WORLD METEOROLOGICAL ORGANIZATION
________________
Distribution: RESTRICTED
ET/DR&C/Doc.3.4(5)
COMMISSION FOR BASIC SYSTEMS
(6.II.2003)
______
MEETING OF EXPERT TEAM ON
DATA REPRESENTATION AND CODES
Third session
Arusha, Tanzania, 17-21 February 2003
Item: 3.4
ENGLISH only
OTHER ADDITIONS TO BUFR/CREX
BUFR regulations: a compression method for BUFR with delayed replication
(Submitted by Atsushi Shimazaki (JMA))
---------------------------------------------------------------------------------------------Summary and Purpose of Document
This document contains a proposal to clarify the compression
method for BUFR with delayed replication.
----------------------------------------------------------------------------------------------
Action Proposed
The Team is invited to examine the proposal with a view to submitting it to the next CBS
session (CBS-XIII)) for approval.
ET/DR&C /Dec.3.4(5) /p.2
DISCUSSION
1.
The last meeting of ET/DR&C noticed a problem on data compression of BUFR
message with delayed replication, and last summer, this matter was discussed among the
member of ET/DR&C, especially members from USA, JCOMM, EUMETSAT, UK and Japan by
e-mail.
2.
If the number of replications in each data subset, which corresponds with a certain
replication operation equals each other, obviously the binary data can be described as follows
regardless of simple or delayed replication.
In non-compressed form
R11
R21
.
Rn1
R12
R22
.
Rn2
R13
R23
.
Rn3
R14
R24
.
Rn4
R15
R25
.
Rn5
......
......
......
......
In compressed form
R1s
R2s
.
Rns
Ro1
Ro2
Ro3
.
Ros
NBINC1
NBINC2
NBINC3
.
NBINCs
I11
I21
I31
.
Is1
I12
I22
I32
.
Is2
......
......
......
......
......
I1n
I2n
I3n
.
Isn
where Rij (i=1 to n, j=1 to s) is jth value of ith data subset, Roj (j=1 to s) is local reference
value for jth value of each data subset, NBINCj (j=1 to s) is the number of bits occupied by the
increment Iji, Iji (j=1 to s, i=1 to n) is an increment for jth value of ith data subset. s is the number
of values per data subset and n is the number of data subsets in the BUFR message.
3.
However, if a delayed replication is employed in a BUFR message and the numbers
of replications are not equal, the binary data in non-compressed form may be described as
follows assuming the values Rij (i=1 to n, j=2 to 4) correspond with the delayed replication, and
the numbers of replications are two for the first subset, one for the second subset, ......, and
three for nth subset.
R11 R12 R13
R14 ...... R1(s-1)
R21 R22
R23 ...... R2(s-2)
.
.
.
.
.
...... .
Rn1 Rn2 Rn3 Rn4 Rn5 ...... Rns
where s is the maximum number of replications for the delayed replication.
4.
In the strict sense, the values R14, R23 and R24 in Item 3 above are nothing (blank)
rather missing according to the definition of BUFR regulations. If missing, the compressed Iji
shall be coded as 1....1 (a value all bits set) according to the regulation 94.1.6, but the
compression method for the case of nothing is not clearly described in the Manual on Codes.
Therefore the lines of Ro3 and Ro4 in compressed form is not defined in this case.
5.
In the course of migration to the table driven codes, centres would be oliged to
combine individual observations into one BUFR message (bulletin) to exchange it through the
GTS. Moreover, there are some types of observations which inevitably require delayed
replications, such as PILOT/TEMP and profiling floats observations and so on. Therefore it is
necessary to define when compression is possible with delayed replication explicitly.
PROPOSAL
Add a subnote to the NOTE (2) of regulation 94.6.3 as follows.
(ix)
When delayed replication is present, it is required that the number of replications shall
be identical for each data subset if data compression is to be used. In such cases,
subnote (vii) shall apply when coding the number of replications.