Hi Roy and Jim,
Thanks for your quick comments on the definitions. I have
just been looking again at the suggested text for yaw_angle:
'Platform yaw angle is the angle between the platform's
longitudinal/X axis and the direction of travel. Zero yaw
angle means the longitudinal axis is aligned with the
direction of travel, or a reference direction if the
platform is stationary. The usual sign convention is that
yaw angle is measured positive when the front or leading
edge of the platform is rotated clockwise from its
orientation (which has the standard name
platform_orientation).'
The problem is how to describe the reference direction which
the angle is calculated relative to. I started out by
talking about 'direction of travel' and later referred to
'platform_orientation'. The definition of
platform_orientation says 'The platform orientation is the
direction in which the "front" or longitudinal axis of the
platform is pointing (not necessarily the same as the
direction in which it is travelling, called
platform_course).' I've realised my new definition doesn't
really make sense if direction of travel and orientation
aren't the same (and clearly they can be different). Also,
if 'orientation' is the instantaneous direction of the
longitudinal axis, then presumably it includes yaw angle, so
it isn't the right reference for measuring yaw.
I've revised the text as follows:
'Platform yaw angle is the angle between the platform's
longitudinal/X axis and the platform's mean orientation
(i.e. its orientation not including high frequency
variations due to swaying and rocking motions, for example,
ship motions caused by the passing of sea surface waves).
Zero yaw angle means the longitudinal axis is aligned with
the mean orientation. The usual sign convention is that yaw
angle is measured positive when the front or leading edge of
the platform is rotated clockwise from its mean orientation
(which has the standard name platform_orientation).
Does it sound okay to refer to a 'mean orientation' in this
way? I'm having trouble thinking of a better wording!
Best wishes,
Alison
------
Alison Pamment Tel: +44 1235 778065
NCAS/Centre for Environmental Data Archival
Email:alison.pamm...@stfc.ac.uk
<mailto:Email:alison.pamm...@stfc.ac.uk>
<mailto:alison.pamm...@stfc.ac.uk>
<mailto:alison.pamm...@stfc.ac.uk>
STFC Rutherford Appleton Laboratory
R25, 2.22
Harwell Oxford, Didcot, OX11 0QX, U.K.
-----Original Message-----
From: CF-metadata<cf-metadata-boun...@cgd.ucar.edu>
<mailto:cf-metadata-boun...@cgd.ucar.edu>
<mailto:cf-metadata-boun...@cgd.ucar.edu>
<mailto:cf-metadata-boun...@cgd.ucar.edu> On Behalf Of
Alison Pamment - UKRI STFC
Sent: 25 July 2018 13:12
To: Hamilton, Steve<sj.hamil...@fugro.com>
<mailto:sj.hamil...@fugro.com>
<mailto:sj.hamil...@fugro.com>
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Subject: Re: [CF-metadata] Platform Heave
Dear Steve, Nan, et al,
Thank you for proposing new standard names for
platform_heave and improved definitions for existing names
for platform pitch, roll and yaw. Thank you also to all
those who submitted comments about these names.
Regarding Steve's proposals for new names, the discussion
seems to have reached consensus on the quantities themselves.
Until now, our usual explanatory sentence for 'platform' has
said 'Standard names for platform describe the motion and
orientation of the vehicle from which observations are made
e.g. aeroplane, ship or satellite.' Nan has suggested
extending the list of possible platforms, which seems fair
enough, so we would now have 'Standard names for platform
describe the motion and orientation of the vehicle from
which observations are made. Platforms include, but are not
limited to, satellites, aeroplanes, ships, instruments, and
buoys.' I've added this into the definitions of Steve's
names, leading to:
platform_heave (m)
'Standard names for "platform" describe the motion and
orientation of the vehicle from which observations are made.
Platforms include, but are not limited to, satellites,
aeroplanes, ships, instruments, and buoys. "Heave" means the
vertical displacement of a platform (positive upwards) over
a measurement time interval.'
platform_heave_rate (m s-1)
'Standard names for "platform" describe the motion and
orientation of the vehicle from which observations are made.
