Evaluation of GNSS Monument Stability
We report on an evaluation of the stability of four different GNSS monuments that was conducted in the summer of 2010. The monuments were monitored by forward intersections using a survey system consisting of two robotic total stations and a set of retro
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Evaluation of GNSS Monument Stability R. Haas, S. Bergstrand, and W. Lehner
Abstract
We report on an evaluation of the stability of four different GNSS monuments that was conducted in the summer of 2010. The monuments were monitored by forward intersections using a survey system consisting of two robotic total stations and a set of retro reflecting prisms. The system was operated for almost 3 months, performing observations in two faces with a repetition cycle of 5 min. Movements in excess of 6 mm were detected. The results show clear evidence that the detected deformations are related to variations in temperature and solar radiation and can be suppressed by simple shielding of the monument. Furthermore, our project is a step towards the realization of continuous cartesian connections at geodetic fundamental stations. Keywords
Geodetic monitoring GNSS monuments Local-tie monitoring Fundamental geodetic stations Global geodetic observing system (GGOS) Co-located space geodetic techniques Continuous cartesian connections (CCC)
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Introduction
Space geodetic techniques and their applications are today dominated by Global Navigation Satellite Systems (GNSS). One of the main objectives of static GNSS is to maintain local, regional, and global reference frames and networks. In Sweden, the National Land Survey (Lantma¨teriet—LM) operates the SWEPOS network since the early 1990s. During the last years, LM has augmented the original network of 21 SWEPOS sites that are used for geophysical research, e.g.
R. Haas (*) Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, SE-439 92 Onsala, Sweden e-mail: [email protected] S. Bergstrand SP Technical Research Institute of Sweden, Measurement Technology, SE-501 15 Bora˚s, Sweden W. Lehner Institute of Geodesy and Geophysics, Vienna University of Technology, AT-1040 Wien, Austria
the BIFROST project (Scherneck et al. 2003), and the whole network now also comprises about 150 additional RTKstations (SWEPOS 2011). The original SWEPOS monuments consist of 3 m tall heated circular concrete pillars that are firmly connected to crystalline bedrock (Scherneck et al. 2002). The monuments were designed this high in order to guarantee full satellite visibility above 10 of elevation, to prevent vandalism and disturbances due to people and animals, and to mitigate snow effects. In the near future, the original 21 SWEPOS sites are to be equipped with additional GNSS monuments for redundancy purposes, and a favorable ratio of monument stability versus financial expense is sought for. The Onsala Space Observatory (OSO) is one of these 21 sites and the decision on the monument design requires a reliable stability evaluation. On their homepage, UNAVCO (2011) suggests a number of monument designs utilized in different regional networks, and lists important aspects when choosing monuments. When external factors (multipath, elevation cut-off, ground stability etc.) are excluded, two important criteria for a good monument design
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