SUMMARY

Writes spectral files to disk as "normal" data files.

SYNTAX

WRITESP {type} {COMMIT|ROLLBACK|RECALLTRACE} {OVER|filelist}

where type is one of the following:

ASIS|RLIM|AMPH|RL|IM|AM|PH

INPUT

ASIS:	Write components in their present format.
RLIM:	Write real and imaginary components.
AMPH:	Write amplitude and phase components.
RL:	Write real component only.
IM:	Write imaginary component only.
AM:	Write amplitude component only.
PH:	Write phase component only.
COMMIT:	Commits headers and waveforms in SAC memory -- removing any previous versions of headers or waveforms from RAM -- prior to writing files. COMMIT is the default.
ROLLBACK:	reverts to the last committed version of the header and waveform before writing files.
RECALLTRACE:	reverts to the last committed version of the waveform, reverts to the last committed version of those header variables closely linked to the waveform, commits those header variables which are loosely linked to the waveform. (use HELP RECALLTRACE for a list of which header variables are committed, and which are rolled back.)
filelis:	A list of SAC binary data files. This list may contain simple filenames and full or relative pathnames.

DEFAULT VALUES

WRITESP ASIS COMMIT

DESCRIPTION

SAC data files may contain either time-series data or spectral data. Certain fields in the header distinguish between the two formats. When you read (see READ) a time-series file into memory, take the fast fourier transform (see FFT), and write the data to disk (see WRITE), then the data on disk will be in the spectral format.

Certain operations can only be performed on time-series data and certain operations only on spectral data. For example, you can't apply a taper to spectral data files or multiply two spectral files together. This is a protection mechanism built into SAC.

Sometimes, however, you may need to perform some of these operations on spectral data. To override SAC's protection mechanism, you can use this command to write spectral data to disk as time-series data. Each component is written as a separate data file. You may then read these files back into SAC and perform any operation that you wish, since SAC thinks they are time series data files. Once these calculations are completed, you may write the modified data back to disk using the WRITE command. If you wish to reconstruct the spectral data file, use the READSP command. To help you keep track of the data on disk, SAC appends a suffix to the filename you request that identifies the spectral component stored in that file. The suffixes are ".RL", ".IM", ".AM", and ".PH"" for the real component, imaginary component, amplitude, and phase respectively.

EXAMPLES

Assume that you want to perform some operations on the spectral amplitude of FILE1:

SAC> READ FILE1
SAC> FFT AMPH
SAC> WRITESP OVER

SAC will then write out two files, FILE1.AM and FILE1.PH. Now you perform the operations on the amplitude file:

SAC> READ FILE1.AM
SAC> ...perform operations.
SAC> WRITE OVER

Now the files on disk represent the modified spectral data. If you wanted to reconstruct the SAC spectral data file and take the inverse transform:

SAC> READSP FILE1
SAC> IFFT
SAC> WRITE FILE2

Note for examples of the behavior of COMMIT, ROLLBACK, and RECALLTRACE, see the commands of the same name.

ERROR MESSAGES

• 1301: No data files read in.
• 1305: Illegal operation on time series file

HEADER CHANGES

B, E, and DELTA for the files on disk will contain the beginning, ending, and incremental frequency in Hz.

SEE COMMANDS

READSP, COMMIT, ROLLBACK, RECALLTRACE

LATEST REVISION

Oct. 27, 1998 (Version 0.58)