FM 94 BUFR andFM 95 CREX

Table Driven Code Forms (or “Self-descriptive” Code Forms).

The term "self-descriptive" means that the form and

content of the data contained within a BUFR or CREX message are described within the BUFR or CREX

message itself. In addition, BUFR offers condensation, or packing,

while the alphanumeric code CREX provides human readability.

• BUFR (Binary Universal Form for Representation meteorological data) – binary data format

• CREX (Character form for Representation and EXchange of data) –

character data format

BUFR was first approved for operational use in 1988. Since that time, it has been used for satellite, aircraft, wind profiler, and tropical cyclone observations, as well as for archiving of all types of observational data. ==============================================

In 1994, CREX was approved as an experimental code form by the WMO Commission on Basic Systems (CBS Ext.94). In 1998, CBS (CBS-Ext. 98) recommended CREX be approved as an operational data representation code form as from 3 May 2000. In 1999, this recommendation was endorsed by the WMO Executive Council (EC-LI (1999)). CREX is already used among centres for exchange of ozone, radiological, hydrological, tide gauge, tropical cyclone, and soil temperature data. ==============================================

BUFR should always be the first choice for the international exchange of observational data. CREX should be used only when BUFR cannot. ==============================================

BUFR and CREX are the only code forms the WMO needs for the representation and exchange of observational data and are recommended for all present and future WMO applications.

Differences • BUFR offers data packing. Therefore, voluminous data (e.g.,

satellites, ACARS, wind profilers,…) will require fewer resources for transmission and storage than CREX. BUFR also permits the transmission of quality information with the original observational data. However, BUFR data is not human readable. Because it is not human readable, BUFR processing assumes the availability of well designed computer programs to process (decode or encode) the messages.

• CREX is simpler than BUFR and consequently easy to understand, to code and, because it is an alphanumeric code form, to read with only several hours of explanation. It is therefore particularly useful where computer equipment is not available. However, CREX does not offer packing, and has much less comprehensive capability for including quality information than BUFR.

Main Advantages

• Partial self-description• Universality • Expandability• Data packing (for BUFR)• Data readability (for CREX)================================= BUFR and CREX are recommended

for all current and future WMO applications

Structure of BUFR report

 Непрерывный поток двоичных данных

Секция 0 Секция 1 Секция 2 Секция 3 Секция 4 Секция 5

Содержание секций формата BUFRSec.# Название Содержание

0 BURF индикатор 1) Термин "BUFR" (в коде АSCII); 2) длина всей телеграммы; 3) номер редакции кода BUFR

1 идентификация данных в телеграмме

1) Длина секции; 2) идентификация данных в телеграмме

2 Факультативная секция

1) Длина секции; 2) дополнительные данные для локального использования Центрами Обработки Данных

3 Описание данных 1) Длина секции; 2) число подмножеств в секции данных;, 3) флаг категории данных; 4) флаг сжатия данных; 5) набор описателей данных, которые (описатели!) определяют форму и содержание каждого элемента секции данных

4 Секция собственно данных

1) Длина секции;2) двоичные данные наблюдений

5 Заключительная секция

"7777" (в коде ASCII)