Thread: Removing Instrument Response

Started: 2016-05-12 13:30:50
Last activity: 2016-05-12 23:00:53
Topics: SAC Help
Narendra Pandey
2016-05-12 13:30:50
Hello,
I am trying to remove instrument correction from seismogram (downloaded through Wilber) using TRANSFER command. But, I am not able to figure out the units. In SAC file the units are given in displacement by default, but the response file units are generally reported in velocity units.
How the transfer command handle these units in FROM & TO options?

Thank you.
Narendra
  • Geo .
    2016-05-12 23:00:53
    Hi,
    Usually, in the rawest form (like the data you download from Wilbur), SAC
    files are in counts, and not displacement. TRANSFER is used to convert
    counts to displacement, velocity, or acceleration. The SAC manual is very
    clear about FROM/TO function.

    "The default input and output "instrument" in TRANSFER is displacement,
    which in SAC is designated as NONE. Hence, if a FROM type or a TO type is
    not specified, SAC assumes it to be NONE. If the output instrument is NONE,
    IDEP in the SAC header is set to DISPLACEMENT (NM). For the seismometers
    listed in the table below, the output units for TO NONE will be in nm,
    SAC's choice for displacement. If TRANSFER has TO VEL or TO ACC, the header
    variable IDEP is changed accordingly for all waveforms in memory."

    If your SAC files are already displacement before applying TRANSFER, based
    on the above, you set FROM NONE, which implies that your data do not
    contain the instrument response to begin with.

    Unless you are reading the headers wrong, here's what I would do to remove
    the instrument response assuming that you have downloaded data as seed
    volumes and that you have extracted response files using rdseed.

    Output: displacement
    TRANSFER FROM EVALRESP FNAME your_response_filename TO NONE FREQ f1 f2 f3 f4

    If you have extracted pole-zeros files instead of response files, then
    TRANSFER FROM POLEZERO SUBTYPE your_pole-zeros_filename TO NONE FREQ f1 f2
    f3 f4

    Where, f1, f2, f3, and f4 are frequencies (See SAC manual)

    Januka.


    Januka Attanayake
    Postdoctoral Research Associate

    Institut für Geophysik
    Westfälische Wilhelms - Universität Münster
    CorrensstraBe 24
    48149 Münster
    Germany

    University email: jattanayake<at>uni-muenster.de
    Homepage: http://sites.google.com/site/janukaattanayake/

    On 12 May 2016 at 15:30, Narendra Pandey <nkpiitr<at>gmail.com> wrote:

    Hello,
    I am trying to remove instrument correction from seismogram (downloaded
    through Wilber) using TRANSFER command. But, I am not able to figure out
    the units. In SAC file the units are given in displacement by default, but
    the response file units are generally reported in velocity units.
    How the transfer command handle these units in FROM & TO options?

    Thank you.
    Narendra

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