Thread: polezero option

Started: 2009-04-24 21:36:39
Last activity: 2009-04-24 21:36:39
Topics: SAC Help
Arthur Snoke
2009-04-24 21:36:39
We are preparing the next update for SAC, and I have been looking at some
"help" files called from within SAC (and in the computer accessible
manual), and have changed a few. Because there were several e-mail
exchanges regarding the polezero option of transfer, I looked closely at

SAC> help transfer

I am attaching my first draft for a replacement of that section of the
transfer help command. Please share comments/corrections, etc.

Others I have already worked on are 04graphics, 09file_format,
begindevices, enddevices.

If there are others you think need updating, please share. It is more
likely they will be included if you send me a suggested revision!

Finally, I have written a C program for doing endian swapping for .sgf
files (SAC Graphics Format files). I have tested it on several platforms,
but if someone would like to try it -- or just want an advance copy -- let
me know.

Arthur Snoke
snoke<at>vt.edu
SAC Command Reference Manual TRANSFER

SUMMARY:
Performs deconvolution to remove an instrument response and convolution to
apply another instrument response.

SYNTAX:
TRANSFER {FROM type {options}} , {TO type {options}} ,
{FREQLIMITS f1 f2 f2 f4} , {PREWHITENING ON|OFF|n}

INPUT:
FROM type : Remove the instrument type by deconvolution.
The allowed instrument types and their options
are listed in a table below.

TO type : Insert the instrument type by convolution.
The allowed instrument types and their options
are listed in a table below.

FREQLIMITS f1 f2 f3 f4 : This is a low- and high-pass taper that can
be used to filter the spectrum. f1 and f2 specify the high-pass
filter and corresponds to the frequencies over which the taper is
applied. The taper is zero below f1 and unity above f2. f3 and f4
specify the low-pass filter and correspond to the frequencies over
which the taper is applied. The taper is unity below f3 and zero
above f4. The defaults provide no tapering for any realistic
seismic signal. Note that the filter applied by TRANSFER is
acausal. If it is important to preserve the character of signal
onsets, you may want to use the default values for FREQLIMITS and
filter the output signal using a single-pass filter of your design.

PREWHITENING {ON} : Turn on prewhitening in the time domain before
spectral operations, and compensating dewhitening in the time
domain after spectral operations. Initially, the option is off.
If the user turns it on without specifying the order, it will
default to 6, unless the order has been changed in the WHITEN
command.

PREWHITENING OFF : Turn off prewhitening.

PREWHITENING n : Turn on prewhitening and change the prewhitening
order to n.

Available instrument types:
*ACC acceleration
BBDISP Blacknest specification of Broadband Displacement
BBVEL Blacknest specification of Broadband Velocity
BENBOG Blacknest specification of Benioff by Bogert
**DBASE search database for applicable file: EVALRESP, POLEZERO, or FAP
Note: In order to use the DBASE type, the user must have access
to an Oracle database with links to the applicable files,
the database must be formatted as described below,
and the user must have the Oracle version of sac2000.
DSS LLNL Digital Seismic System
DWWSSN Digital World Wide Standard Seismograph Station
EKALP6 Blacknest specification of EKA LP6
EKASP2 Blacknest specification of EKA SP2
ELMAG Electromagnetic
**EVALRESP EVRESP code by Thomas J. McSweeney
**FAPFILE reads Frequency, Amplitude, Phase file
GBALP Blacknest specification of GBA LP
GBASP Blacknest specification of GBA SP
GENERAL General seismometer
GSREF USGS Refraction
HFSLPWB Blacknest specification of HFS LPWB
IW EYEOMG-spectral differentiation
LLL LLL broadband analog seismometer
LLSN LLSN L-4 seismometer
LNN Livermore NTS Network instrument
LRSMLP Blacknest specification of LRSM LP
LRSMSP Blacknest specification of LRSM SP
*NONE displacement, this is the default
NORESS NORESS (NRSA)
NORESSHF NORESS high frequency element
OLDBB Old Blacknest specification of BB
OLDKIR Old Blacknest specification of Kirnos
**POLEZERO reads Pole Zero file
PORTABLE Portable seismometer with PDR2
PTBLLP Blacknest specification of PTBL LP
REDKIR Blacknest specification of RED Kirnos
REFTEK Reftek 97-01 portable instrument
RSTN Regional Seismic Test Network
S750 S750 Seismometer
SANDIA Sandia system 23 instrument
SANDIA3 Sandia new system with SL-210
SRO Seismic Research Observatory
*VEL velocity
WA Wood-Anderson
WABN Blacknest specification of Wood-Anderson
WIECH Wiechert seismometer
WWLPBN Blacknest specification of WWSSN long period
WWSP WWSSN short period
WWSPBN Blacknest specification of WWSSN short period
YKALP Blacknest specification of YKA long period
YKASP Blacknest specification of YKA short period

