Browsing by Author "Karatay S."

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Classification of regional ionospheric disturbance based on machine learning techniques
(2016-08-01) Terzi M.B.; Arikan O.; Karatay S.; Arikan F.; Gulyaeva T.
In this study, Total Electron Content (TEC) estimated from GPS receivers is used to model the regional and local variability that differs from global activity along with solar and geomagnetic indices. For the automated classification of regional disturbances, a classification technique based on a robust machine learning technique that have found wide spread use, Support Vector Machine (SVM) is proposed. Performance of developed classification technique is demonstrated for midlatitude ionosphere over Anatolia using TEC estimates generated from GPS data provided by Turkish National Permanent GPS Network (TNPGN-Active) for solar maximum year of 2011. As a result of implementing developed classification technique to Global Ionospheric Map (GIM) TEC data, which is provided by the NASA Jet Propulsion Laboratory (JPL), it is shown that SVM can be a suitable learning method to detect anomalies in TEC variations.
Detection of the ionospheric disturbances on GPS-TEC using Differential Rate Of TEC (DROT) algorithm
(2020-05-15) Karatay S.
The solar, geomagnetic, gravitational and seismic activities can cause spatial and temporal (hourly, diurnal, seasonal and annual) variabilities of the ionosphere. Main observable ionospheric parameters such as Total Electron Content (TEC) can be used to quantify these. TEC is the total number of electrons on a ray path crossing the atmosphere. The network of world-wide Global Positioning System (GPS) receivers provide a cost-effective solution in estimating TEC over a significant proportion of global land mass. This study is focused on the analysis of the variations of ionosphere over a midlatitude region using GPS-TEC estimates for three Sun Spot Numbers (SSN) periods. The investigation is based on a fast and automatic variability detection algorithm, Differential Rate Of TEC (DROT). The algorithm is tested using literature data on disturbances generated by a geomagnetic activity, a Solar Flare, a Medium Scale Travelling Ionospheric Disturbance (MSTID), a Large Scale TID (LSTID) and an earthquake. Very good agreement with the results in the literature is found. DROT is applied to IONOLAB-TEC estimates from nine Turkish National Permanent GPS Network (TNPGN Active) stations over Turkey to detect the any wave-like oscillations, sudden disturbances and other irregularities during December, March, June, September months for 2010, 2011, 2012 years. It is observed that DROT algorithm is capable of detecting both small and large scale variability due to climatic, gravitational, geomagnetic and solar activities in all layers of ionosphere. The highest DROT values are observed in 2010 during winter months. In higher solar activity years of 2011 and 2012, DROT is able to indicate both seasonal variability and severe changes in ionosphere due to increased number of geomagnetic storms and local seismic activities.
Detection of the ionospheric disturbances on GPS-TEC using Differential Rate Of TEC (DROT) algorithm
(2020-05-15) Karatay S.; Karatay, S
The solar, geomagnetic, gravitational and seismic activities can cause spatial and temporal (hourly, diurnal, seasonal and annual) variabilities of the ionosphere. Main observable ionospheric parameters such as Total Electron Content (TEC) can be used to quantify these. TEC is the total number of electrons on a ray path crossing the atmosphere. The network of world-wide Global Positioning System (GPS) receivers provide a cost-effective solution in estimating TEC over a significant proportion of global land mass. This study is focused on the analysis of the variations of ionosphere over a midlatitude region using GPS-TEC estimates for three Sun Spot Numbers (SSN) periods. The investigation is based on a fast and automatic variability detection algorithm, Differential Rate Of TEC (DROT). The algorithm is tested using literature data on disturbances generated by a geomagnetic activity, a Solar Flare, a Medium Scale Travelling Ionospheric Disturbance (MSTID), a Large Scale TID (LSTID) and an earthquake. Very good agreement with the results in the literature is found. DROT is applied to IONOLAB-TEC estimates from nine Turkish National Permanent GPS Network (TNPGN Active) stations over Turkey to detect the any wave-like oscillations, sudden disturbances and other irregularities during December, March, June, September months for 2010, 2011, 2012 years. It is observed that DROT algorithm is capable of detecting both small and large scale variability due to climatic, gravitational, geomagnetic and solar activities in all layers of ionosphere. The highest DROT values are observed in 2010 during winter months. In higher solar activity years of 2011 and 2012, DROT is able to indicate both seasonal variability and severe changes in ionosphere due to increased number of geomagnetic storms and local seismic activities.
