The ISO Data Archive (IDA)
It has been mentioned that ISO performed around 30 000 science observations. If account is taken of obser-vations made in the parallel and serendipity modes of the instruments (observational modes in which an instrument could observe while another instrument was prime) almost 150 000 data sets were recorded with ISO.
Since ISO was operated as an observatory with four complex instruments, the resulting data is very heterogeneous. The data underwent sophisticated processing, including validation and accuracy analysis. In total, there exist around 400 Gb of data. To provide this data to the user community a sophisticated archive has been developed by ISO Data Centre with continuous and fruitful cooperation between users and developers to provide a unique state-of-the art astronomical data archive. In addition to the observational data products, the archive also contains satellite housekeeping data, software tools, documentation, and externally derived products.
The IDA is based on an open and flexible 3-tier architecture comprising the Data Products and Database, the Business Logic and the User Interface. An important consideration was to separate the stored data from their final presentation to the user. The Business Logic and the User Interface have been developed entirely in JAVA and XML which allows the IDA to be accessible from any platform and from the most popular web browsers. This has facilitated its re-use for other archive projects, in particular the XMM-Newton Science Archive reducing significantly development and maintenance costs. A textual and visual presentation of the data is offered to the users to aid them in selecting observations for retrieval.
One of the main features of the ISO Data Archive is the provision of browse products or quick-look data associated with each observation. These products enable users to make informed decisions as to which observations they want to download for detailed astronomical analysis.
The ISO archive is intensively used by the astronomical community. In its first four years of use, the equivalent of more than 7 times the total number of scientific observations in the archive was downloaded, with the monthly retrieval rate currently ranging from 5 to 10%. In total, there are nearly 1400 registered users. About 60 users actually download data each month. The ISO archive incorporates many, and growing, elements of interoperability with other popular astronomical archives, in anticipation of the "Virtual Observatories" (VO) of the future. Target names entered into the IDA user interface are resolved with searches in the NED (NASA/IPEC Extragalactic Database) or SIMBAD (Set of Identifications, Measurements, and Bibliography for Astronomical Data) databases.
Individual observations in the ISO database are linked to related publications listed in the ADS (Astrophysics Data System) database maintained by Harvard. ADS in turn links publications to ISO data sets upon which they are based. Searches in the Strasbourg based CDS/Vizier and the NASA HEASARC browsers also link to ISO observations. Within NASA's Infrared Science Archive IRSA, tools allow overlap of ISO target fields onto IRAS images. More interoperability features are under development, such as integration of the ISO observing log into SIMBAD and the visualisation of ISO images within the CDS based Aladin image stacker. The ISO Data Archive leads the way towards its future integration into the VO concept.
Principal Contents of the ISO Data Archive
Every ISO observation has been run through an automatic data-analysis pipeline called Off-Line Processing, or OLP, to produce standard data products. The automatic data products passed through several generations, until at the end of ISO Post Operations and in the first months of the Active Archive Phase in early 2002 a final full reprocessing of all ISO data was performed, producing the "ISO Legacy Archive". All products were put on hard disk. This supersedes previous product versions.
Interactive Analysis Tools
All interactive analysis tools, including a number of software packages offered to the community for reduction and analysis of ISO data, are archived. These include: