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[Datastream #AYJ-610338]: Level 2 radar delay intentional?

Hi Gilbert,

A quick note to update our conversation on NEXRAD Level II data delivery 
timing...

Chiz and I were talking about this a few minutes ago.  He is guessing that
you may be interpreting the time that a full Level II volume scan is available
on your disk versus the volume scan start time in the product headers as being
the delay you are seeing.  If this is correct, then yes you will see what looks
like a delay even though there is NO _real_ delay.

Currently, a full volume scan is composed of a sequence of products each of 
which
contains 400 radials.  As soon as 400 radials are sampled, a product is created
and inserted into the LDM queue on the injection machine.  The time indicated
in the header of each product is the start time of the volume scan, not the time
that the 400 radial set that comprises the product began.  This means that the
receipt time for the first piece of the volume scan (the first product) will be
very close to the time that you received that piece (since the delivery latency
is typically subsecond).  Since the volume scan takes time to complete (5 
minutes
in storm mode; 6 minutes in precipitation mode; and 10 minutes in clear air 
mode),
the receipt time of the last part of the volume scan will look like it is
significantly older than the time in the header (again, 5 minutes for storm 
mode;
6 minutes for precipitation mode; and 10 minutes for clear air mode).

If you are using the pqact.conf actions that Chiz provides with GEMPAK releases,
the time on the completed volume scan will be the same as the time the last 
piece
of the volume scan was received.  So, it may look to you that there has been a
delay in the transmission of the product, but there is not.  In fact, sites are
receiving the product in as close to real time as possible: the only delay is in
accumulating 400 radials to form a product.

Finally, the Level III products are created and sent as soon as possible.  For
instance, an N0R product is created and sent as soon as the radar is finished 
the
lowestlevel sweep, etc.  Products that require the entire volume to be scanned 
before
creation (e.g., echo tops; vil, etc.) are created after the entire volume has
been scanned.

Cheers,

Tom
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Ticket Details
===================
Ticket ID: AYJ-610338
Department: Support Datastream
Priority: Normal
Status: Closed