*Note: ACC, VEL, and NONE do not refer to actual seismometer specifications
but to acceloration, velocity, and displacement respectively.
When these are specified as the TO type, IDEP is set accordingly.

**Note: DBASE, EVALRESP, FAPFILE, and POLEZERO do not refer to actual
seismometer specifications. They are described in greater detail
below.

options : A set of zero or more of the following depending upon the
specific instrument type:
SUBTYPE subtype
the following types use the following subtypes:
FAP: name of file to be read
LLL: LV, LR, LT, MV, MR, MT, EV, ER, ET, KV, KR, KT
LNN: BB, HF
NORESS: LP, IP, SP
POLEZERO: name of file to be read
RSTN: [CP, ON, NTR, NY, SD][KL, KM, KS, 7S][Z, N, E]
SANDIA: [N, O][T, L, B, D, N, E][V, R, T]
SRO: BB, SP, LPDE
FREEPERIOD v
the following types use FREEPERIOD:
ELMAG, GENERAL, IW, LLL SUBTYPE BB, REFTEK
(v must be 15.0 or 30.0 for ELMAG)
MAGNIFICATION n
the following types use MAGNIFICATION:
ELMAG, GENERAL
(n must be 375, 750, 1500, 3000, or 6000 for ELMAG)
NZEROS n
the following types use NZEROS:
GENERAL, IW
DAMPING v
the following types use DAMPING:
GENERAL, LLL SUBTYPE BB, REFTEK
CORNER v
the following types use CORNER:
LLL SUBTYPE BB, REFTEK
GAIN v
HIGHPASS v
the following types use HIGHPASS:
REFTEK

The following options are used with the EVRESP option.
FNAME filename
STATION sta
CHANNEL chan
NETWORK ntwk
DATE date
TIME time


DEFAULT VALUES:
TRANSFER FROM NONE TO NONE FREQUENCY -2. -1. 1.E5 1.E6

DESCRIPTION:
This command can be used to alter the instrument response of seismic data.
It is a modification of the program TRANSFER developed by Keith Nakanishi. A
frequency domain deconvolution by spectral division is used to remove an
instrument response, and a frequency domain convolution by spectral
multiplication is used to insert a new instrument response.

Most of the implementation is done using double-precision (64-bit) arithmetic.
If the FROM instrument type is NONE, then no instrument is removed, and the
original trace is presumed to be a displacement. This is useful for adding
instrument responses to synthetic seismograms. If TO type is NONE, then no
instrument is inserted.

Many of the instruments have options which further specify the response.
The most common of these options is the instrument subtype. A few instruments
require that certain numerical parameters be specified, and do not use the
subtype option. For a list of instruments, and a list of the instruments
that use subtypes or other parameters, see the tables below.

Optional frequency domain cosine tapering can be used to select a
bandlimited response. Optional prewhitening can also be used to flatten the
spectrum of the input time series before transforming in the frequency domain.
This should reduce the dynamic range of the spectral values, and improve the
accuracy of the overall operation at high frequencies for seismic data.

The header field SCALE is set to 1.0, to prevent redundant scaling.

Unless other units are expected for a given instrument, the TRANSFER's
returned values will be in nanometers (or nm/sec, or nm/sec/sec, etc). When
the EVRESP option is used, the values are conveted to nm before they are
returned to the user.
In versions 58 and 58a-58e, there was an inconsistency; values were
being returned in nm except in the case of EVALRESP, which returned the
values in meters. In addition, the NANO option was provided which, when
turned on, would multiply the values by 1e09 before returning. This option
had the effect of converting meters to nm, but the uninteded consequence
was that it converted nm to something much much smaller. In version 59,
this inconsistancy has been removed, and so has the NANO option.

