How to Get NOAAPORT NEXRAD Data via the LDM


Detailed information about the NOAAPORT NEXRAD feed is available from the Unidata NOAAPORT NEXRAD Feed page, including alternatives to using the LDM to get the data. Most sites will only want to get a subset of the NOAAPORT NEXRAD data via the LDM, because of the large number of products and volume of the data. This document describes how to get selected subsets of the new data stream.

First, determine who your upstream site is for the Family Of Services (FOS) data. There should already be a line in your etc/ldmd.conf configuration file requesting data from your upstream FOS site, which we will call your.floater.feed for the rest of this document. This is the host from which you should get the NEXRAD Floater Feed.

Next, determine who your upstream site is for the NEXRAD feed, by looking at the NEXRAD Feed Scheme, locating your host, and determining the first tier site in italics above your site name. We'll call this your.nexrad.feed in the remainder of this document. This is the assignment for the host from which you will get NEXRAD data other than the NEXRAD Floater Feed, if desired. your.floater.feed and your.nexrad.feed may or may not be identical.

The NEXRAD floater feed is named "FNEXRAD" ("NMC3" for LDM version 5.1.2 and earlier). It is not necessary to upgrade to a later version of the LDM just to be able to use the new FNEXRAD feed type name. In the rest of this document, we will use the "NMC3" feedtype, since a number of sites are still using LDM version 5.1.2 or earlier. "NMC3" will also work for later versions, but if you have LDM 5.1.3 or later, we suggest that you use "FNEXRAD" instead.

Before trying to get the NEXRAD floater data or a subset of the full NEXRAD data feed, you can check that the data is available to you from upstream sites by using the "notifyme" command. To avoid having to wait for new products, you can quickly check data for the previous hour with (-o 3600). For example, for the NEXRAD floater, use:

notifyme -v -l- -h your.floater.feed -f NMC3 -o 3600

where your.floater.feed refers to the upstream source for Family Of Services (FOS) data such as IDS, DDPLUS, and HDS. Similarly, to check availability for the full NEXRAD feed, use:

notifyme -v -l- -h your.nexrad.feed -f NEXRAD -o 3600

To specify what to do with the NEXRAD data

Before you start getting the data, decide what you want to do with it by adding lines to your pqact.conf configuration file for decoding or filing the data.

NEXRAD Feed

You will need to know something about the parts of the product ID for NOAAPORT NEXRAD products if you want to be able to specify actions that depend on information in the product ID. In general, the product ID includes a WMO header followed by a six-character AFOS PILS code following "/p":

  SDUSij cccc ddhhmm /pyyyzzz
i digit identifying the type of data. The first digit is either 2, 3, 5, or 7. See http://www.nws.noaa.gov/datamgmt/x_ref/xr05_X_ref_by_TT.html.
j digit identifying US region, see region list
cccc NWS forecast office
ddhhmm day of month, hour, minute
yyy product code, see NOAAPORT NEXRAD Feed page
zzz radar site code, see site list
  1. Add appropriate NEXRAD entries to your pqact.conf file. Remember to use tabs characters to separate the feedtype, pattern, and action fields. For example, if you wanted to file recent compressed floater data in a "data/nexrad/" directory using the time, station, and product identifier in the file name, you might add an entry something like this to pqact.conf:

           NMC3 SDUS[2357]. .... (......) /p(...)(...)
                    FILE -close -overwrite data/nexrad/\1\3\2.raw
          
    
  2. Check your pqact.conf configuration file to make sure there are no syntax errors:
           ldmadmin pqactcheck
          
    
  3. Send pqact a signal to reread pqact.conf so it can process new NEXRAD data:
           ldmadmin pqactHUP
          

FNEXRAD Feed

To get all of the Unidata NEXRAD floater feed containing data for several NEXRAD sites where "interesting" weather is occurring and composite imagery created by the UPC from select NEXRAD Level III products from all reporting stations:

  1. Edit your ldmd.conf configuration file to contain the line
           request NMC3 ".*" your.floater.feed
          
    
  2. Caution: The NEXRAD composite imagery can consume quite a bit of disk space after decoding. For example, the 1 km National Base Reflectivity Composite gets uncompressed to a 14 MB file. Since his product is transmitted every 6-10 minutes, you can consume a lot of disk space in a short amount of time!

