On-line GPS Integrity Monitoring and Deformation Analysis for Structural Monitoring Applications

Clement Ogaja

Abstract:	Recent reports by investigators describe how high precision GPS sensors deployed on large engineering structures (such as dams, bridges, towers and tall buildings) can provide continuous real-time measurements, which can, in turn, be used to indicate displacements and vibrations caused by temperature changes, wind loading, distant earthquakes, landslides, etc. This information can be made available to the system manager, or interested parties, on a continuous basis, or whenever a preset displacement threshold is exceeded. The response of the structure can then be assessed according to the displacement thresholds reached or the changed dynamic characteristics. In the case of an alarm, the system manager can make a decision to, for example, close the structure for further inspection. This creates an opportunity for real-time structural health monitoring, and therefore leads to enhanced public safety. In designing a GPS-based deformation monitoring scheme, it may be useful to distinguish two types of tasks – the analysis of the non-stationary behaviour of the GPS sensor output or deformation signals, and investigation of any exceptional phenomena in the monitoring system itself (e.g a bias due to GPS sensor degradation or output errors). This problem can be addressed by using statistical tools in which one or several parameters may change abruptly due to natural deformation, an accumulation of sensor errors, or changes in the system operating conditions. In the first instance, the biases (or outliers) due to the GPS sensor malfunction should be detected as soon as possible, and then the sensor isolated or repaired in order to guard against further incorrect (biased) deformation signals. This paper presents an approach based on cusum tests. Two on-line change detection methods utilising the precise RTK coordinate results have been developed. The first method uses between-receiver differences of the measurement residuals of consecutive epochs. In the case of one base or reference GPS station, an array of at least three 'rover' stations deployed on the structure are required to detect a fault and to isolate the receiver responsible. The second method considers the detection of small dynamic changes in the RTK results based on transient changes in harmonic frequencies. The ability of these methods to detect autonomous receiver faults and small dynamic changes in RTK results, and their application for the GPS structural monitoring application, is discussed.
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:	989 - 999
Cite this article:	Ogaja, Clement, "On-line GPS Integrity Monitoring and Deformation Analysis for Structural Monitoring Applications," 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. 989-999.
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