Platforms include, but are not limited to, satellites,
aeroplanes, ships, instruments, and buoys "Heave" means the
vertical displacement of a platform (positive upwards) over
a measurement time interval. "Heave rate" means the rate of
change of vertical displacement of the platform over a
measurement time interval.'
These two names are accepted for publication in the standard
name table and will be added in the next update, planned for
6th August.
We have six existing platform pitch, roll and yaw names:
platform_pitch_angle (degree)
platform_pitch_rate (degree s-1)
platform_roll_angle (degree)
platform_roll_rate (degree s-1)
platform_yaw_angle (degree)
platform_yaw_rate (degree s-1)
Nan has suggested the following definitions, based
onhttps://en.wikipedia.org/wiki/Ship_motions
<https://urldefense.proofpoint.com/v2/url?u=https-3A__en.wikipedia.org_wiki_Ship-5Fmotions&d=DwMDaQ&c=qKdtBuuu6dQK9MsRUVJ2DPXW6oayO8fu4TfEHS8sGNk&r=Vm7o2ZGxPkkqRuPs8nVMVQ&m=fsDk1eg5rM-so0h_XCTK_Pl1w5MGnQK88vuvHcbhUUI&s=gxXkUfvVSqtWNEzxwyAeuKgEMzADzXWv2OOZtOBRAao&e=>
<https://urldefense.proofpoint.com/v2/url?u=https-3A__en.wikipedia.org_wiki_Ship-5Fmotions&d=DwMDaQ&c=qKdtBuuu6dQK9MsRUVJ2DPXW6oayO8fu4TfEHS8sGNk&r=Vm7o2ZGxPkkqRuPs8nVMVQ&m=fsDk1eg5rM-so0h_XCTK_Pl1w5MGnQK88vuvHcbhUUI&s=gxXkUfvVSqtWNEzxwyAeuKgEMzADzXWv2OOZtOBRAao&e=>.
(A quick search of other online sources yields definitions
consistent with these).
Pitch
The up/down rotation of a platform about its transverse/Y
axis. The transverse/Y axis, lateral or pitch axis is an
imaginary line running horizontally across the platform and
through its center of gravity. A pitch motion is an
up-or-down movement of the bow and stern of the platform.
Roll
The tilting rotation of a platform about its longitudinal/X
axis. The longitudinal/X axis, or roll axis, is an imaginary
line running horizontally through the length of the
platform, through its center of gravity, and parallel to the
waterline. A roll motion is a side-to-side or port-starboard
tilting motion of the superstructure around this axis.
Yaw
The turning rotation of a platform about its vertical/Z
axis. The vertical/Z axis, or yaw axis, is an imaginary line
running vertically through the platform and through its
center of gravity. A yaw motion is a side-to side movement
of the bow and stern of the ship.
These are useful and concise definitions. I suggest that we
don't refer anywhere to 'ship', 'bow' or 'stern', since we
want the definitions to apply to all possible platforms. I'm
thinking also that 'port' and 'starboard' may apply to ships
and aeroplanes, but perhaps not to a satellite, so are
probably best avoided. Similarly, 'waterline' only applies
to maritime platforms. I suggest the following amendments to
make the definitions as generic as possible:
Pitch
"Pitch" means rotation of the platform in the vertical plane
about its transverse/Y axis. The transverse/Y axis, also
known as the "lateral axis" or "pitch axis", is an imaginary
line running horizontally across the platform and through
its center of gravity. In pitch motion, the leading edge of
the platform moves vertically upwards while the rear moves
vertically downwards, and vice versa.
Roll
"Roll" means rotation of the platform in the vertical plane
about its longitudinal/X axis. The longitudinal/X axis, also
known as the "roll axis", is an imaginary line running
horizontally through the length of the platform and through
its center of gravity. In roll motion, the platform tilts
such that one side moves vertically upwards while the other
moves vertically downwards, and vice versa.
