Hi all -
The latest version is confusing to me. The term 'a platform that is
nominally at rest' does
not apply to many platforms for which heave is calculated; the original
version of that,
'a moving object?above the vertical level?of that?object when
stationary' was maybe a little
more clear... if also a little wordy.
And, the term? 'vertical displacement determined by integrating vertical
accelerations' may
also not apply - I've been looking at the different ways heave is
calculated, and there
are a few: 'Heave can be computed from GPS RTK height measurements and from
vertical accelerations measured by linear accelerometers'
Why? not keep it simple: platform_heave (m) = upwards?vertical
displacement?? Do we need
to be more specific than that?
Thanks - Nan
On 5/31/18 5:01 AM, Hamilton, Steve wrote:
>
> Thanks for everyone?s input, the below seems acceptable for now
>
> Regards
>
> Steve
>
> From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> On Behalf Of
> Lowry, Roy K.
> Sent: 30 May 2018 21:37
> To: Jim Biard <jbiard at cicsnc.org>; cf-metadata at cgd.ucar.edu
> Subject: Re: [CF-metadata] Platform Heave
>
> An afterthought. Heave is conventionally positive upwards so to make
> this clear I would add?the word 'upwards' thus:
>
> platform_heave (m) = upwards?vertical displacement determined by
> integrating vertical accelerations of a platform that is nominally at
> rest.
>
> platform_heave_rate (m s-1) = upwards?vertical velocity determined by
> integrating vertical accelerations of a platform that is nominally at
> rest.
>
> Cheers. Roy.
>
> I have now retired but will continue to be active through an Emeritus
> Fellowship using this e-mail address.
>
> ------------------------------------------------------------------------
>
> From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu
> <mailto:cf-metadata-bounces at cgd.ucar.edu>> on behalf of Lowry, Roy K.
> <rkl at bodc.ac.uk <mailto:rkl at bodc.ac.uk>>
> Sent: 30 May 2018 21:02
> To: Jim Biard; cf-metadata at cgd.ucar.edu <mailto:cf-metadata at cgd.ucar.edu>
> Subject: Re: [CF-metadata] Platform Heave
>
> Thanks?Jim,
>
> That?work for me.
>
> Cheers, Roy.
>
> ------------------------------------------------------------------------
>
> From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu
> <mailto:cf-metadata-bounces at cgd.ucar.edu>> on behalf of Jim Biard
> <jbiard at cicsnc.org <mailto:jbiard at cicsnc.org>>
> Sent: 30 May 2018 18:39
> To: cf-metadata at cgd.ucar.edu <mailto:cf-metadata at cgd.ucar.edu>
> Subject: Re: [CF-metadata] Platform Heave
>
> Roy,
>
> So, heave is integrated vertical acceleration? How about
>
> platform_heave (m) = vertical displacement determined by integrating
> vertical accelerations of a platform that is nominally at rest.
>
> platform_heave_rate (m s-1) = vertical velocity determined by
> integrating vertical accelerations of a platform that is nominally at
> rest.
>
> Jim
>
> On 5/27/18 5:38 AM, Lowry, Roy K. wrote:
>
> Hi Jim,
>
> Does
>
> ?"Heave" is a term used to describe the vertical?displacement
> of a moving object?above the vertical level?of that?object
> when stationary.
>
> help by getting rid of the semantically-loaded?word 'height'?
> If?not, what would?
>
> I think the confusion is because you are thinking?of heave in
> terms of position within a reference frame. To think of it as the
> vertical displacement between a real platform and a massless
> platform is misleading- such considerations are part of the
> derivation of wave height from high frequency heave?measurements,
> which isn't relevant to?a discussion of the raw measurement.?It's
> also worth bearing in mind that whilst the debate has focused on
> platforms floating on the sea surface, the concept of heave could
> in theory?be applied to objects in the atmosphere.
>
> In practice, heave is measured by accelerometers that are usually
> combined with tilt sensors that?give pitch, roll and yaw. Hence,
> it is totally decoupled from any reference outside the platform.
