Solar radiation components

[carstenhoyerklick]

Description of the issue

Solar radiation has different components, which need to be added to the ontology. We have started discussions about direct, diffuse and global radiation in the issues #1067, #1072 and #1073. To ensure consistency this is merge of the three issues.

Ideas of solution

Direct Radiation
Definition: Direct radiation is the non-scattered radiant flux from the Sun within the extent of the solar disk only (half-angle 0.266 deg).
Comment:

• ISO and WMO CIMO guide use the term “direct radiation” in the sense of direct normal radiation.
• The definition is also in line with (cfconvetions.org): direct_downwelling_shortwave_flux_in_air, with a slight adaption (moved "beam radiation" to alternative term). http://cfconventions.org/Data/cf-standard-names/current/build/cf-standard-name-table.html

Diffuse Radiation
Definition: "Diffuse radiation is radiation that has been scattered by gas molecules in the atmosphere and by particles such as cloud droplets and aerosols."

This definition has been taken vom the cfconventions (cfconvetions.org): diffuse_downwelling_shortwave_flux_in_air. http://cfconventions.org/Data/cf-standard-names/current/build/cf-standard-name-table.html

Global Radiation
This will be a subcasss of solar radiation (.... ocurrent -> process -> radaition -> solar radiation)

Suggested definition: Global Radiation is solar radiation received on a surface from a solid angle of 2pi steradians. It consists of direct radiation and diffuse radiation.
Adapted from WMO G0560.

Direct Normal Radiation
Definition: Direct radiation is the non-scattered radiant flux density collected by a surface normal to the direction of the Sun within the extent of the solar disk only (half-angle 0.266 deg).

• Comment to be added: WMO defines direct solar radiation by the means of the pyrheliometer as a measurement device: Direct solar radiation is measured by means of pyrheliometers, the receiving surfaces of which are arranged to be normal to the solar direction. By means of apertures, only the radiation from the sun and a narrow annulus of sky is measured (half-angle 2.5 deg), the latter radiation component is sometimes referred to as circumsolar radiation or aureole radiation”
• ISO und WMO CIMO Guide label direct normal radiation as it is defined here “direct radiation”

Workflow checklist

• I discussed the issue with someone else than me before working on a solution
• I already read the latest version of the workflow for this repository
• The goal of this ontology is clear to me

I am aware that

• every entry in the ontology should have a definition
• classes should arise from concepts rather than from words

[l-emele]

In the protocol of the OEO Dev 33 I read:

These are differentiated by how you measure them and how you use them

If the difference is the way you measure it then these are not different processes but different quantity values or process attributes.

[mschroedter]

No, the difference in our setup is not the way how you measure it. The difference is a physical process (with/without scattering in the atmosphere or the sum ob both).

There are different measurement devices used, but this is a follow-on, and not the basis of the definition.

And yes, others base their definition on the different measurement systems, but this is not our approach for the OEO. We only mention it as alternative definition someone may find in literature. Therefore, this is inside a comment to make users of the ontology aware.