AvXML-1.1-tutorial-va-sigmet-EGXX-YYYY-MM-25T16Z
Caution - the contents of this tutorial are currently just a copy of those for AvXML 1.0RC2.
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:
| Description | XML Namespace | Default namespace prefix |
| XML Schema | http://www.w3.org/2001/XMLSchema | xsd |
| Schematron | http://purl.oclc.org/dsdl/schematron | sch |
| XSLT v2 | http://www.w3.org/1999/XSL/Transform | xsl |
| XML Linking Language | http://www.w3.org/1999/xlink | xlink |
| OGC GML 3.2.1 | http://www.opengis.net/gml/3.2 | gml |
| ISO/TS 19139:2007 metadata XML schema implementation | http://www.isotc211.org/2005/gmd | gmd |
| OGC OMXML Observations and Measurements | http://www.opengis.net/om/2.0 | om |
| OGC OMXML Sampling Features | http://www.opengis.net/sampling/2.0 | sf |
| OGC OMXML Spatial Sampling Features | http://www.opengis.net/samplingSpatial/2.0 | sams |
| WMO Observable Property Model(1.0RC2) | http://def.wmo.int/opm/2013 | opm |
| WMO METCE (1.0RC2) | http://def.wmo.int/metce/2013 | metce |
| ICAO Simple Aviation Features (1.0RC2) | http://icao.int/saf/1.0RC2 | saf |
| ICAO Meteorological Information Exchange Model (1.0RC2) | http://icao.int/iwxxm/1.0RC2 | iwxxm |
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/1.0RC2"
xmlns:saf="http://icao.int/saf/1.0RC2"
xmlns:metce="http://def.wmo.int/metce/2013"
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/1.0RC2 http://schemas.wmo.int/iwxxm/1.0RC2/iwxxm.xsd
http://def.wmo.int/metce/2013 http://schemas.wmo.int/metce/1.0RC2/metce.xsd"
gml:id="va-sigmet-EGXX-YYYYMM25T160000Z"
status="NORMAL">
<iwxxm:issuingAirTrafficServicesUnit/>
<iwxxm:originatingMeteorologicalWatchOffice/>
<iwxxm:sequenceNumber>4</iwxxm:sequenceNumber>
<iwxxm:validPeriod/>
<iwxxm:phenomenon xlink:href="http://codes.wmo.int/49-2/SigWxPhenomena/VA" xlink:title="Volcanic Ash"/>
<iwxxm:analysis/>
<iwxxm:forecastPositionAnalysis/>
<iwxxm:eruptingVolcano/>
</iwxxm:VolcanicAshSIGMET>The VA SIGMET report comprises:
- (Line 16) a unique identifier for the report (e.g. "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) report status; in this case normal
- (Line 18) information about the issuing Air Traffic Services Unit (elaborated below)
- (Line 19) information about the originating Meteorological Watch Office (elaborated below)
- (Line 20) report sequence number - following the standard ICAO Annex 3 (WMO No. 49 Vol 2) rules for report assigning sequence numbers
- (Line 21) definition of the validity period for this report (elaborated below)
- (Line 22) definition of the significant weather phenomenon that the report describes; in this case Volcanic Ash. Terms are referenced using xlink:href from the WMO Codes Register http://codes.wmo.int/49-2/SigWxPhenomena. xlink:title is provided to supplement human readability. At time of publication of RC2, the WMO Codes Registry is yet to be deployed at http://codes.wmo.int. In the interim, please refer to the BETA deployment at http://test.wmocodes.info; for example - http://test.wmocodes.info/49-2/SigWxPhenomena/VA.
- (line 23) 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> (elaborated below).
- (Line 24) the forecast provides one or more predicted positions of the volcanic ash cloud. This is encoded as an instance of <om:OM_Observation> (elaborated below).
- (Line 25) provides information about the source of the volcanic ash; the name and position of the erupting volcano (elaborated below).
Issuing Air Traffic Services Unit and Originating Meteorological Watch Office
...
