This paper aims at presenting the analysis of the stability of the geodetic network that supports the monitoring of Salto Caxias Hydroelectric Plant. This network consists of five pillars equipped with devices of forced centering, which are located downstream of the dam, and a pin fixed in the crest, located in one of the gates of the dam. The analysis was performed from the GPS data collection and the processing by using appropriate software. We decided to take pillar P1 as reference and its coordinates were determined by relative form (using the Leica Geo Office software v.7.0) four continuous monitoring stations, three belonging to RBMC (PRMA, PRGU and SCCH) and one to Itaipu (ITAI). The coordinates of these bases were transformed and updated to ITRFyy and reference epoch (from Generalized Helmert Transformation) corresponding to the precise ephemeris used and the epoch of data collection. The coordinates of other points of the network were determined in relation to P1, using the relative positioning. To detect observations with blunders, we applied the Data Snooping procedure. The coordinates were transformed from a geocentric to a local geodetic system, in order to better evaluate the displacements, which in turn were validated from the Global Congruency Test. Finally, in order to evaluate the distance between the pillars obtained by GPS data they were compared with the distances obtained with the Total Station Leica TC2003. The results showed that the displacements obtained from GPS data were not consistent with the results obtained from trilateration technique.
Monitoring; Geodetic Networks; Global Congruency Test
