20000209: nldn data

>From: Frank Colby <address@hidden>
>Organization: UMass Lowell
>Keywords: 200002092318.QAA14020

>
>We just started ingesting nldn data.  How do I decode this into
>something gempak can display?  Is it easy/possible to convert it to gif
>format?
>
>Frank Colby
>UMass Lowell
>
>>From address@hidden  Wed Feb  9 16:19:56 2000
>
>
>Just an addendum to the previous message -- I suspect it would be best
>to make the data available only through garp, which gives us absolute
>control over which workstations have access and which don't.  Is it easy
>to put the lightning data into a gempak file which can be integrated
>with one of the headers in garp?
>
>Frank
>
>
>

Frank,

The GEMPAK program dcnldn is used to convert the nldn data into GEMPAK format
ship files.

Here is the sample nldn action for the LDM pqact.conf file as shown
in the decoders section of the GEMPAK tutorial at:
http://www.unidata.ucar.edu/packages/gempak/tutorial/pqact/decoders.tbl

NLDN    ^([0-9][0-9])([0-3][0-9][0-9])([0-2][0-9])([0-5][0-9])([0-5][0-9])
        PIPE    decoders/dcnldn -m 25000 -s minute05
        -d data/gempak/logs/dcnldn.log -v 1
        -p /home/gempak/NAWIPS-5.4/gempak5.4/tables/pack/nldn.pack
        data/gempak/nldn/YYYYMMDDHH_nldn_@@.gem

The above example will bin the strikes into 5 minute groupings for
display. You will of course need to modify the above action for the location
of the decoder executable and the path to the nldn.pack file.

The lightning data is stored in ship format surface files, but because the files
tend to be large during the summer months- more than 30,000 strikes an hour
(as opposed to 3,000 to 10,000 surface observations), there are special versions
of sfmap and sflist in your $GEMEXE directory called ltgmap and ltglist.
You can plot the data the same as any observations, or just plot markers at 
the strike locations, some examples are provided:

http://www.unidata.ucar.edu/packages/gempak/tutorial/exam.html

http://www.unidata.ucar.edu/packages/gempak/examples/lightning/lightning.html

I provided information about using NLDN in Garp at:
http://www.unidata.ucar.edu/glimpse/gembud-list/1162

If you have the current Garp 2.1 distribution, the NLDN entries should be
in the $GARPHOME/config/Garp_defaults file as described in the above URL.
Due to the way Garp looks in files to determine all the available times
to display in the selection widget, and due to the size of nldn files,
it does take some time to initially bring up the surface selection of nldn files
in Garp. 


Steve Chiswell
Unidata User Support