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between the services themselves and the services and the 
framework (Figure 4). 
5. CONCLUSIONS 
Web services allow the exposure of an application 
programming interface over the web to be accessed remotely. 
Web services are implemented using industry agreed on 
standards (XML, SOAP, HTTP), thus holding the promise of 
wider use than competing technologies. By combining 
relatively simple individual Web services with other distributed 
services, a more complex service can be provided in a platform 
independent way. The design of a GIS web service for NDVI 
estimation using satellite imagery was discussed in this study. 
Near real time NOAA/AVHRR data provided by the FORTH 
satellite ground receiving station were used. NDVI calculations 
were performed by Java-based in house software, which was 
provided for use by end users through the developed GIS web 
services’ framework. 
Future research will be concentrated on providing automatic 
registration, description and discovery capabilities to the 
system, developing a pricing system (although one is not 
planned to be used shortly since the service is supposed to 
remain free for the scientific community at large) and mainly 
integrating more environmental related web services based on 
the already available satellite images. These can include but are 
limited to: a service for image orthorectification, a service that 
will provide vector data for the area of interest so as to give the 
user the ability to combine different web services and services 
that will enable the calculation of other environmental 
parameters like surface temperature and perceptible water, 
aerosol distribution etc. 
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