EXAMPLES:
To remove the instrument response from the RSTN station NYKM.Z and
apply the instrument response for DSS without pre- whitening:

u: READ NYKM.Z

u: TRANS FROM RSTN SUBTYPE NYKM.Z TO DSS PREW OFF

To remove the LLL broadband instrument response and apply the SRO instrument
response with frequency tapering and prewhitening:

u: READ ABC.Z

u: TRANS FROM LLL TO SRO FREQ .02 .05 1. 2. PREW 2

The passband of the resulting trace will be flat from .05 Hz to 1 Hz and will
be zero below .02 Hz and above 2 Hz. Prewhitening of order 2 is applied in
the time domain before deconvolution and the effect is removed in the time
domain after convolution.
To transfer from the electromagnetic instrument response to
displacement:

u: READ XYZ.Z

u: TRANSFER FROM ELMAG FREEP 15. MAG 750. TO NONE



POLEZERO OPTION:
One of the instrument types is called POLEZERO. This option uses the
Omega (Omega\) convention. This type lets you describe a general instrument
response by specifying a file which contains its poles and zeros. The options
in the file are keyword driven and the numbers are in free format. You may
specify a multiplicative scaling constant by putting a line in the file
containing the keyword "CONSTANT" followed by a floating point number. The
default for this constant is 1.0 if you omit this line. You specify the
number of poles by putting a line in the file with the keyword "POLES"
following by an integer number. The next lines in the file until another
keyword is read become the poles for this instrument. Each such line contains
two floating point numbers specifying the real and imaginary parts of one of
the poles. If you have fewer lines specifying poles than you stated on the
"POLES" line, the remaining poles are assumed to lie at the origin. You
specify the zeros in the same way with a "ZEROS" keyword line following by
lines specifying the zeros that do not lie at the origin. You may specify up
to 15 poles and 15 zeros. For example, the following is the specification for
the SRO broadband seismometer:

ZEROS 4

-0.125 0.0

-50.0 0.0

POLES 4

-0.13 0.0

-6.02 0.0

-8.66 0.0

-35.2 0.0

CONSTANT -394.0

Notice that since two of the zeros are at the origin, they don't have to be
specified in the file. Also notice that the options may appear in any order
in the file.
To use this option you specify the type to be POLEZERO and the subtype
to be the name of the file. This may be a file in the current directory or in
some other directory if you specify the absolute or relative pathname. It may
also the the name of a global file contained in the "polezero" subdirectory
of the "sacaux" directory. By putting a file in this global directory, anyone
on your system can easily use it. Nakanishi, K., "Computer code for the
transfer function of seismic systems", Lawrence Livermore National Lab.,
UCID-18071, 1979.

EXAMPLE: suppose the file was named sro.pz and you want to remove the instrument
response from station ABC.Z.

u: READ ABC.Z

u: TRANSFER FROM POLEZERO SUBTYPE SRO.PZ TO NONE


EVALRESP OPTION:
This option enables the application of transfer functions extracted from
SEED data volumes using the evresp code (Version 3.2.x) by Thomas J.
McSweeney or rdseed (Version 4.1.x). The RESP files must be
in the current directory or must be specified by full path and name.

To identify the correct RESP file and to extract the proper transfer function
from that file, EVALRESP uses information from the SAC headers. The
fields are station (KSTNM), channel (KCMPNM), date and time (KZDATE & KZTIME),
network (KNETWK), and location ID.

Location ID is refered to as LOCID; it distinguishes between multiple
seismometers with the same station and channel names, operating at the
same time. Data received from IRIS in SAC format (or converted to SAC
with RDSEED) will have KHOLE set to a valid LOCID if one is necessary.
If the user is informed of real LOCIDs in the EVALRESP file, the user
can set KHOLE with CH (HELP CH for details). SAC will use KHOLE as
LOCID if it is a two character alpha-numeric string (padded with spaces
or not). At the present time (7/19/2000), LOCID is useful in a small
number of cases.

It is possible to override the header values by specifying additional options
to EVALRESP. The possible options are:

STATION
CHANNEL
NETWORK
DATE
TIME
LOCID
FNAME

and each option must be followed by an appropriate value. If DATE is not set
in the header and is not specified as an option, then the current date is used
in the search. If TIME is not set in the seismogram header and is not
specified as an option, then the current system time is used in the search. If
network is not specified, then the search for a transfer function defaults to
use any network. If LOCID is not set at the command line or in KHOLE, then
the search for the transfer function defaults to use any LOCID. If TYPE is
not specified and is not set in the seismogram header then a velocity transfer
function is computed. To force TRANSFER to use a specific SEED response file
use the FNAME option followed by the filename.




