Dear Thomas,
Thanks for your response. The names
eastward_sea_ice_displacement; m
northward_sea_ice_displacement; m
sea_ice_x_displacement; m
sea_ice_y_displacement; m
sea_ice_displacement; m
direction_of_sea_ice_displacement; degrees
are all accepted and will be included in the next update of the standard
name table.
Best wishes,
Alison
------
Alison Pamment Tel: +44 1235 778065
NCAS/British Atmospheric Data Centre Fax: +44 1235 446314
Rutherford Appleton Laboratory Email: alison.pamment at stfc.ac.uk
Chilton, Didcot, OX11 0QX, U.K.
> -----Original Message-----
> From: cf-metadata-bounces at cgd.ucar.edu [mailto:cf-metadata-
> bounces at cgd.ucar.edu] On Behalf Of Thomas Lavergne
> Sent: 18 November 2009 16:34
> Cc: cf-metadata at cgd.ucar.edu
> Subject: Re: [CF-metadata] Standard name(s) needed for satellite-based
> icedrift products
>
> Dear Alison,
>
> Thank you for posting this old subject again. I re-read through the
> names, definitions and units and do not wish to modify them as they
> suit my needs and, I think, those of my community. As you noted, they
> are built upon the existing 'sea_ice_velocity' standard names, which
> makes it more easy to accept them, I guess.
>
> As far as the other "open discussion" items you are answering at the
> end of this email, they were merely to bring the discussion forward
and
> it is correct that some of the answers to my questions are now found
in
> other threads, I do not think they should continue in this context.
>
> As far as I am concerned, and unless someone comes with strong opinion
> against them, those names, definitions and units are suitable and I am
> happy if you close the subject.
>
> Cheers,
> Thomas Lavergne,
> Research Scientist, met.no, Oslo, Norway
>
>
>
> ----- "alison pamment" <alison.pamment at stfc.ac.uk> wrote:
>
> > Dear Thomas,
> >
> > Thank you for your email asking about the status of these names.
> > Looking back at your last posting, I think we had essentially
arrived
> > at
> > agreement on the following names, units and definitions:
> >
> > eastward_sea_ice_displacement; m
> > 'Displacement' means the change in geospatial position of an object
> > that
> > has moved over time. If possible, the time interval over which the
> > motion took place should be specified using a bounds variable for
the
> > time coordinate variable. A displacement can be represented as a
> > vector. Such a vector should however not be interpreted as
describing
> > a
> > rectilinear, constant speed motion but merely as an indication that
> > the
> > start point of the vector is found at the tip of the vector after
the
> > time interval associated with the displacement variable. A
> > displacement
> > does not prescribe a trajectory. Sea ice displacement can be defined
> > as
> > a two-dimensional vector, with no vertical component. "Eastward"
> > indicates a vector component which is positive when directed
eastward
> > (negative westward). An eastward displacement is the distance across
> > the
> > earth's surface calculated from the change in a moving object's
> > longitude between the start and end of the time interval associated
> > with
> > the displacement variable.
> >
> > northward_sea_ice_displacement; m
> > 'Displacement' means the change in geospatial position of an object
> > that
> > has moved over time. If possible, the time interval over which the
> > motion took place should be specified using a bounds variable for
the
> > time coordinate variable. A displacement can be represented as a
> > vector. Such a vector should however not be interpreted as
describing
> > a
> > rectilinear, constant speed motion but merely as an indication that
> > the
> > start point of the vector is found at the tip of the vector after
the
> > time interval associated with the displacement variable. A
> > displacement
> > does not prescribe a trajectory. Sea ice displacement can be defined
> > as
> > a two-dimensional vector, with no vertical component. "Northward"
> > indicates a vector component which is positive when directed
> > northward
> > (negative southward). A northward displacement is the distance
> > across
> > the earth's surface calculated from the change in a moving object's
> > latitude between the start and end of the time interval associated
> > with
> > the displacement variable.
