Thread: Java Station and Channel objects provide different values for lat,lon,elev

Started: 2016-05-06 23:24:40
Last activity: 2016-05-07 18:51:30
Topics: Web Services
Using Station web service Java API I notice that elevation, latitude, and longitude can all be obtained either from a Station object or from a Channel object. Usually these values agree, but in some cases they do not. When they differ should that be interpreted as the instrument being offset from the nominal station location?
An example is CM-PRV- *-*
MDA lists:http://ds.iris.edu/mda/CM/PRV/00?timewindow=2015/11/03%2000:00:00-2599/12/31%2023:59:59
Latitude 13.376000
Longitude -81.364000
Elevation 63

The Station object provides:
Latitude 13.376
Longitude -81.364
Elevation 63

The Channel object lists:
BHE-00 lat = 13.376200, lon = -81.363500, elev = 205.000000
BHN-00 lat = 13.376200, lon = -81.363500, elev = 205.000000
BHZ-00 lat = 13.376200, lon = -81.363500, elev = 205.000000
BHE-01 lat = 13.376200, lon = -81.363500, elev = 205.000000
BHN-01 lat = 13.376200, lon = -81.363500, elev = 205.000000
BHZ-01 lat = 13.376200, lon = -81.363500, elev = 205.000000

Notice that all channels report the same values and all disagree with the values from the station object. Is this an error?


Doug Dodge


  • Hi Doug,

    As you say, usually the station and channel elevations agree. But their definitions are not the same and on occasion they differ for good reason. The station elevation is defined (in SEED) as "Elevation of local ground level in meters", whereas the channel elevation is defined as "Elevation of the instrument" followed by "To find the local ground depth, add the depth field to the instrument elevation". So the channel depth field should be the difference between these two elevations. The common case where these values differ are for borehole installations where the station elevation is the elevation of the ground and the channel elevations are down the hole where the actual sensors are located.

    I think the case of CM.PRV and its channels is simply a metadata error. First off, the the channel elevation is higher than the station elevation, which makes no sense. Are the sensors on a tower!? Second, the depth value of 0 does not match the difference in elevations. So one of the two values is probably just wrong. As a data user I would pick the channel values over the station values.

    Just to clarify, this is not specific to our web services or the Java IRIS-WS library, the values are directly from the metadata submitted by the network operator.

    Thanks for reporting this, we'll contact the network operator to pursue a fix. Also, we will add a test to our upcoming metadata validator to flag such things and hopefully avoid the accumulation of more of these.

    Chad


    On May 6, 2016, at 10:27 AM, Doug Dodge <dodge1<at>llnl.gov> wrote:

    Using Station web service Java API I notice that elevation, latitude, and longitude can all be obtained either from a Station object or from a Channel object. Usually these values agree, but in some cases they do not. When they differ should that be interpreted as the instrument being offset from the nominal station location?
    An example is CM-PRV- *-*
    MDA lists:http://ds.iris.edu/mda/CM/PRV/00?timewindow=2015/11/03%2000:00:00-2599/12/31%2023:59:59
    Latitude 13.376000
    Longitude -81.364000
    Elevation 63

    The Station object provides:
    Latitude 13.376
    Longitude -81.364
    Elevation 63

    The Channel object lists:
    BHE-00 lat = 13.376200, lon = -81.363500, elev = 205.000000
    BHN-00 lat = 13.376200, lon = -81.363500, elev = 205.000000
    BHZ-00 lat = 13.376200, lon = -81.363500, elev = 205.000000
    BHE-01 lat = 13.376200, lon = -81.363500, elev = 205.000000
    BHN-01 lat = 13.376200, lon = -81.363500, elev = 205.000000
    BHZ-01 lat = 13.376200, lon = -81.363500, elev = 205.000000

    Notice that all channels report the same values and all disagree with the values from the station object. Is this an error?


    Doug Dodge

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    • Hi Chad,

      ... Also, we will add a test to our upcoming metadata validator to flag
      such things and hopefully avoid the accumulation of more of these.
      Chad

      That list of validation checks would be really useful for finding problems
      on data entry as well ...

      - Mark

      GNS New Zealand

      Notice: This email and any attachments are confidential.
      If received in error please destroy and immediately notify us.
      Do not copy or disclose the contents.



      • ... Also, we will add a test to our upcoming metadata validator to flag such things and hopefully avoid the accumulation of more of these.
        Chad

        That list of validation checks would be really useful for finding problems on data entry as well ...

        Indeed. When our validator is ready for release you'll be able to see all the checks. No doubt they will continue to grow.

        Chad
  • Could easily be an error, but SEED allows for channels that are not
    exactly the same as the station location. Most common usage is
    probably for a borehole sensor where the station is at the surface,
    while the associated channel is down the hole. I think it has to be
    within 1 km to be the same station, but there is nothing that enforces
    this other than words in the spec.

    In this case it could also be that the channel location is just more
    accurate but they didn't want to update the station location as it
    already existed. In general the channel location should give you the
    best location, but many people just use the station location.

    Philip


    On Fri, May 6, 2016 at 1:27 PM, Doug Dodge <dodge1<at>llnl.gov> wrote:
    Using Station web service Java API I notice that elevation, latitude, and
    longitude can all be obtained either from a Station object or from a Channel
    object. Usually these values agree, but in some cases they do not. When they
    differ should that be interpreted as the instrument being offset from the
    nominal station location?

    An example is CM-PRV- *-*

    MDA
    lists:http://ds.iris.edu/mda/CM/PRV/00?timewindow=2015/11/03%2000:00:00-2599/12/31%2023:59:59

    Latitude 13.376000

    Longitude -81.364000

    Elevation 63



    The Station object provides:

    Latitude 13.376

    Longitude -81.364

    Elevation 63



    The Channel object lists:

    BHE-00 lat = 13.376200, lon = -81.363500, elev = 205.000000

    BHN-00 lat = 13.376200, lon = -81.363500, elev = 205.000000

    BHZ-00 lat = 13.376200, lon = -81.363500, elev = 205.000000

    BHE-01 lat = 13.376200, lon = -81.363500, elev = 205.000000

    BHN-01 lat = 13.376200, lon = -81.363500, elev = 205.000000

    BHZ-01 lat = 13.376200, lon = -81.363500, elev = 205.000000



    Notice that all channels report the same values and all disagree with the
    values from the station object. Is this an error?





    Doug Dodge



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