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: [email protected] Chilton, Didcot, OX11 0QX, U.K. > -----Original Message----- > From: [email protected] [mailto:cf-metadata- > [email protected]] On Behalf Of Thomas Lavergne > Sent: 18 November 2009 16:34 > Cc: [email protected] > 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" <[email protected]> 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: > > [email protected] > > Chilton, Didcot, OX11 0QX, U.K. > > -- > > Scanned by iCritical. > > _______________________________________________ > > CF-metadata mailing list > > [email protected] > > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata > _______________________________________________ > CF-metadata mailing list > [email protected] > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata -- Scanned by iCritical. _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
