1. 1 © Crown copyright 2003 GRAS SAF User Workshop Helsingør, Denmark, 11-13 June 2003 WMO BUFR Format for NRT Dissemination of RO Data Dave Offiler

2. GRAS SAF User Workshop Helsingør, Denmark, 11-13 June 2003 2 © Crown copyright 2003 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. GRAS SAF User Workshop Helsingør, Denmark, 11-13 June 2003 3 © Crown copyright 2003 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. GRAS SAF User Workshop Helsingør, Denmark, 11-13 June 2003 4 © Crown copyright 2003 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. GRAS SAF User Workshop Helsingør, Denmark, 11-13 June 2003 5 © Crown copyright 2003 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. GRAS SAF User Workshop Helsingør, Denmark, 11-13 June 2003 6 © Crown copyright 2003 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. GRAS SAF User Workshop Helsingør, Denmark, 11-13 June 2003 7 © Crown copyright 2003 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. GRAS SAF User Workshop Helsingør, Denmark, 11-13 June 2003 8 © Crown copyright 2003 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….