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.
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-boun...@cgd.ucar.edu> on behalf of
Jim Biard <jbi...@cicsnc.org>
*Sent:* 26 May 2018 23:18
*To:* cf-metadata@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.
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On Sat, May 26, 2018 at 3:11 AM, Lowry, Roy K. <r...@bodc.ac.uk
<mailto:r...@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.
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-boun...@cgd.ucar.edu
<mailto:cf-metadata-boun...@cgd.ucar.edu>> on behalf of John Helly
<hel...@ucsd.edu <mailto:hel...@ucsd.edu>>
*Sent:* 26 May 2018 04:48
*To:* Jim Biard; cf-metadata@cgd.ucar.edu
<mailto:cf-metadata@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
<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
CICS-NC <http://www.cicsnc.org/>Visit us on
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On Fri, May 25, 2018 at 7:28 AM, Lowry, Roy K. <r...@bodc.ac.uk
<mailto:r...@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.
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-boun...@cgd.ucar.edu
<mailto:cf-metadata-boun...@cgd.ucar.edu>> on behalf of Nan
Galbraith <ngalbra...@whoi.edu <mailto:ngalbra...@whoi.edu>>
*Sent:* 25 May 2018 14:46
*To:* cf-metadata@cgd.ucar.edu <mailto:cf-metadata@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-boun...@cgd.ucar.edu
<mailto:cf-metadata-boun...@cgd.ucar.edu>> on behalf of
> Hamilton, Steve <sj.hamil...@fugro.com
<mailto:sj.hamil...@fugro.com>>
> *Sent:* 25 May 2018 08:51
> *To:* cf-metadata@cgd.ucar.edu
<mailto:cf-metadata@cgd.ucar.edu>
> *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 <emmer...@ucar.edu
<mailto:emmer...@ucar.edu>>
> *Sent:* 21 May 2018 19:18
> *To:* Hamilton, Steve <sj.hamil...@fugro.com
<mailto:sj.hamil...@fugro.com>>
> *Cc:* cf-metadata@cgd.ucar.edu
<mailto:cf-metadata@cgd.ucar.edu>
> *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.hamil...@fugro.com <mailto:sj.hamil...@fugro.com>
<mailto:sj.hamil...@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
>
>
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