|M.Sc Student||Borko Aviram|
|Subject||Ionospheric Delay and its Influence on Long Range VRS|
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Gilad Even-Tzur|
|Full Thesis text - in Hebrew|
Differential GPS positioning based on VRS data makes it possible to reduce the observation time-span needed for accurate positioning in long range distances from the reference station. The ability to derive an efficient and precise baseline solution with VRS data depends on the level of precision of the ionospheric assumption in the virtual observations. Increasing the ability to produce efficient VRS cover will necessitate the formulation of a trustworthy technique for mapping the ionospheric delay at larger distances (hundreds of kilometers). For the purpose of deriving the minimal conditions needed for such a mapping technique, this study aims to explore how the accuracy of a VRS is impacted by the ionosphere when it is produced at long-ranges from the reference stations using different interpolation methods.
During this study, several experiments that examined the precision of setting up the VRS in different scenarios were conducted in order to achieve the goal of characterizing the optimal method for mapping the ionosphere with the objective of manufacturing VRS for long ranges. The experiments raises two important criteria, both required for an ionospheric model for its compatibility with long-range VRS production: relatively high precision and a precise assessment of the ionospheric change as a function of time.
In light of the above two ionospheric mapping criteria, this research study developed an innovative method for the surveying and creation of VRS, called "Semi-VRS", which allows one to derive the precise position (centimeter-level) of a dual-frequency receiver, far away (hundreds of kilometers) from the reference station. The advantage of the method stems from the fact that it is not based on the usage of models and takes advantage of the dual-frequency observations of the receiver in the area for the benefit of calculating the variability over time of the ionospheric parameter in the virtual observations. The success of the method when tested in a practical scenario confirms that the confluence of the aforementioned criteria is indispensable, having a truly significant impact on the ability to attain accurate GPS positioning at long distances from the reference station.