Quantifying errors in GNSS antenna calibrations
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ORIGINAL ARTICLE
Quantifying errors in GNSS antenna calibrations Towards in situ phase center corrections Sten Bergstrand1
· Per Jarlemark1 · Magnus Herbertsson1
Received: 18 June 2019 / Accepted: 1 September 2020 © The Author(s) 2020
Abstract We evaluated the performance of GNSS absolute antenna calibrations and its impact on accurate positioning with a new assessment method that combines inter-antenna differentials and laser tracker measurements. We thus separated the calibration method contributions from those attainable by various geometric constraints and produced corrections for the calibrations. We investigated antennas calibrated by two IGS-approved institutions and in the worst case found the calibration’s contribution to the vertical component being in excess of 1 cm on the ionosphere-free frequency combination L3. In relation to nearby objects, we gauge the 1σ accuracies of our method to determine the antenna phase centers within ± 0.38 mm on L1 and within ± 0.62 mm on L3, the latter applicable to global frame determinations where atmospheric influence cannot be neglected. In addition to antenna calibration corrections, the results can be used with an equivalent tracker combination to determine the phase centers of as-installed individual receiver antennas at system critical sites to the same level without compromising the permanent installations. Keywords Antenna · Calibration · GNSS · Local tie · Phase center offset · Phase center variation · Terrestrial reference frame · PCC · PCO · PCV · TRF
1 Introduction In a geodetic system where VLBI provides connection to the celestial reference frame and SLR to the center of the terrestrial frame, GNSS ground stations play a key role in the implementation on the observational level (Plag and Pearlman 2009; United Nations 2015; Altamimi et al. 2016). The space geodesy focus lies in the location of the antenna, and particularly its phase center, i.e., the mathematically best fitted non-physical point that relates the incoming electromagnetic signals’ time of arrival to the tangible structure. In other fields of interest, the calibration tables and diagrams used to characterize antennas are dedicated to establish gain characteristics in different directions (e.g., ARRL 2015). As far as we know, the location objective is unique to geodesy which might explain why GNSS antenna calibration is still a field in continual development (Tranquilla and Colpitts 1989;
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Sten Bergstrand [email protected] RISE Research Institutes of Sweden, Box 857, 501 15 Borås, Sweden
Wübbena et al. 1996; Schupler and Clark 2001; Akrour et al. 2005; Bányai 2005; Wübbena et al. 2006; Aerts and Moore 2013; Baire et al. 2014; IGS AWG 2017). From early observations with uncalibrated GPS antennas at the still operative CIGNET stations (Schenewerk 1991) via relative methods (Mader 1999) to the current asserted absolute calibrations (AC) of antennas in the IGS network, the observational vertical error has decreased from 10 cm to an order claimed less than 1 cm (Schmid at al 2005). To
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