Thread: SAC help

Started: 2016-04-27 20:50:17
Last activity: 2016-04-28 13:21:38
Topics: SAC Help
Abhash Kumar
2016-04-27 20:50:17
Hi,
I am using SAC transfer function to correct for the instrument response
as shown below:

SAC> r 2012.159.22.19.00.0195.IU.RSSD.10.BHZ.M.SAC

SAC> rmean

SAC> trans from evalresp fname RESP.IU.RSSD.10.BHZ to vel freqlimits 1 3 10
20

SAC> w 2012.159.22.19.00.0195.IU.RSSD.10.BHZ.M.corrected.SAC


I made an overlapping plot (waveform comparison.png) for the raw data and
instrument response corrected data. The amplitude of instrument corrected
data is exceptionally small. I was wondering if this is due to the wrong
frequency limits I used in the transfer function. As per the SAC manual, I
chose f4=20 (nyquist frequency for sampling interval of 40 samples/sec),
f3=10 (f4/2). I would be extremely grateful if someone can suggest me the
correct values for f1, f2, f3, and f4 based on the sampling interval (40
samples/second) and instrument type (Streckeisen STS-2 high gain).


Thanks

Abhash Kumar

  • Milton Plasencia
    2016-04-28 13:21:38
    Abhash,

    I think the freqlimits 1 3 10 20 is not happy,
    1 3 filtered important part of content freq. of your signal
    20 is correct, but looking the response freq. plot is better to use 15 Hz,
    to stay in the flat part of response curve, see the arrow.


    So, my result using freqlimits 0.1 0.4 10 15
    i applied the pole zero file instead the resp file, but it is not important here.
    The high gain of instrument (~20000) adds to make a difference in amplitude.



    Cheers,

    Milton

    On Apr 27, 2016, at 22:22, Abhash Kumar <abhash.kumar84<at>gmail.com> wrote:

    Hi,
    I am using SAC transfer function to correct for the instrument response
    as shown below:

    SAC> r 2012.159.22.19.00.0195.IU.RSSD.10.BHZ.M.SAC

    SAC> rmean

    SAC> trans from evalresp fname RESP.IU.RSSD.10.BHZ to vel freqlimits 1 3 10
    20

    SAC> w 2012.159.22.19.00.0195.IU.RSSD.10.BHZ.M.corrected.SAC


    I made an overlapping plot (waveform comparison.png) for the raw data and
    instrument response corrected data. The amplitude of instrument corrected
    data is exceptionally small. I was wondering if this is due to the wrong
    frequency limits I used in the transfer function. As per the SAC manual, I
    chose f4=20 (nyquist frequency for sampling interval of 40 samples/sec),
    f3=10 (f4/2). I would be extremely grateful if someone can suggest me the
    correct values for f1, f2, f3, and f4 based on the sampling interval (40
    samples/second) and instrument type (Streckeisen STS-2 high gain).


    Thanks

    Abhash Kumar
    <Waveform comparison.png><2012.159.22.19.00.0195.IU.RSSD.10.BHZ.M.SAC><2012.159.22.19.00.0195.IU.RSSD.10.BHZ.M..SAC><RESP.IU.RSSD.10.BHZ>
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