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WMO BUFR Format for NRT Dissemination of RO Data

WMO BUFR Format for NRT Dissemination of RO Data. Dave Offiler. What’s BUFR??. Binary Universal Format for the Representation of data (aka WMO FM-94 ) WMO standard (binary) format for observational data (like GRIB is for 2-d fields) For transmission on GTS/RMDCN

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WMO BUFR Format for NRT Dissemination of RO Data

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  1. WMO BUFR Format for NRT Dissemination of RO Data Dave Offiler

  2. What’s BUFR?? • Binary Universal Format for the Representation of data (aka WMO FM-94) • WMO standard (binary) format for observational data (like GRIB is for 2-d fields) • For transmission on GTS/RMDCN • Often used for archiving and interface to NWP assimilation systems • Self-defining data stream by use of common tables

  3. BUFR Bits (1) A BUFR message consists of 6 sections: 0) “BUFR” 1) Header - IDs, Date/Time etc 2) Optional data (not often used) 3) List of descriptors 4) User data (bit stream) 5) “7777”

  4. BUFR Bits (2) BUFR is table-driven by descriptors Descriptors types: Element (observation parameters) - Table ‘B’ Repetition (repeated sequences) Operator (change scale, reference values…) Sequence (common sequences) - Table ‘D’ Can give modest compression (typically 2:1) when several like observations are encoded together.

  5. RO in BUFR Guiding Principles • BUFR format is for NRT users - principally NWP • KISS • Minimise number of new Table entries • Re-use existing entries where-ever possible • Only encode parameters useful to the target user-base (sub-set of ‘Level 2’ data) • Generic (mission-independent) RO • Full data still available by other means

  6. Result? • Working prototype at Met Office (see draft doc) • Satellite Ids, Date/Time, RoC, SSV (1 per occ.) • 200 samples for profiles of Impact Parameter and Bending Angle • 150 samples of profiles of Refractivity, P,T,q (incl. B/g T) • Total number of elements: 3088 • Total expanded descriptors: 3496 • Each occultation (uncompressed): 6144 bytes

  7. What Next? • Feedback from this forum • Use ‘delayed’ instead of ‘fixed’ replication - more complex to encode & decode, but more flexible. (Fixed is limited to max. 254 replications). Will we ever need >250? • Remove B/g T & associated meta-data? • Add Q/C information (per sample) • Update & test BUFR; one more round; submit to WMO for formal approval; use on GTS/RMDCN

  8. Over to you! • But remember Guiding Principle No.1: • It’s for NRT dissemination over GTS/RMDCN • It’s targeted specifically for NWP users An intermediate, generic file content and format is also in development, which could provide an interface between mission-specific files and BUFR or other applications. Feedback on this also welcome. Ultimately, users will continue have access to the mission- (and processing centre-) specific full-content files from EUMETSAT (CGS & GRAS SAF), UCAR, JPL, GFZ….

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