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Ticket Resolution Summary Owner Reporter
#105 wontfix Scalar Coordinates cf-conventions@… markh
Description

1. Title

Scalar Coordinates

2. Moderator

unknown

3. Requirement

The ability to store scalar coordinates in CF NetCDF data sets.

Scalar Coordinates are a valuable semantic concept, allowing data variables to encode coordinates which do not vary across the domain of the data variable.

Invariance with respect to the data variable's dimensions is the key characteristic of these coordinates and this is all the meaning that should be explicitly defined for such a coordinate. Further characteristics, such as implied degrees of freedom and potential inter-relationships, may be inferred downstream, at the discretion of the data consumer.

The current conventions provides clear specification on vector coordinates, encoded as either Coordinate Variables or Auxiliary Coordinate Variables. Such variables, which may be encoded as not varying with respect to the data variable, can be used wherever it is vital that the inter-relationship and degree of freedom are explicitly encoded. The specification does not make it clear enough what is meant by a scalar coordinate variable.

The current conventions document (1.6) does not make it clear whether the scalar coordinate variable (section 5.7) is:

an encoding detail with explicitly no semantic content, merely storing vector coordinates:

where the characteristics of these vector coordinates must be inferred by context;

a semantic container enabling scalar coordinates to be stored and recognised as scalar coordinates.

This interpretation requires clarification, which this proposal aim to deliver. Explicitly, this proposal will define the scalar coordinate variable as a semantic container for coordinate information.

4. Initial Statement of Technical Proposal

1.2 Terminology

A NetCDF variable which contains coordinate information for a data variable, where the coordinate information does not vary with respect to the data variable's dimensions.

5.7 Scalar Coordinate Variables

A scalar coordinate variable defines a coordinate which applies to an entire data variable equally. The scalar coordinate does not vary with respect to the data variable's dimensions.

The scalar coordinate variable is associated with a data variable via the coordinates attribute. The scalar coordinate variable does not share any dimensions with the data variable.

The variable name of a scalar coordinate variable must not match the name of any dimension in the file.

Bounds may be defined for a scalar coordinate variable in the same way as other coordinates.

A scalar coordinate variable may be interpreted as implying a potential further dimension, of size one, for the data variable. However, scalar coordinate variables do not define explicit independent dimensions.

Note that use of scalar coordinate variables for latitude, longitude, vertical, or time coordinates will inhibit COARDS conforming applications from recognizing them.

6.1 Labels

... {Unchanged, up to the last sentence}

If a character variable referenced by a data variable's coordinates attribute has only one dimension, the maximum length of the string, it is a string-valued scalar coordinate variable (see Section 5.7 Scalar Coordinate Variables).

9.2 Collections, Instances and Elements

... {First two paragraphs unchanged}

If there is only a single feature to be stored in a data variable, the instance dimension may be omitted. In this case the mandatory space-time coordinate variables will not vary with respect to the instance dimension. These space-time coordinates, as defined in table 9.1, may need to be defined as scalar coordinate variables, to maintain the required relationships for the feature types.

5. Benefits

The community benefits from this proposal by gaining clarity over the interpretation of scalar coordinate variables as a simple semantic concept within CF with a clear encoding.

All use cases presented to the mailing list to date are supported by this proposal, including:

  • encoding of size one explicit coordinate variables as scalar coordinate variables to simplify data variable shape;
  • encoding of coordinates where there are multiple possible inter-dependency relationships, such as:
    • multiple related time coordinates;
    • model, experiment, run identifiers for multi-model analyses;
  • encoding of discrete sampling geometries where there is a single feature;
  • encoding of coefficients as coordinates.

The data producer has the opportunity to select a scalar coordinate as the most appropriate way of describing some aspects of their data. The encoding convenience of omitting dimensions of size one is provided for, with a clear recognition that this encoding option slightly limits the richness of expression available with CF vector coordinates.

6. Status Quo

Currently the interpretation of scalar coordinate variables is unclear. It is recognised that a clarification is required. As such the status quo is deemed undesirable (e.g.4, 15)

There is another ticket, #104, proposing an alternative change. These two tickets should not both be approved, they are mutually exclusive.

