Hi Milan:
I see that in the BUFRDC tables, B0000000000098000000.TXT and
B0000000000098002001.TXT, the 013015 bit width changed from 10 to 12, and
apparently the scale also changed from 1 to 7:
version 0 (B0000000000098000000.TXT):
013015 SNOWFALL (AVERAGE RATE) M/S 1 0 10
and version 2 (B0000000000098002001.TXT):
013015 SNOWFALL (AVERAGE RATE) M/S 7 0 12
I see, as you mention, the change to SI units in version 2, which affects the
scales.
So this is a pretty clear example of changes to scale,reference and/or bit
width to operational descriptors. Without knowing these, any messages that use
those descriptors will be incorrectly decoded.
So how do we know when "links are needed" to other tables? Does the WMO
maintain canonical copies of previous table versions of the Table documents that we can
double check? Should we use BUFRDC tables as canonical ?
Regards,
John
Milan Dragosavac wrote:
Dear John,
I think you can use the latest version 13 of the tables and make links
to any other tables with smaller version number. In my Bufr reference
manual I kept track on difference between version 0 and 2 and I believe
those are the only differences. However, I am not sure if those
differences refer only to Ecmwf's maintained tables or not. All entries
are for table B class 13 where units were changed and consequently
scales. The data width was changed only for 013015 snowfall (average
rate) from 10 to 12.
To summarise, I think it is very safe to use version 13 and make links
to any other when needed.
Best regards
Milan
Milan Dragosavac
ECMWF
Shinfield Park, Reading, Berkshire, RG2 9AX, UK
Tel: (+44 118) 949 9403
Fax: (+44 118) 986 9450
Telex: 847908 ECMWF G
E-mail: milan.dragosavac@xxxxxxxxx