>
> To answer your last muse, to get heave from a high frequency
> height relative to datum time series the method would need to
> determine the height of the object when 'stationary'. In the case
> of objects on the sea, 'stationary' is considered to be a flat
> calm sea (i.e. no waves), which can be approximated by averaging
> the raw time series. So, heave could be approximated by
> differencing the raw and averaged data. However, I can't think why
> anybody would want to do that.
>
> Cheers, Roy.
>
> ------------------------------------------------------------------------
>
> From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu>
> <mailto:cf-metadata-bounces at cgd.ucar.edu> on behalf of Jim Biard
> <jbiard at cicsnc.org> <mailto:jbiard at cicsnc.org>
> Sent: 26 May 2018 23:18
> To: cf-metadata at cgd.ucar.edu <mailto:cf-metadata at cgd.ucar.edu>
> Subject: Re: [CF-metadata] Platform Heave
>
> My biggest concern is that the standard name definition makes it
> clear in some fashion or other that this is a measure of
> deviations from some lower frequency (or low-pass filtered)
> measure of vertical position. (As are sway and surge in relation
> to their corresponding horizontal coordinates.) As was pointed
> out, heave is used in certain communities, so it's reasonable to
> provide a standard name, but it seems rather imprecise as it has
> been described so far.
>
> If I have understood the explanations correctly, a time series of
> platform height relative to a fixed datum that has sufficient
> precision and frequency would fully represent the heave along with
> the more slowly varying effects of tide, waves, etc. So is heave,
> as usually used, the first-order instantaneous difference between
> the height of an actual platform and the height of a massless
> ideal platform that would maintain a fixed offset relative to the
> sea surface? And, just out of curiosity, how would a time series
> of instantaneous measures of height relative to a fixed datum be
> separated in practice into heave and "non-heave" height?
>
> Getting back on track, it seems to me that the definition ought to
> somehow assist the reader in understanding how heave relates to
> other measures of height.
>
>
>
> On Sat, May 26, 2018 at 3:11 AM, Lowry, Roy K. <rkl at bodc.ac.uk
> <mailto:rkl at bodc.ac.uk>> wrote:
>
> Dear Jim and John,
>
> Heave is indeed a height relative to a datum, that datum being
> the?calm sea surface, which is a local short interval?mean sea
> level that isn't linked into any global reference system.?
> Indeed the 'datum' moves relative to the rest of the world -
> but not the platform - as tide rises and falls so?many would
> prefer to call it an 'instrument zero' rather than a 'datum'.
>
> Heave is therefore a very different measurement to any sea
> level parameter and?is the raw measurement recorded at high
> (Hz to?kHz)?frequency as a time series?by floating wave
> instruments such as waveriders and shipborne wave recorders.
> It therefore cannot be sensibly described by the same or
> similar?Standard Name as a measurement of height above a
> globally referenced datum like long-term?mean sea level or
> geoid. Whilst the Standard Name could?be
> 'platform_height_above_calm_sea_surface' or
> 'platform_height_above_stationary_position'?I would argue that
> 'heave' is a term from the same domain vocabulary as 'pitch',
> 'roll' and 'yaw' and therefore should be used.
>
> John is right to point out that the heave measurement is
> affected by the nature of the platform with a 250,000 tonne
> supertanker moving up and down much less than a rowing boat in
> a given wave climate, especially a wind sea. That was what was
> behind the SBWR corrections based on platform dimensions set
> up by Laurie Draper and Tom Tucker back in the 1980s.
>
> Cheers, Roy.
>
> ------------------------------------------------------------------------
>
> From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu
> <mailto:cf-metadata-bounces at cgd.ucar.edu>> on behalf of John
> Helly <hellyj at ucsd.edu <mailto:hellyj at ucsd.edu>>
> Sent: 26 May 2018 04:48
> To: Jim Biard; cf-metadata at cgd.ucar.edu
> <mailto:cf-metadata at cgd.ucar.edu>
> Subject: Re: [CF-metadata] Platform Heave
>
> Can't let go of this yet.
>
> If you think about the inverse problem of deriving the sea
> surface elevation from the heave you would have to account for
> the latency of ship motion relative to the sea-surface. A?
> wave passing under a ship induces motions that are not
> instantaneous either in attack or decay.
>
> J.
