Thread: instrument response removal syntax.

Started: 2014-03-31 06:00:26
Last activity: 2014-04-01 02:58:42
Topics: SAC Help
Martha Savage
2014-03-31 06:00:26
Dear Sac users,

Sorry for adding more questions on instrument response. We have been trying to do instrument response removal and have had the following concern:

I was hoping you might be able to clarify an issue I'm having with the SAC TRANSFER function. In this example, I will use a polezero file, but I found the same problem with response files. My objective is to go from a velocity time series record to a velocity time series record with a removed instrument response.

There are two syntax for removing in instrument response.
Syntax 1:
transfer from polezero subtype $polezerofile to vel freqlimits 0.001 0.002 40 50

Syntax 2:
transfer from vel subtype $polezerofile to vel freqlimits 0.001 0.002 40 50

In some cases, it appears that Syntax 1 interprets the input file as a displacement file, and integrates the result in order to go to velocity. For other response or polezero files, both Syntax 1 and Syntax 2 give the same result. Attached is an example with a small data file. "test_data" is the original data, and "test_pz_transfer1.sac" and "test_pz_transfer2.sac" is the data after the instrument response is removed using Syntax 1 and 2 respectively. Prior to removing the instrument response, the data is detrended and cosine tapered (1%).

Can anyone clarify the difference between using these two syntax? What is causing them to have such different outputs?

Thanks,
-Francesco Civilini
Martha Savage
Professor of Geophysics
SGEES
Victoria University of Wellington
Te Whare Wananga o te Upoko o te Ika a Maui
Temporary office: MY 1114
Box 600, Wellington, 6140
New Zealand

Email: Martha.Savage<at>vuw.ac.nz
DDI: +64 (0)4 463-5961
mobile: 021-262-7516


Attachments
  • George Helffrich
    2014-04-01 01:22:36
    Dear Francesto/Martha -

    A quick answer without looking at the data:- The SUBTYPE option for the VEL instrument type is ignored -- thus it has no meaning in syntax(2). Syntax (1) is what you want.

    What the variable functionality means is that your instrument response (in the cases that it works, and for the data with which it works) may be obtained by simple division/multiplication in the frequency domain by omega (a zero at f=0 in the frequency domain).

    On 31 Mar 2014, at 00:00, Martha Savage wrote:

    Dear Sac users,

    Sorry for adding more questions on instrument response. We have been trying to do instrument response removal and have had the following concern:

    I was hoping you might be able to clarify an issue I'm having with the SAC TRANSFER function. In this example, I will use a polezero file, but I found the same problem with response files. My objective is to go from a velocity time series record to a velocity time series record with a removed instrument response.

    There are two syntax for removing in instrument response.
    Syntax 1:
    transfer from polezero subtype $polezerofile to vel freqlimits 0.001 0.002 40 50

    Syntax 2:
    transfer from vel subtype $polezerofile to vel freqlimits 0.001 0.002 40 50

    In some cases, it appears that Syntax 1 interprets the input file as a displacement file, and integrates the result in order to go to velocity. For other response or polezero files, both Syntax 1 and Syntax 2 give the same result. Attached is an example with a small data file. "test_data" is the original data, and "test_pz_transfer1.sac" and "test_pz_transfer2.sac" is the data after the instrument response is removed using Syntax 1 and 2 respectively. Prior to removing the instrument response, the data is detrended and cosine tapered (1%).

    Can anyone clarify the difference between using these two syntax? What is causing them to have such different outputs?

    Thanks,
    -Francesco Civilini
    Martha Savage
    Professor of Geophysics
    SGEES
    Victoria University of Wellington
    Te Whare Wananga o te Upoko o te Ika a Maui
    Temporary office: MY 1114
    Box 600, Wellington, 6140
    New Zealand

    Email: Martha.Savage<at>vuw.ac.nz
    DDI: +64 (0)4 463-5961
    mobile: 021-262-7516

    <test_evalresp.tar.gz>_______________________________________________
    sac-help mailing list
    sac-help<at>iris.washington.edu
    http://www.iris.washington.edu/mailman/listinfo/sac-help



    George Helffrich
    george.helffrich<at>bris.ac.uk



  • Milton Plasencia
    2014-04-01 02:58:42
    Hi Francesco/Martha

    I see your data, so:
    sac pz files add a zero to response to obtain displacement after transfer command,
    and if you want velocity at end, you have different ways:

    1) r sac_file, rmean, transfer from polezero subtype ./polezero_file to none freqlimits 0.001 0.002 40 50
    and you have displacement, then you can use the dif command to obtain velocity.

    2) r sac file, rmean, transfer from polezero subtype ./polezero_file to vel freqlimits 0.001 0.002 40 50
    and obtain velocity.

    3) Edit the polezero file, change zeros 3 to zeros 2.
    r sac file, rmean, transfer from polezero subtype ./polezero_file to none freqlimits 0.001 0.002 40 50
    and obtain again velocity.

    I attach the results:

    1)




    2)




    3)

    Here, the three results are equals,

    HTH,

    Milton P. Plasencia Linares
    mpplasencia<at>gmail.com



    On Mar 31, 2014, at 1:00 AM, Martha Savage <Martha.Savage<at>vuw.ac.nz> wrote:

    Dear Sac users,

    Sorry for adding more questions on instrument response. We have been trying to do instrument response removal and have had the following concern:

    I was hoping you might be able to clarify an issue I'm having with the SAC TRANSFER function. In this example, I will use a polezero file, but I found the same problem with response files. My objective is to go from a velocity time series record to a velocity time series record with a removed instrument response.

    There are two syntax for removing in instrument response.
    Syntax 1:
    transfer from polezero subtype $polezerofile to vel freqlimits 0.001 0.002 40 50

    Syntax 2:
    transfer from vel subtype $polezerofile to vel freqlimits 0.001 0.002 40 50

    In some cases, it appears that Syntax 1 interprets the input file as a displacement file, and integrates the result in order to go to velocity. For other response or polezero files, both Syntax 1 and Syntax 2 give the same result. Attached is an example with a small data file. "test_data" is the original data, and "test_pz_transfer1.sac" and "test_pz_transfer2.sac" is the data after the instrument response is removed using Syntax 1 and 2 respectively. Prior to removing the instrument response, the data is detrended and cosine tapered (1%).

    Can anyone clarify the difference between using these two syntax? What is causing them to have such different outputs?

    Thanks,
    -Francesco Civilini
    Martha Savage
    Professor of Geophysics
    SGEES
    Victoria University of Wellington
    Te Whare Wananga o te Upoko o te Ika a Maui
    Temporary office: MY 1114
    Box 600, Wellington, 6140
    New Zealand

    Email: Martha.Savage<at>vuw.ac.nz
    DDI: +64 (0)4 463-5961
    mobile: 021-262-7516

    <test_evalresp.tar.gz>_______________________________________________
    sac-help mailing list
    sac-help<at>iris.washington.edu
    http://www.iris.washington.edu/mailman/listinfo/sac-help


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