Thread: Clarification on SAC transfer function

Started: 2018-08-09 20:55:05
Last activity: 2018-08-10 13:51:04
Topics: SAC Help
Phillips-Alonge, Kristin E CIV DTRA R AND D (US
2018-08-09 20:55:05
Hello,

I have some IRIS data converted to SAC format along with the corresponding polezero files and want to use "transfer" along with the pzfiles to perform the deconvolution to remove instrument response. I know that the SAC transfer function is expecting a displacement input. If I am using "TRANS FROM POLEZERO S %pzfile to NONE" or "TRANS FROM POLEZERO S %pzfile to VEL" and my input actually is a displacement, I expect the output to be the displacement for the first command and velocity for the latter command. However if my input is actually proportional to velocity rather than displacement as expected by the transfer function, does the "TRANS FROM POLEZERO S %pzfile to NONE" actually give me velocity? Thanks for any clarification

Kris

  • Milton Plasencia
    2018-08-10 06:50:31
    Hi,

    See inline answers.

    HTH,

    Milton


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    On Thu, 9 Aug 2018 at 15:58, Phillips-Alonge, Kristin E CIV DTRA R AND D
    (US <kristin.e.phillips-alonge.civ<at>mail.mil> wrote:

    Hello,

    I have some IRIS data converted to SAC format along with the corresponding
    polezero files and want to use "transfer" along with the pzfiles to perform
    the deconvolution to remove instrument response.



    I know that the SAC transfer function is expecting a displacement input.

    Why?, I think it is not correct, sac transfer function "look" in the poles
    and zeros files,
    during the conversion (response files to P&Z, the P&Z files have add an
    extra Zero), so
    is not necessary to specify TO NONE it is default value.
    So if you have a velocimeter you give to sac transfer function counts/m/s
    I you have accelerometer you give counts/m2/s (P&Z will have two zeros
    extra)

    If I am using "TRANS FROM POLEZERO S %pzfile to NONE"

    "to none" means output in displacement ( your P&Z file have an zero extra )

    or "TRANS FROM POLEZERO S %pzfile to VEL"

    here the output is velocity obviously ( sac remove ( not use) the zero
    extra in P&Z file)

    and my input actually is a displacement,



    I expect the output to be the displacement for the first command and
    velocity for the latter command.

    This is correct for me if you give counts/m/s as input

    However if my input is actually proportional to velocity rather than
    displacement as expected by the transfer function, does the "TRANS FROM
    POLEZERO S %pzfile to NONE" actually give me velocity?

    No, "TO NONE" give you displacement, and this output is used to calculate
    magnitude...

    Give a look I the transfer command,
    SAC> help transfer

    And check old e-mails in the list about transfer command.


    Thanks for any clarification

    Kris

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  • Geo .
    2018-08-10 13:51:04
    Hello Kris,
    Your input time series should be in counts, not displacement, not velocity.
    If your input trace is velocity or displacement, there is no need to use
    Transfer in the first place.

    Januka

    On Thursday, 9 August 2018, Phillips-Alonge, Kristin E CIV DTRA R AND D (US
    <kristin.e.phillips-alonge.civ<at>mail.mil> wrote:

    Hello,

    I have some IRIS data converted to SAC format along with the corresponding
    polezero files and want to use "transfer" along with the pzfiles to perform
    the deconvolution to remove instrument response. I know that the SAC
    transfer function is expecting a displacement input. If I am using "TRANS
    FROM POLEZERO S %pzfile to NONE" or "TRANS FROM POLEZERO S %pzfile to VEL"
    and my input actually is a displacement, I expect the output to be the
    displacement for the first command and velocity for the latter command.
    However if my input is actually proportional to velocity rather than
    displacement as expected by the transfer function, does the "TRANS FROM
    POLEZERO S %pzfile to NONE" actually give me velocity? Thanks for any
    clarification

    Kris

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