>
> On 5/25/18 20:42, John Helly wrote:
>
> I believe it's a synonym within the oceanographic
> community for the vertical motion of an ocean-going platform.
>
> https://en.wikipedia.org/wiki/Ship_motions
>
> Ship motions - Wikipedia
> <https://en.wikipedia.org/wiki/Ship_motions>
>
> en.wikipedia.org <http://en.wikipedia.org>
>
> Ship motions are defined by the six degrees of freedom
> that a ship, boat or any other craft can experience.
>
> Could just be jargon but it strike me as more complex:
> nonetheless a vertical position relative to a datum, but
> the buoyancy, stability and momentum of the platform are
> implied as part of the dynamics.? It seems that the datum
> is not a geophysical one alone but confounded with the
> 'normal' waterline for a platform so it may be relative to
> the water level in which the platform is embedded. That's
> a tough one. Two different platforms on the same sea
> surface would have different 'heave', for example.
>
> J.
>
> On 5/25/18 19:54, Jim Biard wrote:
>
> Hi.
>
> I get and endorse the need for pitch, roll, and yaw,
> but I remain perplexed about heave. How is a time
> series of 'heave' different from a time series of
> height relative to some vertical datum? I've yet to
> see a proposed definition that convinces me that this
> is a uniquely different quantity.
>
> Grace and peace,
>
> Jim
>
>
>
> On Fri, May 25, 2018 at 7:28 AM, Lowry, Roy K.
> <rkl at bodc.ac.uk <mailto:rkl at bodc.ac.uk>> wrote:
>
> Dear All,
>
> I agree with Nan that definitions of pitch roll
> and yaw would improve the existing Standard Name
> definitions. I also agree with using the existing
> orientation Standard Names?for ADCPs and that the
> 'platform' definition wording could make this
> clearer. However, such an enhancements should be
> submitted as a separate proposal and not be
> considered as part of Steve's proposal.
>
> Cheers, Roy.
>
> ------------------------------------------------------------------------
>
> From: CF-metadata
> <cf-metadata-bounces at cgd.ucar.edu
> <mailto:cf-metadata-bounces at cgd.ucar.edu>> on
> behalf of Nan Galbraith <ngalbraith at whoi.edu
> <mailto:ngalbraith at whoi.edu>>
> Sent: 25 May 2018 14:46
> To: cf-metadata at cgd.ucar.edu
> <mailto:cf-metadata at cgd.ucar.edu>
> Subject: Re: [CF-metadata] Platform Heave
>
> I'd really like to see pitch, roll and yaw defined
> in the CF standard
> name table; currently
> the definitions only say 'Standard names for
> platform describe the
> motion and orientation
> of the vehicle from which observations are made
> e.g. aeroplane, ship or
> satellite.'
>
> Also, not to get too far into the weeds, but many
> of the platform terms
> are important
> for instruments like ADCPs, so I'd just like to
> confirm that these
> definitions - and
> the names themselves - can be used to describe
> instruments, not just
> vehicles
> 'e.g. aeroplane, ship or satellite'. We already
> use pitch roll and
> yaw for these
> instruments on surface moorings, and I hope (and
> assume) this is legal.
>
> Thanks - Nan Galbraith
>
>
> On 5/25/18 8:53 AM, Lowry, Roy K. wrote:
> >
> >
> > Dear Steve,
> >
> >
> > One of the reasons I was interested in your
> definitions was your
> > perspective on the datum (i.e. zero value) for
> heave. The datum
> > 'mean_sea_level' is well used?in CF, but with
> the definition 'time
> > mean of sea surface elevation at a given
> location over an arbitrary
> > period sufficient to eliminate the tidal
> signals.' This is obviously
> > not appropriate for platform heave which doesn't
> take any account of
> > the state of the tide and so I would exclude
> 'mean_sea_level' from the
> > Standard Name.
> >
> >
> > I think my preference would be to keep the term
> 'heave' as we already
> > have 'pitch', 'yaw' and 'roll', giving:
> >
> >
> > platform_heave (m)
> >
> >
> > Standard names for platform describe the motion
> and orientation of the
> > vehicle from which observations are made e.g.
> aeroplane, ship or
> > satellite. "Heave" is a term used to describe
> the vertical
> > displacement of the platform above?its position
> when not moving.