<iwxxm:issuingAirTrafficServicesUnit>
<saf:Unit gml:id="uuid.51cd8be0-b72e-11e2-9e96-0800200c9a66">
<gml:identifier codeSpace="urn:uuid:">51cd8be0-b72e-11e2-9e96-0800200c9a66</gml:identifier>
<saf:name>SHANWICK OCEANIC AREA CONTROL CENTRE</saf:name>
<saf:type>ATCC</saf:type>
<saf:designator>EGXX</saf:designator>
</saf:Unit>
</iwxxm:issuingAirTrafficServicesUnit>
<iwxxm:originatingMeteorologicalWatchOffice>
<saf:Unit gml:id="uuid.7abf6b40-b72e-11e2-9e96-0800200c9a66">
<gml:identifier codeSpace="urn:uuid:">7abf6b40-b72e-11e2-9e96-0800200c9a66</gml:identifier>
<saf:name>UK METEOROLOGICAL OFFICE - EXETER</saf:name>
<saf:type>MWO</saf:type>
<saf:designator>EGRR</saf:designator>
</saf:Unit>
</iwxxm:originatingMeteorologicalWatchOffice>
...- Information about both Issuing Air Traffic Services Unit (ATSU) and Originating Meteorological Watch Office (MWO) is included in the SIGMET report. Both of these entities conform to the Unit data model defined in the Simple Aeronautical Features (SAF). This data model is intended to align with the broader ICAO Aeronautical Information Reference Model (AIRM); albeit only providing a subset of the information required for meteorological products.
- A core feature enabling consistency and alignment within the AIRM, is the use of UUIDs (RFC 4122) for identifying and referencing information about aeronautical features. The use of UUIDs is adopted from Aeronautical Information eXchange Model (AIXM) 5, conjointly developed by EuroControl and US FAA. A managed set of information describing an aeronautical feature is allocated a UUID by the data publisher. The UUID is an opaque identifier and may be automatically generated (e.g. using an online UUID-generator or other mechanism). Once assigned by a data publisher, the UUID may be used as a unique reference to the given set of information, thus enabling distributed systems to assert that they are, indeed, using consistent information.
- Additional information provided about the ATSU and MWO includes:
- name; this must be provided in BLOCK CAPITALS
- type; one of the following options - ARO (Aerodrome Reporting Office/ATS Reporting Office), ATCC (Air Traffic Control Centre), ATSU (Air Traffic Services Unit), FIC (Flight Information Centre) or MWO (Meteorological Watch Office)
- designator; the coded designator associated with the Unit - this may be the ICAO 4-letter Location Indicator as specified in ICAO Doc 7910.
Valid period
...
<iwxxm:validPeriod>
<gml:TimePeriod gml:id="tp-25T16Z-25T22Z">
<gml:beginPosition>YYYY-MM-25T16:00:00Z</gml:beginPosition>
<gml:endPosition>YYYY-MM-25T22:00:00Z</gml:endPosition>
</gml:TimePeriod>
</iwxxm:validPeriod>
...- <iwxxm:validPeriod> defines the period during which this SIGMET is valid; noting the use of YYYY and MM in place of year and month - normally these would be populated (e.g. 2013-05-08T15:58:00Z)
- The <om:OM_Observation> instances for the analysis 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.
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://codes.wmo.int/49-2/observation-type/IWXXM/1.0/SIGMETEvolvingConditionAnalysis"/>
<om:phenomenonTime>
<gml:TimeInstant gml:id="ti-25T16Z">
<gml:timePosition>YYYY-MM-25T16:00:00Z</gml:timePosition>
</gml:TimeInstant>
</om:phenomenonTime>
<om:resultTime xlink:href="#ti-25T16Z"/>
<om:validTime xlink:href="#tp-25T16Z-25T22Z"/>
<om:procedure/>
<om:observedProperty
xlink:href="http://codes.wmo.int/49-2/SigWxPhenomena/VA"
xlink:title="Volcanic ash"/>
<om:featureOfInterest/>
<om:result/>
</om:OM_Observation>
</iwxxm:analysis>
...The analysis <om:OM_Observation> follows the standard OM_Observation pattern:
- (Line 3) the <om:OM_Observation> instance is allocated a unique identifier within the scope of the XML document (e.g. "va-position-and-motion-EGXX-YYYYMM25T16Z"); there are no special rules applied here with regards to the structure of the identifier. The only requirements are that it is unique within the document.
- (Line 4) as outlined in the METAR tutorial, the observation type is specified via reference to a definition published within the WMO Codes Registry. For SIGMET "analysis" this is SIGMETEvolvingConditionAnalysis. At time of publishing RC2 the WMO Codes Registry is not yet deployed operationally at http://codes.wmo.int; please refer to the BETA deployment at http://test.wmocodes.info (e.g. http://test.wmocodes.info/49-2/observation-type/IWXXM/1.0/SIGMETEvolvingConditionAnalysis).
