Radar Menu commands

This dropdown menu provides direct access to United States NEXRAD (WSR-88D) Doppler radar imagery. It accesses Level III high-resolution data directly from sites that carry the data feed. Because there are over 100 radar sites and 31 products at each site that can be used operationally, Digital Atmosphere has implemented a completely separate, unique system for retrieving data. The Data > Retrieve interface used for "normal" weather data is not used. Rather, all choices for obtaining data are built into the radar menu.

To use the radar menu, you simply (1) make sure the station you want is set (with Set NEXRAD Station or Quick Pick); and (2) click on the product you want. The image will be downloaded (taking anywhere from 1 to 30 seconds) and will be displayed immediately on the current workchart.

Special note about choosing multiple stations : Digital Atmosphere can only access a handful of stations at a time. It cannot access all stations in the U.S., because currently no server provides current data combined in one file, and accessing each file individually would take several minutes of time. Digital Atmosphere is also intended to be a tool to view local storms and phenomena rather than to build national mosaics, which are readily available on the Internet from countless sources. If you select two or more stations, polygons created by radar products may overlap; Digital Atmosphere does not yet have a function for prioritizing polygons based on proximity to a radar.

Setting and overriding radar access URLs . Users are able to change URLs corresponding to the desired products. This is done by editing the digatmos.rad file. Within this file you construct a template for retrieving the NIDS Level III radar file. Only the URLs in the "Default" section are used under normal circumstances. However you can override them by creating new sections (which contain a title that starts with an equal sign). To implement any radar access source, set the "Preferred source" in Set NEXRAD Station to something besides Default. If the product you request cannot be found in the override, the one in the default section will be used.

Setting and overriding color schemes . Likewise, users are able to set and override color schemes. To do this, simply edit the digatmos.nex file. To implement any color scheme, go to Set NEXRAD Station and choose something besides the default color scheme. Color schemes for annotations, storm tracks, hail, mesocyclones, and so forth, are handled in the map's color table (you may either edit this in File > Preferences > Colors or by directly editing any file in the /styles directory).

Translucency: Radar echoes are drawn using translucent polygons. For best results, make sure your basemap is as bright or as dark as possible. Before plotting radar echoes, Digital Atmosphere will examine your style file for the background color (bas, in Preferences > Styles) and use the appropriate translucency algorithm based on whether it is closer to white or black. If you get unusual results, change your background color or regenerate the map, preferably towards the white or dark end of the spectrum.

Mosaicing.  When plotting radar imagery for multiple sites, an important problem arises when Digital Atmosphere has to decide which radar's data to use for a particular location.  The rule is that Digital Atmosphere plots the pixel for the nearest radar site.  The exception is when raster images (such as echo tops, composite reflectivity, etc) are displayed; in this case the pixel with the highest detected level is used (this raster rule took effect with Equinox v1.05, 1/16/07, and later versions).

Theory of operation : Data is selected with the digatmos.rad file. Data is imported into queue.nid, then is plotted. The digatmos.nxc file is used to define how fields are plotted, and digatmos.nex defines the colors. Since the station identifier is not contained within the data blocks, the NEXRAD station table (digatmos.nxa) is consulted (this table is built from digatmos.stn whenever doing a Recompile Tables command). For advanced users who are customizing access URLs, a list of valid product codes for Internet retrieval can be found at: http://www.nws.noaa.gov/tg/radfiles.html . To get historical NEXRAD data, visit http://has.ncdc.noaa.gov/plclimprod/plsql/HAS.FileAppSelect?datasetname=7000 . Level II data is at http://has.ncdc.noaa.gov/plclimprod/plsql/HAS.FileAppSelect?datasetname=6500 but is not compatible with Digital Atmosphere at this time.