Standard names: atmospheric radar terms

[ingemarh]

Proposer's name: Ingemar Häggström Date 1 Oct 2021

Term: radial_velocity_of_scatterers_away_from_instrument Description: A velocity is a vector quantity. "Radial velocity away from instrument" means the component of the velocity along the line of sight of the instrument where positive implies movement away from the instrument (i.e. outward). The "instrument" (examples are radar and lidar) is the device used to make the observation. The "scatterers" are what causes the transmitted signal to be returned to the instrument (examples are aerosols, hydrometeors and refractive index irregularities), of whatever kind the instrument detects. A standard name referring to radial velocity "toward_instrument" should be used for a data variable having the opposite sign convention. Units: ms-1

Term: volume_backscatter_of_radiation_power_in_air_of_instrument Description: The "instrument" (examples are radar and lidar) is the device used to make the observation. The "scatterers" are what causes the transmitted signal to be returned to the instrument (examples are aerosols, hydrometeors and refractive index irregularities), of whatever kind the instrument detects. A standard name referring to the recieved power of the signal at the instrument. Units: W

Term: volume_backscatter_radiation_roundtrip_travel_time_in_air_of_instrument Description: The "instrument" (examples are radar and lidar) is the device used to make the observation. The "scatterers" are what causes the transmitted signal to be returned to the instrument (examples are aerosols, hydrometeors and refractive index irregularities), of whatever kind the instrument detects. A standard name referring to time taken for a signal to propagate from the emitting instrument to a reflecting volume and back again to the instrument. Units: s

Term: volume_backscatter_radiation_spectralwidth_in_air_of_instrument Description: The "instrument" (examples are radar and lidar) is the device used to make the observation. The "scatterers" are what causes the transmitted signal to be returned to the instrument (examples are aerosols, hydrometeors and refractive index irregularities), of whatever kind the instrument detects. A standard name referring to frequency width of the received signal. Units: Hz

[feggleton]

Hi Ingemar,

Just spotted your first term 'radial_velocity_of_scatterers_away_from_instrument' already exists in the table (http://cfconventions.org/Data/cf-standard-names/78/build/cf-standard-name-table.html)

Fran

[ingemarh]

OK, good that you spotted it, maybe that line slipped through in my process of request. So, take this away, and please consider the volume_backscatter terms.

[feggleton]

Just re-posting these proposed terms to see if there are any comments or discussion. Thanks

Term: volume_backscatter_of_radiation_power_in_air_of_instrument Description: The "instrument" (examples are radar and lidar) is the device used to make the observation. The "scatterers" are what causes the transmitted signal to be returned to the instrument (examples are aerosols, hydrometeors and refractive index irregularities), of whatever kind the instrument detects. A standard name referring to the recieved power of the signal at the instrument. Units: W

Term: volume_backscatter_radiation_roundtrip_travel_time_in_air_of_instrument Description: The "instrument" (examples are radar and lidar) is the device used to make the observation. The "scatterers" are what causes the transmitted signal to be returned to the instrument (examples are aerosols, hydrometeors and refractive index irregularities), of whatever kind the instrument detects. A standard name referring to time taken for a signal to propagate from the emitting instrument to a reflecting volume and back again to the instrument. Units: s

Term: volume_backscatter_radiation_spectralwidth_in_air_of_instrument Description: The "instrument" (examples are radar and lidar) is the device used to make the observation. The "scatterers" are what causes the transmitted signal to be returned to the instrument (examples are aerosols, hydrometeors and refractive index irregularities), of whatever kind the instrument detects. A standard name referring to frequency width of the received signal. Units: Hz

[JonathanGregory]

Dear @ingemarh

Thanks for your proposals. I may have misunderstood them, since I'm not familiar with the concepts. I am puzzled about a number of things.

• I don't understand the need for volume_ in these names. Is it correct that "volume backscatter" refers to the scattering by unit volume i.e. the backscattered power is normalised to unit volume of the medium? If so, it's not obvious to me how this normalisation could affect the round-trip travel time or the spectral width. I expect that the power would be affected, but in that case I'd expect the unit to be W m-3 to indicate the normalisation. The transmitted power must be relevant as well somehow.

• I don't understand the need to mention the instrument in the names for the radiation power or the round-trip time. This quantities are not properties of the instrument.

• What is the spectral width (I guess this should have a space in it)? Is it a property of the instrument e.g. bandwidth of the transmitted power or the bandwidth the receiver can detect? Is it the "spectrum width" which I find mentioned in some online articles, that is also a property of the scatterers? How is it computed?

• We have some existing standard names containing the phrase "backwards scattering". Is that the same as "backscattering"? I guess it is.

