Standards: Enabling sensor communication

<< Although OGC’s current standards can meet many of the emerging markets’ interoperability requirements, much work remains to be done to make heterogeneous sensors and sensor data stores useful for diverse applications… >>

Wikipedia defines a ‘sensor’ as “a converter that measures a physical quantity and converts it into a signal which can be read by an observer or by an (mostly electronic) instrument.”

A sensor network is a computer accessible network of many spatially distributed sensors to gather information/ monitor conditions at different locations, such as temperature, sound, vibration, pressure, motion or pollutants. A Sensor Web refers to web accessible sensor networks and archived sensor data that can be ‘discovered’ and accessed using standard protocols and Application Program Interfaces (APIs).

There are hundreds of millions of Internet/web enabled sensors on, in and around the earth, and the number is growing rapidly. Enabling Sensor Communication Standardisation is the key requirement for communicating information about sensors and sensor data and for comparing and combining information from different sensors. The OGC’s Sensor Web Enablement (SWE) standards meet this requirement in the most complex as well as very simple applications. Sensor location is usually a key piece of sensor or sensor data information, and SWE standards make it easy to integrate this information into thousands of geospatial applications that implement OGC’s other standards.

Critical Needs and Challenges
Internet-connected sensors are proliferating at a phenomenal rate. Apart from the traditional CCTVs and IR sensors used by security agencies, smartphones typically include a gyroscope, accelerometer, GPS, Wi-Fi, bluetooth, cell, sound, light, magnetic force, time, near-field communications (NFC), compass and a camera. Tiny, inexpensive, geolocated, network-connected sensors like these are rapidly making their way into vehicles, buildings, transportation networks and many other applications. To produce useful information, such data often needs to be ‘fused’ with map data and/ or computer-aided design (CAD) building data, and also text, image, video or sound.

Current standards from the OGC can meet many of these emerging markets’ interoperability requirements, but much work remains to make heterogeneous web-resident sensors and sensor data stores useful to diverse applications that have been developed. Integrating sensors involves semantic understanding of the sensors.

OGC standards provide an important framework for addressing semantics, but more work needs to be done to enable fusion of data from diverse sensor types. Data quality and quality of service are important issues to address in sensor web standards development activities. Indoor location and indoor/ outdoor location integration represent significant challenges for many sensor web applications such as energy management and the smart grid. None of these challenges can be met without further standards work. No single company or technologybiased industry association can meet these challenges.

OGC’s Contribution and the Vital Role of Domain Working Groups (DWGs or WGs)
The OGC is inviting technology users and providers to collaborate in promoting SWE standards in new market domains, inviting contributed specifications for possible adoption as OGC standards, and reaching out to other Standards Development Organizations (SDOs). The challenges of ubiquitous computing and sensing require broader participation by SDOs, technology users and providers, and inter-SDO coordination on an unprecedented scale to avoid costly duplication of effort and unintended new standards stovepipes. Here, a key role is played by the DWG. These provide a forum for discussion on key interoperability requirements and issues, discussion and review of implementation specifications, and presentations on key technology areas relevant to solving geospatial interoperability issues.

The SWE DWG members are specifying interoperability interfaces and metadata encodings that enable real-time integration of heterogeneous sensor webs into the information infrastructure. Developers will use these specifications in creating applications, platforms and products involving web-connected devices such as flood gauges, air pollution monitors, stress gauges on bridges, mobile heart monitors and webcams as well as space and airborne earth imaging devices.

The OGC’s SWE Initiative
Planetary scientists first proposed the concept of standardised description files for sensor location in the early ‘90s. Subsequent work by NASA, the University of Alabama Huntsville and CEOS (Committee on Earth Observation Satellites) was brought into the OGC in 2001 for prototyping, testing and promotion as its SWE activity. OGC took on the task of standardising sensor communication because every sensor, whether in situ (such as a rain gauge) or remote (such as an earth imaging device), has a location, and the location of a sensor is highly significant for many applications.

In the SWE initiative, OGC members have defined and documented a unique and revolutionary framework of open standards for exploiting web-connected sensors and sensor systems of all types. SWE presents many opportunities for adding a real-time sensor dimension to the web. This has a high level of significance for defence and security, disaster management as well as in other areas like environmental monitoring, transportation management, public safety, facility security, Supervisory Control And Data Acquisition (SCADA) operations, industrial controls, science and facilities management.

The resulting suite of SWE standards – now being widely implemented around the world – enables developers to make all types of networked sensors, transducers and sensor data repositories discoverable, accessible and useable via the web or other networks. OGC standards are downloadable at no charge, for use by anyone.

