52°North - Initiative for Geospatial Open Source Software

Effective ocean and coastal data management are needed to manage marine ecosystem health. Past ocean and coastal data management systems were often very specific to a particular application and region, but this focused approach often lacks real-time data and sharing/interoperating capability. The challenge for the ocean observing community is to devise standards and practices that enable integration of data from sensors across devices, manufacturers, users, and domains to enable new types of applications and services that facilitate much more comprehensive understanding and analyses of marine ecosystem. A given kind of sensor may be deployed on various platforms such as floats, gliders or moorings, and thus must be integrated with different operation, and data management systems. Simplifying the integration process in existing or newly established observing systems would benefit system operators and is important for the broader application of diverse sensors. This paper describes a geospatial “sensor web” architecture developed by the “NeXOS” project for ocean and coastal data management, based on the concepts of spatial data infrastructure and the Sensor Web Enablement framework of the Open Geospatial Consortium. This approach reduces the effort to propagate data from deployed sensors to users. To support the realization of the proposed Next generation Ocean Sensors (NeXOS) architecture, hardware and software specifications for a Smart Electronic Interface for Sensors and Instruments (SEISI) are described. SEISI specifies small lower-power electronics, minimal operating system, and standards-basedresearch software to enable web-based sharing, discovery, exchange, and processing of sensor observations as well as operation of sensor devices. An experimental scenario is presented in which sensor data from a low-power glider with low-bandwidth intermittent satellite communications is integrated into the geospatial sensor web using the NeXOS architecture.

The Open Geospatial Consortium (OGC) has conducted much work in the past on event-based models and architectures. However, the current OGC standard baseline only supports synchronous web service capabilities, which have insofar primarily addressed the request/reply model, where a client makes a request and the server usually responds synchronously, with either the requested information or a failure. Recently, the OGC Publish/Subscribe 1.0 Standard has introduced an abstract model for publish/subscribe message exchange, a long-awaited building block in the OGC suite of geospatial standards. The publish/subscribe pattern is distinguished from the request/reply one by the asynchronous delivery of messages and the ability for a client to specify an ongoing, persistent expression of interest. In this work, we report on the experimentation of the new OGC Publish/Subscribe 1.0 Standard in the context of the OGC Testbed-12 initiative and related fields of work, particularly in the application domains of Sensor Web and Aviation. We illustrate and discuss the enhancements in comparison to previous OGC service architectures, highlighting the benefits of introducing the PubSub 1.0 Standard into the considered systems and their workflows.

In recent years, the standards of OGC's Sensor Web Enablement (SWE) initiative have been applied in a multitude of projects to encapsulate heterogeneous geosensors for web-based discovery, tasking and access. Currently, SWE services and the different types of geosensors are integrated manually due to a conceptual gap between these two layers. Pair-wise adapters are created to connect an implementation of a particular SWE service with a particular type of geosensor. This approach is contrary to the aim of reaching interoperability and leads to an extensive integration effort in large scale systems with various types of geosensors and various SWE service implementations.To overcome this gap between geosensor networks and the Sensor Web, this work presents an intermediary layer for integrating these two distinct layers seamlessly. This intermediary layer is called the Sensor Bus as it is based on the message bus architecture pattern. It reduces the effort of connecting a sensor with the SWE services, since only the adaption to the Sensor Bus has to be created. The communication infrastructure which acts as the basis for the Sensor Bus is exchangeable. In this work, the Sensor Bus is based on Twitter. The involved SWE services as well as connected geosensors are represented as user profiles of the Twitter platform.