Thread: a polezero question

Started: 2009-04-30 18:24:54
Last activity: 2009-04-30 18:24:54
Topics: SAC Help
Arthur Snoke
2009-04-30 18:24:54
In preparing an update for the polezero section of the transfer help page,
I decided to try it (I use polezero files, but not within SAC). I found
that the sample given in the current help message does not work, and would
appreciate comments from those who have used it (successfully).

Also, the documentation claims that the search will look for a polezero
file in ${SACHOME}/polezero/. I tried that, but it did not work.

The sample given is

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

Because the displacement response for any seismometer I have worked with
is zero at zero frequencies, the polezero transfer function is zero at
zero frequency. Taking out an instrument means dividing by the transfer
function in the frequency domain, so the above expression will either blow
up or just give an output waveform that is a sinusoid at the fundamental
frequency.

I got results that compared well with my home-grown method within the
passband of interest by using the line

transfer from polezero subtype M06C.pz to NONE FREQ 0.001 0.007 0.1 0.2

The seismometer is an STS-2 and is the BHZ channel at 40 sps. I had
already used decimate (three times) to reduce the sampling rate to 1 sps.

I typically run the equivalent to SAC rtr before doing the instrument
correction. Should that be included in the sample?

I then moved M06C.pz to my ${SACAUX}/polezero directory, I got the
following:

SAC> transfer from polezero subtype M06C.pz to NONE FREQ 0.001 0.007 0.1
0.2 ERROR 108: File does not exist:
SAC> ls /usr/local/sac/aux/polezero
M06C.pz llsn
SAC>

If it does not work as advertised, we should either remove the polezero
subdirectory or make it work. Comments?

Arthur Snoke

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