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Observation, Spain

Ryuichi I.,Space Time Research | Atsutoshi I.,Space Time Research | Atsutoshi I.,Advanced Engineering Services Co. | Hiroshi T.,Space Time Research | And 18 more authors.
Journal of the National Institute of Information and Communications Technology | Year: 2010

We are developing a compact VLBI (Very Long Baseline Interferometry) system with 1.6 m diameter aperture dish in order to provide reference baseline lengths for calibration. The reference baselines are used to validate surveying instruments such as GPS (Global Positioning System) and EDM (Electro-Optical Distance Measurement) and maintained by the Geospatial Information Authority (GSI) of Japan. The compact VLBI system is designed to be assembled with muscle power simply in order to perform short-term (about one week) measurements at several reference baselines in Japan islands. First, we have evaluated a front-end system with a wide- band quad-ridged horn antenna by installing it on the 2.4 m diameter antenna at Kashima as a feasibility study. We have successfully carried out five geodetic VLBI experiments using it during September 2006 to July 2008. In addition we have concluded the new analysis concept to obtain indirectly the group delays on the baseline between two compact dishes is available. Next, we have carried out the VLBI experiments on the Kashima-Tsukuba baseline (about 54 km) using the two compact VLBI system during December 2009 to October 2010. The averaged baseline length and repeatability of the experiments is 541 84875.1±2.5 mm.

Galan-Martin D.,Canal de Isabel II | Galan-Martin D.,Technical University of Madrid | Marchamalo-Sacristan M.,Technical University of Madrid | Martinez-Marin R.,Geodetic Observation Center | And 2 more authors.
International Journal of Civil Engineering | Year: 2013

New advances in geomatics and communications technologies are enabling the development of Automated Auscultation System for structure monitoring. In particular, Differential GPS (DGPS) technique allows real-time monitoring of structures with millimetre accuracy after an appropriate mathematical treatment. The results of real-time DGPS monitoring of a pilot dam over 15 months are presented and compared with the results of pendulums and angular collimation. DGPS monitoring was established to control two points at the top of the dam with reference to an external and stable station. Communications were critical, evolving from initial GPRS connections to more reliable ASDL line in the last months. Real-time DGPS positions were filtered to reach millimetric accuracy through Kalman filter. Two configurations of the filter were tested, one more adapted to predictable and uniform velocity deformations (low frequency) and another more suitable for sudden and large movements (high frequency). Root mean square errors were calculated taking pendulums as a reference. Results show that both DGPS and angular collimation allow monitoring with millimetric accuracy. In the last period, where communications with processing server were stable, a global accuracy of 1.44 and 1.86 mm was reached for real-time DGPS monitoring. RINEX post-processing yielded millimetric results, validating real-time observations. We can affirm that the DGPS system is very useful for dam auscultation and safety as it detects adequately absolute deformations, being a complement to existing methods which should be considered in new safety plans.

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