1. Applicability of WIGOS for EUMETSAT Satellite Earth Observations
TT-WMD-5 (DEC 2016)
Guillaume Aubert

2. Introduction Background:
Assess usage of WIGOS Metadata Standard for EUMETSAT Satellite observations
Target:
Evaluate if the WIGOS standard (abstract model) is suitable (or not) to describe EO data from EUM Meteorological Satellites.
Assumptions:
Lots of the WIGOS elements are not relevant for EO but much more related to in-situ sensors.
Some elements may be missing which are evident for describing EO related datasets.

3. Introduction Objectives:
Define compulsory metadata elements related to earth observation data that are not yet covered by WIGOS Metadata
Provide information on what should be changed / added to allow a correct description of EO data based on satellite observations

4. Experience with metadata for Earth Observation
EUMETSAT involved in interoperability projects for more than 10 years
Earth Observation Product Metadata definition
Participation to ESA Heterogeneous Missions Access (HMA) project
Definition of an information model based on ISO and OGC O&M (OGC r40) profile called HMA O&M EOP
Use of metadata for the EUMETSAT Archive in the Submission Information Package (SIP)
SIP based on O&M EOP
Extensive metadata description for each measurements (every 3 min)
Compare WIGOS against HMA EO Metadata
Similar level of information
Contain minimum level of information to describe EO data

5. Background: Collection and Product Metadata
In HMA EO, metadata was organised with a two-step approach:
EO collections defined as sets of EO products sharing common generic characteristics
e.g. products of the same satellite (e.g. MSG) and the same instrument sensor (e.g. SEVIRI) acquired at different times.
Collection metadata elements:, data access, access constraints, producer, acquisition type (e.g. satellite, sensor instrument) or spatio-/temporal coverage,..)
Used for product discovery
EO products are individual product instances
e.g. one 15 min “image” product from MSG Seviri,
e.g. 3 min Metop ASCAT product,
Metadata more geared to technical details of the acquisition: orbit, calibration, quality, processing, etc
Used for data access

6. Background: Collection and Product Metadata ctd.
Collection Metadata: Based on ISO
Product Metadata:
Based on OGC Earth Observation Profile (OGC r4) of Observations and Measurements (ISO )

7. Assumptions for the Study
WIGOS is not meant to describe single EO products (instance)
The WIGOS repository is not meant to receive one metadata file every 3 min with individual instance parameters
The WIGOS repository contains information about the observation “technical” characteristics
WIGOS is more than discovery metadata
It contains a more exhaustive product description for satellite products (instrument, measurement technicalities)

8. O&M EOP delegates elements to ISO 19115-2 via parentIdentifier link
Considerations
O&M EOP delegates elements to ISO
via parentIdentifier link
Consider ISO for those parts
Validate that the most important metadata model elements of O&M EOP can be mapped with WIGOS
Validate that the minimal required ISO metadata elements can be mapped with WIGOS
For cross checking we also defined mappings from WIGOS to EOP + ISO:
ZPgPG62775RIsh-QMcEbaIHYPUCY/edit#gid=

9. Approach – Mapping ISO19115-2 to WIGOS
Check mapping ISO19115(-2) to WIGOS:
this included:
Check if minimal required ISO19115 (not -2!) elements covered:
Mostly covered*:
abstract/title/keywords/topicCategory (very rudimentary mappable to: 1-01/2-01/2-02/..), originator (10-01), processor (7-02), spatialExtent (1-04), temporalExtent (1-03), constraints (9-02), operationStatus (3-09), creation/revision/publication- date (7-03)
Not covered:
Metadata on metadata: metadata language, datestamp, contact point, metadata standard (name/version)
Checking if minimal important ISO elements are covered:
Covered*:
satellite/satelliteDescription (mapped to 3-06/3-03), instrument/instrumentType (mapped to 5-09 / 5-02)
* in () you´ll find the numbers of the WIGOS elements

10. Approach – Mapping O&M EOP to WIGOS
Mapping OGC O&M EOP to WIGOS:
we checked if (minimally) the most important metadata ele- ments of EOP O&M can be mapped to WIGOS metadata.
URL:
AlxJl-O5D2SAn7vHiveigYafe4w/edit#gid=
EO product specific metadata elements were not checked as it is not the target to describe single EO products

11. Conclusions – Missing Information (1)
QualityInfo is insufficiently considered in WIGOS
productQualityDegradation, productQualityStatus fields missing
Maybe only valid for product instances ?
Orbit Information
platformOrbitType may be interesting to include (GEO/LEO)
Few elements should be checked if those may make sense to include in WIGOS like: orbitDuration, orbitDirection

12. Conclusions – Missing Information (2)
Links to previews could be interesting
BrowseImage, QuickLook, Thumbnails
MaskInformation missing ?
Two kinds of identifier should be added into account: a URI (for being able to deference and link the dataset) and a Digital Object Identifier
Elements describing data access are fully missing
E.g: links (URLs) to direct downloads or access points
Reserved to discovery metadata ?

