Analysis on Temporal-Spatial Variations of Iranian TEC Using GPS Data Print

During the recent years, GPS has been introduced as a unique tool to study the propagation of electromagnetic waves through the atmospheric layers, in particular the ionosphere. The ionosphere is currently the major source of errors in GPS positioning which its effect on wave propagation is dependent on the amount of TEC and signal frequency. In this paper, the temporal-spatial variations in Iranian TEC has been studied using observations of 40 IPGN stations. For this purpose, GPS observation data, consisting 10 days in 2012 and 3 days in 2013 which are the first days of solar months, have been processed via Bernese 5.0 GPS software (first days of each season is included in our data). To do so, regional ionosphere modeling, estimation of TEC values and calculation of the receiver DCB have been performed by expansion of spherical harmonic functions up to the sixth degree and order. Furthermore, the difference between smoothed code observations from the first and second frequencies has been used to eliminate geometric effects, such as satellite and receiver clock biases and tropospheric delays. Blunder and cycle slip detection as well as code observation smoothing have been performed during preprocessing steps. The results have shown that the maximum and minimum ionosphere effects are related to the spring and winter seasons, respectively, and the maximum TEC value occures at about 14:00 local time. Moreover, we can see significant TEC variations in accordance with changes in latitude. on the other hand, the maximum and minimum TEC values in Iran is associated with the minimum and maximum latitudes, respectively. In the spring of 2012, 100 TECU was observed as the TEC value. If the satellites are near the horizon and by using second frequency, It could lead to an error 75 meters on the satellite–receiver range.