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AvXML-1.0RC1-tutorial-VA-sigmet

VA SIGMET for Shanwick Oceanic Flight Information Region, 16:00Z 25-MONTH-YEAR

This VA SIGMET is intended as an example and does not represent actual conditions.

The year and month of the issue of this VA SIGMET are unknown; these have been substituted with YYYY and MM respectively.

This is tutorial is intended as a follow-on from the simple METAR tutorial. Please work through the METAR example first as this VA SIGMET tutorial assumes that many of the key points will already be understood.

The full XML for this example can be found here.


TAC-encoding

This example is based on the following VA SIGMET:

EGGX SIGMET 04 VALID 251600/252200 EGRR-
EGGX SHANWICK OCEANIC FIR VA ERUPTION MT H HEKLA PSN N6359 W01940 VA CLD OBS 1600Z 
SFC/FL550 N OF N6100 W01000 – N5900 W01300 – N6100 W01900 MOV S 60KT NC VA CLD 
FCST 2200Z SFC/FL550 N OF N6100 W01100 – N5800 W01400 – N6100 W01600=



XML Namespaces


The following namespaces are used either directly or indirectly in this example:

DescriptionXML NamespaceDefault namespace prefix
XML Schemahttp://www.w3.org/2001/XMLSchemaxsd
Schematronhttp://purl.oclc.org/dsdl/schematronsch
XSLT v2http://www.w3.org/1999/XSL/Transformxsl
XML Linking Languagehttp://www.w3.org/1999/xlinkxlink
OGC GML 3.2.1http://www.opengis.net/gml/3.2gml
ISO/TS 19139:2007 metadata XML schema implementationhttp://www.isotc211.org/2005/gmdgmd
OGC OMXML Observations and Measurementshttp://www.opengis.net/om/2.0om
OGC OMXML Sampling Featureshttp://www.opengis.net/sampling/2.0sf
OGC OMXML Spatial Sampling Featureshttp://www.opengis.net/samplingSpatial/2.0sams
WMO Meteorological Basic Types (1.0RC1)http://data.wmo.int/def/met-basic/1.0RC1met-basic
WMO Observable Property Model(1.0RC1)http://data.wmo.int/def/opm/1.0RC1opm
WMO METCE (1.0RC1)http://data.wmo.int/def/metce/1.0RC1metce
ICAO Simple Aviation Features (1.0RC1)http://icao.int/saf/1.0RC1saf
ICAO Weather Information Exchange Modelhttp://icao.int/iwxxm/1.0RC1iwxxm


Note that the XML Namespace is distinct from the schema locations. For reference, these are provided here.


Overview: the VA SIGMET report


The XML encoded VA SIGMET has a root element <iwxxm:VolcanicAshSIGMET> within which the XML Namespace information is declared.

The VA SIGMET report is comprised of:
  • report metadata (e.g. status, issuing centre, originating meteorological watch office etc.);
  • one analysis providing the observed or forecast position and motion of the volcanic ash cloud; and
  • one forecast providing one or more predicted positions of the volcanic ash cloud.

The code fragment below illustrates the report structure:

<?xml version="1.0" encoding="UTF-8"?>
<iwxxm:VolcanicAshSIGMET xmlns:iwxxm="http://icao.int/iwxxm/1.0RC1"
    xmlns:saf="http://icao.int/saf/1.0RC1"
    xmlns:metce="http://data.wmo.int/def/metce/1.0RC1" 
    xmlns:om="http://www.opengis.net/om/2.0"
    xmlns:sam="http://www.opengis.net/sampling/2.0"
    xmlns:sams="http://www.opengis.net/samplingSpatial/2.0"
    xmlns:gml="http://www.opengis.net/gml/3.2" 
    xmlns:gmd="http://www.isotc211.org/2005/gmd"
    xmlns:gco="http://www.isotc211.org/2005/gco" 
    xmlns:xlink="http://www.w3.org/1999/xlink"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    xsi:schemaLocation="http://icao.int/iwxxm/1.0RC1 http://schemas.wmo.int/iwxxm/1.0RC1/iwxxm.xsd
    http://data.wmo.int/def/metce/1.0RC1 http://schemas.wmo.int/metce/1.0RC1/metce.xsd"
    gml:id="va-sigmet-EGXX-YYYYMM25T160000Z"
    status="NORMAL">
    <iwxxm:analysis>...</iwxxm:analysis>
    <iwxxm:issuingAirTrafficServicesUnit 
        xlink:href="http://icao.int/id/acc/EGGX" 
        xlink:title="Shanwick Oceanic"/>
    <iwxxm:originatingMeteorologicalWatchOffice 
        xlink:href="http://icao.int/id/mwo/EGRR" 
        xlink:title="UK Meteorological Office - Exeter"/>
    <iwxxm:phenomenon 
        xlink:href="http://data.wmo.int/def/49-2/SigWxPhenomena/VA" 
        xlink:title="Volcanic Ash"/>
    <iwxxm:sequenceNumber>4</iwxxm:sequenceNumber>
    <iwxxm:validPeriod xlink:href="#time-period-25T16Z-25T22Z"/>
    <iwxxm:eruptingVolcano>...</iwxxm:eruptingVolcano>
    <iwxxm:forecastPositionAnalysis>...</iwxxm:forecastPositionAnalysis>
</iwxxm:VolcanicAshSIGMET>



Line 16 (Unique identifier)


...
    gml:id="va-sigmet-EGXX-YYYYMM25T160000Z"
...


  • Each VA SIGMET report should have a unique identifier of the form: va-sigmet-{issuing Air Traffic Service Unit}-{issue date-time}.


Line 17 (Status)


...
    status="NORMAL"
...


  • The status of this VA SIGMET report is "NORMAL".


Line 18 (Analysis)

  • The analysis provides the observed or forecast position and motion of the volcanic ash cloud. This is encoded as an instance of <om:OM_Observation> - see below.

Lines 19-24 (Issuing Air Traffic Services Unit and Originating Meteorological Watch Office)


...
    <iwxxm:issuingAirTrafficServicesUnit 
        xlink:href="http://icao.int/id/acc/EGGX" 
        xlink:title="Shanwick Oceanic"/>
    <iwxxm:originatingMeteorologicalWatchOffice 
        xlink:href="http://icao.int/id/mwo/EGRR" 
        xlink:title="UK Meteorological Office - Exeter"/>
...


  • xlink (with human readable title) is used to reference an externally published definitions of Air Traffic Service Units and Meteorological Watch Offices. We anticipate that ICAO will publish an authoritative register containing these definitions.
  • Each definition will resolve to provide useful information about the entity (e.g. human-readable web-pages or machine-readable content; the format provided will be determined using HTTP content negotiation).

Note that at present, this register of aerodromes does not exist.

Lines 25-27 (Significant weather phenomenon)


...
    <iwxxm:phenomenon 
        xlink:href="http://data.wmo.int/def/49-2/SigWxPhenomena/VA" 
        xlink:title="Volcanic Ash"/>
...


  • <iwxxm:phenomenon> is defined with type AeronauticalSignificantWeatherPhenomenon (from met-basic). This <CodeList> class specifies tagged value "vocabulary" as <http://data.wmo.int/def/49-2/SigWxPhenomena> and contains the set of terms listed in WMO No. 49 C.3.1. sub-clause 1.1.4 (e.g. "VA": "Volcanic Ash").


Line 28 (Sequence number)


...
    <iwxxm:sequenceNumber>4</iwxxm:sequenceNumber>
...


  • <iwxxm:sequenceNumber> provides the sequence number of this SIGMET. Numbering follows the business rules specified in ICAO Annex 3 / WMO No. 49 Volume 2.


Line 29 (Valid period)


...
    <iwxxm:validPeriod xlink:href="#time-period-25T16Z-25T22Z"/>
...


  • <iwxxm:validPeriod> defines the period during which this SIGMET is valid.
  • Here, xlink is used to provide a local reference to an existing period definition within the XML file.
  • The <om:OM_Observation> instances for the analysys and forecast both include the element <om:validTime> which has identical semantics to <iwxxm:validPeriod>.
  • Even though information is logically repeated, <iwxxm:validPeriod> has been retained to make it easier to map the XML encoding onto the ICAO Annex 3 regulation.