Given these comments, I wonder whether the first name could be backwards_scattered_radiative_power_in_air and the second backwards_scattered_radiation_round_trip_time_in_air. I don't understand the third one well enough at the moment to make a suggestion.

Best wishes

Jonathan

[nirithil]

Dear @JonathanGregory

My name is Maria and I work together with Ingemar, we were trying to adjust the terms and our understanding in the last week. We could drop the part _of_instrument for the roundtrip time and power.

• When it comes tovolume_ we use the term volume_backscatter, meaning that it is scattering from a volume we see (and which changes with the distance from the radar and beam parameters) rather than a sheet or point. So mostly to distinguish the mechanism by which the backscatter occurred. Although the measurement is always the sum of all scattering in the given volume, regardless of mechanism. Since it appears thatvolume_ is used in the meaning of per unit volume in the cf vocabulary, maybe we could change to a different denotation. _scattered_by_volume would convey the original meaning of our term as well.

• The spectral width is dependent on both, the properties of the transmitted pulse and properties of scatterers (and thus on the scattering mechanism) We were thinking maybe a better possibility would be to switch it to spectral_width_of_backscatter_radiation_in_air as it is a property of the returned signal.

• The term backscatter_radiation itself doesn’t coincide with your backwards_scattered definition. I’ve also tried to read your discussion with Claudio about the lidar variables, and it might not be that meaning either since this doesn’t denote a coefficient or some property of the scatterer. In general, it has more meaning of a “returned” or “stimulated” signal than mirrored signal. With monostatic radar measurements, it indeed denotes part of the signal returned to the instrument (so whatever scatters backward around 180 degrees from the pointing direction) but with bi- and tri- (or more) static measurements we do not care if it was backward or forward scattered radiation at the place where scattering occurred. It denotes radiation that came back to the receiver site. Maybe one solution would be to change the backscatter to returned_scatter_radiation

If we take into account these changes the terms could look like: Term: returned_scatter_of_radiation_power_scattered_by_volume_in_air Units: W

Term: returned_scatter_radiation_roundtrip_travel_time Units: s

Term: spectral_width_of_returned_scatter_radiation_in_air_of_instrument Units: Hz

I am not sure if this answers your questions. What do you think about our suggestions?

Best regards, Maria

[JonathanGregory]

Dear Maria @majamihi

Thanks for your explanations and your work on these proposals. Since you mentioned radar, I notice that we have an existing standard name of surface_backwards_scattering_coefficient_of_radar_wave. Is that the same sort of "backwards scattering" as you mean? Its definition says, "Scattering of radiation is its deflection from its incident path without loss of energy. Backwards scattering refers to the sum of scattering into all backward angles i.e. scattering_angle exceeding pi/2 radians." Unfortunately its definition does not say what "surface" indicates! Does it mean scattering by the surface, or measured at the surface, I wonder? Do you know, or does anyone else?

Anyway, if this is the same sort of backscattering, maybe could call your quantity in watts backwards_scattered_radiative_power_in_air_due_to_air. I think radiative_power is better than radiation_power because there's one existing name which uses the former, but none the latter. By due_to_air I mean what you explain, that it's the part of scattering due to the medium itself, not point or surface scatterers.

On the model of the existing name acoustic_signal_roundtrip_travel_time_in_sea_water we could maybe call your quantity in seconds radiation_roundtrip_travel_time_in_air.

Given your comments on the quantity in hertz, I would favour something like what you suggested first, spectral_width_of_backwards_scattered_radiation_in_air.

I note that elsewhere we're discussing whether we should say backscatter or backwards_scatter but at the moment the latter is in the majority and we should be consistent. We could change them all at once later (with aliases).

Best wishes

Jonathan

[taylor13]

If we say due_to_air, does that include the cloud and precipitation in the air?

[JonathanGregory]

I suppose it does. We could insert further words to clarify it. It depends whether it's supposed to mean dry air or ambient air.

[nirithil]

Dear Jonathan @JonathanGregory

thank you for the feedback. I've liked your explanation of due_to_air, the only concern I have does your understanding of air include also charged particles or just the neutral atmosphere? The major part of our measurements are measurements of properties of charged particles (free electrons and ions in the ionosphere)based on how they scatter our radio signal. Would your due_to_air include this understanding as well? If it is not the case we will have to change the due_to_air to something else more general. For example to due_to_atmosphere

In our understanding, the meaning of surface in your surface_backwards_scattering_coefficient_of_radar_wave is the same kind of meaning of surface as the volume we have suggested at the beginning. It's scattering from a surface as opposed to a point, line, or volume. So scattering by the surface in your words.

As I've tried to explain last time our understanding of "backscatter" does not coincide with your "backwards scattering" in the present definition which is defined as: "Scattering of radiation is its deflection from its incident path without loss of energy. Backwards scattering refers to the sum of scattering into all backward angles i.e. scattering_angle exceeding pi/2 radians. A scattering_angle should not be specified with this quantity."

