ISO Platforms

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Most of the observations used to characterize and understand our environment are made using instruments that are mounted on platforms, such as ships, satellites or stations. These platforms can change over time so it is important to document them in order to avoid misunderstanding.

ISO 19115-2 Acquisition Details
Platform information is included in the acquisitionInformation section of the ISO 19115-2 standard (see left side of Figure). The description includes five items:
  • citation: This is a reference to a document or a web page that describes some aspect of the platform. Any number of these references can be included and the referenced documents can be in any format. Note that these ISO citations include unique identifiers for the referenced citations.
  • identifier: This is an identifier for the platform. It includes a code and an authority or source for that code. At present the standard allows only one of these for each platform. We are hoping to relax this limitation in the revision of the standard.
  • description: This is a brief paragraph describing the instrument suitable for use on a web page.
  • sponsor: This is generally an organization that sponsors the platform. Note that multiple organizations can be referenced here.
  • instrument: This describes the instrument(s) that are mounted on this platform. It would generally be done with a reference to an instrument described elsewhere in the metadata file.

Connecting Platforms and Instruments

Platforms and Instruments
The ISO 19115-2 Standard is used to describe platforms and instruments used to make observations. These objects are related to one another using the MI_Platform/instrument and MI_Instrument/mountedOn roles (see schematic UML diagram in this Figure). These relationships are illustrated schematically for a data set with two instruments and two platforms in the lower left corner of this Figure. Instrument_1 (I1) is mounted on Platform_2 (P2) and Instrument_2 (I2) is mounted on Platform_1 (P1). The XML describing these relationships is shown on the right side of the Figure. In this case ids and xlink:hrefs are used to identify and reference the instruments and platforms.

Platform Metadata

The example above shows how the platforms and instruments used to make observations are referenced from the metadata for those observations. The ISO Standard also supports the need to document the platforms themselves. This is done using the ISO Dataset Series shown in this Figure. The observing station on top of Mauna Loa provides a good example for exploring approaches to ISO platform documentation.

The Mauna Loa Platform is used for many atmospheric chemistry observations by the Global Monitoring Division of NOAA's Environmental Science Research Laboratory. The platform description provides documentation of the projects and parameters measured at this station in HTML. This documentation is easy for a human reader to understand. It has several sections:

  • The first section of the page provides basic identification and descriptive information about the station. It includes the platform identifier (MLO), coordinates (x, y, z), and contact information. The organization of the page makes it clear that this information applies to all of the observations made at this platform.
  • The remaining sections describe seven projects that use the MLO platform for making observations. Each of these projects has observed a variety of parameters, mostly chemical species, over a variety of time periods.

This page documents the MLO platform very nicely for human readers. It is a web page, so it is written in HTML. How would this same information be presented in ISO metadata?

Metadata Application
The idea of collections of related documentation is included in the ISO Standards as a very general DS_Aggregate object. The <<Abstract>> label and the triangle arrow below the DS_Aggregate object indicate that there are a number of kinds of collections, including those related to a platform (DS_Platform) or to a sensor (DS_Sensor). The MultipleAggregation line to the left of the DS_Aggregate object shows that collections can include other collects as subsets and can be included in larger supersets.