The definition of the <om:validTime> is shown in the code fragment below (noting the use of YYYY and MM in place of year and month):

...
            <om:validTime>
                <gml:TimePeriod gml:id="time-period-25T16Z-25T22Z">
                    <gml:beginPosition>YYYY-MM-25T16:00:00Z</gml:beginPosition>
                    <gml:endPosition>YYYY-MM-25T22:00:00Z</gml:endPosition>
                </gml:TimePeriod>
            </om:validTime>
...



Line 30 (Erupting volcano)

  • <iwxxm:eruptingVolcano> provides information about the source of the volcanic ash; the name and position of the erupting volcano. The code fragment below shows this in more detail:

...
    <iwxxm:eruptingVolcano>
        <metce:Volcano gml:id="volcano-MT-HEKLA">
            <metce:name>MT HEKLA</metce:name>
            <metce:position>
                <gml:Point gml:id="point-MT-HEKLA" 
                    axisLabels="Lat Lon" 
                    srsDimension="2"
                    srsName="http://www.opengis.net/def/crs/EPSG/0/4326">
                    <gml:pos>63.59 -19.40</gml:pos>
                </gml:Point>
            </metce:position>
        </metce:Volcano>
    </iwxxm:eruptingVolcano>
...



Line 31 (Forecast)

  • The forecast provides one or more predicted positions of the volcanic ash cloud. This is encoded as an instance of <om:OM_Observation> - see below.


SIGMET Analysis


The analysis provides the observed or forecast position and motion of the volcanic ash cloud. This is encoded as an instance of <om:OM_Observation>.

The code fragment below illustrates the outline structure of the <om:OM_Observation> instance:

...
    <iwxxm:analysis>
        <om:OM_Observation gml:id="va-position-and-motion-EGXX-YYYYMM25T16Z">
            <om:type 
                xlink:href="http://data.wmo.int/def/observationType/iwxxm/1.0RC1/SIGMETEvolvingConditionAnalysis" 
                xlink:title="SIGMETEvolvingConditionAnalysis"/>
            <om:phenomenonTime>
                <gml:TimeInstant gml:id="time-instant-25T16Z">
                    <gml:timePosition>YYYY-MM-25T16:00:00Z</gml:timePosition>
                </gml:TimeInstant>
            </om:phenomenonTime>
            <om:resultTime xlink:href="#time-instant-25T16Z"/>
            <om:validTime>
                <gml:TimePeriod gml:id="time-period-25T16Z-25T22Z">
                    <gml:beginPosition>YYYY-MM-25T16:00:00Z</gml:beginPosition>
                    <gml:endPosition>YYYY-MM-25T22:00:00Z</gml:endPosition>
                </gml:TimePeriod>
            </om:validTime>
            <om:procedure>
                <metce:Process gml:id="va-sigmet-position-and-motion-analysis">
                    <!-- authoritative documentation reference and title TBC -->
                    <metce:documentationRef
                        xlink:href="http://wis.wmo.int/procedure=Sigmet"
                        xlink:title="WMO No. 49 Volume 2 Meteorological Service for International Air Navigation 
                                     [C.3.1.]7 SIGMET AND AIRMET INFORMATION, AERODROME WARNINGS AND 
                                     WIND SHEAR WARNINGS AND ALERTS"/>
                </metce:Process>
            </om:procedure>
            <om:observedProperty 
                xlink:href="http://data.wmo.int/def/observableProperty/sigmet/evolvingConditionAnalysis"
                xlink:title="Observed position and motion for significant weather phenomenon"/>
            <om:featureOfInterest>...</om:featureOfInterest>
            <om:result>...</om:result>
        </om:OM_Observation>
    </iwxxm:analysis>
...


The analysis <om:OM_Observation> follows the standard OM_Observation pattern;
  • phenomenon time
  • result time
  • valid time (see above for more information)
  • procedure
  • observed property
  • feature of interest
  • result

The IWXXM model requires that the sub-class of OM_Observation used for the analysis is SIGMETEvolvingConditionAnalysis. Rule-based validation is required to ensure the use of the correct sub-class of OM_Observation.

