Hi again -
Part 2, sorry for my piecemeal responses, it's just that kind of a day.
I'm not sure why we'd want to restrict the meaning of platform_orientation
the definition - instantaneous measurements might also have this standard
name, with the user deciding how to filter.
There are different reasons to include platform_orientation in a file,
and we'd
just be limiting the usefulness of this term by making the definition
too complicated.
Thanks - Nan
On 7/25/18 12:34 PM, Alison Pamment - UKRI STFC wrote:
> Like Roy, I had wondered whether 'platform_orientation' should really be an instantaneous quantity or something with high frequency variability removed. If it is the latter (which I think was probably the original intention of the standard name) then we should amend the definition as follows:
> The platform orientation is the direction in which the "front" or longitudinal axis of the platform is pointing with high frequency variations (e.g. the effect of surface waves on a ship) removed. (This is not necessarily the same as the direction in which the platform is travelling, called platform_course).'
>
On 7/26/18 9:34 AM, Nan Galbraith wrote:
> Hi all -
>
> Thank you, Alison and all, this is really good. I haven't looked
> through all the
> current versions of the definitions yet but I hope to do that shortly.
>
> I think the proposed yaw definition may be a bit too detailed; getting
> into
> details like the removal of high frequency variations seems
> unnecessary (and
> maybe counter productive). Could we consider something simpler? (see
> below,
> please)
>
> Second, would it be possible to turn all these definitions around so
> that the
> definition of the concept is at the start, and the term platform comes
> at the
> end?? That would make it much more efficient when people are looking for
> the standard name at cf-standard-name-table.html.
>
> And last, could we specify that the yaw angle value (though not the
> motion
> itself) is clockwise? A phrase like 'usual sign convention' might lead
> to confusion
> interpreting the values, or require extra attributes to clarify.
>
> If that's all acceptable, platform_yaw_angle would be:
>
> "platform_yaw_angle is the rotation of a platform in the horizontal
> plane about its
> vertical/Z axis. This axis, also known as the "yaw axis", runs
> vertically through the
> center of gravity of the platform. In yaw motion, the platform rotates
> horizontally
> relative to its orientation, which has the standard name
> platform_orientation. Yaw
> angle is measured positive clockwise from platform_orientation.
> 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."
>
> Thanks again -
> Nan
>
>
> On 7/25/18 12:34 PM, Alison Pamment - UKRI STFC wrote:
>> Dear Roy and Jim,
>>
>>
>> Thanks again both for your help.
>>
>>
>> Both your replies are saying that referring to direction of motion
>> for measuring yaw is a bad idea, and in any case it doesn't apply to
>> stationary platforms (which presumably have some means of determining
>> their own orientation relative to concepts such as 'up', 'north',
>> etc.)? You are both advising against saying 'mean orientation' and I
>> agree that it's not really a well-defined concept.
>>
>>
>> I like Roy's suggested text which refers to the platform's own axis
>> to define yaw. So the full definition of platform_yaw_angle would be:
>>
>> '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. "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. Platform yaw angle is the angle at a given
>> instant between the platform's longitudinal/X axis and the position
>> of that axis with high frequency variations (e.g. the effect of
>> surface waves on a ship) removed. Zero yaw angle means the
>> longitudinal axis is aligned with the platform_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 the
>> platform_orientation.'
>>
>>
>> Okay?
>>
>>
>> Like Roy, I had wondered whether 'platform_orientation' should really
>> be an instantaneous quantity or something with high frequency
>> variability removed. If it is the latter (which I think was probably
>> the original intention of the standard name) then we should amend the
>> definition as follows:
>>
>> '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. The platform orientation is the direction in which the "front"
>> or longitudinal axis of the platform is pointing with high frequency
>> variations (e.g. the effect of surface waves on a ship) removed.
>> (This is not necessarily the same as the direction in which the
>> platform is travelling, called platform_course).'
>>
>>
>> Okay?
>>
>>
>> As an additional point, I note that besides the names already
>> discussed in this thread, there are a further 11 existing platform
>> names. I will include the new text for 'platform' in their
>> definitions as part of the August standard names update.
