Coupling Wireless Sensor Networks and the Sensor Observation Service - Bridging the Interoperability Gap
Kai Walter, Edward L. Nash · 2009
was coined in 1998 by Al Gore proclaiming a three-dimensional multi-resolution representation of the Earth’s surface holding georeferenced data of any kind (ISDE, 1998). Part of this vision is the ubiquity of observation systems, enabling a digital representation of features such as environmental phenomena with a high spatial and temporal resolution. World wide a vast amount of environmental sensors and other data producers exist, yet measurements as well as their in-terpretation are rarely put to proper use because of their isolated availability within a specific applica-tion domain. Using the internet as a tool for interdisciplinary data exchange, as well as for the exten-sive usage of heterogonous data resources is an important step towards addressing today’s larger scale environmental problems (Bacharach, 2008). By making measurements and results discoverable and accessible over the internet, producers from different areas can reduce data redundancy and existing data sets can be used to their full capacity. The Open Geospatial Consortium (OGC) addresses this requirement by developing the Sensor Web Enablement (SWE) specification series (Botts, 2007). Members of the SWE working group are specifying interfaces, protocols and data types that enable the integration of sensors and sensor webs into (spatial) information infrastructures (OGC, 2008a). While the basic concept and benefits of SWE standards, as described above, are widely accepted in the “spatial” community and are used in many programmes (Bacharach, 2008), very often questions about how to apply standards and services such as SensorML and Sensor Observation Service (SOS) have to be clarified, especially for existing observation and data producing systems, which have not previously been operating in an explicitly spatial context. The project described in the following sec-tions uses existing commercial sensor products, implementing SWE technologies on top as a middle-ware layer to provide the data in an open and interoperable manner. The collaborative research project “Sensor based Landslide Early Warning System” (SLEWS) aims for the systematic development of a prototype alarm and early warning system for mass movements. Project partners are the Department of Engineering Hydrogeology at RWTH Aachen, the Federal In-stitute for Geosciences and Natural Resources (Hannover), the Chair of Geodesy and Geoinformatics at Rostock University and ScatterWeb GmbH (Berlin). Early warning and alarm systems are an effec-tive tool to reduce risks from landslides (Fernandez-Steeger et al., 2008). The main goals of SLEWS are the utilisation of ad hoc wireless sensor networks and spatial data infrastructure technologies ac-cording to OGC guidelines to produce a low-cost, interoperable and performant early warning system. Methods of data access, communication and visualisation are to be implemented using SWE specifi-cations, concurrently offering information resources via open standards to external applications while importing interoperable resources in return. The work described here is concentrated on the design and implementation of a sensor web enabled spatial data infrastructure as part of this project (Bill et al., 2008). This paper initially sums up current progress in converting sensor network data to a stan-dardised SWE-based format to be accessed by a SOS. Based on this experience, an interoperability