#81 fixed new standard names for surface aerosol optical properties cf-standard-names@… markus
Description

Dear all,

since the WMO Global Atmosphere Watch (GAW) programme is moving towards using CF standard names as standard vocabulary, I'd like to propose the following standard names that represent aerosol properties being observed at the GAW surface sites:

1) volume_scattering_coefficient_in_air_due_to_dry_aerosol

The volume scattering coefficient is the fractional change of radiative flux per unit path length due to redirection of an incident light beam by a component in the reference volume. "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). "Dry aerosol" is aerosol at a relative humidity < 40% where it hasn't taken up ambient water by hygroscopic growth. The specification of a physical process by the phrase "due_to_" process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase.

2) volume_absorption_coefficient_in_air_due_to_dry_aerosol

The volume absorption coefficient is the fractional change of radiative flux per unit path length due to absorption of an incident light beam by a component in the reference volume. "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). "Dry aerosol" is aerosol at a relative humidity < 40% where it hasn't taken up ambient water by hygroscopic growth. The specification of a physical process by the phrase "due_to_" process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase.

3) volume_hemispheric_backscattering_coefficient_in_air_due_to_dry_aerosol

The volume hemispheric backscattering coefficient is the fractional change of radiative flux per unit path length due to redirection of an incident light beam into the rearward hemisphere relative to the incident beam by a component in the reference volume. It is distinct from the backscattering coefficient which isn't integrated over the rearward hemisphere. "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). "Dry aerosol" is aerosol at a relative humidity < 40% where it hasn't taken up ambient water by hygroscopic growth. The specification of a physical process by the phrase "due_to_" process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase.

4) surface_volume_scattering_coefficient_at_stp_in_air_due_to_pm1_dry_aerosol

The volume scattering coefficient is the fractional change of radiative flux per unit path length due to redirection of an incident light beam by a component in the reference volume. "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). "Dry aerosol" is aerosol at a relative humidity < 40% where it hasn't taken up ambient water by hygroscopic growth. The specification of a physical process by the phrase "due_to_" process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase. "surface" means the lower boundary of the atmosphere. "at_stp" refers to a volume at standard conditions of temperature (273.15 K) and pressure (1013.25 hPa). "pm1" refers to the fraction of aerosol particles with an aerodynamic diameter of less than or equal to 1 micrometer.

5) surface_volume_scattering_coefficient_at_stp_in_air_due_to_pm10_dry_aerosol

The volume scattering coefficient is the fractional change of radiative flux per unit path length due to redirection of an incident light beam by a component in the reference volume. "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). "Dry aerosol" is aerosol at a relative humidity < 40% where it hasn't taken up ambient water by hygroscopic growth. The specification of a physical process by the phrase "due_to_" process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase. "surface" means the lower boundary of the atmosphere. "at_stp" refers to a volume at standard conditions of temperature (273.15 K) and pressure (1013.25 hPa). "pm10" refers to the fraction of aerosol particles with an aerodynamic diameter of less than or equal to 10 micrometers.

6) surface_volume_absorption_coefficient_at_stp_in_air_due_to_pm1_dry_aerosol

The volume absorption coefficient is the fractional change of radiative flux per unit path length due to absorption of an incident light beam by a component in the reference volume. "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). "Dry aerosol" is aerosol at a relative humidity < 40% where it hasn't taken up ambient water by hygroscopic growth. The specification of a physical process by the phrase "due_to_" process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase. "surface" means the lower boundary of the atmosphere. "at_stp" refers to a volume at standard conditions of temperature (273.15 K) and pressure (1013.25 hPa). "pm1" refers to the fraction of aerosol particles with an aerodynamic diameter of less than or equal to 1 micrometers.

7) surface_volume_absorption_coefficient_at_stp_in_air_due_to_pm10_dry_aerosol

The volume absorption coefficient is the fractional change of radiative flux per unit path length due to absorption of an incident light beam by a component in the reference volume. "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). "Dry aerosol" is aerosol at a relative humidity < 40% where it hasn't taken up ambient water by hygroscopic growth. The specification of a physical process by the phrase "due_to_" process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase. "surface" means the lower boundary of the atmosphere. "at_stp" refers to a volume at standard conditions of temperature (273.15 K) and pressure (1013.25 hPa). "pm10" refers to the fraction of aerosol particles with an aerodynamic diameter of less than or equal to 10 micrometers.

