Thread: work around for constant = 0 in pole zeros?

Started: 2013-10-21 12:00:22
Last activity: 2013-10-21 21:32:22
Topics: SAC Help
Januka Attanayake
2013-10-21 12:00:22
Hi, 
I am just wondering how I should handle instrument response deconvolution when the constant is set to zero in pole zeroes files? Is there a standard practice in this case? 

Thanks !

Januka.
 _______________
Serenity isn't freedom from the storm, but peace within the storm

Januka Attanayake
Postdoctoral Research Associate
Laboratório de Sismologia
Departamento de Física

Instituto Superior Técnico
Av. Rovisco Pais, 1

1049-001 Lisboa, Portugal 

University email: januka.attanayake<at>ist.utl.pt
Home page: http://sites.google.com/site/janukaattanayake/
  • Sheila Peacock
    2013-10-21 21:32:22
    Dear Januka,

    If the poles are not all zero then you know the
    instrument frequency response but not its absolute
    scale. You need the calibration factor of your
    system (seismometer + digitiser), which should be
    on (or derivable from) the manufacturer's data sheet.

    Unfortunately you also have to work out the normalisation
    factor of the poles-and-zeros. It's the ratio
    polynomial of the complex poles / polynomial
    of the complex zeros, at the calibration frequency (i.e. the
    signal frequency at which the calibration factor
    was measured - should also be in the manufacturer's
    data sheet). Fortran or Matlab could be used.
    Scherbaum's book, "of poles and zeros", describes this,
    and there is a brief mention of it in the appendix of
    the SEED manual.

    Dividing this normalisation factor by the
    calibration factor (in nm/count or nm/s/count depending
    on whether your Ps and Zs are in displacement or velocity domain)
    gives you the constant to put
    with your poles-and-zeros before using the SAC
    "transfer" command.

    If you don't know the calibration factor or you can't work out
    the normalisation factor then setting the constant to
    one should allow "transfer" to run and give you a
    seismogram corrected for the frequency response of the
    instrument, but the units on the output seismogram will be
    arbitrary and no use for magnitude calculations or making
    into hodograms in combination with other seismograms.



    Regards,
    Sheila Peacock.



    • Januka Attanayake
      2013-10-21 14:06:21
      Thanks Sheila, it sounds like a doable calculation.

      Januka.
       
      _______________
      Serenity isn't freedom from the storm, but peace within the storm

      Januka Attanayake
      Postdoctoral Research Associate
      Laboratório de Sismologia
      Departamento de Física

      Instituto Superior Técnico
      Av. Rovisco Pais, 1

      1049-001 Lisboa, Portugal 

      University email: januka.attanayake<at>ist.utl.pt
      Home page: http://sites.google.com/site/janukaattanayake/








      On Monday, October 21, 2013 2:33 PM, Sheila Peacock <sheila<at>blacknest.gov.uk> wrote:

      Dear Januka,

      If the poles are not all zero then you know the
      instrument frequency response but not its absolute
      scale.  You need the calibration factor of your
      system (seismometer + digitiser), which should be
      on (or derivable from) the manufacturer's data sheet.

      Unfortunately you also have to work out the normalisation
      factor of the poles-and-zeros.  It's the ratio
      polynomial of the complex poles / polynomial
      of the complex zeros, at the calibration frequency (i.e. the
      signal frequency at which the calibration factor
      was measured - should also be in the manufacturer's
      data sheet).  Fortran or Matlab could be used.
      Scherbaum's book, "of poles and zeros", describes this,
      and there is a brief mention of it in the appendix of
      the SEED manual.

      Dividing this normalisation factor by the
      calibration factor (in nm/count or nm/s/count depending
      on whether your Ps and Zs are in displacement or velocity domain)
      gives you the constant to put
      with your poles-and-zeros before using the SAC
      "transfer" command.

      If you don't know the calibration factor or you can't work out
      the normalisation factor then setting the constant to
      one should allow "transfer" to run and give you a
      seismogram corrected for the frequency response of the
      instrument, but the units on the output seismogram will be
      arbitrary and no use for magnitude calculations or making
      into hodograms in combination with other seismograms.



      Regards,
      Sheila Peacock.
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