> >
> >
> > tendency_of_platform_heave (m s-1)
> >
> >
> > Standard names for platform describe the motion
> and orientation of the
> > vehicle from which observations are made e.g.
> aeroplane, ship or
> > satellite. "Tendency_of_X" means derivative of X
> with respect to time.
> > "Heave" is a term used to describe the vertical
> displacement of the
> > platform above its position when not moving.
> >
> >
> > What do you think?
> >
> >
> > Cheers, Roy.
> >
> >
> > I am retiring on 31/05/2018 but will continue to
> be active through an
> > Emeritus Fellowship using this e-mail address.
> >
> >
> >
> >
> ------------------------------------------------------------------------
> > *From:* CF-metadata
> <cf-metadata-bounces at cgd.ucar.edu
> <mailto:cf-metadata-bounces at cgd.ucar.edu>> on
> behalf of
> > Hamilton, Steve <sj.hamilton at fugro.com
> <mailto:sj.hamilton at fugro.com>>
> > *Sent:* 25 May 2018 08:51
> > *Subject:* Re: [CF-metadata] Platform Heave
> >
> > All,
> >
> > Thanks for all the comments, I have tried to
> capture as below -
> >
> > *Parameter Name***
> >
> >
> >
> > *Standard Name*
> >
> >
> >
> > *Definition*
> >
> >
> >
> > *Canonical Units*
> >
> > Platform Heave
> >
> >
> >
> > Platform_Height_above_mean_sea_Level
> >
> >
> >
> > Standard names for platform describe the motion and
> > orientation of the vehicle from which
> observations are made e.g.
> > aeroplane, ship or satellite. Height above mean
> sea Level is the
> > linear vertical (up/down) distance of the
> platform in respect to the
> > mean sea level.
> >
> >
> >
> > ??????? m
> >
> > Platform Heave Rate
> >
> >
> >
> > Tendency_of_Platform_Height_above_mean_sea_Level
> >
> >
> >
> > Standard names for platform describe the motion and
> > orientation of the vehicle from which
> observations are made e.g.
> > aeroplane, ship or satellite. "tendency_of_X"
> means derivative of X
> > with respect to time. Height above mean sea
> Level is the linear
> > vertical (up/down) distance of the platform in
> respect to the mean sea
> > level.
> >
> >
> >
> > ??????? m s-1
> >
> > Please let me know if you have further comments
> >
> > Thanks
> >
> > Steve
> >
> > *From:*Steven Emmerson <emmerson at ucar.edu
> <mailto:emmerson at ucar.edu>>
> > *Sent:* 21 May 2018 19:18
> > *Subject:* Re: [CF-metadata] Platform Heave
> >
> > Whatever name you come up with, the canonical
> unit of the heave rate
> > shouldn't be "ms-1", but rather one of the
> following:
> >
> >???? m s-1
> >
> >???? m/s
> >
> >???? m.s-1
> >
> > I favor "m/s".
> >
> >
> > Regards,
> >
> > Steve Emmerson
> >
> > On Mon, May 21, 2018 at 6:32 AM, Hamilton, Steve
> > <sj.hamilton at fugro.com
> <mailto:sj.hamilton at fugro.com>
> <mailto:sj.hamilton at fugro.com>> wrote:
> >
> >???? Hi
> >
> >???? I am trying to find the CF name for heave of
> a vessel or
> > platform. platform_roll_angle and
> platform_pitch_angle already
> >???? exist but nothing on heave
> >
> >???? Would be the following be acceptable
> >
> > Platform_heave (m)
> >
> > Platform_heave_rate (ms-1)
> >
> > Standard names for platform describe the motion
> and orientation of
> >???? the vehicle from which observations are made
> e.g. aeroplane, ship
> >???? or satellite.
> >
> >???? Kind Regards,
> >
> >???? Steve
>
--
*******************************************************
* Nan Galbraith Information Systems Specialist *
* Upper Ocean Processes Group Mail Stop 29 *
* Woods Hole Oceanographic Institution *
* Woods Hole, MA 02543 (508) 289-2444 *
*******************************************************
Received on Fri Jun 01 2018 - 09:23:51 BST