8) surface_volume_hemispheric_backscattering_coefficient_at_stp_in_air_due_to_pm1_dry_aerosol

The volume hemispheric backscattering coefficient is the fractional change of radiative flux per unit path length due to redirection of an incident light beam into the rearward hemisphere relative to the incident beam by a component in the reference volume. It is distinct from the backscattering coefficient which isn't integrated over the rearward hemisphere. "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). "Dry aerosol" is aerosol at a relative humidity < 40% where it hasn't taken up ambient water by hygroscopic growth. The specification of a physical process by the phrase "due_to_" process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase. "surface" means the lower boundary of the atmosphere. "at_stp" refers to a volume at standard conditions of temperature (273.15 K) and pressure (1013.25 hPa). "pm1" refers to the fraction of aerosol particles with an aerodynamic diameter of less than or equal to 1 micrometers.

9) surface_volume_hemispheric_backscattering_coefficient_at_stp_in_air_due_to_pm10_dry_aerosol

The volume hemispheric backscattering coefficient is the fractional change of radiative flux per unit path length due to redirection of an incident light beam into the rearward hemisphere relative to the incident beam by a component in the reference volume. It is distinct from the backscattering coefficient which isn't integrated over the rearward hemisphere. "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). "Dry aerosol" is aerosol at a relative humidity < 40% where it hasn't taken up ambient water by hygroscopic growth. The specification of a physical process by the phrase "due_to_" process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase. "surface" means the lower boundary of the atmosphere. "at_stp" refers to a volume at standard conditions of temperature (273.15 K) and pressure (1013.25 hPa). "pm10" refers to the fraction of aerosol particles with an aerodynamic diameter of less than or equal to 10 micrometers.

10) volume_scattering_coefficient_in_air_due_to_aerosol

The volume scattering coefficient is the fractional change of radiative flux per unit path length due to redirection of an incident light beam by a component in the reference volume. "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). "Aerosol" without further qualification such as dry or ambient means that the aerosol humidity state is stated in the data. The specification of a physical process by the phrase "due_to_" process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase.

11) volume_absorption_coefficient_in_air_due_to_aerosol

The volume absorption coefficient is the fractional change of radiative flux per unit path length due to absorption of an incident light beam by a component in the reference volume. "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). "Aerosol" without further qualification such as dry or ambient means that the aerosol humidity state is stated in the data. The specification of a physical process by the phrase "due_to_" process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase.

12) volume_hemispheric_backscattering_coefficient_in_air_due_to_aerosol

The volume hemispheric backscattering coefficient is the fractional change of radiative flux per unit path length due to redirection of an incident light beam into the rearward hemisphere relative to the incident beam by a component in the reference volume. It is distinct from the backscattering coefficient which isn't integrated over the rearward hemisphere. "Aerosol" without further qualification such as dry or ambient means that the aerosol humidity state is stated in the data. The specification of a physical process by the phrase "due_to_" process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase.

13) surface_volume_scattering_coefficient_at_stp_in_air_due_to_pm1_aerosol

The volume scattering coefficient is the fractional change of radiative flux per unit path length due to redirection of an incident light beam by a component in the reference volume. "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). "Aerosol" without further qualification such as dry or ambient means that the aerosol humidity state is stated in the data. The specification of a physical process by the phrase "due_to_" process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase. "surface" means the lower boundary of the atmosphere. "at_stp" refers to a volume at standard conditions of temperature (273.15 K) and pressure (1013.25 hPa). "pm1" refers to the fraction of aerosol particles with an aerodynamic diameter of less than or equal to 1 micrometer.

14) surface_volume_scattering_coefficient_at_stp_in_air_due_to_pm10_aerosol

The volume scattering coefficient is the fractional change of radiative flux per unit path length due to redirection of an incident light beam by a component in the reference volume. "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). "Aerosol" without further qualification such as dry or ambient means that the aerosol humidity state is stated in the data. The specification of a physical process by the phrase "due_to_" process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase. "surface" means the lower boundary of the atmosphere. "at_stp" refers to a volume at standard conditions of temperature (273.15 K) and pressure (1013.25 hPa). "pm10" refers to the fraction of aerosol particles with an aerodynamic diameter of less than or equal to 10 micrometers.

