Accuracy of Displacement Monitoring at Large Dams with GPS

Abstract

The GPS has dramatically changed the way that surveyors, GIS professionals, engineers and others estimate positions by means coordinates. In fact, since the last years of 20th Century, these scientists and practitioners can determine 3D coordinates of points with centimetre-level accuracy, relative to control points located a few hundred kilometres away. However, GPS positioning isn’t still the more used technique in geodetic monitoring of manmade structures, like dams or bridges. There are two main reasons that can explain it: first, GPS techniques have shown some limitations to reach the millimetre-level accuracy; second, the shadow zones generated by the structure itself or by the inclined hillside do not allow good satellite coverage.

In the near future, new developments that are expected for the GPS (L2 civil signal and L5 signal) and the GALILEO implementation will improve the overall system performance accuracy levels. On the other hand, pseudollites that are in a testing phase may improve weak geometry of the GPS satellite constellation. But is static GPS positioning presently competitive with classical geodetic methods?

This paper presents a case study in a Portuguese large dam, where static GPS was compared with classical geodetic measuring methods with submillimetric accuracy. Different observation schemes in static GPS mode were tested to achieve the optimal solution concerning accuracy, cost and reliability.