Meeting notes
Participants: Sebastien Villaume, Gao Chen, Charles Brock, John Nowak, Rebecca Hornbrook, Markus Fiebig, Richard Eckman, Jörg Klausen, Franziska Stürzl
Minutes (Summary)
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Welcome (JK)
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Progress report on issues
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1-01-01: Use of term "aerosol" in observed variable table
(MF) Introduction to the purpose of this issue: The term "aerosol" is defined as a system of gas and particle phase. The variables with the path \Atmosphere\Aerosol refer only to the particle phase. Therefore the subdomain should be names "Particle phase" or "Particulate matter" instead.
(JW) proposes to use "Aerosol particle". For remote sensing observations the term "particle phase" is too specific as the particles itself cannot be measured with these observing method.
(JK) To define an observed variable, what matters is the intention of the observation.
(MF) Possible compromise: Rename the paths to "Particle phase", but keep the term "aerosol" in the variable name, where it makes sense. E.g. \Atmosphere\Particle phase\Optical properties\Aerosol optical depth
(JK) Decision to suggest "Particle phase" to the TT, MF will update the issue.
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1-01-01 Path structure of Aerosol (particle phase) composition variables
(JK) Discussion about subdomain_3 in the branch \Atmosphere\Particle phase\Composition..., the intention behind the categories such as "Inorganic anions", "Inorganic cations" etc. was to facilitate the search for variables in the OSCAR/Surface application, but also to provide context about the intention behind an observation.
(MF) The separation in subdomain_3 is ambiguous. If the categories are supposed to help with the search, it needs to be unique. Remark, that the ambiguity is already there in subdomain_1, because many variables under \Atmosphere\Particle phase also belong into the \Atmosphere\Precipitation branch.
(GC) stresses the importance of having variable descriptions, because the variable name alone cannot include all information.
(MF) Path structure is the attempt to create an ontology, which is a difficult effort. The problem is the strict hierarchy, because there are many variables, which belong into more than one subdomain. That leads to an overcrowded code list, if a variable is included multiple times with all possible paths. It is better to consider creating separate code lists for subdomains.
(JK) Clarification of terms (subdomain_1): "Gas" and "Aerosol"/"Particle phase" refer to constituents IN the atmosphere,"Total atmospheric deposition" variables describe particles in the atmosphere, which accumulate on a surface. A variable like "Ammonium" can appear in "Particle Phase", "Total atmospheric deposition" and "Precipitation". It is one variable, but it needs to be combined with a specific subdomain to describe an observation properly (variable = biogeochemical species or physical quantity, observed variable = domain x subdomain(s) x variable).
(GC) Approach: Subdomains as attributes coming from a fixed codelist (compare Atmospheric Composition Variable Standard Name Recommendations)
(JK) leads the focus back to the original issue: Are categories like "Inorganic anions" etc. an important concept or can it be dropped (subdomain_3)? Do we need to sort particle phase variables into "Composition", "Optical properties" and "Physical properties" (subdomain_2)?
(MF),(GC) agree, that subdomain_3 is unneccessary.
(JK) Consequences for the practical use in OSCAR/Surface (link to the application): Without subdomain_3, the variable tree will have more than 100 endpoints under Atmosphere -> Particle phase -> Composition.
(RH),(MF) If a cateorisation is ambiguous or too difficult to make, a longer list is preferable.
(JW) The same issue applies to the category "Physical properties", the discussion can be extend to subdomain_3 under "Physical properties - primary".
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1-01-01: distinction between primary and secondary physical particle properties
(JK) We need specific proposals, MF will update the issues #181, #257 and #182.
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1-01-01 additional variables (mostly originating from EBAS) postponed
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Difference between code lists and domains
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6-02 Sample treatment (new codelist) postponed
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Issues for gas variables needed?
(RH) has prepared a list of questions and will open an issue for discussion (see: #261)
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Assign responsible persons to specify the requirements for describing the following aspects of an observation:
- particle size, sizing methodology
- relative humidity
- temperature
- pressure
- wave length/frequency
(JK) We need to advance this as soon as possible
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Next meeting in two weeks (31 March, 14 UTC) on MS Teams
Participants: Sebastien Villaume, Dagmar Kubistin, Gao Chen, Charles Brock, Judd Welton, John Nowak, Rebecca Hornbrook, Markus Fiebig, Jörg Klausen, Franziska Stürzl
Agenda:
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Presentation on C-14 and what attributes are used in BUFR to describe an observation (SV) + discussion (all)
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Review notes: Observations, observed variables and sampling procedures (JK, FS)
- definitions of elements to describe observations (WIGOS metadata information model)
- proposals for particle size
- Review tree structure of observed variables (overview, state 11/2020) - postponed
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Definitions of carbon variables (elemental_carbon, equivalent_black_carbon, equivalent_black_carbon_mass, total_carbon) (https://github.com/wmo-im/wmds/issues/168) - postponed
Participants: Sebastien Villaume, Dagmar Kubistin, Gao Chen, John Nowak, Rebecca Hornbrook, Markus Fiebig, Jörg Klausen, Franziska Stürzl
Agenda:
Welcome
Introduction of the participants (10’)
Short explanation of the WIGOS model (jkl 5’)
Goals of this group (stf 5’)
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Improve vocabulary for atmospheric composition variables (including a review of the path structure, overview, state 11/2020)
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Acceptance in other communities
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Ensure interoperability with other vocabularies
Deficiencies in the WIGOS vocabulary for atmospheric variables (stf 5’)
- Combination observed variable + attributes in the variable name
- Variables without descriptions/definitions
WIGOS vocabulary in relation to other vocabularies (stf 5’)
- CF Convention Standard Names, Common Code Table C-14 etc.
