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Please find on this page a deprecated proposal for netCDF output from the spectral wave model SWAN. In the mean time netCDF has been implemented in the SWAN trunk, in a collaboration between Deltares (on behalf or Rijkswaterstaat), BMT Argoss, and TU Delft using somewhat different names (see routine agioncmd.f90). We adopted this page a bit to match the final implementation. There is also a Matlab routine in OpenEarthTools to convert ASCII spectral files into netCDF. Elements from the SWAN input file are here refered to by INPUT*, whereas elements from the SWAN Fortran code swanmain.for are referred to by OV*IVTYPE.

SWAN netCDF-CF CDL scheme

 // A working draft proposal for CF compliance for netCDF output for SWAN
NetCDF SWAN.nc {

// proposal for CF and SWAN meta data in SWAN

dimensions:
	time      = 1; // time:		also put time in for single times
	mx        = 2; // yx:		(mxc+1) for 2D grids
	my        = 3; // xc:		(myc+1) for 2D grids
	direction = 4; // nd: (mdc+1) directions, now called nf90_def_dim
	frequency = 5; // ms: (msc+1) frequencies
	points    = 6; // points:	for 1D grids, for UNSTRUC and for squeezed [mx by my] grids

variables:
// dimensions consistent with ncBrowse, not with native MATLAB netcdf package.
// ----------------- COORDINATES -----------------
// Options:
// * like SWAN use same variable for CARTESIAN and SPHERICAL, but change attributes
// * use different variables for CARTESIAN and SPHERICAL, but change attributes
// if INPUT.CGRID.REGular
	double mx(mx) ;
		mx(mx):swan_xpc     = // INPUT value: optional for input, implemented in output
		mx(mx):swan_xlenc   = // INPUT value: optional for input, implemented in output
		mx(mx):swan_alpc    = // INPUT value: optional for input, implemented in output
		mx(mx):swan_comment = "mxc+1"
		mx(mx):_FillValue   = // INPUT.CGRID.xexc or OVEXCV{IVTYPE}
		mx:actual_range     = [~ ~]
		// if INPUT.CGRID.CARTESIAN
		mx:standard_name    = "projected_x_coordinate"
		mx:units            = "m"
		mx(mx):grid_mapping = "projected_coordinate_system"
		// elseif INPUT.CGRID.SPHERICAL
		mx:standard_name    = "longitude"
		mx:units            = "degrees_east"
		mx(mx):grid_mapping = "wgs84"
		// end
		...
	double my(my) ;
		my(my):swan_ypc     = // INPUT value: optional for input, implemented in output
		my(my):swan_ylenc   = // INPUT value: optional for input, implemented in output
		my(my):swan_alpc    = // INPUT value: optional for input, implemented in output
		my(my):swan_comment = "myc+1"
		my(my):_FillValue   = // INPUT.CGRID.yexc or OVEXCV{IVTYPE}
		my:actual_range     = [~ ~]
		// if INPUT.CGRID.CARTESIAN
		my:standard_name    = "projected_y_coordinate"
		my:units            = "m"
		my(my):grid_mapping = "projected_coordinate_system"
		// elseif INPUT.CGRID.SPHERICAL
		my:standard_name    = "latitude"
		my:units            = "degrees_north"
		my(my):grid_mapping = "wgs84"
		// end
		...
// - - - - - - - - - - - - - - - - - - - - - - - - - - -
// elseif INPUT.CGRID.CURVilinear
	double XP(xc,yc) ;
		// idem
		...
	double YP(xc,yc) ;
		// idem
		...
// - - - - - - - - - - - - - - - - - - - - - - - - - - -
// elseif INPUT.CGRID.UNSTRUCtured
	double x(points) ;
		// idem
		...
	double YyP(points) ;
		// idem
		...
// end
// ----------------- DIRECTIONS -----------------
	double spread_1d(md) ;
		spread_1d:standard_name    = ""
		spread_1d:units            = "degrees_true"
		spread_1d:standard_name    = "sea_surface_wave_from_direction" // sea_surface_wave_to_direction
		spread_1d:nautical         = 1 // or 0
        spread_1d.dir1             = // INPUT value: optional for input, implemented in output
		spread_1d.dir2             = // INPUT value: optional for input, implemented in output
		spread_1d:swan_comment     = "mdc+1"
		...
// ----------------- FREQUENCY -----------------
	double frequency(ms) ;
		frequency:standard_name    = "wave_frequency"
		frequency:long_name        = "frequencies" // absolute vs relative, see attribute 'relative_to_current' of energy
		frequency:units            = "s-1"
		frequency.swan_flow        = // INPUT value: optional for input, implemented in output
		frequency.swan_fhigh       = // INPUT value: optional for input, implemented in output
		frequency:swan_comment     = "msc+1"
		...
// ----------------- COORDINATE SYSTEMS -----------------
// The projected_coordinate_system information could optionally be added to
// either SWAN input or in a post-processing step.
// if INPUT.CGRID.CARTESIAN
//	int32 projected_coordinate_system() ;
//		projected_coordinate_system:name = "Amersfoort / RD New"
//		projected_coordinate_system:epsg = 28992
//		projected_coordinate_system:epsg_name = "Oblique Stereographic"
//		projected_coordinate_system:grid_mapping_name = " "
//		projected_coordinate_system:semi_major_axis = 6.3774e+006
//		projected_coordinate_system:semi_minor_axis = 6.35608e+006
//		projected_coordinate_system:inverse_flattening = 299.153
//		projected_coordinate_system:latitude_of_projection_origin = 52.0922