> >
> > sea_ice_x_displacement; m
> > 'Displacement' means the change in geospatial position of an object
> > that
> > has moved over time. If possible, the time interval over which the
> > motion took place should be specified using a bounds variable for
the
> > time coordinate variable. A displacement can be represented as a
> > vector. Such a vector should however not be interpreted as
describing
> > a
> > rectilinear, constant speed motion but merely as an indication that
> > the
> > start point of the vector is found at the tip of the vector after
the
> > time interval associated with the displacement variable. A
> > displacement
> > does not prescribe a trajectory. Sea ice displacement can be defined
> > as
> > a two-dimensional vector, with no vertical component. "x" indicates
> > a
> > vector component along the grid x-axis, when this is not true
> > longitude,
> > positive with increasing x. An x displacement is calculated from
the
> > difference in the moving object's grid x coordinate between the
start
> > and end of the time interval associated with the displacement
> > variable.
> >
> > sea_ice_y_displacement; m
> > 'Displacement' means the change in geospatial position of an object
> > that
> > has moved over time. If possible, the time interval over which the
> > motion took place should be specified using a bounds variable for
the
> > time coordinate variable. A displacement can be represented as a
> > vector. Such a vector should however not be interpreted as
describing
> > a
> > rectilinear, constant speed motion but merely as an indication that
> > the
> > start point of the vector is found at the tip of the vector after
the
> > time interval associated with the displacement variable. A
> > displacement
> > does not prescribe a trajectory. Sea ice displacement can be defined
> > as
> > a two-dimensional vector, with no vertical component. "y" indicates
a
> > vector component along the grid y-axis, when this is not true
> > latitude,
> > positive with increasing y. A y displacement is calculated from the
> > difference in the moving object's grid y coordinate between the
start
> > and end of the time interval associated with the displacement
> > variable.
> >
> > sea_ice_displacement; m
> > 'Displacement' means the change in geospatial position of an object
> > that
> > has moved over time. If possible, the time interval over which the
> > motion took place should be specified using a bounds variable for
the
> > time coordinate variable. A displacement can be represented as a
> > vector. Such a vector should however not be interpreted as
describing
> > a
> > rectilinear, constant speed motion but merely as an indication that
> > the
> > start point of the vector is found at the tip of the vector after
the
> > time interval associated with the displacement variable. A
> > displacement
> > does not prescribe a trajectory. Sea ice displacement can be defined
> > as
> > a two-dimensional vector, with no vertical component. In that case,
> > "displacement" is also the distance across the earth's surface
> > calculated from the change in a moving object's geospatial position
> > between the start and end of the time interval associated with the
> > displacement variable.
> >
> > direction_of_sea_ice_displacement; degrees
> > 'Displacement' means the change in geospatial position of an object
> > that
> > has moved over time. If possible, the time interval over which the
> > motion took place should be specified using a bounds variable for
the
> > time coordinate variable. A displacement can be represented as a
> > vector. Such a vector should however not be interpreted as
describing
> > a
> > rectilinear, constant speed motion but merely as an indication that
> > the
> > start point of the vector is found at the tip of the vector after
the
> > time interval associated with the displacement variable. A
> > displacement
> > does not prescribe a trajectory. Sea ice displacement can be defined
> > as
> > a two-dimensional vector, with no vertical component.
> > "direction_of_X"
> > means direction of a vector, a bearing. The
> > 'direction of displacement' is the angle between due north and the
> > displacement vector.
> >
> > However, you also raised a number of questions which could affect
the
> > final form of the names and I've tried to address these below.
> >
> > > My displacement is nothing more that a
> > 'change_over_time_in_geoposition'. Is there actually a quantity X
for
> > 'geoposition' (which would be lat/lon)?> I saw that there was a
> > reference to 'position' in
> > magnitude_of_derivative_of_position_wrt_model_level_number where it
> is
> > a
> > 3D position.
