GPS (Global Positioning System) technology is widely used for positioningapplications. Many of them have high requirements with respect to precision,reliability or fast product delivery, but usually not all at the same time asit is the case for early warning applications. The tasks for the GPS-basedcomponents within the GITEWS project (German Indonesian Tsunami Early WarningSystem, Rudloff et al., 2009) are to support the determination of sea levels(measured onshore and offshore) and to detect co-seismic land massdisplacements with the lowest possible latency (design goal: first reliableresults after 5 min). The completed system was designed to fulfil thesetasks in near real-time, rather than for scientific research requirements.The obtained data products (movements of GPS antennas) are supporting thewarning process in different ways. The measurements from GPS instruments onbuoys allow the earliest possible detection or confirmation of tsunami waveson the ocean. Onshore GPS measurements are made collocated with tide gaugesor seismological stations and give information about co-seismic land massmovements as recorded, e.g., during the great Sumatra-Andaman earthquake of2004 (Subarya et al., 2006). This information is important to separatetsunami-caused sea height movements from apparent sea height changes at tidegauge locations (sensor station movement) and also as additional informationabout earthquakes' mechanisms, as this is an essential information to predicta tsunami (Sobolev et al., 2007).This article gives an end-to-end overview of the GITEWS GPS-component system,from the GPS sensors (GPS receiver with GPS antenna and auxiliary systems,either onshore or offshore) to the early warning centre displays. We describehow the GPS sensors have been installed, how they are operated and themethods used to collect, transfer and process the GPS data in near real-time.This includes the sensor system design, the communication system layout withreal-time data streaming, the data processing strategy and the final productsof the GPS-based early warning system components.

With micro-strain resolution and the capability to sample at rates of 100 Hzand higher, fiber optic (FO) strain sensors offer exciting new possibilitiesfor in-situ landslide monitoring. Here we describe a new FO monitoring systembased on long-gauge fiber Bragg grating sensors installed at the RandaRockslide Laboratory in southern Switzerland. The new FO monitoring systemcan detect sub-micrometer scale deformations in both triggered-dynamic andcontinuous measurements. Two types of sensors have been installed: (1) fullyembedded borehole sensors and (2) surface extensometers. Dynamic measurementsare triggered by sensor deformation and recorded at 100 Hz, while continuousdata are logged every 5 min. Deformation time series for all sensors showdisplacements consistent with previous monitoring. Accelerated shorteningfollowing installation of the borehole sensors is likely related to long-termshrinkage of the grout. A number of transient signals have been observed,which in some cases were large enough to trigger rapid sampling. Thecombination of short- and long-term observation offers new insight into thedeformation process. Accelerated surface crack opening in spring is shown tohave a diurnal trend, which we attribute to the effect of snowmelt seepinginto the crack void space and freezing at night to generate pressure on thecrack walls. Controlled-source tests investigated the sensor response todynamic inputs, which compared an independent measure of ground motionagainst the strain measured across a surface crack. Low frequency signalswere comparable but the FO record suffered from aliasing, where undersamplingof higher frequency signals generated spectral peaks not related to groundmotion.