|M.Sc Student||Doron Shaked|
|Subject||Multipath Effect on GPS Antennas|
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Even-Tzur Gilad|
|Full Thesis text - in Hebrew|
The multipath (MP) is a local phenomenon in which the signal reaches the GSP receiver's antenna through several paths as a result of a disruption and its retraction. The error caused by the MP can be as large as a few meters for the code and a few centimeters for the carrier phase. The present research's goal was to assess the MP effect on the Survey Of Israel 17 permanent stations which collect data 24 hours a day and which today, supply data in real time to government and private users. An additional goal was to examine how the elevation angle of the transmitting satellite and the GPS antenna height affect the MP's values that the receiver receives. Since the MP is a phenomenon with a planetary daily cycle, it is possible to compare MP values received on various days as long as the satellite's geometry remains unchanged. Therefore, in order to create a situation in which measurement is identical over the various days, measurement must be carried out at exactly the same time and on consecutive days. The central element we examined through this comparison was the station's location in the area, which allowed us to identify the station whose location was the best and therefore the one which was minimally affected by the MP phenomenon, and the one whose location was the worst and therefore the one which was maximally affected by the MP phenomenon. As part of the research, we examined how the height at which the GPS antenna was positioned on the ground affected MP values and established the desirable height at which a permanent GPS antenna should be positioned in order to reduce the reflections at the station as much as possible. In order to establish this, we created an identical measurement situation in a flat open field, with no obstacles in a radius of hundreds of meters. We carried out measurements during three successive days at the same time over the same point. Each day the antenna phase center was positioned at the different height: about 1.6 m in the first day, 0.8 m in the second day and 0.0 m (ground level) in the last day. From the data we obtained, we arrived at the unequivocal conclusion that the optimal height for positioning the GPS antenna at the permanent station is at ground level.