High Level Architecture
The models, encodings and services of the SWE architecture enable implementation of interoperable and scalable service-oriented networks of heterogeneous sensor systems and client applications. In much the same way that HTML and HTTP standards enabled the exchange of any type of information on the web, the SWE initiative is focussed on developing standards to enable the discovery, exchange and processing of sensor observations, as well as the tasking of sensor systems. The functionality that OCG has targeted within a sensor web includes:

• Discovery of sensor systems, observations and observation processes that meet a user’s immediate needs
• Determination of a sensor’s capabilities and quality of measurements
• Access to sensor parameters that automatically allow software to process and geo-locate observations
• Retrieval of real-time or timeseries observations and coverage in standard encodings
• Tasking of sensors to acquire observations of interest
• Subscription to and publishing of alerts to be issued by sensors or sensor services based upon certain criteria

Within the SWE initiative, the enablement of such sensor webs and networks is being pursued through the establishment of several encodings for describing sensors and sensor observations, and through several standard interface definitions for web services. SWE standards that have been built and prototyped by members of the OGC include the following standards:

• Observations & Measurements Schema (O&M) – An OGC adopted standard that defines conceptual models for encoding observations and measurements from a sensor, both archived and real-time.
• Observations and Measurements XML (OMXML) – XML encoding of the O&M conceptual model.
• Sensor Model Language (SensorML) – An OGC adopted standard that defines standard models and XML Schema for describing sensors systems and processes; provides information needed for discovery of sensors, location of sensor observations, processing of low-level sensor observations, and listing of taskable properties.
• Sensor Observations Service (SOS) – An OGC adopted standard that specifies a standard web service interface for requesting, filtering, and retrieving observations and sensor system information. This is the intermediary between a client and an observation repository or near real-time sensor channel.
• Sensor Planning Service (SPS) – An OGC adopted standard that specifies standard web service interface for requesting user-driven acquisitions and observations. This is the intermediary between a client and a sensor collection management environment.
• SWE Common Data Model – The standard defines low level data models for exchanging sensor related data between nodes of the OGC SWE framework. These models allow applications and/ or servers to structure, encode and transmit sensor datasets in a self-describing and semantically enabled way.
• SWE Services Common – This standard currently defines eight packages with data types for common use across OGC SWE services. Five of these packages define operation request and response types. These packages use data types specified in other standards.
• PUCK Protocol Standard – This standard defines a protocol for RS232 and Ethernet connected instruments. PUCK addresses installation and configuration challenges for sensors by defining a standard instrument protocol to store and automatically retrieve metadata and other information from the instrument device itself. PUCK is the newest addition to the SWE standards suite.
• Sensor Alert Service (SAS) – An OGC discussion paper describing a web service interface for publishing and subscribing to alerts from sensors. This is not an OGC standard.
• Web Notification Services (WNS) – Standard web service interface for asynchronous delivery of messages or alerts from SAS and SPS web services and other elements of service workflows. This is not an OGC standard.

The goal of SWE is to enable all types of web and/ or internetaccessible sensors, instruments and imaging devices to be accessible and, where applicable, controllable via the web. The vision is to provide a standards foundation for ‘plug-and-play’ web-based sensor networks. SWE standards, therefore, have been harmonised with other OGC standards for geospatial processing. The SWE standards foundation also references other relevant sensor and alerting standards such as the IEEE 1451 ‘smart transducer’ family of standards and the OASIS Common Alerting Protocol (CAP), Web Services Notification (WS-N) and Asynchronous Service Access Protocol (ASAP) specifications. OGC works with the groups responsible for these standards to harmonise them with the SWE specifications.

Advances in digital technology are making it practical to link virtually any type of sensor or locally networked sensor system with wired or wireless connections. Such connections support remote access to the devices’ control inputs and data outputs as well as their identification and location information. For both fixed and mobile sensors, sensor location is often a vital sensor parameter. A variety of location technologies such as the GPS and Cell-ID with triangulation make mobile sensing devices capable of reporting their geographic location along with their sensor-collected data.

SWE standards have been implemented in hundreds of applications by private sector, government and university developers. For example, US National Ocean and Atmospheric Administration (NOAA), Integrated Oceans Observing System (IOOS); German Indonesian Tsunami Early Warning System (GITEWS); Asian Institute of Technology, Thailand – Nepal Wireless Project for Monitoring Climate Change in the Himalayas; Japan National Institute of Advanced Industrial Science & Technology (AIST): Earthquake Monitoring and Warning System (QuiQuake); Europe Emergency Response: . eu) an infrastructure based on SOS, SPS and SES to provide real-time information to crisis managers during abnormal events to improve the management between forces on the ground (like police and fire fighters) and the control centres; US Department of Homeland Security (DHS) Unified Incident Command and Decision Support (UICDS).

Conclusion
Standardisation is the key requirement for communicating information about sensors, its data and for comparing and combining information from various sensors. OGC recognises this challenge and is working actively with other agencies, industries and users for building standards.

REFERENCES

• Wikipedia
• OGC (www.opengeospatial.org.)
• OGC White Paper- “OGC® Sensor Web Enablement: Overview and High Level Architecture