CREX APPLICATIONS

1. CREX APPLICATIONS 14 December 2005 (Joël Martellet, WMO, World Weather Watch, Data Processing and Forecasting Systems)

2. CREX APPLICATIONS • WHAT ARE THE MAIN CHARACTERISTICS OF THE CODE? • WHAT CAN BE ITS USE? • EXAMPLES

3. CREX MAIN CHARACTERISTICS • CREX is coded in characters (not bits), in the same manner as traditional WMO codes • CREX has no compression scheme • CREX allows other units than SI units (temperature can be in Celsius rather than Kelvin) • CREX is readable by human • CREX is expandable • CREX is self-descriptive

4. Main CREX Use: Represent New Information With Readability Requirements • New types of data continue to become available • Requests for additions to current data types continue to be made • The pace of this evolution continues to accelerate, and the traditional character code forms are not well suited to meet this challenge. • The self‑descriptive feature of CREX leads directly to its most significant advantage over the traditional alphanumeric code forms – the ability of CREX to adapt to represent new information quickly and easily – BUFR can do this too. However, since CREX is also an alphanumeric code form it is human readable. This additional characteristic makes it the code form of choice when there is a requirement for manual encoding or no binary transmission is possible. • As with BUFR, if all the necessary table entries are available one may in principle immediately encode CREX messages with new information and automated decoding software will not have to change at all. If the CREX descriptors required for the new information do not exist, fast track table updates are made each year, and in special circumstances twice per year. The relatively trivial procedure of updating the CREX tables is all that the software would require.

5. CREX FOR WHAT, THEN? (1) • To code new observations which cannot be coded in BUFR, why? for example because there is no binary transmission capability or processing capability, and for which no Traditional Alphanumeric Codes exists • After a transmission in BUFR, to convert back from BUFR to alphanumeric form for re-transmission or processing in CREX because a Centre cannot process binary data but wants to benefit of all data passed in the original BUFR message • To visualize a BUFR message, the conversion is simple, almost one to one (descriptors and data), from bits-field to characters (although display software usually satisfy other requirements: special format, parameter name, etc…) • CREX could be an interim step for the migration, if one wants to encode more data, meta-data, without binary capability, then one switches to CREX, but observers need to be trained! As well as national users! And national data processing must be adapted! That has to be planned within a national migration plan. • CREX is a teaching tool to understand Table Driven Codes.

6. CREX FOR WHAT, THEN? (2) • How to Include Quality and Monitoring Information: Quality and monitoring information can be included in CREX in optional Section 3. Section 3 must begin with the characters “SUPP” and terminate with a section terminator (the characters “++”). Section 3 could contain quality and/or monitoring information about the observations contained in the Data Section (Section 2) of a CREX message. Unlike BUFR, there are no CREX data description operators to facilitate the inclusion of quality and/or monitoring messages. The choice to not develop such operators in CREX was made to facilitate its human readability by keeping the code form as simple as possible. • Facilitate Data Exchange: CREX complements BUFR in the area of data exchange, and its human readability facilitates exchange of data wherever BUFR cannot be used. The combination of BUFR and CREX satisfies data exchange requirements for every conceivable type of meteorological, oceanographic, or other environmental data. • Reduce Training Costs: Since each traditional alphanumeric code form addresses only one specific type of data, there are many such code forms (47 in WMO Volume I.1, Part A). Because there are so many traditional alphanumeric code forms, and because individual Members may be using a number of them, Members often find themselves providing training for their employees in a number of these code forms. Such training activities can consume valuable resources. Because CREX and BUFR are self-defining code forms, however, they are capable of replacing all currently used traditional alphanumeric code forms. This means the Members’ training program need only instruct their employees on BUFR and CREX. It is therefore to be expected that the migration will ultimately reduce the Members’ training costs.

7. EXAMPLES OF • CREX Operational exchange of: • ozone data (RA VI, RA II, RA IV) • radiological data (RA VI) • tide gauge data (RA IV, RA V) • hydrological data (RA I, RA VI) • soil temperature data (RA VI) • tropical cyclone information (RA II, RA V) • Squall Lines (RA I)

10. CREX will help the migration to TDCF • Coupled with the fact that it is technically capable of replacing ALL traditional character code forms, CREX becomes a powerful tool to advance the migration to self-descriptive code forms. • Wherever use of BUFR is not possible, CREX should be seriously considered. • And it is a teaching tool!