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A preponderance of data from NASA's Earth Observing System (EOS) is archived in the HDF Version 4 (HDF4) format. The long-term preservation of these data is critical for climate and other scientific studies going many decades into the future. HDF4 is very effective for working with the large and complex collection of EOS data products. Unfortunately, because of the complex internal byte layout of HDF4 files, future readability of HDF4 data depends on preserving a complex software library that can interpret that layout. Having a way to access HDF4 data independent of a library could improve its viability as an archive format, and consequently give confidence that HDF4 data will be readily accessible forever, even if the HDF4 library is gone.
To address the need to simplify long-term access to EOS data stored in HDF4, a collaborative project between The HDF Group and NASA Earth Science Data Centers is implementing an approach to accessing data in HDF4 files based on the use of independent maps that describe the data in HDF4 files and tools that can use these maps to recover data from those files. With this approach, relatively simple programs will be able to extract the data from an HDF4 file, bypassing the need for the HDF4 library.
A demonstration project has shown that this approach is feasible, and now the project is in a second phase, in which the mapping tools and XML schema are made production quality, the mapping schema are integrated with existing XML metadata files in several data centers, and outreach activities are carried out to encourage and facilitate acceptance of the technology.
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