared with GPS-STEC computed according to the estimation method developed by the IONOLAB group and includes the receiver bias as IONOLAB-BIAS （IONOLAB-STEC）. Using Symmetric Kullback-Leibler Distance （SKLD）, Cross Correlation （CC） coefficient and the metric norm （L2N） to compare IRI-Plas-STEC and IONOLAB-STEC for the month of October 2011 over the Turkish National Permanent GPS Network （TNPGN- Active）, it has been observed that SKLD provides a good indicator of disturbance for both earthquakes and geomagnetic storms.

关键词： IonosphereTotal Electron Content (TEC)GPSIRI-Plas

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