Estimation of frequency and duration of ionospheric disturbances over Turkey with IONOLAB-FFT algorithm
(2020-09-01) Karatay S.
One of the more common methods of observation of variability of the Earth’s ionosphere is based on total electron content (TEC) estimated from ground-based dual-frequency Global Positioning System (GPS) receivers. Variations in solar, geomagnetic and seismic activity cause depletions or enhancements in the ionospheric electron concentrations that can be detected as disturbances. Some of these disturbances have wave-like characteristics, where frequency of oscillation can be used to identify and classify the disturbance. In this study, the frequency of such periodic disturbances is estimated using a fast Fourier transform (FFT)-based method, namely IONOLAB-FFT, in the spectral domain. IONOLAB-FFT, which was initially developed to be used on slant TEC (STEC), is modified to be applied to TEC in the local zenith direction of the receiver. The algorithm is tested using literature data on disturbances generated by a geomagnetic activity, a solar flare, a medium-scale traveling ionospheric disturbance (MSTID), a large-scale TID (LSTID) and an earthquake. An accordance with these known disturbances is observed in running IONOLAB-FFT, and the main frequencies and durations of the disturbances are estimated. IONOLAB-FFT method is applied to TEC computed from Turkish Permanent GPS Network (TNPGN-Active) which lies in mid-latitude region to detect the any wave-like oscillations, sudden disturbances and other irregularities during December, March, June and September months for 2010, 2011 and 2012 years. It is observed that a large number of the estimated frequencies are accumulated between 0.08 and 0.14 MHz corresponding to periods of 3.5 h to 2 h. The significant frequencies are grouped less than 0.28 MHz. A large number of the durations of the oscillations are between 425 and 550 min in 2010, 300 and 550 min in 2011 and 350 and 400 min in 2012. The longest duration (around 800 min: 13.33 h) is observed in December months, and the shortest duration (around 2 h) is observed in September months.
Estimation of frequency and duration of ionospheric disturbances over Turkey with IONOLAB-FFT algorithm
(2020-09-01) Karatay S.; Karatay, S
One of the more common methods of observation of variability of the Earth’s ionosphere is based on total electron content (TEC) estimated from ground-based dual-frequency Global Positioning System (GPS) receivers. Variations in solar, geomagnetic and seismic activity cause depletions or enhancements in the ionospheric electron concentrations that can be detected as disturbances. Some of these disturbances have wave-like characteristics, where frequency of oscillation can be used to identify and classify the disturbance. In this study, the frequency of such periodic disturbances is estimated using a fast Fourier transform (FFT)-based method, namely IONOLAB-FFT, in the spectral domain. IONOLAB-FFT, which was initially developed to be used on slant TEC (STEC), is modified to be applied to TEC in the local zenith direction of the receiver. The algorithm is tested using literature data on disturbances generated by a geomagnetic activity, a solar flare, a medium-scale traveling ionospheric disturbance (MSTID), a large-scale TID (LSTID) and an earthquake. An accordance with these known disturbances is observed in running IONOLAB-FFT, and the main frequencies and durations of the disturbances are estimated. IONOLAB-FFT method is applied to TEC computed from Turkish Permanent GPS Network (TNPGN-Active) which lies in mid-latitude region to detect the any wave-like oscillations, sudden disturbances and other irregularities during December, March, June and September months for 2010, 2011 and 2012 years. It is observed that a large number of the estimated frequencies are accumulated between 0.08 and 0.14 MHz corresponding to periods of 3.5 h to 2 h. The significant frequencies are grouped less than 0.28 MHz. A large number of the durations of the oscillations are between 425 and 550 min in 2010, 300 and 550 min in 2011 and 350 and 400 min in 2012. The longest duration (around 800 min: 13.33 h) is observed in December months, and the shortest duration (around 2 h) is observed in September months.
