Impact of individual Receiver Antenna Code Phase Variation on the Ambiguity Resolution

The Institut für Erdmessung (IfE) is an official IGS antenna calibration institution, calibrating carrier-phase center variations (PCV) for receiver antennas routinely in the field, using the actual GNSS satellite signals in space. Current research activities are focussed on the antenna code-phase calibration with the Hannover Concept of absolute antenna calibration. Besides PCV, the receiving antenna introduces systematic effects, currently known as Group Delay Variations (GDV), i.e. azimuth and elevation dependent code-phase delays. These delays can be determined by precisely rotating and tilting the antenna under test. Forming imedifferenced single differences with respect to a near (ca. 8m) fixed reference station, the GDV can be separated from further systematic effects like tropospheric delays, which are reduced far below the code observation noise level. Depending on the antenna design, suitable for specific applications, different magnitudes and features of GDV has been determined at IfE. In previous papers the authors could elaborate that GDV are antenna specific and they systematically affect the code observation up to 1.8m as well as the obtained coordinates, (Kersten and Schön, 2013). The impact depends on the corresponding magnitude of the GDV pattern. In several studies, improvements were obtained for static code based single point positioning (SPP) as well as for code based differential positioning when applying GDV corrections. This contribution discusses the current investigations at IfE on GDV within combined code and carrier phase processing strategies. The study of the GDV impact on the Melbourne-Wübbena linear combination (MW-LC) which is widely used for cycle slip detection and ambiguity resolution is of special interest, since due to the linear combination GDV effects on both code phases are amplified. We detect systematic effects and significant trends in the MW-LC time series due to receiver antenna specific GDV with an amount of up to 0.8-0.95 widelane cycles. Depending on the reference satellite chosen, improvements of MW-LC ambiguity fixing are obtained by considering GDV corrections. Improvements of up to one cycle can be shown. Subsequently, the impact on the coordinate time series is discussed, when ambiguities are not correctly fixed. References: Kersten, T. and Schön, S. (2013). Analysis of IfE-Robot based Group Delay Variations for the Positioning and Navigation of Mobile Platforms. In Proceedings of the European Navigation Conference 2013, April 22.-25., Vienna, Austria, pages: 10.