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. 
82 
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