- (Lines 5-9) the phenomenon time indicates the time-instant associated with the given position and motion of the volcanic ash cloud described in the result below. In this example, the observed position and motion of the ash cloud is provided, thus the phenomenonTime is commensurate with the beginning of the SIGMET report validity period. The phenomenon time is expressed in ISO 8601 format; "YYYY-MM-25T16:00:00Z" (noting that YYYY and MM would normally specify year and month respectively).
- (Line 10) the result time indicates the time-instance at which the information about the position and motion of the volcanic ash cloud was made available. This always commensurate with the beginning of the SIGMET report validity period. In this case, this is the same time-instant that was used to describe the phenomenon time thus xlink:href is used to refer to the earlier definition.
- (Line 11) the valid time indicates the time-period for which the information about the position and motion of the volcanic ash cloud is valid - in this case according to international regulation. This is identical to the valid period defined in the body of the SIGMET report, thus xlink:href is used to refer to the earlier definition.
- (Line 12) the procedure by which the position and motion of the volcanic ash cloud was observed (elaborated below).
- (Lines 13-15) the observed property identifies the physical phenomenon being observed. Following consideration, it seems appropriate to reference "volcanic ash" as the observed property, rather than an aggregate of "position and motion" about some undefined significant weather phenomena! The observed property is used a key when searching for content within a service conforming to the Open Geospatial Consortium's Sensor Observation Service (SOS) specification; it seems likely that consumers of the data product will search based on the type of significant weather phenomena rather than the characteristics of that phenomenon. Given that observed property must be a reference (e.g. specified using xlink:href), we reference a term from the WMO Codes Registry (e.g. http://codes.wmo.int/49-2/SigWxPhenomena/VA). xlink:title provides a supplemental human-readable description. At time of publishing RC2 the WMO Codes Registry is not yet deployed operationally at http://codes.wmo.int; please refer to the BETA deployment at http://test.wmocodes.info (e.g. http://test.wmocodes.info/49-2/SigWxPhenomena/VA).
- (Line 16) the feature of interest provides information about the real world feature that the observation pertains to - in this case a Flight Information Region (elaborated below).
- (Line 17) the result provides the information about the observed characteristics of the volcanic ash cloud (elaborated below).
SIGMET Analysis: Procedure
...
<om:procedure>
<metce:Process gml:id="p-49-2-va-sigmet">
<gml:description>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
</gml:description>
</metce:Process>
</om:procedure>
...As outlined in the METAR example, the procedure is constrained such that is must be an instance of METCE Process. As described therein, <gml:description> is used to cite a well-known reference - in this case the appropriate clause from the ICAO Annex 3 (WMO No. 49 Vol 2) technical regulations.
SIGMET Analysis: Feature of interest
...
<om:featureOfInterest>
<sams:SF_SpatialSamplingFeature gml:id="ss-SHANWICK_OCA">
<sam:type xlink:href="http://www.opengis.net/def/samplingFeatureType/OGC-OM/2.0/SF_SamplingSurface"/>
<sam:sampledFeature>
<saf:Airspace gml:id="uuid.37a7f1d0-b731-11e2-9e96-0800200c9a66">
<gml:identifier codeSpace="urn:uuid:">37a7f1d0-b731-11e2-9e96-0800200c9a66</gml:identifier>
<saf:type>FIR</saf:type>
<saf:designator>EGXX</saf:designator>
<saf:name>SHANWICK OCEANIC FLIGHT INFORMATION REGION</saf:name>
<saf:geometryComponent>
<saf:AirspaceVolume gml:id="av-SHANWICK_OCA">
<!-- note that upper limit and lower limit of the airspace volume are excluded -
implying that the volume extends from ground/sea surface to upper limit of aeronautical operations -->
<saf:horizontalProjection>
<gml:Polygon gml:id="boundary-geometry-SHANWICK_OCA"
uomLabels="deg deg"
axisLabels="Lat Lon"
srsDimension="2"
srsName="http://www.opengis.net/def/crs/EPSG/0/4326">
<gml:exterior>
<gml:LinearRing>
<!-- SHANWICK FIR boundary (positions defined based on reference to map so possibly incorrect) -->
<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
60.0 -30.0
</gml:posList>
</gml:LinearRing>
</gml:exterior>
</gml:Polygon>
</saf:horizontalProjection>
</saf:AirspaceVolume>
</saf:geometryComponent>
</saf:Airspace>
</sam:sampledFeature>
<sams:shape xlink:href="#boundary-geometry-SHANWICK_OCA"/>
</sams:SF_SpatialSamplingFeature>
</om:featureOfInterest>
...The feature of interest for the SIGMET analysis is intended to describe the Flight Information Region associated with the SIGMET report. As such, the feature of interest is constrained such that it must be an instance of SF_SamplingSurface and thus follows the standard pattern for all SF_SpatialSamplingFeatures:
- (Line 3) the <sams:SF_SpatialSamplingFeature> instance is allocated a unique identifier within the scope of the XML document (e.g. "ss-SHANWICK_OCA"); there are no special rules applied here with regards to the structure of the identifier. The only requirements are that it is unique within the document.
