GPS ile troposfer ve koordinat kestirimleri üzerindeki yüksek dereceli iyonosferik etkiler

The tropospheric delay and gradient can be estimated from dual-frequency GPS observations with removing the ionospheric delay, which has been widely used for atmospheric study and weather forecasting. However, high-order ionospheric (HOI) effects are generally ignored in tropospheric and coordinate estimation. In this study, high-order ionospheric effects on GPS-estimated tropospheric delay, gradients and coordinates have been investigated for the first time from 30 days of GPS data in June 2011 at 8 GPS stations in Turkey. Firstly, the second and third-order effects on GPS data are corrected in RINEX using IGRF11 (International Geomagnetic Reference Field: 11th generation) model, and then tropospheric delay and gradient values are obtained from raw and corrected RINEX data using the GAMIT software. Results show that high-order ionospheric effects are up to 6 mm on zenith tropospheric delay (ZTD), 4 mm on North-South (NS) gradient and 12 mm on East-West (EW) gradient during this period, but can reach over 30 mm in slant tropospheric delay. Furthermore, the high-order effects on tropospheric delay and gradient are larger in the day time than in the night time. Also, solar activity effects on high-order ionospheric delay corrections are further investigated. The high-order ionospheric effects on GPS estimated tropospheric delay and gradient in high solar activity days are much larger than those in low solar activity days. While RMS values are 0.40 mm, 086 mm, 0.69 mm in low solar activity days, in peak solar activity days they can increase up to 0.81 mm, 2.74 mm, 2.20 mm on ZTD, North-South, and East-West gradients, respectively. Global Positioning System (GPS) gives a chance for users to obtain high precision positioning information with the real time applications. Precise positioning components can be obtained using observation files evaluated on academic GAMIT/GlobK software with post processing applications. When the same GPS data in June 2011 has been used for precise positioning before and after HOI corrections, results show that, 10, 7 and 24 mm changes occurred in order of north, east and up components. When the data during the peak solar activity day observation files are used for same stations in 2011, it is observed that, high-order ionospheric effects on north, east and up components can be reached in order of 18, 11 and 43 mm change.