| Carrier phase-based single reference station (SRS) positioning is capable of providing decimetre to centimetre-level accuracy for static and kinematic positioning under normal atmospheric conditions where the inter-antenna distance is relatively short, namely below ten to twenty kilometres. However, under highly localized atmospheric activity, and/or with a longer inter-antenna distance, the residual differential error increases and the accuracy degrades. Carrier phase integer ambiguity resolution may be impossible.; Multiple reference station (MRS) approaches uses a network of GPS reference stations to predict the differential errors over a geographic region. The University of Calgary standard MRS approach uses a conditional least-squares adjustment technique. During the past few years, an MRS tightly-coupled approach, which used all available observables obtained at rover and network reference stations in one filter, was also developed; the objective of this approach was solely to estimate states such as ambiguities, rover position and ionospheric error, if specified.; This thesis focuses on an evaluation of the above-mentioned MRS approaches relative to the SRS approach in the observation, position and ambiguity domains under various ionospheric conditions, ranging from quiet to extremely active, using a medium scale reference network, with inter-reference station distances of 30 to 70 km. Long-term and short-term convergence accuracy tests are used to assess the effectiveness of each approach. The reference network used is located in Southern Alberta and consists of dual-frequency receivers. The results show various levels of MRS performance compared to the equivalent SRS approach, ranging from unfavourable to significant, depending on many different parameters, chiefly ionospheric condition and carrier phase combination options. A major conclusion is that, under a highly disturbed ionosphere, the spatial correlation of the latter over distance of several tens of kilometres is weak, resulting in marginal improvements of MRS approaches. |