EXAMPLES:
To remove the instrument response from the seismogram in memory (assuming
a response file exists):

u: TRANSFER FROM EVALRESP

To remove the instrument response from 16.42.05.5120.TS.PAS.BHZ.SAC
and apply the response from station COL, channel BHZ for the same time period:

u: r 16.42.05.5120.TS.PAS.BHZ.SAC
u: TRANSFER FROM EVALRESP TO EVALRESP STATION COL

To plot the instrument response in units of displacement for station COL,
channel BHZ, network IU, for the date 1992/02 and time 16:42:05:

u: funcgen impulse npts 16384 delta .05 begin 0
u: transfer to evalresp station COL channel BHZ network IU type DIS date &
1992/2 time 16:42:05
u: fft
u: psp am
(NOTE: the & only indicates a continued line in the documentation.)

To remove the instrument response from 16.42.05.5120.TS.PAS.BHZ.SAC
using a response contained in file /tmp/Responses/RESP.TS.PAS.BHZ:

u: r 16.42.05.5120.TS.PAS.BHZ.SAC
u: TRANSFER FROM EVALRESP FNAME /tmp/Responses/RESP.TS.PAS.BHZ TO NONE



DBASE OPTION:
Note: In order to use the DBASE type, the user must have access
to an Oracle database with links to the applicable files,
the database must be formatted as described below,
and the user must have the Oracle version of sac2000.

This option enables the deconvolution of transfer functions extracted from SEED
response files using the evresp Version 3.2.6 code by Thomas J. McSweeney.
The response files are assumed to have been extracted from SEED (VERSION 4.1.x),
and the locations of the appropriate files must be stored in an accessible
Oracle database using the INSTRUMENT and SENSOR tables of the CSS 3.0 schema.
(See help for the READDB command for more information on the database
requirements.) Fields which must be set are:
instrument.inid
instrument.dir
instrument.dfile
instrument.rsptype
sensor.sta
sensor.chan
sensor.time
sensor.endtime
sensor.inid

The instrument.rsptype fields must contain the string 'evresp' and the remaining
fields must be set as appropriate to join and point to the correct dir and dfile
given the correct station, channel, and time. The DBASE option can only be used
after the keyword FROM. In other words, TRANSFER FROM DBASE is OK but
TRANSFER TO DBASE is not. If the database query is unsuccessful, TRANSFER will
attempt to find an appropriate response file in the current directory. If that
fails, the seismogram is not modified.


FAPFILE OPTION:
This option is similar to the POLEZERO option, but instead reads a Frequency -
Amplitude - Phase (FAP) file in the standard format used at the Center for
Monitoring Research (pIDC). A (partial) example of such a file is shown below.

#
# Displacement response for Array
#
# Example: ST01 z
#
# Geotech 23900 seismometer
#
# Phase unwrapped
#
theoretical 0 instrument fap Organization
40
0.100000 1.576582e-01 -52.923801 0.000000 0.000000
0.125990 3.511520e-01 -61.669102 0.000000 0.000000
0.200000 1.634426e+00 -79.966599 0.000000 0.000000
0.368400 1.171214e+01 -107.522003 0.000000 0.000000
0.500000 3.135000e+01 -126.447998 0.000000 0.000000
0.683990 8.322500e+01 -155.035004 0.000000 0.000000
0.800000 1.273452e+02 -174.207001 0.000000 0.000000

In this format, lines starting with a "#" sign are comments.
The line: theoretical 0 instrument fap Organization is ignored
by SAC.

The next line ("40") is the number of fap lines to follow.
The remaining lines are frequency, amplitude, phase,
amplitude error, and phase error.

The error columns are not used by SAC, but must be present in order for
the file to be parsed correctly.


EXAMPLE: suppose the fap file was named ABC.PAZ and you want to remove
the instrument response from station ABC.Z.

u: READ ABC.Z

u: TRANSFER FROM FAPFILE SUBTYPE ABC.PAZ TO NONE


SEE COMMANDS:
WHITEN


ACKNOWLEDGEMENTS: Roger Hanscom did the original conversion of Keith
Nakanishi's TRANSFER program. George Randall added the prewhitening option
and was a major contributor to the testing and documentation of this command.

LATEST REVISION:
May 06, 1998 (Version 00.57)

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