Thread: Interpolate

Started: 2014-11-10 12:03:23
Last activity: 2014-11-10 18:20:48
Topics: SAC Help
Hamidatul Husna Matondang
2014-11-10 12:03:23
Dear Sir

I have a local event recorded by 4 stations that have different sampling frequencies, are 20 Hz and 25 Hz.Therefore I set a new sampling rate to uniform sampling frequency. Previously I checked the maximum frequency signals are recorded by the stations, the maximum frequencies are12 Hz. Then, I decided to choose 25 Hz, given that the minimum sampling frequency is twice the maximum frequency recorded by the station. In this case, I think the seismometers with a sampling frequency of 20 Hz should been covered. Then, I did command "interpolate delta 0.04". FurthermoreI did deconvolution using a response file which got from rdseed, with command "transfer from evalresp fname "response file" to none freq 0025 12:05 10 20". But the result was aliasing signal at the station that originally had a sampling rate of 0.05. Is there a connection with the contents of the RESPfile of the aliasing ? Could anyone please help me solving this problem?
Thank You

Regards,
Ami
  • Suzan van der Lee
    2014-11-10 18:20:48
    Amik,
    The maximum frequency of a signal that you can record (the Nyquist Frequency) is *half* that of the sampling frequency.
    For example, for a station that samples at 20 Hz, the maximum frequency to which you can analyze your signal is 10 Hz.
    You may of course interpolate to 25 Hz but that doesn’t change the Nyquist frequency of the instruments passband.
    Regardles of how much you interpolate, you cannot analyze any signals above 10 Hz for a station that samples at 20 Hz.
    Suzan

    Begin forwarded message:

    From: amik Amik <amik.mamat<at>yahoo.co.id>
    Subject: [SAC-HELP] Interpolate
    Date: November 9, 2014 at 9:03:23 PM GMT+1
    To: "sac-help<at>iris.washington.edu" <sac-help<at>iris.washington.edu>
    Reply-To: amik Amik <amik.mamat<at>yahoo.co.id>

    Dear Sir

    I have a local event recorded by 4 stations that have different sampling frequencies, are 20 Hz and 25 Hz.Therefore I set a new sampling rate to uniform sampling frequency. Previously I checked the maximum frequency signals are recorded by the stations, the maximum frequencies are 12 Hz. Then, I decided to choose 25 Hz, given that the minimum sampling frequency is twice the maximum frequency recorded by the station. In this case, I think the seismometers with a sampling frequency of 20 Hz should been covered. Then, I did command "interpolate delta 0.04". Furthermore I did deconvolution using a response file which got from rdseed, with command "transfer from evalresp fname "response file" to none freq 0025 12:05 10 20". But the result was aliasing signal at the station that originally had a sampling rate of 0.05. Is there a connection with the contents of the RESPfile of the aliasing ? Could anyone please help me solving this problem?
    Thank You

    Regards,
    Ami

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

08:25:08 v.9a3bf08e