Siti Sarah Nik Zulkifli

Application of 3-D Ray-Tracing for Accurate GPS Range Finding

Ionospheric error affects the accuracy of global positioning system (GPS). This paper studies the ionospheric error on transionospheric signal propagation from satellite to ground paths using readily available GPS satellites utilizing Jones 3-D ray-tracing. The ionospheric delay or advance is obtained from the difference between the distance of the ray path to the receiver from the satellite determined from the ray-tracing and the distance for propagation over the line of sight (LOS) at the velocity of light in vacuum. The residual range error (RRE), that is the difference between the standard dual frequency models corrected range and LOS, is calculated. Results show that the RRE of group value is different from RRE of phase advance. The higher order term in total electron content (TEC) calculation that relates to the refractive index is normally neglected due to its small value, but the results of ray-tracing clearly show that it does have some effects. These results should be considered for accurate GPS range finding.

Total Electron Content During Travelling Ionospheric Disturbance in Parit Raja, Johor

Travelling ionospheric disturbance (TID) is a phenomenon caused by solar activity and TID strength varies by locations, especially in equatorial regions. This phenomenon affects the local total electron content (TEC), especially during the daytime. Because of this, research regarding augmenting TEC values during TID is done by comparing TEC values obtained from the IRI2001 and NeQuick models with IONEX data. By using Global Positioning System (GPS) data obtained from the Parit Raja station in the southern part of Malaysia (1o 52’ N, 103o 06’ E) as reference, research was conducted during geomagnetic quiet day as well as on the disturbed day. The occurrence of TID can clearly be seen when using the real TEC data from IONEX and WARAS. Result obtained from Parit Raja station shows a much more significant effect of TID occurrence on TEC than what was shown by IONEX data. However, the TEC values obtained from the IRI2001 and NeQuick models were influenced by the number of sunspots and were only applicable in geomagnetic quiet days. In order to obtain more accurate TEC values, it is necessary to ensure that TID condition is included in the IRI2001 and NeQuick models.

Variation of elevation angle and total electron content (TEC) and profile shape using Modified Jones 3D Ray Tracing for differential Global Positioning System (dGPS) in equatorial

The difference in ionospheric delay between paths to the reference and mobile stations for differential GPS has been quantified for equatorial region. This small additional ionospheric error can be evaluated and predicted for the mobile station by means of a determined differential delay along the baseline so that accurate correction can be made for the most precise positioning. In this paper we studies the ionospheric delay on the Global Positioning System (GPS) signal due to the variation of elevation angle and variation in total electron content (TEC) and ionospheric profiles utilizing the Modified Jones 3D Ray Tracing method. The differential delay can be determined for any azimuth angle of propagation and for any baseline direction, providing the approximate difference in line-of-sight (LOS) between the stations. Result show that the variations of elevation angle and TEC give effects on the difference in delay between the two stations in differential GPS (dGPS). This analysis determined the difference in ionospheric delay expected over a short baseline so that a more accurate differential GPS correction can be made.