Dear Bert The new quantities you want to name deserve standard names, I agree.
> * thickness_of_sediment_layers_below_sea_floor Is below_sea_floor necessary in this name? If the aim is to indicate what sediment you mean, would thickness_of_sea_floor_sediment_layer be OK? > * mass_content_of_sediment_fraction_in_sediment_layer > * volume_fraction_of_sediment_fraction_in_sediment_layer sediment_fraction_of_sediment_layer sounds odd to me. Isn't it 100%? Perhaps it means solid_fraction_of_sediment_layer? In using mass_content you are following other standard names, I know, but it might not be clear what it means, and I wonder if mass_per_unit_area might be better, which is also in use. Could "layer" be omitted from the volume_fraction? - it's an intensive quantity, not dependent on layer thickness. Should these names also have sea_floor in them? > * soil_porosity It's OK to reuse this if it's exactly what you mean, but if sediment is not soil, you could propose a new name. Your suggestion for formula_terms isn't what this attribute is intended for, I would say. Its aim is to indicate how parametric vertical coordinates are converted into dimensional geolocated ones. I understand your need, to compute the bottom of the layer from the layer thicknesses and the vertical coordinate of the sea floor, but I wonder whether a CF convention is required. Are there other similar use-cases which would make this a more general need? Best wishes Jonathan ----- Forwarded message from Bert Jagers <bert.jag...@deltares.nl> ----- > Date: Sun, 1 Nov 2015 09:46:04 +0000 > From: Bert Jagers <bert.jag...@deltares.nl> > To: CF Metadata Mail List <cf-metadata@cgd.ucar.edu> > Subject: [CF-metadata] standard names and vertical coordinate for bed > stratigraphy / sediment layers > > Dear all, > > We are trying to capture bed stratigraphy in a CF compliant NetCDF file. What > do I mean by bed stratigraphy? Well, if you start digging in the ground you > will come across sediment layers with different properties - that layering is > referred to as bed stratigraphy. For biochemical models we may be interested > in representing layers of just a few mm thick (to capture transitions been > oxygen based chemistry to nitrate or sulfur based chemistry) while for > coastal/estuarine/river morphodynamic studies the modeled layers would > typically be 0-50 cm thick. On the other end of the spectrum we do studies to > capture the long-term build-up of bed stratigraphy for future oil and gas > reservoirs and then layers may be even thicker. See for instance the > white-yellow-red-black colors representing the sand/clay ratio in this figure: > https://www.deltares.nl/app/uploads/2015/09/Morphology-and-stratigraphy-in-a-numerical-analogue-735x389.png > > For the time being we can assume the number of layers fixed, but the > thickness and properties of layers and vertical position of the layers varies > over time due to processes such as erosion and deposition, consolidation, and > bioturbation. With a significant number of layers included in the model and a > fair number of output times to capture the processes responsible for the > development of the bed stratigraphy, storage efficiency is important. For > this reason I'm trying to avoid the classic CF route of storing a vertical > position for each layer center plus for each layer the upper and lower bound > which duplicates a lot of vertical information. Our proposal is to introduce > a quantity with the following standard name: > > * thickness_of_sediment_layers_below_sea_floor > This would typically be a NTIME x NCELLS x NLAYERS array (where NCELLS could > be 1-dimensional for an unstructured grid or 2-dimensional, i.e. IMAX x JMAX, > for a structured grid model) representing the the thickness of the NLAYERS > sediment layers. By the way please note that the administration of layers is > in general carried independently per computational cell, so layer k of cell > j1 does not need to be connected to layer k of neighboring cell j2. We would > also like to use this array as auxiliary vertical coordinate in a way similar > to the dimensionless vertical coordinates. The addition "below_sea_floor" > hints at this second purpose. We would like to reuse the formula_terms > attribute of the dimensionless vertical coordinates here: > > float DZSED(NTIME, NCELLS, NLAYERS) ; > DZSED:long_name = "thickness of modelled sediment layers" ; > DZSED:standard_name = "thickness_of_sediment_layers_below_sea_floor" ; > DZSED:formula_terms = "zref: BL thick: DZSED lyrdim: NLAYERS" > > where > - zref would point to a variable "sea_floor_depth_below_geoid" or an altitude > equivalent thereof since we can't differentiate between the altitude of the > sea floor, the river bed, or the flood plains and the latter ones are > commonly stored positive upward. > - thick refers to the thickness variable itself. > - lyrdim refers to the dimension associated with the layers; we need this > since contrary to the dimensionless vertical coordinates this auxiliary > vertical coordinate will typically have multiple dimensions. > > The vertical position of the top of layer k would then be computed as > > z(n,ji,k) = zref(n,ji) - sum(thick(n,ji,lyrdim), lyrdim = 1:k-1) > > and the bottom of the layer would be located at: > > z(n,ji,k) = zref(n,ji) - sum(thick(n,ji,lyrdim), lyrdim = 1:k) > > where n represents the typical time dimension and ji reprent one or two > horizontal dimensions. Note that this formula assumes that lyrdim = 1 > corresponds to the top layer. We don't specify a specific formula for the > representative center of the layer; it's a location that we don't use. > > Associated with each layer we aim to store quantities such as: > > * mass_content_of_sediment_fraction_in_sediment_layer > Typically a NTIME x NCELLS x NLAYERS x NFRAC array containing the mass per > unit area per sediment fraction per layer per time step stored (unit kg/m2). > > and optionally: > > * volume_fraction_of_sediment_fraction_in_sediment_layer > "Volume fraction" is used in the construction volume_fraction_of_X_in_Y, > where X is a material constituent of Y. Typically a NTIME x NCELLS x NLAYERS > x NFRAC array containing the volume fraction per sediment fraction per layer > per time step stored (unit 1). The dimension representing the number of > sediment fractions NFRAC may include multiple model dependent gravel, sand, > silt, clay fractions, so we need to generalize beyond the scope of the > currently existing standard names of > volume_fraction_of_clay/sand/silt_in_soil. > > * soil_porosity > The soil porosity is the proportion of its total volume not occupied by soil > solids. This is an existing standard_name which most likely can be reused. > > The last two items link to already existing CF standard names based on the > word "soil". Since we typically focus only on the physical processes of > sediment transport, we usually refer to the layers as sediment_layers, but it > might be okay to generalize the above to soil_layers. > > We are starting with the in-house implementation now, but the code will start > to be spread more widely early next year. So, I'm looking forward to your > feedback and hope to make good progress on the storage convention. > > Best regards, > > Bert > DISCLAIMER: This message is intended exclusively for the addressee(s) and may > contain confidential and privileged information. If you are not the intended > recipient please notify the sender immediately and destroy this message. > Unauthorized use, disclosure or copying of this message is strictly > prohibited. The foundation 'Stichting Deltares', which has its seat at Delft, > The Netherlands, Commercial Registration Number 41146461, is not liable in > any way whatsoever for consequences and/or damages resulting from the > improper, incomplete and untimely dispatch, receipt and/or content of this > e-mail. > _______________________________________________ > CF-metadata mailing list > CF-metadata@cgd.ucar.edu > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata ----- End forwarded message ----- _______________________________________________ CF-metadata mailing list CF-metadata@cgd.ucar.edu http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