- (Line 4) the type of the <sams:SF_SpatialSamplingFeature> instance; in this case a SF_SamplingSurface.
- (Lines 5-42) the sampled feature describes the real world feature to which the observation pertains; in this case the Shanwick Oceanic Flight Information Region.
- (Lines 6-41) in lieu of an authoritative web-accessible register of information about Flight Information Regions, the information about Shanwick Oceanic FIR must be embedded within the SIGMET report. The data model used to describe the FIR is Airspace from Simple Aeronautical Features (SAF). This data model is intended to align with the broader ICAO Aeronautical Information Reference Model (AIRM); albeit only providing a subset of the information required for meteorological products. A core feature enabling consistency and alignment within the AIRM, is the use of UUIDs (RFC 4122) as outlined above (ATSU and MWO) - see lines 6-7. Additional information provided about the Airspace includes:
- (Line 8) type; one of FIR (Flight Information Region), UIR (Upper flight Information Region) or CTA (Control Area)
- (Line 9) designator; a coded designator associated with the Airspace - in this case the ICAO location indicator "EGXX"
- (Line 10) name; the textual name allocated to the Airspace by the responsible authority - this must be provided in BLOCK CAPITALS
- (Lines 11-40) geometry component; providing a 2.5-dimensional description of the Airspace using an instance of <saf:AirspaceVolume>. In the case of this FIR, only the horizontal projection is given; the omitted upper limit and lower limit imply that the AirspaceVolume extends from ground/sea surface to the upper limit of aeronautical operations. The horizontal projection is provided as an instance of <gml:Polygon> uniquely identified as "boundary-geometry-SHANWICK_OCA". Note that, as per the GML specification, the first and last points defining the polygon are coincident. Also note that for this example, the geometry may not accurately reflect the true boundary of Shanwick Oceanic FIR.
- (Lines 6-41) in lieu of an authoritative web-accessible register of information about Flight Information Regions, the information about Shanwick Oceanic FIR must be embedded within the SIGMET report. The data model used to describe the FIR is Airspace from Simple Aeronautical Features (SAF). This data model is intended to align with the broader ICAO Aeronautical Information Reference Model (AIRM); albeit only providing a subset of the information required for meteorological products. A core feature enabling consistency and alignment within the AIRM, is the use of UUIDs (RFC 4122) as outlined above (ATSU and MWO) - see lines 6-7. Additional information provided about the Airspace includes:
- (Line 43) shape is a mandatory part of the <sams:SF_SpatialSamplingFeature>. For a sampling surface, shape must refer to a 2-dimensional geometry. In this case, the extent of the sampling surface matches that of the FIR thus we use xlink:href to refer to the earlier definition of the FIR bounding polygon "boundary-geometry-SHANWICK_OCA".
SIGMET Analysis: Result
...
