Absolute robotic GNSS antenna calibrations in open field environment
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GNSS IN PROGRESS
Absolute robotic GNSS antenna calibrations in open field environment Igor Sutyagin1 · Dmitry Tatarnikov1 Received: 28 January 2020 / Accepted: 10 June 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract We consider robotic calibrations of GNSS receiving antennas in an open field environment. At the newly built test range, the sky is unobstructed down to 10° elevation; an industrial robot with six degrees of freedom is employed. The antenna calibration algorithm uses single differences of carrier phases. Two types of antennas are tested, a common choke ring ground plane antenna and a rover-type antenna. Three types of errors are analyzed in detail: far-field multipath, near-field multipath, and errors of antenna positioning by the robot. For far-field multipath, it has been shown that the notion of the satellite signal reflection by the plain surface underneath the antenna fits well with the observed data. Parallel vertical antenna displacements are analyzed to decrease the test time. It has been shown that the near-field multipath originating from the body of the robot is the main contribution to the remaining error of calibrations: while error components related to the remaining far-field multipath and inaccuracies in the geometry of the installation are estimated at 0.1 mm each, the overall accuracy of achieved calibrations is estimated as 0.3 mm for choke ring-type antenna and as 0.7 mm for rover-type antenna. A comparison of the obtained calibrations with Geo++® GmbH data is provided. Keywords Satellite positioning · Antenna calibrations · Antenna phase center · Phase center variations
Introduction Calibration of GNSS receiving antennas for land survey, geodesy, construction, and machine control is widely recognized as a necessity for precise positioning. Calibration means determining the antenna phase center offset (PCO) against the antenna reference point (ARP) and determining the phase center variations (PCV) as a function of satellite elevation angle and azimuth. In Rothacher et al. (1995), Mader (1999), the relative mode of antenna calibrations is described. The absolute robotic calibration is introduced in Wübbena et al. (1997). In Wübbena et al. (2000), a procedure of absolute automatic calibration is presented. In Bilich and Mader (2010), the absolute calibration using the triple difference of carrier phase observables between the test and reference antennas with a robot having two degrees of freedom is described. A similar approach to robotic calibration using a robot with six degrees of freedom is shown in Hu et al. (2015). However, as discussed in Bilich et al. (2012), the antenna calibration data from various sources differ to a * Igor Sutyagin [email protected] 1
Topcon Positioning Systems, Livermore, USA
certain extent. That is the reason, we find it useful to evaluate further the systematic errors of the calibrations. The errors are related to far-field multipath and near-field multipath and to incorrect antenna positioning with the robot. The
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