> > > Displacements can be 3D so 'displacement' is maybe nothing more
> than
> > a
> > 'change_over_time_in_position', with 'position' being a 3D point. I
> > do
> > not
> > > know if we will win anything in recognizing the aliasing but it
> > might
> > help understanding how to build the standard_name as well as the
time
> > bounds
> > > thing. Plus, I did not find the definition of what
> > 'change_over_y_in_x' describes but it is clear that we cannot use it
> > for
> > displacement if the
> > > 'change' is intended as being 'continuous', like dx/dy = constant
> > for
> > all y.
> >
> > There is no standard name for 'geoposition'. Indeed, recently there
> > was
> > a discussion thread entitled "standard name for position" (see
> > http://mailman.cgd.ucar.edu/pipermail/cf-metadata/2009/003011.html
> > and
> > followups) in which this same issue arose. The general conclusion
> > was
> > that "position" or "geoposition" is already given by the values of
> > variables with the standard names "latitude" and "longitude" and
> > there
> > was not a strong case for introducing a separate name for the
> > combination of coordinates.
> >
> > 'Change_over_y_in_x' currently only appears in standard names for
the
> > case where y is time, but I dare say it could be defined for other
> > situations if it became necessary. 'Change_over_time_in_X' is
> > defined
> > as 'change in a quantity X over a time-interval, which should be
> > defined
> > by the bounds of the time coordinate' and doesn't impose any
> > condition
> > about the change being continuous. However, if we were to change to
> > your
> > alternative suggestion of 'change_over_time_in_position', rather
than
> > 'displacement', I think your names actually become more difficult to
> > express. For example, initially I considered that
> > eastward_sea_ice_displacement might become
> > change_over_time_in_sea_ice_longitude, but that would have units of
> > degrees instead of metres which isn't what you are after. If we
used
> > something like change_over_time_in_sea_ice_eastward_position I think
> > that it still isn't obviously a quantity in metres (although
> > change_over_time_in_sea_ice_x|y_position might be OK for
> > displacements
> > on your map projection). I think the point is that we need to get
> > across the idea of moving through a distance measured in units of
> > length, rather than a change in coordinate with its associated
units,
> > and 'displacement' is a concise way of doing that.
> >
> > Names such as eastward_sea_ice_displacement are consistent with
> > existing
> > names like eastward_sea_ice_velocity and names proposed for the
CMIP5
> > model data, such as eastward_sea_ice_transport, which I think is
> > another
> > argument for sticking with the names we had agreed.
> >
> > Importantly, I don't think the choice of standard name for the
> > displacements really affects your treatment of the time coordinate
> > variable and time bounds, which is really a separate question. For
> > this
> > and all the other reasons, I think we should stick with the agreed
> > names.
> >
> > >
> > > I would however like to discuss here the time bounds thing and see
> > if
> > > someone can help me
> > > understanding how/if I can apply the concept to my data model.
> > >
> > > I think we agree that :
> > > 1) the time interval is crucial for the displacement variable to
be
> > > interpreted;
> > > 2) that time bounds is the current implementation of an interval.
> If
> > I
> > > want CF compliance, I should
> > > live with this fact.
> > >
> >
> > I note that you have sought further discussion of the time
coordinate
> > and time_bounds question in the "Cell bounds associated with
> > coordinate
> > variable rather than data variable" thread, so I have not discussed
> > it
> > further here. I think discussing the issues separately is probably
> > the
> > best way to proceed.
> >
> > Best wishes,
> > Alison
> >
> > ------
> > Alison Pamment Tel: +44 1235 778065
> > NCAS/British Atmospheric Data Centre Fax: +44 1235 446314
> > Rutherford Appleton Laboratory Email:
> > alison.pamment at stfc.ac.uk
> > Chilton, Didcot, OX11 0QX, U.K.
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