Thread: Amplitude error in header

Started: 2022-02-13 15:23:31
Last activity: 2022-02-14 10:18:40
Topics: SAC Help
Guilherme de Melo
2022-02-13 15:23:31
Dears,

I am applying the maximum wave amplitude for a specific time window, using
the values informed in ymax and ymin in header of the data.

So, I would like to know how much accurate is the value informed in "sh"
header command? I mean, how much percent can I consider an error of
measurement?

Best,
Guilherme de Melo

  • Arthur Snoke
    2022-02-13 21:33:40
    My guess is that you are concerned about precision, round-off, etc.  But there
    is another possible consideration:sample rate.

    To see what I mean, look at
    http://ds.iris.edu/files/sac-manual/manual/saclib.html#interpolation-using-cubic-splines

    The second paragraph in Interpolation using cubic splines starts with "With
    digital data, the extrema may not be at digitized points, ", and the figure at
    the end of the section shows that just using the digital points can give results
    off by several percent.

    On 2/13/22 6:24 PM, Guilherme de Melo (via IRIS) wrote:

    Dears,

    I am applying the maximum wave amplitude for a specific time window, using the
    values informed in ymax and ymin in header of the data.

    So, I would like to know how much accurate is the value informed in "sh"
    header command? I mean, how much percent can I consider an error of measurement?

    Best,
    Guilherme de Melo



  • George Helffrich
    2022-02-14 10:18:40
    Dear All -

    DEPMIN and DEPMAX are the file header variables that give the extremal values of the time series. SAC refreshes these whenever a file is read in (or changed by the result of a SAC command). On disk, the data might be manipulated by an auxiliary program and the extremal values in the time series might change, but DEPMAX and DEPMAN might not be updated. That is one reason for a divergence between values on disk and in memory.

    Another reason might be that DEPMIN and DEPMAX apply to the whole file. By using MTW or CUT, you can select a subset of the time series on disk and, when SAC applies those limits, it might change the values of DEPMIN and DEPMAX.

    On 13 Feb 2022, at 23:24, Guilherme de Melo (via IRIS) <sac-help-bounce<at>lists.ds.iris.edu> wrote:


    Dears,

    I am applying the maximum wave amplitude for a specific time window, using the values informed in ymax and ymin in header of the data.

    So, I would like to know how much accurate is the value informed in "sh" header command? I mean, how much percent can I consider an error of measurement?

    Best,
    Guilherme de Melo

    ----------------------
    SAC Help
    Topic home: http://ds.iris.edu/message-center/topic/sac-help/ | Unsubscribe: sac-help-unsubscribe<at>lists.ds.iris.edu

    Sent from the IRIS Message Center (http://ds.iris.edu/message-center/)
    Update subscription preferences at http://ds.iris.edu/account/profile/



    George Helffrich
    george<at>elsi.jp


14:53:40 v.22510d55