The translation of this UML into a picture relevant to the MLO case is shown in the MLO UML Figure. The observations made at platform MLO include subsets made by the Carbon Cycle Surface Flask sensor, the HATS In Situ Observatory sensor, and the Surface Ozone sensor (as well as four other sensors that were left out of the picture). This conceptual model is represented (schematically) in ISO 19139 XML as:
   <gmd:composedOf/> <!-- Empty at present, no data outside of subsets -->
   <gmd:seriesMetadata/> <!-- Described below -->
   <gmd:subset> <!-- Carbon Cycle Surface Flasks -->
         <gmd:composedOf/> <!-- Observation Documentation -->
         <gmd:seriesMetadata/> <!-- Sensor Documentation -->
   <gmd:subset> <!-- Carbon Cycle In Situ Observatory -->
         <gmd:composedOf/> <!-- Observation Documentation -->
         <gmd:seriesMetadata/> <!-- Sensor Documentation -->
   <gmd:subset> <!-- HATS In Situ Observatory: -->
      <gmd:composedOf/> <!-- Observation Documentation -->
      <gmd:seriesMetadata/> <!-- Sensor Documentation -->
   <gmd:subset> <!-- Aerosol Surface, Continuous Measurements -->
         <gmd:composedOf/> <!-- Observation Documentation -->
         <gmd:seriesMetadata/> <!-- Sensor Documentation -->
   <gmd:subset> <!-- Surface Ozone -->
          <gmd:composedOf/> <!-- Observation Documentation -->
          <gmd:seriesMetadata/> <!-- Sensor Documentation -->
   <gmd:subset> <!-- Meteorology -->
         <gmd:composedOf/> <!-- Observation Documentation -->
         <gmd:seriesMetadata/> <!-- Sensor Documentation -->

Note that this structure is not limited to collections from particular sensors. They could be any collection that makes sense and helps users understand the observations made at the platform.

This Figure also includes some of the other elements that are available in the DS_Platform and DS_Seneor objects. First is the seriesMetadata element. The UML above shows that this object is a MI_Metadata object, a complete metadata record. It holds documentation that is shared by all of the observations made by this platform. This is exactly the information that is included in the first section of the HTML version of the MLO platform description. Some details of the seriesMetadata will be discussed below.

The other additional element that is shown is the composedOf element. This is a DS_DataSet object that contains (has) one or more MI_Metadata objects. These are the members of the collection. They could be metadata records that describe the products available for each sensor or they could describe different deployments. Once again, their content is determined by the data provider and, ultimately, the users of the data.

At this point it seems reasonable to conclude that the structure that makes sense to human readers in HTML can be replicated in the ISO Standard. Note that this structure is also very similar a directory structure that might be used to hold metadata records or data files. The top level directory would be the platform and it would have a sub-directory for each project or sensor on the platform. Each of those sub-directories would hold data files which are equivalent to the MI_Metadata records included in the DS_DataSet. All of the directories could contain a readme.txt file that described the contents of the directory which is equivalent to the seriesMetadata.

Platform seriesMetadata

The seriesMetadata section of the HTML page holds documentation that is relevant to all of the observations made at the platform, including the basic identification and descriptive information from the HTML version of the documentation (platform identifier (MLO), coordinates (x, y, z), and contact information). Most of this information fits easily into the MD_IdentificationInformation section. The seriesmetadata also contains ISO Boilerplate and other information to facillitate discovery. Specifically:


Gives a citation to the platform description. The originator of the page this page is the Global Monitoring Division website.


Gives a short description of the Platform. It is the Description from the platform description:

   <gco:CharacterString>Mauna Loa Observatory is located on the Island of Hawaii at an elevation of 3397 m on the northern
      flank of Mauna Loa volcano at 200 north. Established in 1957, Mauna Lao Observatory has grown to become the premier
      long-term atmospheric monitoring facility on earth and is the site where the ever-increasing concentrations of global
      atmospheric carbon dioxide were determined. The observatory consists of 10 buildings from which up to 250 different
      atmospheric parameters are measured by a complement of 12 NOAA/ESRL and other agency scientists and engineers


Gives contact information for the platform:

            <gco:CharacterString>John Barnes</gco:CharacterString>
            <gco:CharacterString>DOC/NOAA/ESRL/GMD > Global Monitoring Division, Earth System Research Laboratory, NOAA, U.S. Department of
            <gco:CharacterString>NOSA Observing System Manager</gco:CharacterString>
                            <gco:CharacterString>(808) 933-6965</gco:CharacterString>
                            <gco:CharacterString>NOAA - Mauna Loa Observatory 1437 Kilauea Ave. #102</gco:CharacterString>
                    <gco:CharacterString>7:30 - 5:00 UTC-10</gco:CharacterString>
            <gmd:CI_RoleCode codeList="" codeListValue="pointOfContact">pointOfContact</gmd:CI_RoleCode>


