Using Global Positioning System techniques in landslide monitoring

The precise determination of point coordinates with conventional Global Positioning System (GPS) techniques often required observation times of one to several hours. In the last few years, new GPS methods have been developed (among them, the fast-static and real time kinematic), with higher productivity and good theoretical precision. The main objective of this paper is to ascertain the performance of these methods in landslide monitoring practice. We present, first of all, the basic principles of the GPS, the equipment and working procedures. We discuss afterwards the applicability of the GPS to the monitoring of landslide surface displacements. Compared with the classical surveying methods, the GPS allows a larger coverage and productivity with similar accuracy. Furthermore, it can work in all kinds of weather conditions and a direct line of sight between stations is not required. Finally, we present an example of the performance of the GPS equipment in the landslide of Vallcebre, Eastern Pyrenees (Spain). This landslide has been periodically monitored since 1987 with terrestrial photogrammetry and geodetic measurements [theodolite, electronic distance metres (EDM)]. The movement extends over an area of 0.8 km2 and has experienced displacements as large as 1.6 m during the period 1996–1997. 14 campaigns, over a period of 26 months, using both static and kinematic GPS methods have been carried out. The GPS measurements have been compared with the results obtained with the EDM, inclinometers and wire extensometers, and checked against fixed stable points. The precision achieved with the GPS measurements is 12 to 16 mm in the horizontal plane and 18 to 24 mm in elevation.