As in the METAR example, the procedure is constrained such that is must be an instance of METCE Process. Again, a simple documentationRef is used; on this occasion to refer to the technical regulations for SIGMET creation.

The observedProperty refers to an externally published instance of CompositeObservableProperty wherein the position and motion properties are listed.

Note that the CompositeObservableProperty definition is not yet available for 1.0RC1.

Please refer to the METAR example for more information about CompositeObservableProperties.


Analysis: feature of interest


The feature of interest for the SIGMET analysis is constrained such that it must be an instance of SF_SamplingSurface. We anticipate providing validation rules (e.g. schematron) to validate this constraint in subsequent releases.

The feature of interest is shown in code fragment below:

...
            <om:featureOfInterest>
                <sams:SF_SpatialSamplingFeature gml:id="sampling-surface-SHANWICK_OCA">
                    <sam:type 
                        xlink:href="http://www.opengis.net/def/samplingFeatureType/OGC-OM/2.0/SF_SamplingSurface" 
                        xlink:title="SF_SamplingSurface"/>
                    <!-- Shanwick Oceanic Flight Information Region -->
                    <sam:sampledFeature 
                        xlink:href="http://icao.int/def/fir/SHANWICK_OCA" 
                        xlink:title="Shanwick Oceanic"/>
                    <sams:shape>
                        <gml:Polygon gml:id="boundary_geometry-SHANWICK_OCA" 
                            axisLabels="Lat Lon" 
                            srsDimension="2"
                            srsName="http://www.opengis.net/def/crs/EPSG/0/4326">
                            <gml:exterior>
                                <gml:LinearRing>
                                    <!-- SHANWICK FIR boundary -->
                                    <gml:posList>
                                        60.0 -30.0 
                                        60.0 -10.0 
                                        54.0 -10.0 
                                        53.0 -15.0 
                                        51.0 -15.0 
                                        51.0 -8.0 
                                        45.0 -8.0 
                                        45.0 -30.0
                                    </gml:posList>
                                </gml:LinearRing>
                            </gml:exterior>
                        </gml:Polygon>
                    </sams:shape>
                </sams:SF_SpatialSamplingFeature>
            </om:featureOfInterest>
...


For a SIGMET, the sampled feature is a Flight Information Region (FIR); such as Shanwick Oceanic. xlink is used to reference an externally published resource. We anticipate that ICAO will publish an authoritative register containing the definition of FIRs.

Each definition will resolve to provide useful information about each FIR (e.g. human-readable web-pages or machine-readable content; the format provided will be determined using HTTP content negotiation).

Note that at present, this register of aerodromes does not exist.

The geometry of the FIR is provided as a 2-dimensional polygon.

Note that these values may not accurately reflect the true boundary of Shanwick Oceanic FIR.

Analysis: result


The analysis result provides the observed or forecast position and motion characteristics of the volcanic ash cloud.

As required by the SIGMETEvolvingConditionAnalysis, the result is constrained such that it must be an instance of EvolvingMeteorologicalCondition.

This class has been specifically designed to meet the requirements published in ICAO Annex 3 / WMO No. 49 Volume 2 regulation.

IWXXM relies on rule-based validation to ensure that the appropriate type of entity is used for the result.

The code fragment below illustrates the encoding of <iwxxm:EvolvingMeteorologicalCondition>:

...
            <om:result>
                <iwxxm:EvolvingMeteorologicalCondition 
                    gml:id="va-obs-EGXX-YYYYMM25T16Z" 
                    intensityChange="NO_CHANGE">
                    <iwxxm:directionOfMotion uom="http://data.wmo.int/def/uom/degrees-true">
                        180
                    </iwxxm:directionOfMotion>
                    <iwxxm:geometry>
                        <saf:AirspaceSolid gml:id="va-geometry-EGXX-YYYYMM25T16Z">
                            <saf:horizontalProjection>
                                <gml:Polygon gml:id="volcanic-ash-cloud-polygon-EGXX-YYYYMM25T16Z" 
                                    axisLabels="Lat Lon" 
                                    srsDimension="2"
                                    srsName="http://www.opengis.net/def/crs/EPSG/0/4326">
                                    <gml:exterior>
                                        <gml:LinearRing>
                                            <gml:posList>
                                                60.0 -11.5
                                                59.0 -13.0
                                                60.0 -16.0
                                            </gml:posList>
                                        </gml:LinearRing>
                                    </gml:exterior>
                                </gml:Polygon>
                            </saf:horizontalProjection>
                            <saf:upperLimit uom="http://opengis.net/def/uom/UCUM/0/%5Bft_i%5D">
                                55000
                            </saf:upperLimit>
                        </saf:AirspaceSolid>
                    </iwxxm:geometry>
                    <iwxxm:speedOfMotion uom="http://opengis.net/def/uom/UCUM/0/knot">
                        60
                    </iwxxm:speedOfMotion>
                </iwxxm:EvolvingMeteorologicalCondition>
            </om:result>
...