Ionospheric responses during equinox and solstice periods over Turkey
(2017-11-01) Karatay S.; Cinar A.; Arikan F.
Ionospheric electron density is the determining variable for investigation of the spatial and temporal variations in the ionosphere. Total Electron Content (TEC) is the integral of the electron density along a ray path that indicates the total variability through the ionosphere. Global Positioning System (GPS) recordings can be utilized to estimate the TEC, thus GPS proves itself as a useful tool in monitoring the total variability of electron distribution within the ionosphere. This study focuses on the analysis of the variations of ionosphere over Turkey that can be grouped into anomalies during equinox and solstice periods using TEC estimates obtained by a regional GPS network. It is observed that noon time depletions in TEC distributions predominantly occur in winter for minimum Sun Spots Numbers (SSN) in the central regions of Turkey which also exhibit high variability due to midlatitude winter anomaly. TEC values and ionospheric variations at solstice periods demonstrate significant enhancements compared to those at equinox periods.
Prediction of GPS-TEC on Mw>5 Earthquake Days Using Bayesian Regularization Backpropagation Algorithm
(2023-01-01) Karatay S.; Gul S.E.
Detection of earthquake precursor signals a few days before the earthquake day is one of the most studied subjects today. In recent years, a strong correlation is observed between earthquakes and ionospheric parameters. In this study, a Feed Forward Backpropagation Artificial Neural Network Bayesian Regularization algorithm is applied to detect the seismic disturbances and anomalies by predicting GPS-TEC on earthquake days with magnitude greater than 5. It is observed that TEC is predicted with greater error margins for the stations at a maximum distance of 50 km from the epicenters. The errors for earthquakes less than Mw 7 are smaller than those for greater than 7.
Space weather studies of IONOLAB group
(2016-10-19) Arikan F.; Sezen U.; Toker C.; Artuner H.; Bulu G.; Demir U.; Erdem E.; Arikan O.; Tuna H.; Gulyaeva T.; Karatay S.; Mosna Z.
IONOLAB is an interdisciplinary research group dedicated for handling the challenges of near earth environment on communication, positioning and remote sensing systems. IONOLAB group contributes to the space weather studies by developing state-of-the-art analysis and imaging techniques. On the website of IONOLAB group, www.ionolab.org, four unique space weather services, namely, IONOLAB-TEC, IRI-PLAS-2015, IRI-PLAS-MAP and IRI-PLAS-STEC, are provided in a user friendly graphical interface unit. Newly developed algorithm for ionospheric tomography, IONOLAB-CIT, provides not only 3-D electron density but also tracking of ionospheric state with high reliability and fidelity. The algorithm for ray tracing through ionosphere, IONOLAB-RAY, provides a simulation environment in all communication bands. The background ionosphere is generated in voxels where IRI-Plas electron density is used to obtain refractive index. One unique feature is the possible update of ionospheric state by insertion of Total Electron Content (TEC) values into IRI-Plas. Both ordinary and extraordinary paths can be traced with high ray and low ray scenarios for any desired date, time and transmitter location. 2-D regional interpolation and mapping algorithm, IONOLAB-MAP, is another tool of IONOLAB group where automatic TEC maps with Kriging algorithm are generated from GPS network with high spatio-temporal resolution. IONOLAB group continues its studies in all aspects of ionospheric and plasmaspheric signal propagation, imaging and mapping.
Spatio-Temporal Prediction of Ionospheric Total Electron Content Using an Adaptive Data Fusion Technique
(2019-12-01) Faruk Erken; Karatay S.; Cinar A.
