Testing of low-cost GNSS receivers for landslide monitoring

Landslides are dangerous natural hazards, responsible for considerable loss of property and lives worldwide. Key indicator for stability assessment of sliding slopes is usually displacements at the surface, which must be determined with accuracy in the centimeter range. Geodetic GNSS (Global Navigation Satellite System) receivers are traditionally used in these applications because of a high level of accuracy. Due to the price of geodetic receivers are high, the unstable slopes may collapsed and destroy the receivers, slopes are monitored sporadically only. Early warning of landslides monitoring requires a permanently operable measuring system on site. Thus low-cost GNSS receivers can be used for such demanding challenges. Over the last twenty years, positioning with low-cost GNSS sensors have rapidly developed around the world at both commercial and academic research level. The aim of this thesis is to test the actual performance of low-cost GNSS receivers, with the purpose of verifying if they can be used for landslides monitoring. To achieve the target, both geodetic and low-cost receivers are used in the experiment: Leica GX1230 GG and single frequency u-blox EVK-7P receivers. To simulate the displacement of landslides, a sliding device built by Laboratory of Topography of the Politecnico di Torino was used. The antenna of low-cost receiver was placed on the sliding device, which can be moved on both vertical and horizontal direction. The experiment was planned and performed in Como, the antenna of u-blox EVK-7P receiver was moved by 5mm increments alternating the horizontal and vertical direction every two hours. In total, the antenna has been moved 10 cm both in the horizontal and vertical direction. Then the data was processed by LGO (Leica Geo Office) and RTKLIB. The experiment proved that u-blox EVK-7P receiver is capable in detecting displacements at centimeter level, even sub-centimeter level for the horizontal direction. The first three chapters introduce relevant background material to this thesis, the research approach, results, conclusion and recommendations are presented in the last three chapters. • Chapter 1 is the introduction of the research including motivation and objective. • GNSS systems, including the history, the constellation, signal spectrum and latest update of satellites are discussed in Chapter 2. • Chapter 3 describes the fundamental of GPS positioning, including the pseudorange observation, carrier phase observation, error sources and principle of differential GPS. • Chapter 4 introduces the approach used in this investigation. The details on how, where, and when the experiment was setup and data acquisition are given in this chapter. The software used for data processing is also introduced in this chapter. • Chapter 5 presents the results processed by commercial software LGO and open source software RTKLIB, the displacements detected by the low-cost receiver comparing with the theoretical movements are discussed in this chapter. • Chapter 6 gives some conclusions of this research, and recommendation for future work. Low-cost GNSS receiver u-blox EVK-7P can be trusted for applications that require centimeter level accuracies.