HMA Product Metadata Workshop CNES and CLS remarks on altimetry specificities

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

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

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

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

Altimetry specificities HMA Product Metadata Workshop

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

HMA Product Metadata Workshop

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

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

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

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

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

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