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Viewer Basics: Getting Started

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This tutorial will focus on a few of the basics of the viewer. For detailed descriptions of each feature, please refer to the help files in the viewer.

Jump to a section:: Ordering Data; Level-II Options; Level-III Options; Stage III, XMRG Data; Overlays/WMS; Filtering; Range Rings; Animations

Ordering Data

When the viewer first opens, the NEXRAD Data Selector window opens. This is where data can be accessed from your local system, NCDC (data previously ordered) or from a custom URL.

To order data, choose Order Data from the Data menu:

This opens the NCDC NEXRAD Data Inventory Search page in the default browser. From here, you can either choose a site from the map (hovering over a marker will display the radar station's call sign) or choose a site from the drop-down menu. Once a site is chosen, you are taken to a page with more details about the site, metadata, and the period of record for that site. Choose the date and product desired from the drop-down menus. The create graph button displays the data available and whether the radar was in clear air mode or precip mode:

From here, you can choose to display list of files, which will bring up a window listing the available files for download. Filenames are in the format:

   YYYY = year, MM = month, DD = day, HH = hour, MM = minute, SS = second
   Level-II: AAAAYYYYMMDD_HHMMSS.Z or 6500AAAAYYYYMMDD_HHMMSS.Z
   Where AAAA = 4-letter Radar ID, .Z = File Compression Type
   Example: KHTX20020424_164107.Z or 6500KHTX20020424_164107.Z

   Level-III: ABBB_CCCCCC_DDDAAA_YYYYMMDDHHMM
   Where: AAAA = 4-letter ID of source Radar, BBB = 3-letter ID of transmitting Radar, 
   CCCCCC = WMO Abbreviated Heading, DDD = Level-III Product Code.
   Example: KMHX_SDUS52_N0RMHX_200309182020 or 7000KMHX_SDUS52_N0RMHX_200309182020

The same information is available from the Order Data option. This is where you can actually choose the files (times) you would like to download. You must enter a valid email address at which to receive notification that your order is complete. Once the order is placed, you will see a message with a HAS ID for the order and a link where you can monitor the progress of your order:

Typically, orders are processed quickly; small orders can be ready within five minutes. Once your order is ready, you will receive an email telling you how to access your data:

   Your request (HAS000287082) has completed. The procedure to ftp the data 
   is as follows:

   open ftp1.ncdc.noaa.gov - Logon to NCDC system
   anonymous               - login userid
   user@internet          - enter your e-mail address as a password
   binary                  - changes transfer mode to binary
   cd /pub/has/HAS000287082  - changes to correct directory

    -- OR --

   You can also go to the following URL to retrieve your data files:

   http://www1.ncdc.noaa.gov/pub/has/HAS000287082

   NOTE: You must pick up your data within 7 days of this notice.

At this point, you can either download the data directly to your own system, or, if you won't be needing it for more than a few days, you may want to view it directly from NCDC.

To access the data directly from NCDC, enter the HAS number in the window under the NCDC tab, as seen to the right, then click Submit.

If the data has been downloaded to your system, choose the Local tab. Browse Local will take you to a window where you can navigate to where your files are stored. Once you have loaded data, those directories will be available in the pull-down menu in future sessions. Only directories will show in the browse menu. Once you have chosen a directory, click Submit and the data files in that directory will appear. (In the "choose directory of Nexrad files" window, you must first select Open to get back to "data selector" window.)

You can also put a custom URL under the Custom tab. Pasting the URL from the email message above has the same result as putting the HAS number under the NCDC tab.

You can get some basic information on any data file in the window by highlighting the file and choosing Describe. A window will open, giving file details, such as station, date, time, lat/lon, and elevation.

After selecting a data file, there are two choices for viewing the data: Load and Quick Load.

The Quick Load option uses Java-IRAS to display Level-II and Non-Alphanumeric Level-III data:

Java-IRAS has several analysis features, such as CAPPI (Constant Altitude Plan Position Indicator) and RHI (Range Height Indicator). A simple view with range rings allows for a quick look at the data. For a more in-depth description of the features of Java-IRAS, please see the Java-IRAS web page or the Java-NEXRAD help.

The Load option loads the chosen data into the main Viewer window.

Level-II Options

When a Level-II data set is opened, the Level-II Properties window will automatically open. It can also be accessed by choosing Level-II Properties from the View menu.

By default, the lowest elevation angle of reflectivity data is loaded. The available moments for viewing are:

Reflectivity: A display of echo intensity measured in dBZ. This product is used to detect precipitation, evaluate storm structure, locate boundaries and determine hail potential.
Velocity: A measure of the radial component of the wind, either toward the radar (negative values) or away form the radar (positive values). Negative values are represented by cool colors (green), while positive values are represented by warm colors (red). This product is used to estimate wind speed and direction, locate boundaries, locate severe weather signatures, and identify suspected areas of turbulence.
Spectrum Width: A measure of velocity dispersion within the radar sample volume. The primary use of this product is to estimate turbulence associated with mesocyclones and boundaries.

Depending upon the location of the radar station and the scanning mode (clear air vs. precip), there are a variety of different elevation angles which can be viewed. Each elevation yields different potential information.

