Sensor web is a type of

sensor network Wireless sensor networks (WSNs) refer to networks of spatially dispersed and dedicated sensors that monitor and record the physical conditions of the environment and forward the collected data to a central location. WSNs can measure environmental ...

that heavily utilizes the

World Wide Web The World Wide Web (WWW or simply the Web) is an information system that enables Content (media), content sharing over the Internet through user-friendly ways meant to appeal to users beyond Information technology, IT specialists and hobbyis ...

and is especially suited for

environmental monitoring Environmental monitoring is the processes and activities that are done to characterize and describe the state of the environment. It is used in the preparation of environmental impact assessments, and in many circumstances in which human activit ...

. OGC's '' Sensor Web Enablement'' (SWE) framework defines a suite of web service interfaces and communication protocols abstracting from the heterogeneity of sensor (network) communication.

Definition

The term "sensor web" was first used by Kevin Delin of NASA in 1997, to describe a novel wireless sensor network architecture where the individual pieces could act and coordinate as a whole. In this sense, the term describes a specific type of

: an amorphous network of spatially distributed

sensor A sensor is often defined as a device that receives and responds to a signal or stimulus. The stimulus is the quantity, property, or condition that is sensed and converted into electrical signal. In the broadest definition, a sensor is a devi ...

platforms (pods) that wirelessly communicate with each other. This amorphous architecture is unique since it is both synchronous and router-free, making it distinct from the more typical

TCP/IP The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suite are ...

-like network schemes. A pod as a physical platform for a sensor can be orbital or terrestrial, fixed or mobile and might even have real time accessibility via the

Internet The Internet (or internet) is the Global network, global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a internetworking, network of networks ...

. Pod-to-pod communication is both omni-directional and bi-directional where each pod sends out collected data to every other pod in the network. Hence, the architecture allows every pod to know what is going on with every other pod throughout the sensor web at each measurement cycle. The individual pods (nodes) were all hardware equivalent and Delin's architecture did not require special gateways or routing to have each of the individual pieces communicate with one another or with an end user. Delin's definition of a sensor web was an ''autonomous, stand-alone, sensing entity – capable of interpreting and reacting to the data measured – that does not necessarily require the presence of the World Wide Web to function''. As a result, on-the-fly data fusion, such as false-positive identification and plume tracking, can occur within the sensor web itself and the system subsequently reacts as a coordinated, collective whole to the incoming data stream. For example, instead of having uncoordinated smoke detectors, a sensor web can react as a single, spatially dispersed, fire locator. The term "sensor web" has also morphed into sometimes being associated with an additional layer connecting sensors to the

. The Sensor Web Enablement (SWE) initiative of the

Open Geospatial Consortium The Open Geospatial Consortium (OGC) is an international voluntary consensus standards organization that develops and maintains international standards for geospatial content and location-based services, sensor web, Internet of Things, Geographi ...

(OGC) defines service interfaces which enable an interoperable usage of sensor resources by enabling their ''discovery'', ''access'', ''tasking'', as well as ''eventing and alerting''. By defining standardized service interfaces, a sensor web based on SWE services hides the heterogeneity of an underlying sensor network, its communication details and various hardware components, from the applications built on top of it. OGC's SWE initiative defines the term "sensor web" as ''an infrastructure enabling access to sensor networks and archived sensor data that can be discovered and accessed using standard protocols and application programming interfaces''. Through this abstraction from sensor details, their usage in applications is facilitated.

Characteristics of Delin's ''sensor web'' architecture

Delin designed a sensor web as a web of interconnected pods. All pods in a sensor web are equivalent in hardware (there are no special "gateway" or "slave" pods). Nevertheless, there are additional functions that pods can perform besides participating in the general sensor web function. Any pod of a sensor web can be a ''portal pod'' and provides users access to the sensor web (both input and output).
NASA Creates Thinking RF Sensors
Access can be provided by RF modem,

cell phone A mobile phone or cell phone is a portable telephone that allows users to make and receive calls over a radio frequency link while moving within a designated telephone service area, unlike fixed-location phones ( landline phones). This radio ...

connections, laptop connections, or even an

Internet server A server is a computer that provides information to other computers called "Client (computing), clients" on a computer network. This Systems architecture, architecture is called the client–server model. Servers can provide various functionali ...

. In some cases, a pod will have an attached removable memory unit (such as a USB stick or a laptop) that stores collected data. The term of ''mother pod'' refers to the pod that contains the master clock of the synchronous sensor web system. The mother pod has no special hardware associated with it, its designation as a mother is merely based on the ID number associated with the pod. Often the mother pod serves as a primary portal point to the Internet, but this is done only for deployment convenience. Early papers referenced the mother pod as "a prime node" if it additionally contained special hardware for a particular type of input/output device (say an RF modem). Because of the inherent hopping of data within a sensor web, a pod with no attached sensors can be deployed as a ''

relay A relay Electromechanical relay schematic showing a control coil, four pairs of normally open and one pair of normally closed contacts An automotive-style miniature relay with the dust cover taken off A relay is an electrically operated switc ...

'' with the single purpose of facilitating communication between the other pods and to expand the communication range to a particular end-point (such as a mother pod). Sensors can be attached to relay pods at a later time and relays can also serve as portal pods. Each pod usually contains: * one or more sensor leading to one or more data channel, * a processing unit such as a micro-controller or

microprocessor A microprocessor is a computer processor (computing), processor for which the data processing logic and control is included on a single integrated circuit (IC), or a small number of ICs. The microprocessor contains the arithmetic, logic, a ...

, * a two-way communication component such as a

radio Radio is the technology of communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connec ...

and antenna (radio ranges are typically limited by government spectrum requirements; unlicensed bands will allow for communication of a few hundred yards in unobstructed areas, although line of sight is not a requirement), * an energy source such as a battery coupled with a

solar cell A solar cell, also known as a photovoltaic cell (PV cell), is an electronic device that converts the energy of light directly into electricity by means of the photovoltaic effect.

, * a package to protect components against sometimes harsh environment, Each pod also typically requires a support such as a pole or tripod.
Sensor Web in Antarctica: Developing an intelligent, autonomous platform for locating biological flourishes in cryogenic environments
The number of pods may vary, with examples of sensor webs with 12 to 30 pods. The shape of a sensor web may impact its usefulness, for instance a particular deployment made sure each pod was in range to communicate with at least two other pods. Sensor web measurement cycles have typically been between 30 seconds and 15 minutes for deployed systems thus far. Sensor webs consisting of pods have been deployed that have spanned miles and run continuously for years. Sensor webs have been fielded in harsh environments (including deserts, mountain snowpacks, and Antarctica) for the purposes of environmental science and have also proved valuable in urban

search and rescue Search and rescue (SAR) is the search for and provision of aid to people who are in distress or imminent danger. The general field of search and rescue includes many specialty sub-fields, typically determined by the type of terrain the search ...

and infrastructure protection. The technology is not only monitoring the environment but sometimes also controlling the environment by actuating devices.

References

External links

SensorWare Systems
- The company spun out of NASA to commercialize the sensor web technology.
Sensor Web Alliance
– An organization that is developing a collaborative research platform called the Sensor Web Alliance (SWA). The aim is to pool resources in the SWA, coordinate research and allow participating organisations to share IP, which will spread risk and lower the cost of entry.
SenseWeb Project
– A Microsoft Research project that lets users visualize and query real-time data using a geographical interface such as Windows Live Local and allows data owners to easily publish their live data using a web service interface. Networks Web Geographic information systems Sensors

Definition

Characteristics of Delin's ''sensor web'' architecture

See also

References

Further reading

External links