Thread: components swapped at IU.HRV in time period 2013-12-19 to 2014-01-16?

Started: 2017-01-18 01:39:24
Last activity: 2017-01-18 01:39:24
Topics: Report a QA Issue
Paula Koelemeijer
components swapped at IU.HRV in time period 2013-12-19 to 2014-01-16?
2017-01-18 01:39:24
To whom it may concern,

I have been looking at data from station HRV in the IU network:
http://ds.iris.edu/mda/IU/HRV

I noticed that in the time span from December 2013 to January 2014, the
BH2 and BHZ components seem wrong, when looking at the dip and azimuth
of the channels:

For BH2 it seems to have the attributes of a vertical component:
http://ds.iris.edu/mda/IU/HRV/00/BH2?timewindow=2013/12/19%2001:00:00-2014/01/16%2020:32:00

For BHZ it seems to have the attributes of a horizontal component:
http://ds.iris.edu/mda/IU/HRV/00/BHZ?timewindow=2013/12/19%2001:00:00-2014/01/16%2020:32:00

I haven't been able to find anything about this on the webpages, or in
the DPR.

My question is therefore; are the components actually swapped? And is
this corrected for in the stationXML file? Or has this been a typo
between a "Z" and a "2"?

And my other question, more in general: when stations have components
BH1 and BH2, is it safe to assume (at least within data downloaded from
the DMC) that these correspond to the North and East components
respectively? Or should one really look at the dip and azimuth of the
channels, also when processing large datasets?
The webpages only say that IRIS uses the SEED convenction from the
appendix A in the manual, but that doesn't provide many more insights.

Many thanks, and best wishes,

Paula Koelemeijer

  • Mary Templeton
    Re: components swapped at IU.HRV in time period 2013-12-19 to 2014-01-16?
    2017-01-17 19:04:12
    Hi Paula,

    Thanks for your email!

    On Jan 17, 2017, at 10:43 AM, Paula Koelemeijer <paula.koelemeijer<at>univ.ox.ac.uk> wrote:

    To whom it may concern,

    I have been looking at data from station HRV in the IU network:
    http://ds.iris.edu/mda/IU/HRV

    I noticed that in the time span from December 2013 to January 2014, the
    BH2 and BHZ components seem wrong, when looking at the dip and azimuth
    of the channels:

    For BH2 it seems to have the attributes of a vertical component:
    http://ds.iris.edu/mda/IU/HRV/00/BH2?timewindow=2013/12/19%2001:00:00-2014/01/16%2020:32:00

    For BHZ it seems to have the attributes of a horizontal component:
    http://ds.iris.edu/mda/IU/HRV/00/BHZ?timewindow=2013/12/19%2001:00:00-2014/01/16%2020:32:00

    I haven't been able to find anything about this on the webpages, or in
    the DPR.

    My question is therefore; are the components actually swapped?

    Yes, the network operator has confirmed to us that channels 2 and Z were in
    fact reversed as described in the metadata.

    And is
    this corrected for in the stationXML file? Or has this been a typo
    between a "Z" and a "2”?

    It’s not a typo. The metadata is describes the reversal correctly according to the
    network operator.

    And my other question, more in general: when stations have components
    BH1 and BH2, is it safe to assume (at least within data downloaded from
    the DMC) that these correspond to the North and East components
    respectively?

    Or should one really look at the dip and azimuth of the
    channels, also when processing large datasets?

    Different networks may treat this differently, so I would always consult the
    metadata. It’s the GSN’s convention that, if you think of the default “N”
    and “E” as Y and X in cartesian coordinates, 1 is equivalent to Y. (Note
    that if Y is oriented W and X is oriented N, 1 will be W and 2 will be N.)

    But I have known other networks who archive data at the DMC that use
    the reverse convention (Y=2, X=1).

    The webpages only say that IRIS uses the SEED convenction from the
    appendix A in the manual, but that doesn't provide many more insights.

    The best insight is to consult the metadata in each case…

    cheers,
    Mary


    Many thanks, and best wishes,

    Paula Koelemeijer

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