YKS AĞI TABANLI TOPLAM ELEKTRON İÇERİĞİ VE ALICI YANLILIĞI KESTİRİMİ
Özet
Ionosphere is an anisotropic, dispersive and inhomogenous region of atmosphere whose spatio-temporal trends have an important affect on satellite based systems and HF communication. The variability in the temporal and spatial trends of the ionosphere is dependent on solar, geomagnetic, seismic and gravitational activities. Total Electron Content (TEC) is one of the most important parameters in observing the structural variability of the ionosphere. Slant Total Electron Content (STEC) is the total number of electrons on the receiver-satellite link. In this thesis, for the fist time spatio-temporal varying nature of the ionosphere over Turkey is investigated using STEC data. STEC values are obtained by applying IONOLAB-STEC method to recorded data from Turkish National Permanent GPS Network (TNPGN) – Active stations that are located in the midlatitude region of the ionosphere. TNPGN-Active GPS network is partitioned into 19 regions of 2ºx3º latitude and longitude respectively to investigate the ionosphere. For every region, the station that is equal distance to other receivers is chosen as reference station. The other receivers are called as neighbor stations. In order to investigate the space varying structure of the ionosphere for the first time using STEC data for every reference and neighbor station similarity of STEC values and the relation between ionospheric piercing points which is dependent on the satellite track are compared using Symmetric Kullback Leibler Distance (SKLD), Metric Distance (L2N), Cross Correlation (CC), Burg Entropy (BE) and Dual Bit Entropy (DBE). This comparison is implemented throughout 2011 for all seasons, quiet and disturbed days of ionosphere and all hours of the day. It is observed that the closest neighbor station to the reference station has the most similar STEC values compared to reference station STEC values. In order to investigate the time varying structure of the ionosphere for the first time using STEC data, Sliding Window Analysis (SWA) method is applied to STEC values between reference station and satellite pairs to estimate Wide Sense Stationarity (WSS) period. This method is implemented throughout 2010-2012 for all seasons, quiet and disturbed days of the ionosphere and all hours of the day to observe the affects of seasonal, annual and diurnal variations of the ionosphere. It is observed that during quiet days WSS period of ionosphere get as long as 13 minutes and during disturbed days WSS period can get as short as 3 minutes. During 2010-2012 for all reference stations, satellites, seasons and hours of the day median value of the WSS period is found to be 11 minutes. Spatio-temporal investigation results of the ionosphere are used to estimate STEC data and receiver bias over a midlatitude GPS network during 2011, for quiet and disturbed days. Reference station STEC values are estimated using least squares fit to STEC values calculated from empirical, climatic model of ionosphere, STEC values of the closest neighbor station and reference station STEC values of the day before. It has been observed that STEC values of the closest station are the most similar values to the reference receiver, compared to other STEC values used in least squares fit. For reference stations STEC and receiver bias values are estimated using least squares fit and estimated values are compared with reference station STEC values using Symmetric Kullback Leibler Distance (SKLD), Metric Distance (L2N) and normalized percentage error methods. In the future studies, the results of this thesis will be used to threat and risk asessment, threat detection and error correction caused by ionospheric disturbances.