Line 4 (Intensity change)

  • Attribute intensityChange is specified as "NO_CHANGE".


Lines 5-7 (Direction of motion)

  • Element <iwxxm:directionOfMotion> provides the direction of motion of the significant meteorological feature; in this case 180 degrees from true-north (e.g. directly south).


Lines 8-30 (Position)

  • Element <iwxxm:geometry> describes the position and shape of the ash cloud.
  • The geometry of the volcanic ash cloud is described as a 2.5-dimensional object; horizontal projection plus (optional) lowerLimit and upperLimit describing the vertical extent.
  • A missing lowerLimit indicates that the phenomenon extends to the surface, whilst a missing upperLimit indicates that it extends above the range of aeronautical operations.
  • The geometry is encoded using an instance of <saf:AirSpaceSolid> (from ICAO Simple Aeronautical Features).
  • Following advice from ICAO sercretariat, the horizontal projection of the significant meteorological feature must always be defined as a closed polygon. In this case, the geometry is derived from the area defined in the SIGMET report (e.g. N OF N6100 W01000 – N5900 W01300 – N6100 W01900) and clipped to the FIR boundary.


Lines 26-28 (Upper limit of feature)

  • Note that the unit of measure "foot" (ft) as defined in the Unified Code for Units of Measure (UCUM)) specifies the symbol as [ft_i]. However, square-brackets [ and ] are not permitted as normal characters within a URI and are thus encoded as %5B and %5D respectively.


Lines 31-33 (Speed of motion)

  • Element <iwxxm:speedOfMotion> specifies the speed of the significant meteorological feature; in this case 60 knots.

SIGMET Forecast


The forecast provides one or more predicted positions of the volcanic ash cloud. This is encoded as an instance of <om:OM_Observation>.

Only VA and TC SIGMETS include this forecast section.

The IWXXM model requires that the sub-class of OM_Observation used for the forecast is SIGMETPositionAnalysis. Rule-based validation is required to ensure the use of the correct sub-class of OM_Observation.

The code fragment below illustrates the encoding of the forecast:

<iwxxm:forecastPositionAnalysis>
        <om:OM_Observation gml:id="va-position-EGXX-YYYYMM25T22Z">
            <om:type 
                xlink:href="http://data.wmo.int/def/observationType/iwxxm/1.0RC1/SIGMETPositionAnalysis" 
                xlink:title="SIGMETPositionAnalysis"/>
        </om:OM_Observation>
            <om:phenomenonTime>
                <gml:TimeInstant gml:id="time-instant-25T22Z">
                    <gml:timePosition>YYYY-MM-25T22:00:00Z</gml:timePosition>
                </gml:TimeInstant>
            </om:phenomenonTime>
            <om:resultTime xlink:href="#time-instant-25T16Z"/>
            <om:validTime xlink:href="#time-period-25T16Z-25T22Z"/>
            <om:procedure>
                <metce:Process gml:id="va-sigmet-position-forecast">
                    <metce:documentationRef
                        xlink:href="http://wis.wmo.int/procedure=Sigmet"
                        xlink:title="WMO No. 49 Volume 2 Meteorological Service for International Air Navigation 
                                     Appendix 6 TECHNICAL SPECIFICATIONS RELATED TO SIGMET AND AIRMET INFORMATION, 
                                     AERODROME WARNINGS AND WIND SHEAR WARNINGS AND ALERTS"/>
                </metce:Process>
            </om:procedure>
            <om:observedProperty 
                xlink:href="http://data.wmo.int/def/observableProperty/sigmet/positionAnalysis"
                xlink:title="Observed position and motion for significant weather phenomenon"/>
            <om:featureOfInterest xlink:href="#sampling-surface-SHANWICK_OCA"/>
            <om:result>...</om:result>
        </om:OM_Observation>
    </iwxxm:forecastPositionAnalysis>