Yaw
"Yaw" means rotation of the platform in the horizontal plane
about its vertical/Z axis. The vertical/Z axis, also known
as the "yaw axis", is an imaginary line running vertically
through the platform and through its center of gravity. In
yaw motion, the platform rotates clockwise or counter
clockwise in the horizontal, relative to its orientation,
which has the standard name platform_orientation.
Are these okay?
For names such as platform_view_angle and
platform_zenith_angle we also describe how the angle itself
is measured. We should do the same for pitch, roll and yaw
angles while we are in the process of updating the
definitions. I have come up with the following:
Pitch angle
Platform pitch angle is the angle between the local
horizontal and the platform's longitudinal/X axis. Zero
pitch angle means the longitudinal axis is horizontal. The
usual sign convention is that pitch angle is measured
positive when the front or leading edge of the platform is
elevated above the horizontal, negative when it is below the
horizontal.
Roll angle
Platform roll angle is the angle between the local
horizontal and the platform's lateral/Y axis. Zero roll
angle means the lateral axis is horizontal. The usual sign
convention is that roll angle is measured positive when the
right hand edge of the platform (when viewing towards the
orientation direction or "front" of the platform) is
elevated above the horizontal, negative when it is below the
horizontal.
Yaw angle
Platform yaw angle is the angle between the platform's
longitudinal/X axis and the direction of travel. Zero yaw
angle means the longitudinal axis is aligned with the
direction of travel, or a reference direction if the
platform is stationary. The usual sign convention is that
yaw angle is measured positive when the front or leading
edge of the platform is rotated clockwise from its
orientation (which has the standard name platform_orientation).
Just so we can see a couple of examples of pulling all this
together, I've written out the full revised definitions of
platform platform_pitch_angle and platform_pitch_rate below.
platform_pitch_angle (degree)
'Standard names for "platform" describe the motion and
orientation of the vehicle from which observations are made.
Platforms include, but are not limited to, satellites,
aeroplanes, ships, instruments and buoys. "Pitch" means
rotation of the platform in the vertical plane about its
transverse/Y axis. The transverse/Y axis, also known as the
"lateral axis" or "pitch axis", is an imaginary line running
horizontally across the platform and through its center of
gravity. In pitch motion, the leading edge of the platform
moves vertically upwards while the rear moves vertically
downwards, and vice versa. Platform pitch angle is the angle
between the local horizontal and the platform's
longitudinal/X axis. Zero pitch angle means the longitudinal
axis is horizontal. The usual sign convention is that pitch
angle is measured positive when the front or leading edge of
the platform is elevated above the horizontal, negative when
it is below the horizontal.'
platform_pitch_rate (degree s-1)
'Standard names for "platform" describe the motion and
orientation of the vehicle from which observations are made.
Platforms include, but are not limited to, satellites,
aeroplanes, ships, instruments and buoys. "Pitch" means
rotation of the platform in the vertical plane about its
transverse/Y axis. The transverse/Y axis, also known as the
"lateral axis" or "pitch axis", is an imaginary line running
horizontally across the platform and through its center of
gravity. In pitch motion, the leading edge of the platform
moves vertically upwards while the rear moves vertically
downwards, and vice versa. The quantity with standard name
platform_pitch_rate is the change per unit time in the
quantity with standard name platform_pitch_angle.'
The roll and yaw definitions would be constructed similarly.
The pitch/roll/yaw names are still under discussion. I'd
welcome further comments on these.
Best wishes,
Alison
------
Alison Pamment Tel: +44 1235 778065
NCAS/Centre for Environmental Data Archival
Email:alison.pamm...@stfc.ac.uk
<mailto:Email:alison.pamm...@stfc.ac.uk>
<mailto:alison.pamm...@stfc.ac.uk>
<mailto:alison.pamm...@stfc.ac.uk>
STFC Rutherford Appleton Laboratory
R25, 2.22
Harwell Oxford, Didcot, OX11 0QX, U.K.