Abstract: The ionosphere, a part of upper atmosphere, plays an important role on the propagation of radio waves. Hence, understanding, remote sensing and monitoring of the ionospheric phenomena can provide a compressive description to the physical process that are affected by the behavior of ionosphere. One of descriptive quantity of ionosphere is Total Electron Content (TEC). TEC is the total number of electrons integrated between two points and characterized by observing carrier phase delays of received radio signals transmitted from satellites located above the ionosphere, often using Global Positioning System (GPS) satellites. In this study, TEC is predicted from TEC estimates obtained from GPS network located in Turkey in space and time using an Adaptive Data Fusion Technique (ADF). It is observed that characteristic distributions of the predict TEC and original TEC values are similar with each other. Mean Square Errors are less than 4 TECU. ADF has a high performance for the spatio-temporal prediction when the results are compared with the techniques used in the related studies in the literature.
Temporal variations of the ionospheric disturbances due to the seasonal variability over Turkey using IONOLAB-FFT algorithm
(2020-05-01) Karatay S.
The ionosphere is exposed to forcing from below due to gravitational, geomagnetic and seismic activities, and above due to solar wind. These forces cause some medium and large scale irregularities and disturbances into the upper atmosphere and ionosphere. Some of these disturbances occur in the form of wave-like oscillations in the ionosphere which propagate at a certain frequency, duration and velocity. These disturbances can be detected by monitoring the ionosphere using Total Electron Content obtained from Global Positioning System (GPS-TEC). In this study, the temporal analysis of these disturbances due to the seasonal variability is carried out for a mid-latitude GPS network using Ionosphere Research Laboratory TEC (IONOLAB-TEC) over Turkey. The IONOLAB Fast Fourier Transform (FFT) algorithm is applied to GPS-TEC obtained from nine Turkish National Permanent GPS Network (TNPGN) active stations in Turkey for December (winter solstice), March (spring equinox), June (summer solstice), September (autumn equinox) months in 2010 (low solar activity), 2011 and 2012 (moderate solar activity). It is observed that the highest frequency accumulates around 0.2 mHz at morning and afternoon hours while it accumulates around 0.1 mHz at noon and night hours. The frequency increases from solar quiet year 2010 to solar quiet active year 2012. In all years, it is observed that most frequencies are grouped at higher frequencies for the equinox months. The lower frequencies are observed for the solstice months for all time intervals. The largest numbers of the durations accumulate around 100 min (1.66 h) for morning hours, 200 min (3.33 h) for noon hours, 200 min (3.33 h) for afternoon hours and 150 min (2.5 h) for night hours. After sunrise and sunset, the durations of the disturbances are shorter than those observed for noon and afternoon times. The duration shortens from solar quiet year 2010 to solar quiet active year 2012. The durations for equinox months are shorter than those for the solstice months.
Temporal variations of the ionospheric disturbances due to the seasonal variability over Turkey using IONOLAB-FFT algorithm
(2020-05-01) Karatay S.; Karatay, S
The ionosphere is exposed to forcing from below due to gravitational, geomagnetic and seismic activities, and above due to solar wind. These forces cause some medium and large scale irregularities and disturbances into the upper atmosphere and ionosphere. Some of these disturbances occur in the form of wave-like oscillations in the ionosphere which propagate at a certain frequency, duration and velocity. These disturbances can be detected by monitoring the ionosphere using Total Electron Content obtained from Global Positioning System (GPS-TEC). In this study, the temporal analysis of these disturbances due to the seasonal variability is carried out for a mid-latitude GPS network using Ionosphere Research Laboratory TEC (IONOLAB-TEC) over Turkey. The IONOLAB Fast Fourier Transform (FFT) algorithm is applied to GPS-TEC obtained from nine Turkish National Permanent GPS Network (TNPGN) active stations in Turkey for December (winter solstice), March (spring equinox), June (summer solstice), September (autumn equinox) months in 2010 (low solar activity), 2011 and 2012 (moderate solar activity). It is observed that the highest frequency accumulates around 0.2 mHz at morning and afternoon hours while it accumulates around 0.1 mHz at noon and night hours. The frequency increases from solar quiet year 2010 to solar quiet active year 2012. In all years, it is observed that most frequencies are grouped at higher frequencies for the equinox months. The lower frequencies are observed for the solstice months for all time intervals. The largest numbers of the durations accumulate around 100 min (1.66 h) for morning hours, 200 min (3.33 h) for noon hours, 200 min (3.33 h) for afternoon hours and 150 min (2.5 h) for night hours. After sunrise and sunset, the durations of the disturbances are shorter than those observed for noon and afternoon times. The duration shortens from solar quiet year 2010 to solar quiet active year 2012. The durations for equinox months are shorter than those for the solstice months.
