Interesting approach; it would be a good mental game to see how much the SBN
time differs from the internet provided atomic clock NTP.
Certainly, NOAAPort receive paradigms differ from vendor to vendor -
especially when it comes to injecting data from the SBN into an LDM. One
reason that our time stamps on some of the first NEXRAD products for a volume
scan are the same as the header - i.e. a 1730Z product being completely
written by 1730Z on the system - is that our LDM injection facility streams
the data directly to the queue, as opposed to buffering and pqing'ing. I
can't say that one method is better than the other . . . just different. It
does help explain differences in latency, though, when troubleshooting larger
issues external to the NOAAPort receiver - such as NCF uplink issues,
internet drops on IDD, etc.
We've sufficiently beat that dead horse.
On Thursday 29 November 2001 22:16, Jim Koermer wrote:
> We've got things reversed--our NTP server is the final receptor and our
> four NOAAport systems synch off that server. The times in our filenames
> are pulled right from the headers. The directory listing times are times
> that the files were received by the server. As I indicated, the NOAAPORT
> machine feeding the LDM on the server buffers the data in one minute
> files and then dumps the buffer files at one minute intervals for LDM
> ingest on the server. It seems to do this at 30 seconds after the
> previous minute's buffer has been built. Hence, the data actually do
> come in "at least" a minute (since seconds aren't recorded) earlier.
> It's certainly close enough to real-time for our purposes.
> We used to grab the data via NFS directly from the NOAAport ingestor,
> but our hard drives are now way too small to hold very much data because
> of the deluge from the new NIDS products, so we now move them over to a
> server where we have a large RAID system, which allows us to store all
> products from all the NIDS sites for a much longer period.
> James P. Koermer E-Mail: koermer@xxxxxxxxxxxxxxxxx
> Professor of Meteorology Office Phone: (603)535-2574
> Natural Science Department Office Fax: (603)535-2723
> Plymouth State College WWW: http://vortex.plymouth.edu/
> Plymouth, NH 03264
Stonie R. Cooper,
Planetary Data, Incorporated
3495 Liberty Road
Villa Rica, Georgia 30180
ph. (770) 456-0700; pg. (888) 974-5017; fx. (770) 459-0016