-----Original Message-----
From: CF-metadata<cf-metadata-boun...@cgd.ucar.edu>
<mailto:cf-metadata-boun...@cgd.ucar.edu>
<mailto:cf-metadata-boun...@cgd.ucar.edu>
<mailto:cf-metadata-boun...@cgd.ucar.edu> On Behalf Of
Hamilton, Steve
Sent: 11 July 2018 10:52
To:cf-metadata@cgd.ucar.edu
<mailto:To:cf-metadata@cgd.ucar.edu>
<mailto:cf-metadata@cgd.ucar.edu>
<mailto:cf-metadata@cgd.ucar.edu>
Subject: Re: [CF-metadata] Platform Heave
Hi Nan,
I agree expanding on the existing standard name descriptions
does make sense and standardising for _rate and _angle
What you suggest below seems acceptable
Thanks
Steve
-----Original Message-----
From: CF-metadata<cf-metadata-boun...@cgd.ucar.edu>
<mailto:cf-metadata-boun...@cgd.ucar.edu>
<mailto:cf-metadata-boun...@cgd.ucar.edu>
<mailto:cf-metadata-boun...@cgd.ucar.edu> On Behalf Of Nan
Galbraith
Sent: 10 July 2018 17:39
To:cf-metadata@cgd.ucar.edu
<mailto:To:cf-metadata@cgd.ucar.edu>
<mailto:cf-metadata@cgd.ucar.edu>
<mailto:cf-metadata@cgd.ucar.edu>
Subject: Re: [CF-metadata] Platform Heave
Hi Alison, Steve, and all -
Since we have a little time to finalize this, could we also
consider updating the definitions of platform_pitch_angle,
platform_roll_angle and platform_yaw_angle?
Currently, these all say 'Standard names for platform
describe the motion and orientation of the vehicle from
which observations are made e.g. aeroplane, ship or satellite.'
John Helly pointed to the helpful Wikipedia page for ship
motion,https://en.wikipedia.org/wiki/Ship_motions
<https://urldefense.proofpoint.com/v2/url?u=https-3A__en.wikipedia.org_wiki_Ship-5Fmotions&d=DwMDaQ&c=qKdtBuuu6dQK9MsRUVJ2DPXW6oayO8fu4TfEHS8sGNk&r=Vm7o2ZGxPkkqRuPs8nVMVQ&m=fsDk1eg5rM-so0h_XCTK_Pl1w5MGnQK88vuvHcbhUUI&s=gxXkUfvVSqtWNEzxwyAeuKgEMzADzXWv2OOZtOBRAao&e=>
<https://urldefense.proofpoint.com/v2/url?u=https-3A__en.wikipedia.org_wiki_Ship-5Fmotions&d=DwMDaQ&c=qKdtBuuu6dQK9MsRUVJ2DPXW6oayO8fu4TfEHS8sGNk&r=Vm7o2ZGxPkkqRuPs8nVMVQ&m=fsDk1eg5rM-so0h_XCTK_Pl1w5MGnQK88vuvHcbhUUI&s=gxXkUfvVSqtWNEzxwyAeuKgEMzADzXWv2OOZtOBRAao&e=>.
The suggestions below are merged from different sections of
that page, and might be a little ... long, but I'd also like
to append something like 'Platforms include but are not
limited to satellites, aeroplanes, ships, instruments, and
buoys.'
Pitch
The up/down rotation of a platform about its transverse/Y
axis. The transverse/Y axis, lateral or pitch axis is an
imaginary line running horizontally across the platform and
through its center of gravity. A pitch motion is an
up-or-down movement of the bow and stern of the platform.
Roll
The tilting rotation of a platform about its longitudinal/X
axis. The longitudinal/X axis, or roll axis, is an imaginary
line running horizontally through the length of the
platform, through its center of gravity, and parallel to the
waterline. A roll motion is a side-to-side or port-starboard
tilting motion of the superstructure around this axis.
