International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B-YF. Istanbul 2004
communication equipment; and improved small-scale energy
supplies, have combined with reduced manufacturing costs 10
provide an emerging vision for sensor communication: wireless
sensor networks.
Wireless sensor networks consist of compact, power efficient,
battery powered nodes with low range radios and low-cost
sensors. Wireless sensor networks have attracted a tremendous
amount of attention and media publicity from both the research
community and industry.(Hellerstein et al., 2003) A wireless
sensor network is low cost, self organizing, self-configuring,
and easily expandable. These features allow large scale and
random sensor deployment in the field. Thus, a wireless sensor
network provides better spatial coverage than traditional sensor
networks and better temporal resolution than remote sensing.
From a geomatics perspective it is important to note that
location has been identified as the key for wireless sensor
networks and that localization has become a major research
focus in the field of sensor networks.(Hightower and Borriello,
2001) In the future, the aim is to make all sensors location-
aware. This provides a great research opportunity for the GIS
community since GIS is specialized in dealing with locational
data. Figure 3 shows an example of a sensor node that is
equipped with a GPS receiver.
Figure 3. A sensor board that is equipped with a GPS receiver.
(MTS420CA, Crossbow Inc.)
It is expected that most communication layers within the sensor
web will be hybrid systems, with different solutions being
implemented under different constraints. However, ultimately
the transferred sensing information is routed through the
Internet to the information layer.
1.3.3 Information Layer:
The Information layer is the place where the sensing resources
can be stored, disseminated, exchanged, managed, displayed
and analyzed. Sensing resources include sensors; sensors’
locations; sensors! real-time, near real-time or archived
measurements; command and control to sensors; models which
need sensor measurements as inputs and other related
information for users' applications.
The Information Layer of the sensor web has enormous variety
of data transport and access demands, data uses and data users.
Interoperability is the key to a successful information layer for
the sensor web. Users should be able to seamlessly access and
readily use sensing resources of the sensor web despite the
presence of significant heterogeneity of data, infrastructure
(different setting of sensor and network layers) and user
requirements. Information layers should support that data from
different sources be combined and integrated. Meta data of the
sensors and its measurements is also a core for an information
layer. Data quality should be described, measured and
guaranteed for more sophisticated applications.
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One of the critical components in the information layer of the
SW is to build a geospatial information structure, which
spatially enables the sensor web. Any phenomenon measured
by sensors must occur at a particular location. Location is an
enabling key to make sensors' observations meaningful. As
technology advancements in communication and sensor
technologies are made, we will see more and more mobile
sensors (i.e., moving while collecting measurements). An
infrastructure which could store, disseminate, exchange,
manage, display and analyze spatial information is vital for the
sensor web. The spatial sensor web infrastructure also must
meet the requirements of interoperability, openness,
transparency, and intelligence, as discussed above. The goal of
GeoSWIFT is to provide the missing GlService components to
spatially enable the sensor web.
2. GEOSWIFT (GEOSPATIAL SENSOR
INFORMATION FUSION TESTBED)
At York University's GeoICT Lab, our goal is to develop an
open geospatial sensing service for sensor web. In order to
have a comprehensive understanding of the research challenges
and future applications of sensor web, we establish a testbed
environment for sensor web — GeoSWIFT (Geospatial Sensor
Web Information Fusion Testbed). GeoSWIFT contains the
three layers we discuss above — sensor layer, communication
layer, and information layer. The core of GeoSWIFT is an
open geospatial sensing service, which serves as a single
queryable “global sensor” for sensor web users. GeoSWIFT
sensing service includes a GeoSWIFT Server and a GeoSWIFT
Viewer. It serves as a gateway for sensor web users; fuses
heterogeneous sensing sources and spatial information, such as
vector and raster data; and provides transparent sensing
information access. GeoSWIFT serves as a proof of the
spatial centred sensor web concept. This real-world exercise
serves to identify important areas of further work in spatial
sensor web and its implication to Geomatics.
2.1 GeoSWIFT Sensing Service
We use a new technology framework, Web Services, to design
the architecture of GeoSWIFT open geospatial sensing service.
Web Services represent the convergence between the service-
oriented architecture (SOA) and the World Wide Web. The
basic idea of web services is similar to SOA, however,
traditional SOA is tightly coupled with specific protocols. Each
of the protocols is constrained by dependencies on vendor
implementations, platforms, languages, or data encoding
schemes that severely limit interoperability. Web services
emphasize loose-coupling, openness, interoperability, and
simplicity. Web Services support Web-based access, easy
integration, and service reusability. For web service's openness,
interoperability, and extensibility, it serves as a good
foundation to build an open geospatial sensing service for
GeoSWIFT.
GeoSWIFT is designed with the architecture of GlServices.
GIService is to build GISystems with a service-oriented
approach that allows users to access and assemble
geoprocessing components that are distributed across a network
through Internet. GeoSWIFT is adopting OGC Web Service
standards for its sensing service. OpenGIS Web Service is a
breed of web service and a standards-based framework that will
enable seamless integration of a variety of online geoprocessing
and geodata services. OGC Web Services will allow distributed