This is not what we call backscatter or we do not understand your definition. That is why we make a different suggestion.

Also the radiative and radiation we find to be not exchangeable as according to the term that uses the radiative_power, it seems to be a different concept.

Though, based on the already existing terms you mentioned and your suggestions it would be better to use:

radio_signal_roundtrip_travel_time_in_air -as opposed to an acoustic signal we are using a radio signal and measuring its roundtrip in the atmosphere

spectral_width_of_radio_wave_scattered_in_air_due_to_air -because when we define that a radio wave is being scattered we do not need to define the _of_instrument

and in a similar manner, we could define then: power_of_radio_wave_scattered_in_air_due_to_air -in this case, we would avoid mentioning backscatter and define the character of the wave, which is a radio wave that was scattered in the atmosphere by changes in the refractive index.

Would you agree with these suggestions?

[JonathanGregory]

Dear Maria @majamihi

Thanks for your explanation. I think radio_signal_roundtrip_travel_time_in_air and spectral_width_of_radio_wave_scattered_in_air_due_to_air are both fine. In the third one, I think we could indicate that it's the returned signal you're interested in by calling it received_power_of_radio_wave_scattered_in_air_due_to_air - would that make sense?

radio_wave is a phrase we haven't used before. I think it's similar to radiation, which appears in many standard names, but "radio" limits it to a particular part of the electromagnetic spectrum.

Yes, I think in_air means the ambient air and everything that medium contains. In general, standard names are interpreted as including everything by default, and restrictions have to be specified.

Best wishes

Jonathan

[nirithil]

Dear Jonathan @JonathanGregory

thanks for your input. Yes, we can agree with the last term in the form with received_ at the beginning. Just to confirm the terms would be then: received_power_of_radio_wave_scattered_in_air_due_to_air Units: W radio_signal_roundtrip_travel_time_in_air Units: s spectral_width_of_radio_wave_scattered_in_air_due_to_air Units: Hz

[JonathanGregory]

Dear Maria

We agree on those then! That's good. But - just at the last moment - I'm concerned that "due to air" isn't clear enough. Maybe received_power_of_radio_wave_in_air_scattered_by_air and spectral_width_of_radio_wave_in_air_scattered_by_air would be clearer - what do you think?

Thanks

Jonathan

[nirithil]

Dear Jonathan,

sorry for the late reply. Yes, it is fine to use by_air instead of due_to_air in the terms. It might be indeed more clear.

Thanks Maria

[feggleton]

As far as I can see, these are the latest terms:

received_power_of_radio_wave_scattered_by_air Units: W radio_signal_roundtrip_travel_time_in_air Units: s spectral_width_of_radio_wave_scattered_by_air Units: Hz

We will now need to update the descriptions to match as they still contain instrument phases. @majamihi Thanks.

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[feggleton]

@majamihi if you could amend the descriptions since the name has changed, we can hopefully come to some agreement. Thanks

[feggleton]

@nirithil @ingemarh could you rework the description since the term name changes and then we can look to get these agreed and added to the next update. Thanks

[nirithil]

Sorry for a very late reply. We've updated the Descriptions as following:

received_power_of_radio_wave_in_air_scattered_by_air Description: Power of a radio wave, that was transmitted by an instrument and propagates in the air where it's scattered by the air due to which its properties change, and it is received again by an instrument. The "instrument" (examples are radar and lidar) is the device used to make the observation. The "scatterers" are what causes the transmitted signal to be returned to the instrument (examples are aerosols, hydrometeors and refractive index irregularities in the air). A standard name referring to the received power of the signal at the instrument. Units: W

radio_signal_roundtrip_travel_time_in_air Description: Time it takes for a radio wave, that was transmitted by an instrument to propagate through the air to the volume of air where it is scattered and return back to an instrument. The "instrument" (examples are radar and lidar) is the device used to make the observation. The "scatterers" are what causes the transmitted signal to be returned to the instrument (examples are aerosols, hydrometeors and refractive index irregularities in the air). A standard name referring to time taken for a radio signal to propagate from the emitting instrument to a scattering volume and back to an instrument. Units: s

spectral_width_of_radio_wave_in_air_scattered_by_air Description: Frequency width of the radio wave, that was transmitted by an instrument and propagates in the air where it's scattered by the air due to which its properties change, and it is received by an instrument. The "instrument" (examples are radar and lidar) is the device used to make the observation. The "scatterers" are what causes the transmitted signal to be returned to the instrument (examples are aerosols, hydrometeors and refractive index irregularities in the air). A standard name referring to frequency spectra width of the signal received at the instrument. Units: Hz

[efisher008]

Dear @nirithil, @feggleton,

I have updated these terms in the CF editor according to the new descriptions and marked them as "under discussion". Were there any further points/changes for these names, or could we now start the waiting period for the term changes to be accepted?