Yaw
The turning rotation of a platform about its vertical/Z
axis. The vertical/Z axis, or yaw axis, is an imaginary line
running vertically through the platform and through its
center of gravity.
A yaw motion is a side-to side movement of the bow and stern
of the ship.
And we had something like this for heave:
platform_heave (m) = upwards vertical displacement
I suppose these could also be applied to platform_*_rates.
Regards -
Nan
On 7/4/18 4:47 AM, Alison Pamment - UKRI STFC wrote:
Dear Steve, > > Thank you for your message and apologies
for not
having processed
> your proposals as yet. I have been working on the CMIP
names, but > they are reaching a conclusion and I will
shortly be looking through > the many other proposals that
have been waiting for attention. > > A quick look through
the discussion of your names shows they are > pretty much
agreed. You need take no further action at this time - I >
will check that the names and definitions are clear and
consistent > with existing names and get back to you on the
list with any final > comments or questions. Version 56 of
the standard name table will be > published later today - I
think we can probably finalise your names > in time for
version 57. > > Best wishes, Alison
________________________________
From: Hamilton, Steve<sj.hamil...@fugro.com>
<mailto:sj.hamil...@fugro.com>
<mailto:sj.hamil...@fugro.com> <mailto:sj.hamil...@fugro.com>
Sent: 03 July 2018 09:12
Please can you advise if this standard name has now been
accepted and
when it will be included in the CF Standard Names
If there is something else to do please let me know
Thanks
Steve
________________________________
From: Jim Biard <jbi...@cicsnc.org
<mailto:jbi...@cicsnc.org> <mailto:jbi...@cicsnc.org>
<mailto:jbi...@cicsnc.org><mailto:jbi...@cicsnc.org>
<mailto:jbi...@cicsnc.org> <mailto:jbi...@cicsnc.org>
<mailto:jbi...@cicsnc.org>>
Sent: 01 June 2018 22:56
Nan,
Thanks for pulling things back in. I very much like the
idea of keeping technology or specific methods out of the
definition if at all possible, so I like your proposal. I
expect we should include platform in the definition, as
well as an indication that this is dynamic (over time). How
about these definitions?
platform_heave (m) = upwards vertical displacement of a
platform over
a measurement time interval platform_heave_rate (m s-1) =
upwards rate
of change in vertical displacement of a platform over a
measurement time interval They leave out some detail but
capture the relative nature of the quantities.
(In my mind, the primary detail being left out is the 'net
zero'
nature of the quantities, which gets back to defining the
'moving-mean' sea level reference point.) Grace and peace,
Jim
On 6/1/18 11:23 AM, Nan Galbraith wrote:
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
From: Lowry, Roy K.
Sent: 30 May 2018 21:37
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.
----------------------------------------------------------------------
--
From: Lowry, Roy K. <r...@bodc.ac.uk <mailto:r...@bodc.ac.uk>
<mailto:r...@bodc.ac.uk>
<mailto:r...@bodc.ac.uk><mailto:r...@bodc.ac.uk>
<mailto:r...@bodc.ac.uk> <mailto:r...@bodc.ac.uk>
<mailto:r...@bodc.ac.uk>
Sent: 30 May 2018 21:02
Thanks Jim,
That work for me.
Cheers, Roy.
