Permanent Object Monitoring with GPS with 1 Millimeter Accuracy

Gerhard Wubbena, Andreas Bagge, Gerald Boettcher, Martin Schmitz and Peter Andree

Abstract:	GPS is best suited to permanently monitor the deformations of buildings, dams etc. in real-time. However, there often exist some additional requirements, e.g. higher accuracy, multiple sensors, cheap equipment, which cannot be solved with standard RTK solutions. Geo++® has developed their system GNPOM (Geodetic Navstar - Permanent Object Monitoring) to overcome these restrictions. GNPOM is based on the multi-station real-time software GNNET, which is able to process the carrier phase observations of multiple receivers simultaneously. The result is not a set of single baselines, but a homogeneous set of coordinates with a realistic variance-covariance estimation for all stations. Cheap GPS sensors without any RTK or memory can be used, because all processing is done with separate software on standard PC hardware. Object monitoring is normally done within small areas. Over short distances the most limiting factors for accuracy are antenna phase center variations (PCV) and the influence of multipath propagation. GNPOM takes advantage of absolute calibrated antennas, so antenna PCV induced errors can be reduced below the sub- millimeter level. Multipath is very often present in construction and urban environments, and can amount to an error of a few centimeters. For individual GPS satellites, multipath influence is significantly correlated between subsequent days, because the satellite constellation repeats after a siderial day, and thus multipath geometry is very similar for a given station environment. Using the data from previous days, GNPOM is able to separate multipath from the carrier phase observations. Other limiting error sources like orbit, ionosphere or troposphere are either not significant, due to small distances, or can be eliminated by use of several base stations in the GNNET multi-station adjustment. The remaining observations are free from any systematic errors, with an accuracy better than 1 millimeter. Recent results allow to track the dynamic deformation of a building with amplitudes of 25 millimeters and accuracy of 1 millimeter.
Published in:	Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001) September 11 - 14, 2001 Salt Palace Convention Center Salt Lake City, UT
Pages:	1000 - 1008
Cite this article:	Wubbena, Gerhard, Bagge, Andreas, Boettcher, Gerald, Schmitz, Martin, Andree, Peter, "Permanent Object Monitoring with GPS with 1 Millimeter Accuracy," Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001), Salt Lake City, UT, September 2001, pp. 1000-1008.
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