Overview (History) of Continuity Atmosphere Data Versions
Instrument/Platform: VIIRS/SNPP & MODIS/AQUA
Last Updated: 10 April 2019
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What are Data Versions?
A specific Version of data generally stays "current" (is distributed) for approximately 1 to 4 years. Typically the previous Version of data continues to be distributed while a new Version is being processed and distributed. So in many instances, two Data Versions are in the public archive. Subsequent data Versions typically increment by one: 001, 002, 003, etc. Detailed documentation for the latest Version can typically be found on webpages in the Documentation Section.
During the processing of a particular Data Version, an attempt is made to use the same iteration of the Science Algorithms, also known as the Product Generation Executive (PGEs). However, sometimes several new PGE's (algorithm updates) are released during a particular Data Version to fix bugs or make improvements to the data. For bug fixes, if the bug is not serious, forward processing will continue with the new corrected PGE, while old previously processed data (which was produced with an older version algorithm (PGE)) are left in the archive.
When more serious bugs are found or more profound fixes are implemented, a decision is sometimes made to reprocess the entire record with an "incremental" Data Version (for example Version 000 to Version 001). When enough changes or improvements are made to the science algorithms, the entire dataset (from launch) is reprocessed and then tagged & distributed as a new Data Version (for example going from Version 001 to Version 002). Preparation to go to a new Version can be a major effort that can take multiple months to several years to prepare for and complete.
It should be noted that issues, anomalies, and problems in a particular Version are noted on the Data Issues section of this website as they are discovered. Eventually a fix is implemented which incrementally rolls forward the PGE Version while the Data Version number might remain the same. One can always identify the Data Version number for a particular NetCDF4 file as it's always included (as a 3 digit number) as part of the NetCDF4 filename (for example "001").