  3. Stop your ldm:
           ldmadmin stop
          
    
  4. Make sure you wait until all the ldm processes have died before restarting:
           ldmadmin start
          
    

To get a subset of the NEXRAD Level III products for the floater sites, for example only the base reflectivity and velocity products for the lowest tilt (N0R and N0V products), replace the pattern for all products ".*" in the above with a pattern for the specific products you want:

  1. Edit your ldmd.conf configuration file to contain the line
           request NMC3 "/p(N0R|N0V)" your.floater.feed
          
    
    3-character AFOS PIL codes for NEXRAD products are available from the NOAAPORT NEXRAD Feed page.
  2. Stop your ldm with
           ldmadmin stop
          
    
  3. Wait until all the ldm processes have died before restarting, with
           ldmadmin start
          
    

To get only the composite images in PNG-compressed format, replace the pattern for all products ".*" in the above with a pattern for the specific products:

  1. Edit your ldmd.conf configuration file to contain the line
           request NMC3 "^(pnga2area|rad)" your.floater.feed
          
    
  2. Stop your ldm with
           ldmadmin stop
          
    
  3. Wait until all the ldm processes have died before restarting, with
           ldmadmin start
          
    

To help you refine your ldmd.conf requests for FNEXRAD data, we provide the following examples of IDD headers for the PNG-compressed composite images (current as of May 17, 2002):

Product Description Example IDD Header
1 km National Base Reflectivity (GINI format)  rad/NEXRCOMP/1km/n0r_20020517_2035
2 km National 1-hour Precipitation (GINI format)  rad/NEXRCOMP/2km/n1p_20020517_2038
4 km National Storm Total Precipitation (GINI format)  rad/NEXRCOMP/4km/ntp_20020517_2039
6 km National Base Reflectivity (AREA format)  pnga2area Q5 RL 300 RADAR BREF 6km 20020517 1949
10 km National Radar Coded Message (AREA format)  pnga2area Q5 RN 500 RADAR BREF 10km 20020517 1945


To get the NEXRAD products for a few selected sites

To specify a few select sites for which NEXRAD data is always desired, first get the 3-character site codes for the sites from the NEXRAD Site List or from a NEXRAD Site Map. For the examples, let's assume you choose to get data from sites designated "ABC" and "XYZ":

  1. Edit your ldmd.conf configuration file to contain the line
           request NNEXRAD "/p...(ABC|XYZ)" your.nexrad.feed
          
    
    after any other request lines, using tabs to delimit the fields.
  2. Stop your ldm with
           ldmadmin stop
          
    
  3. Make sure you wait until all the ldm processes have died before restarting, with
           ldmadmin start
          
    

Note that if you want to change the site selection, it is necessary to repeat all three of the above steps: there is no way to get the LDM to reread the ldmd.conf file without stopping and restarting it.

To get just a subset of products, say base reflectivity and base radial velocity for the lowest tilt (N0R and N0V products), replace the product pattern "..." in the above with a pattern for the specific products you want:

request NNEXRAD "/p(N0R|N0V)(ABC|XYZ)" your.nexrad.feed

which specifies 2 products from each of 2 sites.

To specify NEXRAD products from one of 10 U.S. regions, you can specify a pattern that matches NEXRAD products from only the desired region. For example, "SDUS[2357]4" designates products from the South Central U.S. (TX, AL, MS, LA, AR, TN, OK):

request NNEXRAD "^SDUS[2357]4" your.nexrad.feed

If you only wanted base reflectivity and base radial velocity for the lowest tilt (N0R and N0V products) for radars in this region, use:

request NNEXRAD "^SDUS[2357]4 .* /p(N0R|N0V)" your.nexrad.feed