15) surface_volume_absorption_coefficient_at_stp_in_air_due_to_pm1_aerosol

The volume absorption coefficient is the fractional change of radiative flux per unit path length due to absorption of an incident light beam by a component in the reference volume. "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). "Aerosol" without further qualification such as dry or ambient means that the aerosol humidity state is stated in the data. The specification of a physical process by the phrase "due_to_" process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase. "surface" means the lower boundary of the atmosphere. "at_stp" refers to a volume at standard conditions of temperature (273.15 K) and pressure (1013.25 hPa). "pm1" refers to the fraction of aerosol particles with an aerodynamic diameter of less than or equal to 1 micrometers.

16) surface_volume_absorption_coefficient_at_stp_in_air_due_to_pm10_aerosol

The volume absorption coefficient is the fractional change of radiative flux per unit path length due to absorption of an incident light beam by a component in the reference volume. "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). "Aerosol" without further qualification such as dry or ambient means that the aerosol humidity state is stated in the data. The specification of a physical process by the phrase "due_to_" process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase. "surface" means the lower boundary of the atmosphere. "at_stp" refers to a volume at standard conditions of temperature (273.15 K) and pressure (1013.25 hPa). "pm10" refers to the fraction of aerosol particles with an aerodynamic diameter of less than or equal to 10 micrometers.

17) surface_volume_hemispheric_backscattering_coefficient_at_stp_in_air_due_to_pm1_aerosol

The volume hemispheric backscattering coefficient is the fractional change of radiative flux per unit path length due to redirection of an incident light beam into the rearward hemisphere relative to the incident beam by a component in the reference volume. It is distinct from the backscattering coefficient which isn't integrated over the rearward hemisphere. "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). "Aerosol" without further qualification such as dry or ambient means that the aerosol humidity state is stated in the data. The specification of a physical process by the phrase "due_to_" process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase. "surface" means the lower boundary of the atmosphere. "at_stp" refers to a volume at standard conditions of temperature (273.15 K) and pressure (1013.25 hPa). "pm1" refers to the fraction of aerosol particles with an aerodynamic diameter of less than or equal to 1 micrometers.

18) surface_volume_hemispheric_backscattering_coefficient_at_stp_in_air_due_to_pm10_aerosol

The volume hemispheric backscattering coefficient is the fractional change of radiative flux per unit path length due to redirection of an incident light beam into the rearward hemisphere relative to the incident beam by a component in the reference volume. It is distinct from the backscattering coefficient which isn't integrated over the rearward hemisphere. "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). "Aerosol" without further qualification such as dry or ambient means that the aerosol humidity state is stated in the data. The specification of a physical process by the phrase "due_to_" process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase. "surface" means the lower boundary of the atmosphere. "at_stp" refers to a volume at standard conditions of temperature (273.15 K) and pressure (1013.25 hPa). "pm10" refers to the fraction of aerosol particles with an aerodynamic diameter of less than or equal to 10 micrometers.

#49 fixed Clarification of flag_meanings attribute jonathan martin.juckes
Description

1. Title

Clarification of flag_meanings attribute

2. Moderator

Jonathan Gregory

3. Requirement

Clear definition and greater range of characters in flag_meanings attribute.

4. Initial Statement of Technical Proposal

Section 3.5 of the convention states "The flag_meanings attribute is a string whose value is a blank separated list of descriptive words or phrases, one for each flag value.", and a "word" is currently interpreted by the CF-checker to consist only of alphanumeric characters, ruling out hyphens and brackets which may be useful in this context. The proposal is that a word in this context should be defined to consist of alphanumeric characters plus underscore '_', period '.', plus '+', hyphen '-', or "at" sign '@', to be consistent with the character set allowed for netCDF variable/dim/attr names [there is no particular need for this consistency, except to avoid having multiple definitions of what constitutes a word].

The above sentence from section 3.5 should be modified to read "The flag_meanings attribute is a string whose value is a blank separated list of descriptive words or phrases, one for each flag value. Each word or phrase consisting of characters from the alphanumeric set or from the following four: '-', '.', '+', '@'.",

5. Benefits

More meaningful "flag_meanings" will be possible.

E.g. for a dataset of eco-regions, flag_meanings such as "Alberta-British Columbia foothills forests" could be used.

6. Status Quo

There is ambiguity in the current standard, which I believe should be alleviated.

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