Ocean observing systems demystified

An ocean observing system could be defined as a set of independent elements that interact to form a whole for the purpose of observing ocean data. But, what is a system? Is a sensor a system? Is a buoy a system? Is a collection of stations a system? This paper defines the components of an ocean observing system and how they relate to each other for the purpose of streaming real time sensed data. This paper answers these questions based on results from the Open Geospatial Consortium (OGC) Ocean Science Interoperability Experiment. The paper also provides a conceptual model of an ocean observing system and web services examples based on OGC Sensor Observation Services (SOS) and the IEEE 1451 set of standards. The OOSTethys group, leader of the OGC Ocean Science Interoperability Experiment, has been building a community of interest, developing reference implementations, and maintaining a test-bed environment to advance the OGC Sensor Observation Service (SOS) and IEEE 1451 standards. The primary goal of the OOSTethys project is to accelerate the pace at which ocean observations and associated technologies become more broadly and publicly available by expediting the community-wide adoption, installation, and updating of standards-compliant web services. Published in 2007, SOS is a relatively new OGC standard. Even so, the SOS standard has been broadly implemented and has been adopted by the Integrated Ocean Observing System (IOOS) Program Office within the National Oceanic and Atmospheric Administration (NOAA). The European Seafloor Observatory Network (ESONET), as well as many other projects and organizations are also considering adopting SOS. SOS provides the framework to access and publish observations in a very general form. For example, it can be configured to publish observations from a collection of heterogeneous sensors, a platform, an individual sensor, or even from a numerical model or a human observer. SOS defines the operations (describe Sensor, get Observation, etc.) that a system should implement to publish observations. SOS is built on other standards, such as OGC Observation and Measurement (O&M), OGC Sensor Model Language (SensorML) and the OGC Sensor Web Enablement common data model (SWECommon). IEEE 1451 is a suite of standards that define a model and interfaces to connect transducers (e.g., sensors) to systems and networks. It defines a smart transducer composed of Transducer Interface Module (TIM) and a Network capable Application processor (NCAP). Both provide the functional components to enable interoperability of instruments in sensor networks. The OOSTethys community, using SensorML, O&M, and IEEE 1451 has specified a simplified conceptual model for an observing system. SensorML provides the capabilities to describe the composition of systems. OOSTethys defines a system to be a procedure and a collection of components. A procedure, as specified in O&M, is in charge of creating the observation. A procedure has an output, which is the result of the observation. The components are themselves considered systems. For example, an instrument and a sensor can each be treated as systems. It is also possible to describe a regional observing system as composed of a set of platforms, platforms as a set of instruments and instruments as a set of sensors. As such, each system could provide its own observation offering. SOS allows service providers to offer ad-hoc observation offerings. The OOSTethys community believes that an offering should be related to one and only one system. For example, a platform could have its own offering allowing users get all the data related to the platform deployment from one service end point. Even systems that integrate observations from multiple sources can provide observation offerings for their unique combinations of data. By presenting a unified underlying meaning of what defines an observing system and implementing its concrete representation using OGC SOS services, we are advancing interoperable solutions for complex observing systems. Furthermore, by fostering community agreements we are aligning standards best practices for the NOAA IOOS program office, ESONET and other initiatives. This paper will help SOS providers better configure their observation offerings, thus better enabling cross community interoperability. The results are not only applicable to ocean observing systems, but could be generalized to any kind of observing system such as components that are part of the Global Earth Observing System of Systems (GEOSS).