Changes from the Envisat/Aura metadata standard to GEOMS v1.0, December 01, 2021

• Organizational and structural updates and changes
  • The maintenance of template guidelines in external documents is discontinued. Templates are now online extensions GEOMS-TE to the standard.
  • Table attribute values (TAV) are removed from the GEOMS document and are now online extensions GEOMS-AV to the standard. TAV files to be used for file generation are continued to be issued.
  • Setup of a discussion group (email list) for update and evolution of GEOMS.
  • Harmonization of existing flavors of the Envi/Aura metadata standard.
• Changes to file formats
  • Next to HDF4 and HDF5, the netCDF format is supported.
  • Recommendations on the generation of HDF4, HDF5, and netCDF files updated.
• Changes to attributes
  • Non-standard attributes are allowed.
  • Global attributes
    • New attributes
      • DATA_STOP_DATE (mandatory)
      • DATA_QUALITY (optional)
      • DATA-TEMPLATE (optional/mandatory): Includes name and version number, e.g. for the LIDAR this is e.g. GEOMS-TE-LIDAR-001.
      • DATA_PROCESSOR (optional): Store processor information (former sometimes stored in DATA_FILE_VERSION) allows to give data processor name an version.
      • FILE_DOI (mandatory): Currently left empty, definition will follow.
    • Updated attributes
      • DATA_FILE_VERSION is only a three-digit running index now.
      • DATA_SOURCE updates for FTIR, still in discussion LIDAR and UVVIS.
      • FILE_NAME now contains DATA_STOP_DATE, has updated DATA_FILE_VERSION, and dropped DATA_LEVEL/DATA_TYPE.
    • Removed attributes
      • DATA_LEVEL/DATA_TYPE
  • Variable attributes
    • Removed attributes
      • VAR_DIMENSION
      • VAR_AVG_TYPE
      • VIS_LABEL
      • VIS_FORMAT
      • VIS_PLOT_TYPE
      • VIS_SCALE_TYPE
      • VIS_SCALE_MIN
      • VIS_SCALE_MAX
    • Updated attributes
      • VAR_DATA_TYPE
      • VAR_FILL_VALUE
• Important updates to DATA_VARIABLES
  • Entries in GEOMS-AV are color coded to indicate the status of a data variable.
    • 0: grey: expired variable
    • 1: [no color]: reserved for data center internal purposes
    • 2: black: regular variable
    • 3: red: major change to variable or new variable
    • 4: green: small change to variable (e.g. typo correction)
    • 5: orange: variable in review
  • The concept of axis variables is introduced. An axis variable (DATETIME, LATITUDE, LONGITUDE, and e.g. ALTITUDE), which is by definition independent, must use its own variable name as a dependent variable in VAR_DEPEND. Axis variables can be multi-dimensional.
  • Variable modes are optional (like already optional variable descriptors)
  • Removed data variables
    • CONCENTRATION was replaced by MIXING.RATIO, NUMBER.DENSITY, and PARTIAL.PRESSURE
    • AIR.MASS.FACTOR
    • RESOLUTION.TIME
  • New data variables
    • SOURCE.PRODUCT allows to store information of original products before conversion into GEOMS
  • Updated data variables
    • INTEGRATION.TIME variable name from former variable descriptor
    • DATETIME.[START|STOP] variable names from former variable descriptors [START|STOP].TIME
    • Special rules apply for variable names referring to air. The variable name to be used does not explicitly carry the AIR keyword, but implicitly refers to air, e.g. TEMPERATURE instead of AIR.TEMPERATURE. In case another medium than AIR is measured, the medium or identifier will be on the first position, e.g. INTERNAL.BOX.TEMPERATURE, ICE.TEMPERATURE, or SURFACE.TEMPERATURE. The same approach is valid for gases mixed in air, e.g. CH4.MIXING.RATIO.
    • DATETIME, LATITUDE, LONGITUDE, ALTITUDE[.GPH], PRESSURE, DEPTH: These variable names refer to effective geolocation (mid-time/point) of a reported parameter.
    • AVK and AMF are used as a variable descriptors
    • COLUMN.VERTICAL discontinued, instead COLUMN refers to total vertical column, COLUMN.PARTIAL to partial vertical (e.g. tropospheric) column
    • GEOMS is compatible with the unidata UDUNITS package for units conversion. To achieve this following variables were renamed:
      • MJD2000 -> MJD2K
      • DIMENSIONLESS -> 1 (a mathematical operator)
    • VAR_SI_CONVERSION updated