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MMS Team members are welcome to ADD ADDITIONAL QUANTITIES as they are defined.


The CDF Format Guide requires that UNITS and SI_CONVERSION must be specified for each parameter.

  • It is proposed that conventions should be defined, so that a standard nomenclature is used for these metadata. 
  • UNITS attribute
    • units in Level 2 CDF files shall be taken from the list above
    • The units shall be specified as a human-readable ASCII string, using the abbreviations listed above. 
    • guidelines for unit nomenclature are proposed, below.
  • SI_CONVERSION attribute
    • Gives the conversion from the MMS unit of measure to SI units
    • This attribute allows for plotting/analysis tools to combine MMS data with data from other missions which use different units. 
    • Guidelines for SI unit nomenclature are proposed, below.
    • Requires guidelines for syntax, which are also included below.

Proposed convention for unit nomenclature and SI conversion attribute:

  • SI unit symbols to be used for SI conversion (rather than SI unit names) without SI prefixes: e.g. T, rather than nT or Tesla; sr, rather than steradians.
    The SI_CONVERSION from nT would then be "1.0e-9>T".
  • SI prefixes are allowed in variable units, but not in the converted SI unit (units of [km] are required for distances, but the SI conversion must be to [m]).
  • Note that the SI unit for angles is radians [rad]. 
    The SI_CONVERSION for angles (in degrees as defined above) would be "pi/180>rad" (Alternative 1: uses division in unit conversion but preserves precision.)
    The SI_CONVERSION for angles (in degrees as defined above) would be "0.0174532925>rad" (Alternative 2: gives number in unit conversion but loses precision.)
  • Dimensionless variables are required (by ISTP standard) to be a blank character. For consistency the conversion should also be a blank character.
    The SI_CONVERSION for a dimensionless variable would be " > ".
  • Units that are already SI (e.g. Hz, V) will have a multiplicative factor of 1, so the SI_CONVERSION for spacecraft potential would be "1.0>V".

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