3 File Format of the MODIS VI Products

The MODIS production and science team chose the Hierarchical Data Format-Earth Observing System (HDF-EOS) format, which is the standard archive format for EOS Data Information System (EOSDIS) products. Each MODIS-VI file contains two separate structures:

1. Scientific data sets (SDS) which are the actual data stored in array format (2-D, 3-D and even 4-D).

2. Three sets of metadata:

   • structural metadata that describes the actual content of the file,

   • core metadata that describes the projection and grid name,

   • archive metadata that describes various aspects of the file in terms of dates, times, statistics about quality, useful to archive and search the product.

All MODIS VI products are in a grid structure, which are defined as projected, fixed-area size files. This was done for geolocation purposes and to facilitate the correlation between the data and its actual location on Earth. Other formats used to store MODIS data are the point structure and the swath structure. The use of metadata is meant to enhance the self-describing characteristics of HDF files and is useful to the end user, facilitating the archiving and searching of files. Parameter Value Language (PVL) is used to write the various metadata to the product file as:

   PARAMETER = VALUE

There are two types of metadata attributes: 1) global attributes which are general to all MODIS products and 2) product specific attributes (PSA). From a practical perspective, metadata will provide the user with general information about the file contents, its characteristics and quality (through the QA PSA), which is used to decide if the file is useful. The scientific data sets (SDS) could then be used for further analyses and use of the product.