Millimeter-accuracy GPS landslide monitoring using Precise Point Positioning with Single Receiver Phase Ambiguity (PPP-SRPA) resolution: A case study in Puerto Rico

Abstract

Continuous Global Positioning System (GPS) monitoring is essential for establishing the rate and pattern of superficial movements of landslides. This study demonstrates a technique which uses a stand-alone GPS station to conduct millimeter-accuracy landslide monitoring. The Precise Point Positioning with Single Receiver Phase Ambiguity (PPP-SRPA) resolution employed by the GIPSY/OASIS software package (V6.1.2) was applied in this study. Two-years of continuous GPS data collected at a creeping landslide were used to evaluate the accuracy of the PPP-SRPA solutions. The criterion for accuracy was the root-mean-square (RMS) of residuals of the PPP-SRPA solutions with respect to "true"landslide displacements over the two-year period. RMS is often regarded as repeatability or precision in GPS literature. However, when contrasted with a known "true"position or displacement it could be termed RMS accuracy or simply accuracy. This study indicated that the PPP-SRPA resolution can provide an accuracy of 2 to 3 mm horizontally and 8 mm vertically for 24-hour sessions with few outliers (< 1%) in the Puerto Rico region. Horizontal accuracy below 5 mm can be stably achieved with 4-hour or longer sessions if avoiding the collection of data during extreme weather conditions. Vertical accuracy below 10 mm can be achieved with 8-hour or longer sessions. This study indicates that the PPP-SRPA resolution is competitive with the conventional carrier-phase double-difference network resolution for static (longer than 4 hours) landslide monitoring while maintaining many advantages. It is evident that the PPP-SRPA method would become an attractive alternative to the conventional carrier-phase double-difference method for landslide monitoring, notably in remote areas or developing countries.