<om:result>
<iwxxm:EvolvingMeteorologicalCondition gml:id="emc-va-obs-EGXX-YYYYMM25T16Z" intensityChange="NO_CHANGE">
<iwxxm:directionOfMotion uom="deg">180</iwxxm:directionOfMotion>
<iwxxm:geometry>
<saf:AirspaceVolume gml:id="av-va-obs-position-EGXX-YYYYMM25T16Z">
<!-- omitted lower-limit implies that the volcanic ash cloud extends to ground/sea surface -->
<saf:upperLimit uom="[ft_i]">55000</saf:upperLimit>
<saf:upperLimitReference>STD</saf:upperLimitReference>
<saf:horizontalProjection>
<gml:Polygon gml:id="polygon-va-obs-position-EGXX-YYYYMM25T16Z"
uomLabels="deg deg"
axisLabels="Lat Lon"
srsDimension="2"
srsName="http://www.opengis.net/def/crs/EPSG/0/4326">
<gml:exterior>
<gml:LinearRing>
<!-- bounding polygon clipped to edge of FIR @ 60N -->
<gml:posList>
60.0 -11.5
59.0 -13.0
60.0 -16.0
60.0 -11.5
</gml:posList>
</gml:LinearRing>
</gml:exterior>
</gml:Polygon>
</saf:horizontalProjection>
</saf:AirspaceVolume>
</iwxxm:geometry>
<iwxxm:speedOfMotion uom="knot">60</iwxxm:speedOfMotion>
</iwxxm:EvolvingMeteorologicalCondition>
</om:result>
...The analysis result provides the observed position and motion characteristics of the volcanic ash cloud. In order to align with timings for Volcanic Ash Advisory (VAA) products, the SIGMET analysis may describe the characteristics of the volcanic ash cloud at some point in the near future (e.g. up to 2-hours hence); e.g. a forecast of the volcanic ash cloud characteristics.
As required by 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 Vol 2) regulation and allows one to specify both the position and motion of a meteorological features (e.g. the volcanic ash cloud or other significant weather phenomena).
The code fragment above illustrates the encoding of <iwxxm:EvolvingMeteorologicalCondition>:
- (Line 3) the instance of <iwxxm:EvolvingMeteorologicalCondition> is uniquely identified within the scope of the XML document. Additionally, we see the intensity change specified as an XML attribute. In this case the value is "NO_CHANGE". The permitted set of options also include "WEAKEN" and "INTENSIFY" as per the ICAO Annex 3 (WMO No. 49 Vol 2) technical regulation.
- (Line 4) specifies the direction of motion of the volcanic ash cloud specified in degrees from true-north; in this case the value is 180 degrees (e.g. due south).
- (Lines 5-30) specifies a 2.5-dimensional representation of the observed geometry of the volcanic ash cloud using an instance of <saf:AirspaceVolume>. In this case, the horizontal projection is given (lines 10-28) along with the upper limit of 55000 feet (line 8); the omitted lower limit implies that the AirspaceVolume extends to the ground/sea surface. Note the UCUM symbol for unit of measure feet: "ft_i" (line 8). Also note that the upper-limit height is specified as measured in the ICAO standard atmosphere "STD" thus allowing for assessment of altitude as a linear distance when reading converting from barometric pressure (line 9). The horizontal projection is provided as an instance of <gml:Polygon> uniquely identified as "polygon-va-obs-position-EGXX-YYYYMM25T16Z" (lines 11-27). Note that, as per the GML specification, the first and last points defining the polygon are coincident. Following advice from ICAO sercretariat, the horizontal projection of the significant meteorological feature must always be defined as a closed polygon. This 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.
- (Line 31) specifies the speed of motion of the volcanic ash cloud; in this case a velocity of 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 code fragment below illustrates the encoding of the forecast:
...
<iwxxm:forecastPositionAnalysis>
<om:OM_Observation gml:id="va-forecast-position-EGXX-YYYYMM25T22Z">
<om:type xlink:href="http://codes.wmo.int/49-2/observation-type/IWXXM/1.0/SIGMETPositionAnalysis"/>
<om:phenomenonTime>
<gml:TimeInstant gml:id="ti-25T22Z">
<gml:timePosition>YYYY-MM-25T22:00:00Z</gml:timePosition>
</gml:TimeInstant>
</om:phenomenonTime>
<om:resultTime xlink:href="#ti-25T16Z"/>
<om:validTime xlink:href="#tp-25T16Z-25T22Z"/>
<om:procedure xlink:href="#p-49-2-va-sigmet"/>
<om:observedProperty
xlink:href="http://codes.wmo.int/49-2/SigWxPhenomena/VA"
xlink:title="Volcanic ash"/>
<om:featureOfInterest xlink:href="#ss-SHANWICK_OCA"/>
<om:result/>
</om:OM_Observation>
</iwxxm:forecastPositionAnalysis>
...The IWXXM model requires that the sub-class of OM_Observation used for the forecast is SIGMETPositionAnalysis, thus the forecast follows the standard OM_Observation pattern outlined above for the SIGMET analysis;
- (Line 4) observation type; for SIGMET "forecast" this is SIGMETPositionAnalysis. At time of publishing RC2 the WMO Codes Registry is not yet deployed operationally at http://codes.wmo.int; please refer to the BETA deployment at http://test.wmocodes.info (e.g. http://test.wmocodes.info/49-2/observation-type/IWXXM/1.0/SIGMETPositionAnalysis).
