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20001126: Level-III on NOAAPort

Glen,

At present, the Level 3 NIDS data is encrypted for all sites.
There is also one site being broadcast in compressed but
unencrypted mode such as will be available after January 1.
The site available is SDUS53 KARX. The NWS is providing this
one site as a basis for allowing data users to prepare for
the unencrypted data.

Since all the nids products for a single site use the same WMO header, we
utilize the PIL (the line following the WMO) in the LDM product identifiers
(eg, we label the products in the LDM product queue like:
SDUS53 KARX 271200 /pN0RARX

(Our ingestion program (pqing) creates the product header that is used within
the LDM for identification. No modification to the data is performed.
So, we can key on the N0R, N0V, N0S, VIL,  etc. Also, the radar identifier
is not the same as the CCC broadcast identifier for all radars, for instance
the FTG radar is broadcast under the KBOU header, but the PIL uses the FTG id.
So, keying on the PIL allows both identification of the different products, as
well as determining the radar ID.

We are preparing for the compressed data in 2 ways.
First, I have created a standalone inflator program which will accept the
product piped from the LDM and write out an uncompressed product which can 
be used with the current software.

Second, I have made modifications to GEMPAK to read the compressed data
as we deliver it via the IDD. I will be releasing this with GEMPAK 5.6a
soon along with decoders for the new format MRF and AVN mos, and assorted
other bug fixes from the 5.6 distribution.

The compressed products as we deliver them on the IDD look like:

^A \r \r \n
seqno \r \r \n
SDUS5x CCCC DDHHNN \r \r \n
NNNXXX \r \r \n
{zlib compressed portion}
\r \r \n ETX

GEMPAK will read the above formated products, find the zlib compressed portion
and inflate that to find the actual NIDS product.

The zlib compressed portion will expand to a product which appears as:
CCB
SDUS5x CCCC DDHHNN \r \r \n
NNNXXX \r \r \n
NIDS product


Recall that our IDD feed does not have the CCB (communications control block)
in it as yours does from FSL. However, when you expand the zlib compressed
portion of the message, there is another CCB, WMO, and PIL wrapped within
the product (eg, the comprete product as would be sent on NOAAPORT is
zlib compressed, and then another header is wrapped on the product for
the SBN.

ALl of this information is on the NWS NOAAPORT home pppage under the What's New
section.

The zlib software distribution includes a sample program called inflate.c. This
is the program with minimal that I used to create the program to uncompress the
data stream from our LDM. Other ldm-users have used a Perl module to accomplish
the same.


Steve Chiswell


On Fri, 24 Nov 2000 address@hidden wrote:

> 
> 
> Steve (or other)
> Do you have any info on that WSR Level-III data is avbl on NOAAPort and if
> it's compressed or encrypted?  I believe these data are the SDUS5x product
> suite.  How does Unidata pipe these around on the IDD?  I do see SDUS5x
> products on noaaport, but they do not lend themselves to display.  Any
> thoughts?  How would I identify these products beyond the generic header to
> velocity reflectivity etc.?   Thanks, Glenn
> 
> 
>