>>
>>
>> Best wishes,
>>
>> Alison
>>
>> ________________________________
>> From: Lowry, Roy K. <rkl at bodc.ac.uk>
>> Sent: 25 July 2018 16:35:27
>> To: Pamment, Alison (STFC,RAL,RALSP); cf-metadata at cgd.ucar.edu
>> Subject: Re: [CF-metadata] Platform Heave
>>
>>
>> Hi again,
>>
>>
>> This is an area where it is easy to get tied up in knots because
>> there are multiple reference frames. If we talk ships then there is
>> the platform_orientation (or heading) which is measured using a
>> gyro-compass - a stabilised instrument that eliminates high-frequency
>> variations in where the bow is actually pointing and provides the
>> zero reference point for yaw.
>>
>>
>> The concept of 'travel' relates to another reference frame external
>> to the platform - say a GPS CRS? - but yaw only has relevance to the
>> platform's internal reference frame. So you are right that bringing
>> 'direction of travel' into a definition of yaw is a bad thing even
>> though it's reasonably common practice to do so.
>>
>>
>> Mean orientation is also possibly best avoided as the
>> platform_orientation isn't necessarily determined by averaging
>> instantaneous longitudinal axis orientations.? It could be - and
>> often is - measured by something that has greater inertia than the
>> platform.
>>
>>
>> So how about using :
>>
>>
>> Platform yaw angle is the angle at a given instant between the
>> platform's longitudinal/X axis and the position of that axis with
>> high frequency variations (e.g. the effect of surface waves on a
>> ship) removed. Zero yaw angle means the longitudinal axis is aligned
>> with the platform_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 the platform_orientation.
>>
>>
>> This raises the question as to whether the platform_orientation
>> definition should have the clarification 'with high-frequency
>> variability removed' added. This would be an explicit statement of
>> what - to me at least - is commonly understood meaning of 'heading'.
>>
>>
>> Does that help?
>>
>>
>> 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> on behalf of
>> Alison Pamment - UKRI STFC <alison.pamment at stfc.ac.uk>
>> Sent: 25 July 2018 14:37
>> To: cf-metadata at cgd.ucar.edu
>> Subject: Re: [CF-metadata] Platform Heave
>>
>> 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.pamment at stfc.ac.uk
>> STFC Rutherford Appleton Laboratory
>> R25, 2.22
>> Harwell Oxford, Didcot, OX11 0QX, U.K.
>>
>> -----Original Message-----
>> From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> On Behalf Of
>> Alison Pamment - UKRI STFC
>> Sent: 25 July 2018 13:12
>> To: Hamilton, Steve <sj.hamilton at fugro.com>; cf-metadata at cgd.ucar.edu
>> 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 on
>> https://en.wikipedia.org/wiki/Ship_motions. (A quick search of other
>> online sources yields definitions consistent with these).
>> Ship motions - Wikipedia<https://en.wikipedia.org/wiki/Ship_motions>
>> en.wikipedia.org
>> Ship motions are defined by the six degrees of freedom that a ship,
>> boat or any other craft can experience.
>>
>>
>>
>> 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.pamment at stfc.ac.uk
>> STFC Rutherford Appleton Laboratory
>> R25, 2.22
>> Harwell Oxford, Didcot, OX11 0QX, U.K.
>>
>> -----Original Message-----
>> From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> On Behalf Of
>> Hamilton, Steve
>> Sent: 11 July 2018 10:52
>> To: cf-metadata at 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-bounces at cgd.ucar.edu> On Behalf Of Nan
>> Galbraith
>> Sent: 10 July 2018 17:39
>> To: cf-metadata at 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. 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.hamilton at 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 <jbiard at cicsnc.org<mailto:jbiard at 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. <rkl at bodc.ac.uk<mailto:rkl at bodc.ac.uk>
>>> Sent: 30 May 2018 21:02
>>>
>>> Thanks Jim,
>>>
>>> That work for me.
>>>
>>> Cheers, Roy.
>>>
>>> ----------------------------------------------------------------------
>>> --
>>>
>>> From: Jim Biard <jbiard at 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 <jbiard at cicsnc.org><mailto:jbiard at 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 <hellyj at 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
>>>
>>> ????????????? Ship motions - Wikipedia
>>>
>>> <https://en.wikipedia.org/wiki/Ship_motions><https://en.wikipedia.org/
>>> wiki/Ship_motions>
>>>
>>> ????????????? en.wikipedia.org
>>> <http://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:? Nan Galbraith <ngalbraith at 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 *
*******************************************************
Received on Thu Jul 26 2018 - 07:47:31 BST
