File reference date and revision date
The file reference date indicates the start point of the time axis in the file.
The time axis is stated in days and begins at 00 UTC on the file reference date.
For example, a time stamp for 5 January 2012, 0 UTC may be stated with a reference date of 2012 01 05 in line 7 and a day of 0.000000 in the data section, or with a reference date of 2012 01 01 in line 7 and a day of 4.000000 in the data section.
The revision date is the date when the file was created or last updated. Both dates are space separated, and stated in the format YYYY MM DD.
<YYYY> <MM> <DD> <YYYY> <MM> <DD>