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As the volume of data increased and with 
growing interest in change detection and 
assessment, the need for more sophisticated tools 
became more apparent. GCNet is a system 
developed at CCRS in 1990 [1,2] in response to 
this requirement to provide users better access to 
remote sensing and other data required by 
Global Change scientists. 
This article provides an overview of the services 
offered by GCNet in support of earth 
observation data management at CCRS; presents 
some statistics about GCNet utilization and looks 
at future developments and services to be offered 
by GCNet. 
2. OVERVIEW OF GCNET 
The GCNet system is developed around a Digital 
micro-VAX 3100 running under the VAX/VMS 
operating system. It is accessible 24 hours a day 
via Direct Dial, DATAPAC, Internet and NSI- 
DECnet. 
The services provided by GCNet are the 
following: Directory, Inventory, Bulletin Board 
and a Remote-Sensing Bibliographic service 
(RESORS). There are no usage fees, except for 
RESORS, but the user may have to pay long 
distances charges where it applies. No special 
Username/Password is required with the 
exception of RESORS again. 
* Directory Service 
The GCNet Directory provides a single point of 
contact for Canadian Global Change scientists 
and other users who want to obtain information 
about CCRS and other Canadian data holdings. 
It also provides direct network links to 
international directories and inventories 
The GCNet directory function is provided 
through the International Directory Network 
(IDN) Master Directory (MD) developed by 
NASA [3,4]. The MD data base contains 
descriptive information for over 2000 datasets in 
various countries. These datasets are organized 
by Disciplines and Sub-disciplines. Figures 1 
and 2 give a breakdown of the datasets among 
19 
them. The data base can be searched by 
numerous criteria such as parameter keywords, 
geographic location, and time. The MD data 
base implementation follows an internationally 
accepted standard [5]. The fields stored in the 
MD data base for each dataset are: 
* Directory entry identifier 
* Directory entry title 
* Start and Stop dates 
* Sensor name, Source name 
* Investigator, Technical contact 
- Data centre (name, contact person) 
Dataset identifier 
« Originating centre, Campaign or Project 
name 
Storage medium 
* Parameter measured 
* Discipline keywords, 
keywords, General keywords 
* Dataset Coverage 
* Revision date, Science review date, 
Future review date 
* Reference 
* Summary 
Location 
  
Entries in IDN Master Directory 
CBy Discipline) 
Planetary Science 6% 
   
Earth Sciences 70% 
  
  
  
Figure 1 Distribution of the datasets in the IDN 
Master Directory among the five supported 
disciplines.