The analysis of the effects of the earthquakes in the ionosphere over Turkey
(2018-01-01) Karatay S.
Earth’s ionosphere is a dominant factor in space weather and the variability of the ionosphere is important for the ionospheric physics and radio communications. The characterizing property of the ionosphere is the electron density distribution that shows variation as a function of height, latitude, longitude, and geomagnetic, solar and seismic activities. An important measurable quantity about the electron density is the Total Electron Content (TEC), which is proportional to the total number of electrons on a line crossing the atmosphere. In this study, TEC obtained for eleven Turkish National Permanent GPS Network (TNPGN-Active) Global Positioning System (GPS) stations located in Turkey are compared with each other using the Cross Correlation Coefficient (CCC), Symmetric Kullback-Leibler Distance (KLD) and L2-Norm (L2N) for quiet days of the ionosphere, during severe geomagnetic storms, and earthquakes having different magnitudes. It is observed that only KLD and L2N can differentiate the seismic activity from the geomagnetic disturbance and quiet ionosphere if the stations are in a radius of 340 km. When TEC for each station is compared with an average quiet day TEC for all periods using CCC, KLD and L2N, it is observed that, again, only KLD and L2N can distinguish the approaching seismicity for stations that are within 150 km radius to the epicenter.
The relationship between the Quasi Biennial Oscillation and Sunspot Number
(2015-01-01) Sagir S.; Karatay S.; Atici R.; Yesil A.; Ozcan O.
In this study, the relationship between the monthly mean values of the Quasi Biennial Oscillation (QBO) measured at 10 hPa and 70 hPa altitudes and Sunspot Number (SSN) for solar maxima and solar minima conditions is analyzed. Before applying the model for the statistical analysis of the study, the stationary of the variables is investigated by using the unit root test. Existence of a long-term relationship between the variables is also investigated by using the co-integration test. Positive and negative relationships between SSN and QBO obtained for 10 hPa and 70 hPa are observed for the solar maxima and the solar minima, respectively. The explainable effects of the SSN on the QBO at 10 hPa altitude are greater than those at 70 hPa. When the calculated coefficients are analyzed, it is observed that the variation of QBO up to 16 m/s is due to SSN. The rest of at least 34 m/s are seen to be based on the other variables.
The seasonal anomalies in ionosphere over Turkey
(2016-06-20) Cinar A.; Karatay S.; Arikan F.
The ionosphere is a region on the Earth's upper atmosphere which extends between 50 km to 1000 km from the ground. It is a layer that consists gases which are ionized by solar radiation. Solar radiation and incident angle of the Sun is important to understand how the Ionosphere affects the radio waves. Total Electron Content (TEC) is one of the important parameters that characterizes Ionosphere and directly related with the Sun's activity. The Ionosphere reflects radio waves and provides communication to distance places in short wave radio communication. In this study, behaviours of the Ionosphere in Turkey are examined for soltice and equinox periods between the years 2009 and 2012 which are one of solar minima and solar maxima periods, respectively by using Symmetric Kullback-Leibler Distance and L2 Norm methods.