----------------------------------------------------------------------
--
From: Jim Biard<jbi...@cicsnc.org>
<mailto:jbi...@cicsnc.org> <mailto:jbi...@cicsnc.org>
<mailto:jbi...@cicsnc.org>
Sent: 30 May 2018 18:39
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:Jim Biard<jbi...@cicsnc.org>
<mailto:jbi...@cicsnc.org> <mailto:jbi...@cicsnc.org>
<mailto:jbi...@cicsnc.org><mailto:jbi...@cicsnc.org>
<mailto:jbi...@cicsnc.org> <mailto:jbi...@cicsnc.org>
<mailto:jbi...@cicsnc.org>
Sent: 26 May 2018 23:18
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. 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: John Helly<hel...@ucsd.edu>
<mailto:hel...@ucsd.edu> <mailto:hel...@ucsd.edu>
<mailto:hel...@ucsd.edu>
Sent: 26 May 2018 04:48
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://urldefense.proofpoint.com/v2/url?u=https-3A__en.wikipedia.org_wiki_Ship-5Fmotions&d=DwMDaQ&c=qKdtBuuu6dQK9MsRUVJ2DPXW6oayO8fu4TfEHS8sGNk&r=Vm7o2ZGxPkkqRuPs8nVMVQ&m=fsDk1eg5rM-so0h_XCTK_Pl1w5MGnQK88vuvHcbhUUI&s=gxXkUfvVSqtWNEzxwyAeuKgEMzADzXWv2OOZtOBRAao&e=>
<https://urldefense.proofpoint.com/v2/url?u=https-3A__en.wikipedia.org_wiki_Ship-5Fmotions&d=DwMDaQ&c=qKdtBuuu6dQK9MsRUVJ2DPXW6oayO8fu4TfEHS8sGNk&r=Vm7o2ZGxPkkqRuPs8nVMVQ&m=fsDk1eg5rM-so0h_XCTK_Pl1w5MGnQK88vuvHcbhUUI&s=gxXkUfvVSqtWNEzxwyAeuKgEMzADzXWv2OOZtOBRAao&e=>
Ship motions - Wikipedia
<https://en.wikipedia.org/wiki/Ship_motions>
<https://en.wikipedia.org/wiki/Ship_motions>
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<https://urldefense.proofpoint.com/v2/url?u=https-3A__en.wikipedia.org_wiki_Ship-5Fmotions&d=DwMDaQ&c=qKdtBuuu6dQK9MsRUVJ2DPXW6oayO8fu4TfEHS8sGNk&r=Vm7o2ZGxPkkqRuPs8nVMVQ&m=fsDk1eg5rM-so0h_XCTK_Pl1w5MGnQK88vuvHcbhUUI&s=gxXkUfvVSqtWNEzxwyAeuKgEMzADzXWv2OOZtOBRAao&e=><https://en.wikipedia.org/
wiki/Ship_motions>
<https://en.wikipedia.org/wiki/Ship_motions>
<https://urldefense.proofpoint.com/v2/url?u=https-3A__en.wikipedia.org_wiki_Ship-5Fmotions&d=DwMDaQ&c=qKdtBuuu6dQK9MsRUVJ2DPXW6oayO8fu4TfEHS8sGNk&r=Vm7o2ZGxPkkqRuPs8nVMVQ&m=fsDk1eg5rM-so0h_XCTK_Pl1w5MGnQK88vuvHcbhUUI&s=gxXkUfvVSqtWNEzxwyAeuKgEMzADzXWv2OOZtOBRAao&e=>
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en.wikipedia.org
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<http://en.wikipedia.org> <http://en.wikipedia.org>
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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.
<r...@bodc.ac.uk <mailto:r...@bodc.ac.uk>
<mailto:r...@bodc.ac.uk>
<mailto:r...@bodc.ac.uk><mailto:r...@bodc.ac.uk>
<mailto:r...@bodc.ac.uk> <mailto: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.
----------------------------------------------------------------------
--
From: Nan
Galbraith<ngalbra...@whoi.edu> <mailto:ngalbra...@whoi.edu>
<mailto:ngalbra...@whoi.edu> <mailto:ngalbra...@whoi.edu>
Sent: 25 May 2018 14:46
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.
--
*******************************************************
* Nan Galbraith Information Systems Specialist *
* Upper Ocean Processes Group Mail Stop 29 *
* Woods Hole Oceanographic Institution *
* Woods Hole, MA 02543 (508) 289-2444 *
*******************************************************
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