Best regards (and happy Easter/Ramadan), Ellie

[nirithil]

I'm not aware of any further changes for these names so for my side yes.

[efisher008]

Hi Maria and Ingemar,

In that case, I think we can say that unless there are further comments/issues raised within the next 7 days, these term changes will be accepted and published in the next CF standard names table release (which is planned for the first half of April, i.e. this month).

Thanks and best wishes, Ellie

[JonathanGregory]

Dear Maria @nirithil, @ingemarh and Ellie @efisher008

These look good, thanks. Does "spectral width" have a precise quantitative definition e.g. in terms of the spectrum? I think it would be useful to be more precise in the description of the quantity if possible.

Best wishes

Jonathan

[efisher008]

Dear Maria, Ingemar and Jonathan,

For your information, I have now accepted the two names radio_signal_roundtrip_travel_time_in_air and received_power_of_radio_wave_in_air_scattered_by_air, but have kept the name spectral_width_of_radio_wave_in_air_scattered_by_air as 'under discussion', waiting for a reply to Jonathan's comment.

Best, Ellie

[nirithil]

Hi Jonathan, would did change work for you? we had a bit of discussion how/if it would be possible to do more exact and this is what we came up with:

spectral_width_of_radio_wave_in_air_scattered_by_air Description: Frequency width of the radio wave, that was transmitted by an instrument and propagates in the air where it's scattered by the air due to which its properties change, and it is received by an instrument. The "instrument" (examples are radar and lidar) is the device used to make the observation. The "scatterers" are what causes the transmitted signal to be returned to the instrument (examples are aerosols, hydrometeors and refractive index irregularities in the air). A standard name referring to the positive square root of the frequency spectra's second moment gained from the signal received at the instrument. Units: Hz

Maria

[JonathanGregory]

Dear Maria @nirithil and Ellie @efisher008

I am amazed to discover that spectral_width_of_radio_wave_in_air_scattered_by_air is already in the standard name table! I think it appeared in version 80, in February 2023. Did we have exactly the same discussion, reaching the same conclusion, more than a year ago? The existing definition does not say exactly what "spectral width" means, though. Thanks for the extra sentence. I think it would be slightly better to say The "spectral width" is the positive square root .... I suppose that this is the same moment as "variance spectral density second frequency moment" in the existing standard name sea_surface_swell_wave_mean_period_from_variance_spectral_density_second_frequency_moment, is it? If so, to be even more precise you could say use that phrase, I suppose.

Best wishes

Jonathan

[nirithil]

Hi Jonathan, we are not sure if we understand what you meant. It would work like this according to us:

spectral_width_of_radio_wave_in_air_scattered_by_air Description: Frequency width of the radio wave, that was transmitted by an instrument and propagates in the air where it's scattered by the air due to which its properties change, and it is received by an instrument. The "instrument" (examples are radar and lidar) is the device used to make the observation. The "scatterers" are what causes the transmitted signal to be returned to the instrument (examples are aerosols, hydrometeors and refractive index irregularities in the air). A standard name referring to the positive square root of variance spectral density second frequency moment gained from the signal received at the instrument. Units: Hz

Best regards, Maria

[JonathanGregory]

Thanks, Maria. That is almost what I meant! I was suggesting we could make the last sentence more obviously an explanation of the "spectral width" phrase. The description would be like this:

Frequency width of the radio wave, that was transmitted by an instrument and propagates in the air where it's scattered by the air due to which its properties change, and it is received by an instrument. The "instrument" (examples are radar and lidar) is the device used to make the observation. The "scatterers" are what causes the transmitted signal to be returned to the instrument (examples are aerosols, hydrometeors and refractive index irregularities in the air). The "spectral width" means the positive square root of the variance spectral density second frequency moment gained from the signal received at the instrument.

No different in meaning! If you're happy with that, so am I. Thanks for your patience. Jonathan

[nirithil]

Hi Jonathan,

yes we are happy with that formulation!

Thanks and best regards, Maria and Ingemar

[efisher008]

Dear Maria @nirithil and Ingemar @ingemarh,

The last name spectral_width_of_radio_wave_in_air_scattered_by_air with its updated description has now been accepted and will be published alongside your other proposed names received_power_of_radio_wave_in_air_scattered_by_air and radio_signal_roundtrip_travel_time_in_air in the next release of the standard names table, v86, which is currently anticipated for summer 2024. Thank you again for your proposal!

Best wishes, Ellie

[efisher008]

This has been published in v86 of the Standard Names Table (released 5 September 2024).