# Middleware for Plug and Play Integration of Heterogeneous Sensor Resources into the Sensor Web
## 6 Use Cases
### NeXOS Project  
The NeXOS project was an EU-funded project that aimed to develop cost-effective, innovative and compact multifunctional systems which can be deployed on fixed and mobile platforms [42], with special emphasis on interoperability and SWE-based architectures. Within this project the acquisition chain presented in Section 3 was arranged into the Smart Electronic Interface for Sensor Interoperability (SEISI) [43]. Different demonstration mission where performed using different sensors deployed on platforms such as gliders, underwater observatories, buoys and profilers among others. In this section the focus is put on the integration of two different NeXOS sensor developments into the SeaExplorer Glider.  
Two different NeXOS-developed sensors where deployed in the SeaExplorer Glider [44], the Mini.1 and the A1 Hydrophone. The Mini.1 is an optical sensor that measures hydrocarbon concentrations in water while the A1 Hydrophone is a smart acoustical sensor with embedded real-time processing capabilities for noise measurements and mammal detection (shown in Figure 14). Both sensors implemented the OGC PUCK protocol and had their own SDF embedded within their respective payloads, describing the sensors and their mission. These files are available at [37].  
Within the SeaExplorer controller, which runs an embedded Linux operating system, two instances of the SWE Bridge software were executed. These instances where in charge of retrieving and interpret the SDF and setup the data acquisition process. As the SeaExplorer glider is a mobile platform, a resource abstraction wrapper was developed in order to relate the acquired data with the vehicle position, based on socket communication between the GPS driver and the SWE Bridge. The SeaExplorer used an Iridium satellite link to communicate with the shore station. The management of this power-consuming and low-bandwidth communications in power-constrained platforms is critical. Thus, the satellite-link is controlled by the platform operators, deciding when and how the generated files will be sent to shore. The acquisition chain is showed in Figure 15.  
The SWE Bridge generated two sets of data files: a subsampled data set sent in near real-time through the glider's satellite-link and a full data set, stored locally and recovered with the glider at the end of the mission. In Figure 16 the SWE Bridge mission scheduler configuration workflow is shown. The data is retrieved from the sensor by the Instrument Command process. Afterwards the Sampling Geometry process associates the latest platform position to each measurement. The data is then passed to two different branches. The first branch sends the data to an Insert Result process, which stores the full data set locally. The second branch subsamples the incoming data before passing it to another to another Insert Result process. This process stores the subsampled data set into O&M files, which is transmitted to a shore station through the glider's satellite link. A subsampled acoustic noise data set gathered by the A1 Hydrophone sent in near-real during field trials can be seen at Figure 17.  
Figure 14: NeXOS A1 Hydrophone integrated on the SeaExplorer glider as payload.