Significant wave Height (spectral vs direct method)

[anapatvn]

Question

Before the CF Standard Name Table was updated, the significant wave height was distinguished using either the spectral method ('sea_surface_wave_significant_height') or the direct method ('sea_surface_wave_significant_height_zero_upcrossing'). Now, I can't find the spectral variable. From analysing the descriptions, it seems that the name of the spectral variable now belongs to the direct method variable, and that the spectral variable no longer exists. Is this correct?

Thank you.

[DocOtak]

Hi @anapatvn

I still see sea_surface_wave_significant_height on the table however the "upcrossing" names appear to have been renamed a few years ago:

• sea_surface_swell_wave_zero_upcrossing_period -> sea_surface_swell_wave_mean_period
• sea_surface_wave_zero_upcrossing_period -> sea_surface_wave_mean_period
• sea_surface_wind_wave_zero_upcrossing_period -> sea_surface_wind_wave_mean_period

[ChrisBarker-NOAA]

I'm going to guess (I don't recall the conversation -- it might have been before my time) that this was due to the nature of standard names -- they are (ideally) a name for some physical property -- how the value was obtained (measurement, model, computation) is supposed to be specified in some other way.

So whether you compute the significant wave height (or any other statistic) via zero-upcrossing analysis or spectral analysis -- it's the same "thing", and thus the same standard name.

[DocOtak]

I've misread and conflated period and height when looking at the table.

@anapatvn Where have you seen the name sea_surface_wave_significant_height_zero_upcrossing? I wasn't able to find anything with a google/ddg search. I would be very surprised if something was straight removed from the CF standard name tables if they ever existed there. I do know that I have seen standard_name attributes in real world data files that did not contain a valid standard name, it was just made up by the data producer.

[ChrisBarker-NOAA]

I see these:

sea_surface_infragravity_wave_significant_height 
sea_surface_primary_swell_wave_significant_height  
sea_surface_secondary_swell_wave_significant_height  
sea_surface_swell_wave_significant_height -- alias: significant_height_of_swell_waves
sea_surface_tertiary_swell_wave_significant_height
sea_surface_wave_significant_height -- alias: significant_height_of_wind_and_swell_waves
sea_surface_wave_significant_period
sea_surface_wind_wave_significant_heightalias: significant_height_of_wind_waves

I recall not too long ago adding the swell vs wind_wave distinctions, but don't recall anything about zero_upcrossing.

I suspect @DocOtak is right -- it's a name that's been seen in the wild but was never an actual standard_name.