The Binary Universal Form for the Representation of meteorologicaldata is a binarydata format maintained by the World Meteorological Organization. The latest version is BUFR Edition 4. BUFR Edition 3 is also considered current for operational use. BUFR was created in 1988 with the goal of replacing the WMO's dozens of character-based, position-driven meteorological codes, such as SYNOP, TEMP and CLIMAT. BUFR was designed to be portable, compact, and universal. Any kind of data can be represented, along with its specific spatial/temporal context and any other associated metadata. In the WMO terminology, BUFR belongs to the category of table-driven code forms, where the meaning of data elements is determined by referring to a set of tables that are kept and maintained separately from the message itself. BUFR is a complex format that can be difficult to use and it presents some weaknesses. The introduction of BUFR format lead to data "disparition" and many formatting errors.
Description of format
A BUFR message is composed of six sections, numbered zero through five.
Sections 0, 1 and 5 contain static metadata, mostly for message identification.
Section 2 is optional; if used, it may contain arbitrary data in any form wished for by the creator of the message.
Section 3 contains a sequence of so-called descriptors that define the form and contents of the BUFR data product.
Section 4 is a bit-stream containing the message's core data and meta-data values as laid out by Section 3.
The product description contained in Section 3 can be made sophisticated and non-trivial by the use of replication and/or operator descriptors.
Templates
Section 3 contains a short header followed by a sequence of descriptors that matches the contents of Section 4's bit-stream. The sequence of descriptors in Section 3 could be understood as the template of the BUFR message. The template contains the information necessary to describe the structure of the data values embedded in the matching bit-stream. It is to be interpreted in a step-by-step, algorithm-like manner. Given a set of BUFR messages, the values contained in Section 4 may differ from one message to the next, but their ordering and structure will be kept predictable if the template provided in Section 3 remains unchanged. Templates can be designed to meet the requirements of a specific data product. Such templates can then be used to standardize the content and structure of BUFR data products. The WMO has released a number of BUFR templates for surface and upper air observational data.
Descriptors
All descriptors, 16 bits wide, have a F-X-Y structure, where F refers to the two most significant bits ; X refers to the 6 middle bits and Y to the least significant 8 bits. The F value determines the type of descriptor.
Element descriptors : As the name implies, these descriptors are used to convey elemental data and related meta-data. The X value identifies the Class of the descriptor. The Y value is the descriptor's number within its class. Element descriptors classes 1 through 9 have the special property of remaining in effect from the moment they appear throughout the remainder of the BUFR template, unless contradicted or cancelled. In practice, class 1 through 9 descriptors are used for spatial, temporal and other meta-data that is applicable to the core data of the BUFR message. All element descriptors are defined in a section of the BUFR specification known as "Table B". The addition of new element descriptors in Table B does not require changes to the BUFR software specification. The Table B definition of an element descriptor includes its number, short text definition, decoding parameters, and type.
Replication descriptors : Special descriptors that allow for the controlled repetition of a chosen number of descriptors. This is a very powerful operation that introduces loop-like structures in BUFR templates. The X value specifies the number of following descriptors to be included in the replication; the Y value indicates how many times the replication is to take place. If Y=0, then the replication is called a "delayed replication" and the number of replications is to be obtained from the value of a special element descriptor.
Operator descriptors : These descriptors convey special operations that can modify the character of data or allow for the creation and manipulation of additional data alongside the original. The X value identifies the operator and the Y value is used to control its application. These descriptors are defined in a section of the BUFR specification known as "Table C". The addition of new operator descriptors in Table C does require changes to the BUFR software specification, and therefore leads to a new BUFR Edition Number.
Sequence descriptors : A single sequence descriptor is an alias for a sequence of other descriptors, including replication descriptors and Table B, C and D entries. These descriptors are defined in a section of the BUFR specification known as "Table D". The use of the X and Y value is the same as with Element Descriptors.
Subsets
The data structure established in the Section 3 template may be re-used multiple times within a single BUFR message. In such a case, Section 4 will contain a succession of so-called subsets. For instance, subsets could be used to convey observations from several locations in a single message.
Online BUFR validators
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Software libraries
ECMWF provided and the new . and Metview use these to process and visualise BUFR data.