- (Line 5-9) phenomenon time; on this occasion referring to the time associated with the forecast position of the volcanic ash cloud - 22:00hrs (e.g. forecast for T+6 hours).
- (Line 10) result time; as both SIGMET "analysis" and "forecast" are made available at the same time, commensurate with the beginning of the SIGMET report valid period, we can use xlink:href to refer to the earlier definition.
- (Line 11) valid time; once more this is identical to the SIGMET report valid period; xlink:href is used to refer to the earlier definition.
- (Line 12) procedure; given that the ICAO Annex 3 (WMO No. 49 Vol 2) clause cited within the SIGMET "analysis" covers all parts of the SIGMET generation procedure, the process definition can be reused here. xlink:href is used to refer to the previous definition.
- (Lines 13-15) observed property; as defined above within the SIGMET "analysis" - volcanic ash.
- (Line 16) feature of interest; both SIGMET "analysis" and "forecast" refer to the same FIR thus the previous definition of the sampling surface can be reused (e.g. "ss-SHANWICK_OCA"). xlink:href is used to refer to the earlier definition.
- (Line 17) result provides one or more predicted postions of the volcanic ash cloud (elaborated below).
SIGMET Forecast: Result
...
<om:result>
<iwxxm:MeteorologicalPositionCollection gml:id="mpc-EGXX-YYYYMM25T16Z">
<iwxxm:member>
<iwxxm:MeteorologicalPosition gml:id="mp-va-fcst-EGXX-YYYYMM25T16Z">
<iwxxm:geometry>
<saf:AirspaceVolume gml:id="av-va-fcst-position-EGXX-YYYYMM25T22Z">
<!-- omitted lower-limit implies that the volcanic ash cloud extends to ground/sea surface -->
<saf:upperLimit uom="[ft_i]">55000</saf:upperLimit>
<saf:upperLimitReference>STD</saf:upperLimitReference>
<saf:horizontalProjection>
<gml:Polygon gml:id="polygon-va-fcst-position-EGXX-YYYYMM25T22Z"
uomLabels="deg deg"
axisLabels="Lat Lon"
srsDimension="2"
srsName="http://www.opengis.net/def/crs/EPSG/0/4326">
<gml:exterior>
<gml:LinearRing>
<!-- bounding polygon clipped to edge of FIR @ 60N -->
<gml:posList>
60.0 -12.0
58.0 -14.0
60.0 -15.35
60.0 -12.0
</gml:posList>
</gml:LinearRing>
</gml:exterior>
</gml:Polygon>
</saf:horizontalProjection>
</saf:AirspaceVolume>
</iwxxm:geometry>
</iwxxm:MeteorologicalPosition>
</iwxxm:member>
</iwxxm:MeteorologicalPositionCollection>
</om: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.
The code fragment above illustrates the encoding of <iwxxm:MeteorologicalPositionCollection>:
- (Lines 3-34) define the collection - on this occasion with just a single member (e.g. only one position is predicted for the volcanic ash cloud at T+6hrs).
- (Lines 5-32) define the position of the volcanic ash cloud at 22:00Z. The SIGMET "forecast" only requires the geometry of the volcanic ash cloud to be provided - once more via an instance of <saf:AirspaceVolume> (lines 7-30).
Erupting volcano
...
<iwxxm:eruptingVolcano>
<metce:Volcano gml:id="v-MT-HEKLA">
<metce:name>MT HEKLA</metce:name>
<metce:position>
<gml:Point gml:id="ref-point-MT-HEKLA"
uomLabels="deg deg"
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>
...The final element of the VA SIGMET report is provision of information about the source of the volcanic ash; the name and position of the erupting volcano. The code fragment above illustrates:
- (Line 3) erupting volcano; a uniquely identified instance of <metce:Volcano>. METCE also provides a EruptingVolcano class which the provision for stating the date of the volcanic eruption if known. However, there is no requirement to provide this information within the VA SIGMET.
- (Line 4) volcano name. Note that the "Global Volcanism Program" provides an online, searchable catalogue of volcanoes which may assist in identifying the authoritative name for a given volcano feature.
- (Lines 5-13) position specifies the geographic location of the volcano using an instance of <gml:Point>.