Gives links to pictures of the platform:

            <gco:CharacterString>A collection of images of MLO</gco:CharacterString>


Gives information about the native format(s) of the platform observations:

        <gmd:version gco:nilReason="unknown"/>


Gives information about programs/projects that the Platform is part of (largerWorkCitations) or related to (crossReferences). See ISO AggregationInformation for more information. Citations to these programs/projects are likely to be used in many records, so this is a good place to taks advantage of ISO Components:

<gmd:aggregationInfo xlink:href=""/><!-- Global Monitoring Division -->
<gmd:aggregationInfo xlink:href=""/><!-- Carbon Cycle Surface Flasks -->
<gmd:aggregationInfo xlink:href=""/><!-- Carbon Cycle In Situ Observatory -->
<gmd:aggregationInfo xlink:href=""/><!-- HATS In Situ Observatory -->
<gmd:aggregationInfo xlink:href=""/><!-- Surface Ozone -->
<gmd:aggregationInfo xlink:href=""/><!-- Dobson Total Ozone -->
<gmd:aggregationInfo xlink:href=""/><!-- Meteorology -->


Gives keywords from various controlled vocabularies in order to facilitate discovery. The keyword lists from the NASA Global Change Master Directory and the NIST Chemistry Webbook (for chemical compounds) might be useful for the MLO data:

            <gco:CharacterString>Carbon Dioxide</gco:CharacterString>
            <gco:CharacterString>Carbon Monoxide</gco:CharacterString>
            <gco:CharacterString>other compounds measured at MLO fill out this list</gco:CharacterString>
            <gmd:MD_KeywordTypeCode codeList="" codeListValue="theme">theme</gmd:MD_KeywordTypeCode>
                    <gco:CharacterString>NIST Chemistry WebBook NIST Standard Reference Database Number 69</gco:CharacterString>
                            <gmd:CI_DateTypeCode codeList="" codeListValue="revision"/>
                            <gco:CharacterString>P.J. Linstrom and W.G. Mallard</gco:CharacterString>
                            <gco:CharacterString>DOC/NIST > National Institute of Standards and Technology, U.S. Department of Commerce</gco:CharacterString>
                                            <gco:CharacterString>NIST Chemistry WebBook NIST Standard Reference Database Number 69</gco:CharacterString>
                                            <gco:CharacterString>The NIST Chemistry WebBook provides users with easy access to chemical and physical property data for chemical species through the
                                                internet. The data provided in the site are from collections maintained by the NIST Standard Reference Data Program and outside contributors. Data in
                                                the WebBook system are organized by chemical species. The WebBook system allows users to search for chemical species by various means. Once the desired
                                                species has been identified, the system will display data for the species. </gco:CharacterString>
                            <gmd:CI_RoleCode codeList="" codeListValue="custodian">custodian</gmd:CI_RoleCode>


Gives the bounding temporal and spatial extent of the observations from the Platform. This is the union of the subset extents. It includes the id="boundingExtent" in order to simplify external access to this information and facilitate discovery:

    <gmd:EX_Extent id="boundingExtent">
            <gco:CharacterString>MLO Bounding Extent</gco:CharacterString>
            <gmd:EX_GeographicBoundingBox id="boundingGeographicBoundingBox">
            <gmd:EX_TemporalExtent id="boundingTemporalExtent">
                    <gml:TimePeriod gml:id="tp_bound">
                            <gml:TimeInstant gml:id="tp_start">
                            <gml:TimeInstant gml:id="tp_end">
                                <gml:timePosition indeterminatePosition="now"/>
                <gmd:verticalCRS gco:nilReason="unknown"/>