1. HMA Product Metadata Workshop
CNES and CLS remarks on altimetry specificities

2. Table of content Objectives and introduction Context of the study
Altimetry specificities (JASON)
Altimetry specificities
Work done : metadata comparison
Conclusions from metadata comparison
HMA Product Metadata Workshop

3. Objectives and introduction
The objectives of this study is
to provide inputs for the integration of altimetry thematic in HMA
In CNES,
we have started to implement HMA compliant interfaces for HMA-OPT product
SPOT and PLEIADES data
We have a generic data valorization tool : SIPAD-NG
Used for Mercator, CDPP, SMOS, SSALTO
And soon on ICARE, DECLIC, SERAD
We want to implement a HMA compliant interface to our generic tool
Activity started in the frame of ICARE with POLDER data
We have started the development linked to POLDER
Activity started in the frame of SSALTO in altimetry thematic
Need for a specialization of HMA metadata for altimetry
HMA Product Metadata Workshop

4. Context of the study The target of our study is
Nadir altimeter like JASON1, JASON2, …
The reference taken for this study is
JASON2
Most recent altimeter
Most complete metadata
Our feeling is that HMA is more mature for OPT products
Work is to be done in the other thematics
ATM
ALT
Altimetry is different from OPT
Then these differences / specificities have to be taken into account
HMA Product Metadata Workshop

5. Altimetry specificities (JASON)
High altitude : 1336 km
To minimise interactions with atmosphere and Earth gravity field
To improve orbite determination
Inclination : 66°
Allow to cover most of non frozen seas
Repeatable orbit
Roughly 10 days (10 days minus 2h)
The satellite measure the same points every 10 days
With a 1km precision
Non heliosynchroneous orbit
HMA Product Metadata Workshop

6. Altimetry specificities
HMA Product Metadata Workshop

7. Altimetry specificities
The elementary measure is a point
Measures can be taken at various frequencies
1 Hz : 1 measure per second
20 Hz : 20 measures per second
It is possible to find products with both frequencies
Data are gathered in files : one file per track
One track is a half-orbit (descending or ascending)
A cycle is composed of 254 tracks and covers one revisit period of time
One track is a line, not a surface
The altimeter measure do not have any width
This is a specificity versus OPT measures
HMA Product Metadata Workshop

8. HMA Product Metadata Workshop

9. Altimetry specificities
Data can be produced in several modes
Del ayedTime,, NRT, nonTimeCritical, realTime, shortTimeCritical
Delay versus quality
Specific Ellipsoid
No EPSG code : TOPEX
Geolocalisation metadata available in other ellipsoids (WGS84, …)??
Specific level of products
L0, L1, L1a, L1b, L2, L3, L4
Not the same meaning as for OPT thematic
L1, L2 or L3/L4 users are not the same
Which data have to be taken into account by HMA?
HMA Product Metadata Workshop

10. Work done
Excel sheet
displaying differences and correspondences between HMA and JASON2 metadata (on SIPAD-NG)
Discussed with EUMETSAT
The identified differences are available in the ISO 19115
If mandatory some fields could be available in both ISO19115 and HMA metadata
is available on demand
HMA Product Metadata Workshop

11. Conclusions from metadata comparison : data organization
It should be checked that the specific altimetry product data organization can be represented with HMA
Cycle / track notions
Cycle_min, Cycle_max
<eop:EarthObservationEquipment>, with orbit information
What is the granularity of the data handled with HMA
What is the product levels that have to be considered? L1 L2
L3/L4
Beta product ?
HMA Product Metadata Workshop

12. Conclusions from metadata comparison : processing info
Is it possible to represent the processing temporal mode / timeline information
NRT, realTime, …
there are some existing definition in the frame of SENTINEL program using the concepts of ‘short time/non time critical’.
also something  identified within MyOcean project
To be added in EOP
<eop:EarthObservationResult> (with version)
or <eop:EarthObservationMetadata with creation date
Is the meaning of the altimetry product level compliant with the one defined by HMA
HMA Product Metadata Workshop

13. Conclusions from metadata comparison : data content
Is it possible to use TOPEX ellipsoid
There is no EPSG code for TOPEX!
Resolution information as a sampling frequency (1 Hz, 20 Hz, both) to be added?
The altimetry products provides several variables
Sea surface height, wave, wind, …
Correction measurements (meteo fields, tides, …)
Standardization of this has already been done in CF metadata
CF  Climate and Forecast
already used for Jason-2 products
For each geophysical variable there is one CF standard_name (see screen capture j2-metadata.jpeg).  Each standard name correspond to one entry in CF, with a definition (see cf-ssh.jpg).
HMA Product Metadata Workshop

14. Conclusions from metadata comparison : info representation
How to take into account that the measure is a line?
Is it required to produce thumbnail / quicklook
description + vocabularies
Eop:EarthObservationEquipment
platform/sensor/instrument
just take care to take the same references (MyOcean project).
Some OWL/SKOS vocabularies would be a good thing.
HMA Product Metadata Workshop