Thread: Instrument response removal

Started: 2011-05-07 00:01:01
Last activity: 2011-05-07 00:01:01
Topics: SAC Help
Ivan
2011-05-07 00:01:01
Dear Colleague,

I hope that I am at the right address to launch my question.
I was using SAC polezero option recently to remove the instrument
response from my data and to add it to synthetics.
However, I realized that this option is acting as a 2-pass acausal
filter. AS the actual seismometer filters the ground motion as 1-pass
causal filter, it seems to me that it is impossible to recover actual
ground motion by using this option.
It is not very obvious with very band limited data, but it is more than
obvious for the data with static shift, where the waveform is changed
before time 0 (which is impossible for any physical device including
seismometer).
Do you maybe know if there's any option in SAC that will add/remove
instrument's response as of the actual physical device (causally)?

Thank you in advance for your answer
A great job is done with all the manuals and software. Thanks for that

Kind regards,

Ivan

--
______________________________________________
Ivan Lokmer
Seismology and Computational Rock Physics Lab.
Geophysics Group
School of Geological Sciences
University College Dublin
Belfield
Dublin 4
Ireland

Phone: +353 1 7162079
Fax: +353 1 2837733
Mobile:+353 87 2553638
_____________________________


  • Arthur Snoke
    2011-05-06 22:11:51
    This is the correct address. However, I cannot follow the logic in your
    message so (for me at least) you need to provide more information.

    By construction, a pole-zero file is causal. However, if you include with
    that step a "freqlimits" call, that call is not causal. The number of
    poles for a p-z file depends on whether you are correcting to
    displacement, velocity, etc. If your data came from a SEED volume, the
    RESP file makes clear what the correction is for.

    For use to help, you need to provide more information. If you have not
    already, I suggest you look at the transfer help file:
    http://www.iris.edu/software/sac/commands/transfer.html.

    On Fri, 6 May 2011, Ivan Lokmer wrote:

    Dear Colleague,

    I hope that I am at the right address to launch my question.
    I was using SAC polezero option recently to remove the instrument response
    from my data and to add it to synthetics.
    However, I realized that this option is acting as a 2-pass acausal filter. AS
    the actual seismometer filters the ground motion as 1-pass causal filter, it
    seems to me that it is impossible to recover actual ground motion by using
    this option.
    It is not very obvious with very band limited data, but it is more than
    obvious for the data with static shift, where the waveform is changed before
    time 0 (which is impossible for any physical device including seismometer).
    Do you maybe know if there's any option in SAC that will add/remove
    instrument's response as of the actual physical device (causally)?

    Thank you in advance for your answer
    A great job is done with all the manuals and software. Thanks for that

    Kind regards,

    Ivan

    --
    ______________________________________________
    Ivan Lokmer
    Seismology and Computational Rock Physics Lab.
    Geophysics Group School of Geological Sciences
    University College Dublin
    Belfield
    Dublin 4
    Ireland

    Phone: +353 1 7162079
    Fax: +353 1 2837733
    Mobile:+353 87 2553638

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