Thread: CMPINC convention

Started: 2012-04-18 22:26:37
Last activity: 2012-04-19 16:02:21
Topics: SAC Help
Carl Tape
2012-04-18 22:26:37
Dear sac-help:

I was wondering if you could clarify the convention for CMPINC.

CMPINC is define here
http://www.iris.edu/software/sac/manual/file_format.html as "Component
incident angle (degrees from vertical).

vang in the antelope schema is defined as:
This attribute measures the angle between the sensitive axis of a
seismometer and the outward-pointing vertical direction. For a vertically
oriented seismometer, vang = 0, or 180 (to reverse the sense of the
instrument). For a horizontally oriented seismometer, vang = 90. See hang.

The definition for CMPINC is somewhat ambiguous, since "vertical" is a
line, not a vector. Does "vertical" mean "outward-pointing vertical
direction"?

Thanks,
Carl

  • Yingcai Zheng
    2012-04-19 03:06:00
    upward : cmpinc = 0
    downward: cmpinc = 180

    north component: cmpinc = 90
    east component: compinc = 90

    also :

    cmpaz =0 for north component
    cmpaz=90 for east component

    am i right?

    Yingcai zheng

    mit

    On Wed, Apr 18, 2012 at 7:26 PM, Carl Tape <carltape<at>gi.alaska.edu> wrote:

    Dear sac-help:

    I was wondering if you could clarify the convention for CMPINC.

    CMPINC is define here
    http://www.iris.edu/software/sac/manual/file_format.html as "Component
    incident angle (degrees from vertical).

    vang in the antelope schema is defined as:
    This attribute measures the angle between the sensitive axis of a
    seismometer and the outward-pointing vertical direction. For a vertically
    oriented seismometer, vang = 0, or 180 (to reverse the sense of the
    instrument). For a horizontally oriented seismometer, vang = 90. See hang.

    The definition for CMPINC is somewhat ambiguous, since "vertical" is a
    line, not a vector. Does "vertical" mean "outward-pointing vertical
    direction"?

    Thanks,
    Carl

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



    • Chad Trabant
      2012-04-19 00:19:31

      The below outline matches my understanding of the common usage, basically vertical is positive up or "outward-pointing". This also matches the convention implied when the DMC converts a SEED dip to a SAC inclination.

      Chad
      IRIS DMC

      On Apr 18, 2012, at 5:06 PM, Yingcai Zheng wrote:

      upward : cmpinc = 0
      downward: cmpinc = 180

      north component: cmpinc = 90
      east component: compinc = 90

      also :

      cmpaz =0 for north component
      cmpaz=90 for east component

      am i right?

      Yingcai zheng

      mit

      On Wed, Apr 18, 2012 at 7:26 PM, Carl Tape <carltape<at>gi.alaska.edu> wrote:
      Dear sac-help:

      I was wondering if you could clarify the convention for CMPINC.

      CMPINC is define here http://www.iris.edu/software/sac/manual/file_format.html as "Component incident angle (degrees from vertical).

      vang in the antelope schema is defined as:
      This attribute measures the angle between the sensitive axis of a seismometer and the outward-pointing vertical direction. For a vertically oriented seismometer, vang = 0, or 180 (to reverse the sense of the instrument). For a horizontally oriented seismometer, vang = 90. See hang.

      The definition for CMPINC is somewhat ambiguous, since "vertical" is a line, not a vector. Does "vertical" mean "outward-pointing vertical direction"?

      Thanks,
      Carl

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


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


      • Carl Tape
        2012-04-19 16:02:21
        Thanks, folks. I suppose the only concrete change would be to add a word or
        two to the manual definition of CMPINC, like "upward-pointing vertical
        direction" or "outward-pointing vertical direction".

        Thanks,
        Carl

        On Wed, Apr 18, 2012 at 4:19 PM, Chad Trabant <chad<at>iris.washington.edu>wrote:


        The below outline matches my understanding of the common usage, basically
        vertical is positive up or "outward-pointing". This also matches the
        convention implied when the DMC converts a SEED dip to a SAC inclination.

        Chad
        IRIS DMC

        On Apr 18, 2012, at 5:06 PM, Yingcai Zheng wrote:

        upward : cmpinc = 0
        downward: cmpinc = 180

        north component: cmpinc = 90
        east component: compinc = 90

        also :

        cmpaz =0 for north component
        cmpaz=90 for east component

        am i right?

        Yingcai zheng

        mit

        On Wed, Apr 18, 2012 at 7:26 PM, Carl Tape <carltape<at>gi.alaska.edu> wrote:

        Dear sac-help:

        I was wondering if you could clarify the convention for CMPINC.

        CMPINC is define here
        http://www.iris.edu/software/sac/manual/file_format.html as "Component
        incident angle (degrees from vertical).

        vang in the antelope schema is defined as:
        This attribute measures the angle between the sensitive axis of a
        seismometer and the outward-pointing vertical direction. For a vertically
        oriented seismometer, vang = 0, or 180 (to reverse the sense of the
        instrument). For a horizontally oriented seismometer, vang = 90. See hang.

        The definition for CMPINC is somewhat ambiguous, since "vertical" is a
        line, not a vector. Does "vertical" mean "outward-pointing vertical
        direction"?

        Thanks,
        Carl

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


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




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