13. Conclusions – Questions
Are more elements to describe Abstract and keywords needed ?
In OGC/HMA this is usually overtaken by ISO19115 elements.
But it stays minimal to not overload the product metadata
It might be important to have link to related information. In HMA EOP there are:
parentIdentifier: used to link to the collection identifier
linkedWith: used to link another EO product (e.g. ERS1 and ERS2 interferometric pair)
subsetOf: used to link to the “father” EO product
composedOf: used to link to EO product that is part of this EO product

14. WIGOS abstract mode can be used to describe Earth Observation Products
Conslusions
WIGOS abstract mode can be used to describe Earth Observation Products
What about WMDR the metadata exchange format ?
To be verified in 2017 by CGMS Task Force on Metadata Implementation

15. Thank you !
Questions ?

16. More details below are provided if necessary
Appendix
More details below are provided if necessary

17. Approach – Mapping O&M EOP to WIGOS
Summary evaluations of mappings (see Fig.) are given in the following for groups of EO metadata elements (aligned with the groups found in OGC r4)
eop:EarthObservation
eop:EarthObservationMetaData
eop:EarthObservationEquipment
eop:Footprint
eop:EarthObservationResult
Per group the status is defined including what is not yet covered so that improvements / extensions are required.
* WIGOS element

18. Results eop:EarthObservation
The observation core (eop:EarthObservation) is sufficiently covered.
eop:EarthObservationMetaData
most elements are sufficiently mapped, others are just related to product instances (e.g. acquisitionDate, archivingDate) and are not considered
ProcessingInformation is sufficiently mapped.
some elements may need to be covered or need improvements
e.g. statusSubtype
QualityInfo is insufficiently considered in WIGOS, e.g. productQualityDegradation, productQualityStatus, productQualityDegradationTag, productQualityReportURL
To decide if this just relates to single Product instances

19. Results eop:EarthObservationEquipment
Platform and Instrument/Sensor seem sufficiently be covered.
platformOrbitType may be interesting to include (GEO/LEO)
Few elements should be checked if those may make sense to include in WIGOS like: orbitDuration, orbitDirection
Some acquisition information are too specific for metadata describing collections (more related to single product instances)
e.g. orbitNumber or ascendingNodeLongitude
sensorSwathIdentifier, sensorWavelengthInformation / discreteWavelengths etc…
eop:Footprint is covered
1-04

20. Results eop:EarthObservationResult
context is more related to single product instances
especially ProductInformation could be skipped if no single product instances shall be described
Maybe links to previews (BrowseImage, Quicklook, Thumbnail) could be interesting
what about MaskInformation ?
General observations
Minimally two kinds of identifier should be taken into account: a URI (for being able to deference and link the dataset) and a DOI.
The descriptions of different metadata elements need an update when those shall also be applied for EO related information:
e.g. description of “platform” to be extended to cover “satellite”
Elements describing data access are fully missing
For example: general access points (e.g. link to Order App) or links (URLs) to direct downloads could be addressed.

21. Results Maybe more elements needed to describe abstract and keywords.
In OGC/HMA this is usually overtaken by ISO19115 elements.
Need to be limited to basic information to not overload it
especially with regard to the case that in the future WIGOS metadata may also be used to describe single EO products.
For the future it would be important to have some hooks to link to related information. In HMA E&P we have:
parentIdentifier: used to link to the collection identifier.
Could be used in WIGOS to link e.g. to more general information (e.g. CGMS metadata if ISO19115 elements will not be covered)
subsetOf: used to link to the “father” EO product (e.g. a phr:Scene is a subset of a phr:DataStrip)
composedOf: used to link to EO product that is part of this EO product (e.g. a phr:DataStrip is composed of one or more phr:Scene)
linkedWith: used to link another EO product (e.g. ERS1 and ERS2 interferometric pair)