Discussion and next steps (30’)
- Standard conditions (RH, T, P,…?) as code lists or by numbers?
- Assign experts to the relevant issues
- Next meeting (17.02.21?)
Minutes TT-WIGOSMD WG-ACV-1
(JK) Welcome to all participants to the first meeting of WG-ACV, an ad-hoc group of experts supposed to advise the TT-WIGOSMD on the vocabulary for atmospheric composition measurements. The objective is to improve the vocabulary used in the WIGOS metadata standard and, where necessary, the standard itself, so that it becomes more useful for the wider community. Note that the proposals by this group should not only work for atmospheric composition, but essentially all observations in the scope of WIGOS.
(FS) Previous discussions with Gao and Markus lead to the conclusion that attributes should be removed from the variable names and stored in a different way. It is our intention to normalise the table, and connect variables with more information to describe an observation by adding attributes from external code lists. The following definitions are suggested to foster a common understanding of terms:
| Term | Definition |
|---|---|
| Observed variable | a biogeochemical species or physical quantity and an endpoint in a path (providing context but not a description of process of observation) |
| Process of observation | procedures involved in making an observation or measurement that may impact the result. Such procedures may include a specific observing methodology, conditions of sampling and processing the measurand etc. that may be viewed as characteristic attributes of an observation. |
| Observation | Observed variable x process of observation x geometry of observation |
Examples:
- CO2 x dry air
- Mg++ x PM2.5, 40% RH, 20°C, 1013 hPa
- Scattering coefficient x PM10, 40% RH, 20°C, 1013 hPa, 525nm
Characteristic attributes identified thus far that are at least relevant for aerosol observations:
- size range,
- pressure, temperature, humidity,
- wave length (range?)
(SV) The Common Code Table C-14 specifies only chemical species. Information on size range, wave length etc. come from other tables. Improving the communication between the team for C-14 and the WIGOS team will be appreciated and a benefit to both.
(MF) A generic approach for attributes (attribute category) is preferable, such as adding attributes as name-value pairs. This would avoid the problem that new attributes need to be added constantly. Idea: (attribute type, attribute value) with a table for attribute types.
(JK) This is a technical issue. First of all, we need to be concerned with which attributes are important. Another important aspect is the realisation in the application. This leads to questions such as: How would you like to see attributes in a station report? What does this mean for the search function? The model has the objective to define a metadata standard, which can document observations for adequate use of observational data now and in the future. A name-value approach is technically possible (in the schema), but contradicts the idea of a standard, if there are no limitations.
(GC) The change from "Aerosol" to "Particle phase" is acceptable. Another important issue is the structure of the variables, which is too detailed.
(JK) The structure of the variable tree is based on the way the GAW program was traditionally organized. The organisation of the variable structure can be changed, if the community thinks it needs to be changed!
(MF) The number of levels in the variable tree should be limited, currently it seems to be overly structured.
Actions
- Presentation on C-14 and what attributes are used in BUFR to describe an observation (SV, the next meeting)
- Review definitions proposed above and improve if needed (all, for approval at next meeting)
- Proposal for distinct attributes needed to meaningfully describe and group observations, e.g. standard conditions (stable or variable) and how to include them in the WIGOS metadata model (FS, JK, for discussion at next meeting)
Next meeting Feb 17, 15 - 16 UTC+1
Participants: Gao Chen, Jörg Klausen, Franziska Stürzl
Observed variable in WIGOS Metadata Standard
Definition: “Variable indended to be measured, observed or derived, including the biogeophysical context” [Guide to the WMO Integrated Global Observing System]
Currently the codelist for for observed vaiables (atmosphere) (table 1-01-01) is a mixture of constituents and constituents + certain conditions. Possible combinations of variables and observing conditions leads to a long list of observed variables.
Example: The variable “\Atmosphere\Aerosol\Composition\Inorganic anions\Chloride (Cl-), PM1” consists of the name of the constituents itself: Chloride (Cl-) and the size cut-off PM1 as an attribute.
