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The Goddard Earth Sciences (GES) DAAC has an extensive archive of atmospheric, ocean, and radiance data products (MODIS, AIRS, Aura, etc.). Many of these are stored in the HDF-EOS or HDF file formats, in either version 4 or the new version 5. Many of these data products are too large to use in their full format, and thus it becomes ecessary to subset only that information which is truly useful to the user. For high spatial resolution data, this involves subsetting the data by latitude and longitude. For hyper- or multi-spectral data, it involves subsetting the data by channel or band. Some data files contain many different measured parameters, and thus subsetting by geophysical parameter becomes important. There are other methods of reducing the data volume, such as only retrieving those regions that are cloud free, for example.
Some data products are on-line (anonymous ftp data pool) and thus require subsetting on-the-fly, while other data are backed up in the near-line archive and must be subsetted on-demand. A third option involves pre-selected subsets (such as a geographic region, or set of popular parameters). Of course every data product ends up having some unique properties that makes generic subsetting non-trivial. The GES DAAC has experience with all of these cases and is in the process of tailoring many of its data products to suit users needs. In this presentation we provide an overview of the various ongoing subsetting activities at the GES DAAC.
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