The Effect of the Changes in the TEC, Inosphere Profile and the Position of Receiver Station towards Inosphere Error Experienced by GPS System

Global Positioning System (GPS) is a satellite-based navigation radio system which is used to determine the location of a site. Since the termination of selective availability (SA) on 1 May 2000, ionospheric error has become the largest source of error in GPS positioning. The aim of this research is to analyse ionospheric error that is caused by the changes in TEC value and the ionosphere profile experienced by GPS signals. Apart from that, analysis was also carried out to find out the effect of the changes in the direction of mobile station positions in short distance differential GPS application (dGPS) (≤10 km) on the ionospheric error experienced by the GPS system. The data was based on GPS stations in UKM (2° 55 N, 101°46 E) and in UPM Serdang, UPMS (2° 59 N, 101° 43 E). From the analysis on the effect of TEC changes, it was found that the increase in the TEC value led to the increment of the ionospheric error because in the TEC analysis, a profile with 100 TECU yielded ionospheric error of 46.7 m while a profile with 11 TECU yielded only 5.13 m. The analysis of the ionospheric profile changes did not give any significant result. Meanwhile, the analysis on the effect of the position changes of the rover stations showed that the irregularities of the ionospheric behaviours gave different range of ionospheric errors for the signal propagation orientation between the satellite and its receiver. The difference in ionospheric error for the separation of the rover station at North 0° direction was equal to the difference in ionospheric error at South 180°, while the ionospheric error at East 90° wasfound equal to the West 270°, and North-West 315° equal to the South-East 135°, while North-East 45° was equal to the South-West 225°. All these factors should be considered in order to obtain an accurate GPS precise positioning.