Thread: How to remove the instrument response?

Started: 2009-02-11 22:44:38
Last activity: 2009-02-17 00:32:46
Topics: SAC Help
Mohamed Kamaleldin Abdel Galeil Salah
How to remove the instrument response?
2009-02-11 22:44:38
Hi all,

I have some BB SAC files for a sensor CMG-40TD (Guralp systems) and I
want to remove the instrument response from the seismogram.
I prepared a file ´pz´'as follows:
ZEROS 4
0 0
0 159

POLES 3
-50.0 0.0
-0.02356 + j0.02356
-0.02356 - j0.02356

CONSTANT -0.314

I have two questions:

1. Is such data ok for the instrument type given above?
2. when I run the command: transfer from polezero subtype pz to none,
from within SAC, I get the following message:

Extracting polezero response for MTE , BHZ...

Station (MTE ), Channel (BHZ)
Calper is not available. Cannot tell if response is normalized, so
transfer function will be used without scaling.
Calib is not available. Cannot tell if scale factor has been applied
on input, so transfer function will be used without scaling.
Waveform multiplied by 1.000000 after deconvolution.

How I can fix this error?

Thanks



  • Sheila Peacock
    Re: How to remove the instrument response?
    2009-02-16 18:12:40
    Dear Mohammed,

    Guralp data sheets list the poles and zeros in units of Hz, not radians,
    and usually for velocity or acceleration as appropriate for the instrument
    (see the details on the actual data sheet).
    For use in SAC you have to convert them to displacement in radians i.e. x2pi, then
    add one zero at (0,0) if they are in velocity or two if they are in acceleration.

    Regards,
    Sheila



    • Onur Tan
      Re: How to remove the instrument response?
      2009-02-17 00:32:46

      Dear Mohammed,

      You must also calculate the CONSTANT from the Guralp's A0 value .
      Read this:
      www.le.ac.uk/seis-uk/downloads/seisuk_data_manage.pdf

      best regards
      Onur Tan

      Dr. Onur TAN |------------------------------------------------------------
      ------------- |
      | TÜBİTAK Marmara Araştırma Merkezi | TUBITAK Marmara Research Center |
      | Yer ve Deniz Bilimleri Enstitüsü | Earth and Marine Sciences Institute |
      | Gebze - Kocaeli | Gebze - Kocaeli - TURKEY |
      --------------------------------------------------------------------------


      -----Original Message-----
      From: sac-help-bounces<at>iris.washington.edu [sac-help-bounces<at>iris.washington.edu] On Behalf Of Sheila Peacock
      Sent: Monday, February 16, 2009 12:13 PM
      To: Mohamed Kamaleldin Abdel Galeil Salah
      Cc: sac-help<at>iris.washington.edu
      Subject: Re: [SAC-HELP] How to remove the instrument response?

      Dear Mohammed,

      Guralp data sheets list the poles and zeros in units of Hz, not radians, and usually for velocity or acceleration as appropriate for the instrument (see the details on the actual data sheet).
      For use in SAC you have to convert them to displacement in radians i.e. x2pi, then add one zero at (0,0) if they are in velocity or two if they are in acceleration.

      Regards,
      Sheila


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