Mainly in the context of global climate change the awareness of landslide hazards has risen considerably in most mountainous regions worldwide in the last years. National and regional hazard mapping programs were set up in many countries and most of the potentially endangered sites have been identified. Although exclusive geodetic and geotechnical instrumentation is available today, due to some economical reasons only few of the identified potentially risky landslides are monitored permanently. The intention of the alpEWAS research project is to develop and to test new techniques suitable for e‰cient and cost-e¤ective landslide monitoring. These techniques are combined in a geo sensor network with an enclosed geo data base and a developed software package to use the whole system for stakeholder information and early warning purposes. The core of the project is the development and testing of the three innovative measurement systems time domain reflectometry (TDR) for the detection of subsurface displacements in boreholes and reflectorless video tacheometry (VTPS) and a low cost GNSS sensor component for the determination of 3D surface movements. Essential experiences obtained during the project will be described.

The paper reports on the principles, experiences and first results made with a low cost satellite based sensor network recently developed especially for landslide monitoring. Central idea of the system is the permanent broadcast of carrier phase (CP) raw data from the sensor nodes to a base station, where an automated near real time processing (NRTP) takes place. Low cost means the utilization of simple navigation receivers with the required capability of read-out the CP raw data. Depending on the di¤erent filter options during analysis the system generates sensor node positions with sub centimetre accuracy. The challenge of the still ongoing development is to have a flexible, robust (weatherproof ), commercial o¤-the-shelf GNSS sensor network of high-quality available -concerned not only for landslide monitoring in future.

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In context of global climate change and the continuous extension of settlement areas in the Alps, especially due to tourism, an increasing conflict can be observed between land use and natural hazard prevention. This also includes deep-seated landslides, which can cause considerable damage to settlements and infrastructure when they occur and even endanger lives.The hazard potential of slow deep-seated landslides has often been underestimated up till now. For economic reasons, such potentially dangerous instable slopes often are only monitored sporadically if at all. The alpEWAS project ("development and testing of an integrative 3D early warning system for instable alpine slopes") is currently developing a low cost 3D monitoring and early warning system for landslides based on three innovative continuous measurement systems for underground and surface deformations: Time Domain Reflectometry, reflectorless video tacheometry and low cost global navigation satellite system. These are merged with other sensors, which monitor typical trigger mechanisms (e.g. precipitation), into a geo sensor network, providing remote online access to all data in near real time in a WebGIS environment.The alpEWAS system has been installed at the Aggenalm Landslide for a first field test. The experiences made there will be of great importance for the medium-term goal: the development of a market-ready, flexible and economic early warning system for landslides.

Simple navigation receivers can be used for positioning with sub-centimeter accuracy in a wireless sensor network if the read-out of the carrier phase (CP) data is possible and all data are permanently broadcast to a central processing computer. At this base station an automated near real-time processing takes place and a precise differential GNSS-based positioning of the involved sensor nodes is computed. The paper describes the technical principles of such a system with its essential demands for the sensing, the communication, and the computing components. First experiences in a research project related to landslide monitoring are depicted. Of course the developed system can also be embedded for location finding in a widespread multifunctional geo sensor network. The quality of the obtained result is restricted due to the fact that the CP measurements must be recorded over a certain time span, usually a few minutes for every independent position solution. As far as possible a modular structure with commercial off-theshelf components, e.g. standard wireless local area network for communication, and in cooperation of existing proofed and powerful program tools is chosen. Open interfaces are used as far as possible.