Spectrum files, input and output

This appendix described the format of the files for spectral input (command BOUNdspec) and output (commands SPECout and NESTout) by SWAN. The files are recognized by SWAN or another reading program by the presence of the keyword SWAN and a version number on the first line of the file. This description is valid for version number 1.

These files contain the following information:

Note that the true variance or energy densities are obtained by multiplying each number by the factor given under the keyword FACTOR.

Formal description of the 1D- and 2D-spectral file

This description refers to either write or read energy/variance density spectra to or from the file.

The description of the file to write or read source terms is identical to this description except that the quantities obviously differ.

The format that is used by SWAN or should be used by the user when offering the file to SWAN is free format (FORTRAN convention) except that all keywords and names of quantities (see below) should start on the first position of the line on which they appear (see Appendix B for the syntax of keywords). This format implies that all information on each line after the required input for SWAN is ignored by SWAN. This can be used to enter user's information at the discretion of the user.

First line	the keyword SWAN followed by version number
Then	if nonstationary computation: the keyword TIME
	if stationary computation: not present
Then	if nonstationary computation: time coding option; ISO-notation (=1) is recommended
	if stationary computation: not present
Then	$\bullet$ the description of the locations:
	if Cartesian coordinates: the keyword LOCATIONS
	if spherical coordinates: the keyword LONLAT
	$\bullet$ number of locations
	$\bullet$ for each location
	if Cartesian coordinates: and coordinate (in m, problem coordinates)
	if spherical coordinates: longitude and latitude
	Note that if the file is used for input for SWAN (but not generated by
	SWAN) and the user so desires, the names of locations can be written
	behind the two coordinates; these names are ignored by SWAN when
	reading the file (see remark on format above).
Then	the frequency data (for 1D- and 2D-spectra):
	$\bullet$ the keyword AFREQ or RFREQ (to distinguish between absolute and relative frequencies)
	$\bullet$ number of frequencies
	$\bullet$ a column with frequencies always in Hz (each on a new line)
Then	the direction data (only for 2D-spectra):
	$\bullet$ the keyword NDIR or CDIR (to distinguish between nautical and Cartesian direction)
	$\bullet$ number of directions
	$\bullet$ a column with directions always in degrees (each on a new line)
Then	the group describing the quantities in the tables of this file (see the above examples):
	$\bullet$ the keyword QUANT
	$\bullet$ number of quantities
	for each quantity
	$\bullet$ name of the quantity
	$\bullet$ unit of the quantity
	$\bullet$ exception value of the quantity, i.e. the value that is written
	instead of a computed value if that is undefined
	Note for 1D spectra:
	the number of quantities is always 3, and the quantities are always: energy
	(or variance) density, average direction (CDIR for Cartesian direction or
	NDIR for nautical direction) and directional spreading (DSPR in terms of
	DEGREES (SWAN write the keyword DSPRDEGR, SWAN reads the keyword
	DSPRD or DEGR in case of option DEGREES or the keywords DSPRP or POWER
	in case of option POWER in command BOUND SHAPE). The quantities appear
	in the order in which they appear in this description.
	Note for 2D spectra:
	the number of quantities is always 1; the quantity is always energy or
	variance density (EnDens is the (short) name of true energy densities,
	VaDens for variance densities).
Then	the group with the tables of the quantities:
VVV	$\bullet$ date and time (not present for stationary computation)
	for each location:
	if 2D spectrum:
	$\bullet$ the keyword FACTOR. This keyword is replaced by the keyword ZERO
	if the spectrum is identical 0 or it is replaced by NODATA if the
	spectrum is undefined (not computed e.g., on land; no numbers follow)
	$\bullet$ the factor to multiply the values in the following table
	$\bullet$ scaled energy/variance densities (truncated by SWAN to integer values
	for compact writing; SWAN accepts these values as reals when reading
	this file; other programs (e.g. for postprocessing) should also accept these
	values as reals; the values should be multiplied by the factor to get the
	proper values of the densities).
	else, if 1D spectrum:
	$\bullet$ the keyword LOCATION followed by the index of the location (on the
	same line). This is replaced by the keyword NODATA if the spectrum is
	undefined (not computed e.g. on land; no numbers follow).
	$\bullet$ a table containing three columns: the 3 quantities per frequency:
	energy (or variance) density, average direction (CDIR for Cartesian
	direction and NDIR for nautical direction) and directional spreading
	(DSPR in terms of DEGREES (writing or reading the file) or POWER
	(only reading the file), see note for 1D spectra above); the quantities
	appear in the order in which they appear in this description.