Monitoring and Early Warning of Slope Instabilities and Deformations by Sensor Fusion in Self-Organized Wireless ad-hoc Sensor Networks

Abstract

Geohazards, like landslides in soil and rocks which are induced by rainfall, flooding, earthquakes and human activity are dramatically increasing worldwide. Apart from socio-economic factors, like increasing population and concentrations of settlements on endangered areas, extreme weather conditions are the main reasons for this ascent. But, these occurrences are not only concentrated on the high mountain ranges with steep slopes and strong relief. In February 2003, a landslide in the middle of Germany near the village of Wolfstein-Rossbach damaged some houses (one of them totally). Another example is the Manshiet Nasser failure in Cairo in September 2008, where a large rock tilt buried many houses. This few examples show the devastating effect of geohazards in settlement areas and the need for precise monitoring systems to protect human life and property. In the frame of the special program “Geotechnologien” of the German Federal Ministry of Education and Research (BMBF), the joint project “Sensorbased Landslide Early Warning System” (SLEWS) aims at the development of a prototypic Alarm- and Early Warning system (EWS) for different types of landslides using wireless sensor networks (WSN) for real-time monitoring. The WSN consists of a number of so called sensor nodes and a data collecting point (gateway). The solar powered gateway is connected either directly or by GSM/GPRS to the internet and subsequently to a data infrastructure to process the sensor data. Each node has a sensor board were the measuring sensors and the communication and processing unit are integrated. Special features of the Network are the real-time ability, self-organization and self-healing capacity, energy efficiency, bidirectional communication skills and data interfaces regarding OGC (Open Geospatial Consortium) specifications. The bidirectional structure of the system enables data transfer not only from each node to the spatial data infrastructure (SDI), but also to transmit commands or software-updates to individual or a group of nodes. Special sensor nodes for the monitoring of surface deformations due to landslides, measuring acceleration, tilting or extension, were developed and tested. Apart from the detection of direct deformations caused for example by landslide movements, the system also allows the monitoring of indirect deformations on buildings and constructions, like bridge or retaining walls. Furthermore, the remote monitoring of flood control basins, dams or tailings in or close to housing areas becomes easy to set up in a cost-effective way. Open structures of the system enable a very rapid and flexible adjustment to the changed conditions and also permit a simple linkage with other data sources (e.g. climate data) or other sensor networks. Also, temporal deployments for safety purposes in road construction or foundation engineering become possible as the WSN is self-powered, the components are quite small and easy to set up. In the future other sensors may be integrated into the sensor notes so further tasks in spatial environmental monitoring may be covered. Keywords: Slope instability, deformation, sensor fusion, sensor networks