//		projected_coordinate_system:longitude_of_projection_origin = 5.23155
//		projected_coordinate_system:false_easting = 155000
//		projected_coordinate_system:false_northing = 463000
//		projected_coordinate_system:scale_factor_at_projection_origin = 0.999908
//                // optional PROJ4 REQUIRED FOR ADAGUC.KNMI.NL
//		projected_coordinate_system:proj4_params = "+proj=sterea +lat_0=52.15616055555555 +lon_0=5.38763888888889 +k=0.999908 +x_0=155000 +y_0=463000 +ellps=bessel +units=m +towgs84=565.4174,50.3319,465.5542,-0.398957388243134,0.343987817378283,-1.87740163998045,4.0725 +no_defs"
//		projected_coordinate_system:EPSG_code = "EPSG:28992"
//		projected_coordinate_system:projection_name = "Dutch rijksdriekhoek system"
// - - - - - - - - - - - - - - - - - - - - - - - - - - -
// elseif INPUT.CGRID.SPHERICAL
// The (lat,lon) coordinates information could be hard-coded into SWAN
// with each of the options: CCM, QC or REPEATING
		int32 wgs84() ;
		wgs84:name = "WGS 84"
		wgs84:epsg = 4326
		wgs84:grid_mapping_name = "latitude_longitude"
		wgs84:semi_major_axis = 6.37814e+006
		wgs84:semi_minor_axis = 6.35675e+006
		wgs84:inverse_flattening = 298.257
                // optional PROJ4 REQUIRED FOR ADAGUC.KNMI.NL
		wgs84:proj4_params = "+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs "
		wgs84:EPSG_code = "EPSG:4326"
		wgs84:projection_name = "Latitude Longitude"
		wgs84:wkt = "GEOGCS["WGS 84",...
// end
// ----------------- PRIMARY VARIABLES -----------------
	single density(), shape = [~ ~] // density_1d for 1D, density for 2D
		density:relative_to_current   = 0 // or 1, depending on respectively. AFREQ vs RFREQ
		density:swan_code             =            // OVKEYW{IVTYPE} = 'VaDens';
		density:swan_name             =            // OVSNAM{IVTYPE} = 'VaDens';
		density:long_name             =            // OVLNAM{IVTYPE} = 'spectral variance density';
		density:swan_units            =            // OVUNIT{IVTYPE} = 'm2/Hz';
		density:valid_range(1)        =            // OVLEXP{IVTYPE} = 0.;
		density:valid_range(2)        =            // OVHEXP{IVTYPE} = 100.;
		density:_FillValue            =            // OVEXCV{IVTYPE} = -99.;
// - - - - - - - - - - - - - - - - - - - - - - - - - - -
		density:units                 =            // OVCFUD{IVTYPE} = ''; NEW TABLE NEEDED INSIDE SWAN
		density:standard_name         =            // OVCFSN{IVTYPE} = ''; NEW TABLE NEEDED INSIDE SWAN
		// these do not need to be mapped         // OVSVTY{IVTYPE} = 5;     // means vector, scalar etc.
		// these do not need to be mapped         // OVLLIM{IVTYPE} = 0.;    // print width for ascii output
		// these do not need to be mapped         // OVULIM{IVTYPE} = 1000.; // print width for ascii output
// - - - - - - - - - - - - - - - - - - - - - - - - - - -
		density:actual_range          = [~ ~]      // add optionally as extra service to user
		density:coordinates           = "XP YP"    //
		// if INPUT.CGRID.CARTESIAN
		density():grid_mapping        = "projected_coordinate_system"
		// elseif INPUT.CGRID.SPHERICAL
		density():grid_mapping        = "wgs84"
		// end
// ----------------- GLOBAL META_DATA -----------------
//global Attributes:
		:title = "INPUT.PROJECT.name,INPUT.PROJECT.nr"
		:institution = ""
		:source = ""
		:history = "Data produced by SWAN version 40.72AB"
		:references = ""
		:email = ""
		:comment = "INPUT.PROJECT.title1,INPUT.PROJECT.title2,INPUT.PROJECT.title3"
		:version = ""
		:Conventions = "CF-1.5"
		:CF:featureType = "Grid"
		:terms_of_use = "These data can be used freely for research purposes provided that the following source is acknowledged: institution"
		:disclaimer = "This data is made available in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE."
}
  

Mapping of SWAN names to CF standard names

SWAN Standard names

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2 Comments

  1. We are looking to store observed spectral wave data in NetCDF, and this looks pretty good!

    Has there been any evolution of this standard? 

    Is it being used?

    Would you recommend a modified version of this for observation spectral wave data (e.g. from a wave buoy)?

    Thanks,

    Rich

    1. Recenty SWAN has been extended to produce netCDF-CF (SWAN 40.91AB, http://swanmodel.sourceforge.net/). The SWAN netCDF eventually became somewhat different than the proposal in this wiki. I will update this wiki in the near future to reflect the latest SWAN netCDF-CF developments.

      The netCDF code in SWAN is a seperate netCDF-wave library from BMT Argoss (http://www.bmtargoss.com) that they developed initially for WAVEWATCHII, so netCDF files of SWAN and WAVEWATCHII are now fully identical. Deltares (on behalf of our government: Rijkswaterstaat) and BMT Argoss have an ongoing collaboration to make this netCDF-wave library even better CF compliant. Please contact us for that yet unpublished version. Merging that improved version with the official SWAN release from TU Delft is still under debate.