Thread: remove instrument response

SAC treats any polezero file as though it were a transfer function between counts and displacement, so using one prepared for use in SAC by an external source will not be changed by putting “to gel” in the transfer line. In order to get el or acc from transfer with a from polezero option one must alter the number of zeros in the numerator of the poolezero file.

The from evalresp call in transfer, which uses a RESP file produced by RDSEED, will change response depending on to gel or to acc etc. SAC’s implementation of EVALRESP also corrects the units from the rest of the world’s m or m/s to nm or nm/s. The polezero option does not.

Milton gives good advice on choosing FREQLIMITS. For fine-tuning, I compare spectra for a desired waveform with the noise window before it with the same length and filtering.

These questions come up a lot on sac-help, and we have revised the TRANSFER help file to try to clarify these issues. It will come out in the revised manual with the next SAC update, but attached is a copy.

On Sep 14, 2016, at 12:36 AM, Milton Plasencia <mplasencia<at>inogs.it> wrote:

Hi

see below,

M.
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Milton P. PLASENCIA LINARES

Centro di Ricerche Sismologiche (CRS)
OGS - Istituto Nazionale di Oceanografia e di Geofisica Sperimentale

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On Sep 14, 2016, at 01:45, kejie <whuckj<at>gmail.com <whuckj<at>gmail.com>> wrote:

To whom it may concern:

I just downloaded SAC and SACPZ file from IRIS Wilber. What I want is ground motion velocity during earthquake times, So I run the following:

r sacfilename
rmean
taper
transfer from polezero subtype PZfile to vel freqlimits 0.001 0.002 40 50

My question is:

Is the result unit m/s?

YES

How should I determine the freqlimits? In the further step, I am also going to do a band passing for the velocity time series.

Freqlimits must be choice depending the frequency band of your instrument.
In your case you assume a band of 1000 to 0.02 seconds, it seems not realistic, but i do not know instrument with 1000 sec of period.
so, assuming you have an instrument from 100 s to 50 Hz , the freqlimits should be 0.01 0.02 40 45 for example.

HTH,

Milton

All the best!

Kejie