Browsing by Subject "IRI-Plas"

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    3D electron density estimation in the ionosphere
    (IEEE, 2014) Tuna, Hakan; Arıkan, Orhan; Arıkan, F.
    Ionosphere has ion distribution which is variable in space and time. There have been physical and empirical studies for modeling the ionosphere. International Reference Ionosphere extended to Plasmasphere (IRI-Plas) is the most recent model developed for this purpose. However, IRI-Plas presents a model about the ionosphere and its compliance with the instantaneous state of the ionosphere does not provide the accuracy needed for engineering purposes. One of the important information sources about the instantaneous state of the ionosphere is GPS signals. In this study, constructing the ionosphere which is compatible with both the instantaneous ionosphere measurements and the physical structure of the ionosphere is presented as an optimization problem, and solved by using the particle swarm optimization technique. The ionosphere over Turkey is investigated by using the proposed optimization method and the importance of the instantaneous ionosphere measurements obtained from GPS signals is demonstrated.
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    Performance of GPS slant total electron content and IRI-Plas-STEC for days with ionospheric disturbance
    (KeAi Communications Co., 2016) Arikan, F.; Shukurov, S.; Tuna, H.; Arıkan, Orhan; Gulyaeva, T. L.
    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 estimation of TEC between the earth based receiver and Global Positioning System (GPS) satellites became the major means of investigation of local and regional disturbance for earthquake precursor and augmentation system studies. International Reference Ionosphere (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 (www.ionolab.org) 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.
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    Regional model-based computerized ionospheric tomography using GPS measurements: IONOLAB-CIT
    (Wiley-Blackwell Publishing, Inc., 2015) Tuna, H.; Arıkan, Orhan; Arikan, F.
    Three-dimensional imaging of the electron density distribution in the ionosphere is a crucial task for investigating the ionospheric effects. Dual-frequency Global Positioning System (GPS) satellite signals can be used to estimate the slant total electron content (STEC) along the propagation path between a GPS satellite and ground-based receiver station. However, the estimated GPS-STEC is very sparse and highly nonuniformly distributed for obtaining reliable 3-D electron density distributions derived from the measurements alone. Standard tomographic reconstruction techniques are not accurate or reliable enough to represent the full complexity of variable ionosphere. On the other hand, model-based electron density distributions are produced according to the general trends of ionosphere, and these distributions do not agree with measurements, especially for geomagnetically active hours. In this study, a regional 3-D electron density distribution reconstruction method, namely, IONOLAB-CIT, is proposed to assimilate GPS-STEC into physical ionospheric models. The proposed method is based on an iterative optimization framework that tracks the deviations from the ionospheric model in terms of F2 layer critical frequency and maximum ionization height resulting from the comparison of International Reference Ionosphere extended to Plasmasphere (IRI-Plas) model-generated STEC and GPS-STEC. The suggested tomography algorithm is applied successfully for the reconstruction of electron density profiles over Turkey, during quiet and disturbed hours of ionosphere using Turkish National Permanent GPS Network.