GPS data processing in deformation monitoring networks

To measure deformations with the GPS technique, one usually establishes a monitoring network, conducts measuring campaigns through time and compares the network's station coordinates obtained it, each measurement session. Two methods can be used to calculate the coordinates. The classic method involves calculation of independent baseline components between two or more pairs of stations: double differences carrier phase solution. These components are then adjusted to obtain the absolute coordinates of the network stations and their rms. The second method involves direct calculation of the coordinates: in this case, the Precise Single Point Positioning model is used. For extensive networks and multi-day processing, the second method provides coordinates with greater reliability than those obtained with the double differences carrier phase solution. However, if the deformations are small and measured within a brief time period, this reliability may not be assured. In these conditions, one can improve the results by combining the second method with a particular calculation technique. In this paper, we describe this technique and report the results obtained in two applications: determination of vertical sinking of a large metallic structure and calculation of horizontal movement of a landslide.