Constituent/physical quantity + Size range + reference conditions (humidity, temperature, pressure)
The code list for observed variables should be reduced to contain only the constituents. Size range and reference conditions are stored separately. The proposed approach in the issues (#111, #112) needs to be reviewed. Idea: Create a new code table for size ranges, information on humidity, temperature and pressure should be expressed numerically without a code table.
Approach for aerosol variables in the Atmospheric Composition Variable Standard Name Recommendations
Source: https://www-air.larc.nasa.gov/missions/etc/AtmosphericCompositionVariableStandardNames.pdf
Standard Name = MeasurementCategory_CoreName_MeasurementMode_DescriptiveAttributes
The “CoreName” represents the constituent, while information on the size range and other conditions are provided as “DescriptiveAttributes”. Depending on the “MeasurementCategory” there are five tables for “DescriptiveAttributes”: Relative humidity, sizing technique, size range, wave length and reporting attributes.
- Size ranges (Table 4.3.3)
| SizeRange | Description |
|---|---|
| Nucl | Nucleation-mode aerosols: 0.001-0.1 μm diameter |
| Accu | Accumulation-mode aerosols: 0.1-1 μm diameter |
| Coarse | Coarse-mode aerosols: greater than 1 μm diameter |
| Bulk | No distinction in size of particle being measured |
| PM1 | Submicron aerosols: less than 1 μm diameter |
| PMx | Particles with diameter under X μm diameter |
| XtoY | Size Range from X to Y, e.g., NucltoAccu |
Nucl + Accu = PM1
A similar code table needs to be implemented in WIGOS (concrete proposal required!), including the following entries.
PMx: PM2.5, PM10
XtoY: PM10toPM1, PM10toPM2.5
- Relative humidity (Table 4.3.1)
| MeasurementRH | Description |
|---|---|
| RHd | Reduced relative humidity in the sampling system, typically less than 40 % |
| RHa | Relative humidity at ambient conditions |
| RHsp | Sampling system relative humidity at specified level |
| None | Not applicable to variable |
This is similar to the distiction between “ambient” and “heated” in the proposed table for the sampling procedure (#111). It is preferred to be able to give a numeric value specifying the relative humidity.
- Sizing technique (Table 4.3.2)
It needs to be determined whether these attributes are necessary in WIGOS.
Actions:
- create proposal for a size range table
- determine other critical issues: variables for mixtures, treatment of other modifiers (not in the context of aerosols)
Participants: Markus Fiebig, Jörg Klausen, Franziska Stürzl
Results
Semantic inconsistency in aerosol vocabulary
Definition: Aerosol: gas phase + particle phase (liquid or solid)
Therefore the distinction between \Atmosphere\Gas and \Atmosphere\Aerosol is semantically incorrect. It was proposed to replace the term "Aerosol" by "Particle phase" (see issue #181).
Modifiers currently in use in table 1-01-01 are ambiguous: "total aerosol", meaning “without size cut-off” -> replace by "TSP" ("total suspended particles" "total aerosol", meaning “gas and particle phase” -> replace by "gas + particle phase" (similar to "in air and aerosol") To do: identify how variables are used in OSCAR (establish list of stations, with last update and by whom)
Systematic approach for modifiers
Modifiers connect variable names with information about reference conditions and size fractions.
Issue: The use of modifiers in table 1-01-01 is not ideal as it leads to an unnecessarily long list of variables, if all possible combinations are included.
Proposal: Separate modifiers from variable names (see issue #173). Review elements proposed for new table "Sampling procedure" (Issue #111) that currently combines size cut off + sampling condition. Review elements proposed for new table "Sample treatment" (Issue #112). Establish new elements for reference conditions (referencePressure, referenceTemperature, referenceHumidity) for use in DataTypes ‘Sampling’ and ‘Reporting’. This involves an extension of the WMDR model (!).
Action:
- Review issues #111, #112. Postpone to FT-2021-2
- Create new issue for additional elements to describe reference conditions. Determine if these should be code lists or ‘free text’. For example for referenceTemperature, a code table could include elements ambient, heated, 20°C, 25°C, 0°C.
[A posteriori considerations] Side effects: The search filter of OSCAR/Surface does not include the possibility to select observations/stations based on any particular size-cutoff or reference conditions. Thus, if these are removed from the variable name, any search on the (new) variables would return a mix of specific observations. A challenge is how OSCAR/Surface can convey information on these details to the user even in a station report. An observation is defined in the WMDS as a combination of observing facility + observed variable + geometry of observation. This is also how they are implemented in the application. Details like size-cutoff and reference conditions would be defined on the level of deployment, but these details are not presently shown in the sub-headings. A user-friendly solution for this needs to be found in the application (and related CRs be prioritized …).
Introduction: presentation slides