The forecast <om:OM_Observation> follows the standard OM_Observation pattern;
  • phenomenon time
  • result time
  • valid time (see above for more information)
  • procedure
  • observed property
  • feature of interest
  • result

As the same feature of interest is used for both analysis and forecast, an xlink is used to refer to the definition of the feature of interest from the analysis; there is no need to repeat the definition.

Note that whilst the resultTime and validTime are identical to the values used in the analysis, the phenomenonTime is specified as 22:00Z (e.g. forecast for T+6 hours).

Forecast: result


The forecast result provides one or more predicted positions of the volcanic ash cloud.

As required by SIGMETPositionAnalysis, the result is constrained such that it must be an instance of MeteorologicalPositionCollection (from IWXXM). This class comprises one or more members, each of which must be of type MeteorologicalPosition (from IWXXM).

Once again, these classes have been specifically designed to meet the requirements published in ICAO Annex 3 / WMO No. 49 Volume 2 regulation.

IWXXM relies on rule-based validation to ensure that the appropriate type of entity is used for the result.

Each instance of MeteorologicalPosition shall contain one property geometry specified with type AirSpaceSolid (from ICAO Simple Aeronautical Features).

The code fragment below illustrates the encoding of <iwxxm:MeteorologicalPositionCollection>:

...
            <om:result>
                <iwxxm:MeteorologicalPositionCollection gml:id="collection-EGXX-YYYYMM25T16Z">
                    <iwxxm:member>
                        <iwxxm:MeteorologicalPosition gml:id="va-fcst-EGXX-YYYYMM25T16Z">
                            <iwxxm:geometry>
                                <saf:AirspaceSolid gml:id="va-geometry-EGXX-YYYYMM25T22Z">
                                    <saf:horizontalProjection>
                                        <gml:Polygon gml:id="volcanic-ash-cloud-polygon-EGXX-YYYYMM25T22Z" 
                                            axisLabels="Lat Lon" 
                                            srsDimension="2"
                                            srsName="http://www.opengis.net/def/crs/EPSG/0/4326">
                                            <gml:exterior>
                                                <gml:LinearRing>
                                                    <gml:posList>
                                                        60.0 -12.0 
                                                        58.0 -14.0 
                                                        60.0 -15.35
                                                    </gml:posList>
                                                </gml:LinearRing>
                                            </gml:exterior>
                                        </gml:Polygon>
                                    </saf:horizontalProjection>
                                    <saf:upperLimit uom="[ft_i]">
                                        55000
                                    </saf:upperLimit>
                                </saf:AirspaceSolid>
                            </iwxxm:geometry>
                        </iwxxm:MeteorologicalPosition>
                    </iwxxm:member>
                </iwxxm:MeteorologicalPositionCollection>
            </om:result>
...


The <saf:AirSpaceSolid> element provides the forecast position of the volcanic ash cloud at 22:00Z. The structure follows the pattern outlined earlier in the analysis result.

Note that line 24 specifies the unit of measure (e.g. uom) as [ft_i]. This is an alternative method of specifying the unit of measure "foot"; in this case the unit of measure is assumed to be specified in the Unified Code for Units of Measure (UCUM).


VA SIGMET as basis for VOLCANIC ASH ADVISORY (VAA)?

Finally, we note that the model and XML Schema elements developed to support the ICAO VA SIGMET requirement should provide an adequate basis for modelling and encoding the Volcanic Ash Advisory (VAA) product. Changes would be required to describe the report itself (e.g. allowing for a larger number of forecast elements etc.), but the OM_Observation-based approach using result types of EvolvingMeteorologicalCondition and MeteorologicalPositionCollection / MeteorologicalPosition with AirSpaceSolid to describe the shape of the ash cloud should be adequate.

Page last modified on Thursday 06 of December, 2012 15:52:31 CET