NOTE:
The Level-II Properties window does not close automatically. This can cause an exception when switching from viewing a higher elevation angle (such as in precip. mode) to opening another file that does not have that elevation angle (clear air mode). To avoid this error, either switch to the first cut view before changing files or close the properties window before opening another file.

For a more in-depth explanation of Doppler radar, please visit: NOAA/NWS Jetstream Doppler Radar

Level-III Options

Level-III data loads into the viewer without automatically bringing up the Properties window. The Display Properties for Level-III data can be accessed through View Properties under the View menu. There are four tabs of options:

Display: Auto-Refresh will enable layers to refresh automatically (default) with a change in map extent (zoom, etc.). This feature may be turned off by removing the check in the box. The display may also be manually refreshed by clicking the Manual NEXRAD Refresh button.
Raster: Adjustable raster properties include the grid size (default 800) and the No Data Value (default -999.0). Each of these can be explicitly set. Grid size units are in decimal degrees. The smaller the grid size, the finer the image, but file size and processing time increase.
Legend: Editable legend properties include font, text color, and background color. Many standard fonts are available in sizes 9 to 72, along with selectable options for bold and italic. Text and background colors can be chosen from color swatches, HSB, or RGB settings.
Smoothing: At times it may be desirable to smooth the radar image for easier identification of some features, such as hook echoes. A smoothing algorithm, similar to that found in image manipulation software, is applied to the data, averaging the value of each pixel with that of its neighbors to "blur" the image. The actual data values are changed, so use with extreme caution. This feature is not applicable with some products.


Image without smoothing		Same image smoothed by a factor of 8

Stage III, XMRG Data

Stage-III XMRG Multisensor Precipitaion Estimator Data is produced at the River Forecast Centers by mosaicking the Level-III DPA product from multiple NEXRAD sites into defined regions. Manual QC and gauge data are integrated to form hourly regional precipitation estimates. More information can be found at:

NOAA's Distributed Model Intercomparison Project and Archive of River Forecast Center Operational NEXRAD Data

Overlays/WMS

There are a number of enhancement options available through the Overlay Selector option via the Data menu. The map is customizable by turning on/off layers, such as state or county borders, radar sites, and cities. The colors of these layers are completely adjustable. In addition, labels can turned on/off by selecting/deselecting the label option by each layer. For example, the NEXRAD Sites layer will put a dot at the location of all radar stations within the viewing area. The checkbox in the label field will display the call letters of the stations. Shapefiles can also be loaded to the view, if available.

Likewise, additional options are available through the WMS (Web Map Services) tab. Aerial photographs, topo maps, etc., are available as background images. USGS Reference Layers are also included. This is also where the radar data transparency can be set, allowing the background images to be viewed through the radar image. A transparency of 0% allows the radar data to completely obscure the background; 100% makes the radar data imvisible. The transparency is completely adjustable for a ideal viewing.

Please view the help files or browse through the window options for a more complete list of customizable features.

Filtering

Data Filtering options are available by choosing NEXRAD Filter from the Tools menu.

filter window

Multiple max-min ranges can be created for the value filter. Use a comma-separated list of min values with a comma-separated list of max values. For example, min values of '-200,30' and max values of '-30,200' creates 2 value ranges of -200 to -30 and 30 to 200. This is useful for velocity products where the strongest winds are of most interest. The Category Override allows non-numeric fields (such as 'RF' for range folding) to be included if desired.

Range Rings

Range rings can be added to an image by choosing Range Rings from the View menu.

range ring window

Minimum/maximum range as well as ring increments can be adjusted through the drop-down menus or can be explicitly typed. Available units are kilometers, miles, and nautical miles. The color of the rings can be chosen as well as the line/text thickness (1-4). There is a checkbox for labeling the rings and spokes. The rings are labeled along the vertical axis, only. Each spoke is labeled, with the default zero degree axis being North, increasing in a clockwise direction.

Animations

Note: Before beginning the animation process, it is preferable to have one file from the desired data set displayed in the viewer at the desired zoom level. The software will only process and allow you to save the data displayed in the viewing area. Wisely choosing the area of interest can also cut down on the processing necessary to produce the animation, as well as the file size of the finished product. The steps below allow you to choose the time span of the animation itself.

Also, take care in choosing files to animate. Make sure the block of files chosen is a contiguous block of the same product. Jumps in time or product can produce undesired results: Mixed Product Animation Example.
For more information on radar products and product codes, please visit NCDC's Radar Products Page

Only Level-III and XMRG data can be animated. Automated animation is not provided for Level-II data because each file may contain a different number of cuts and different elevations for those cuts. To animate Level-II data through different files or cuts, use the Screen Capture feature under the Tools menu to manually create the animation frames.

The Level-III Animation generator can be accessed from the Tools menu by selecting NEXRAD Animation. There are two methods for creating animations. The animation can be created and sent to the viewer (and subsequently saved) or it can be sent directly to a file for later viewing.

For smaller time intervals or just to get a feel for the process, animating directly to the viewer may be the better choice. Animating directly to a file is an option that uses fewer resources and may provide quicker results for comparable input.

Animating to the Viewer

9 hours of data, 1 GB of RAM

As noted above, it may be advisable to choose a starting file for the animation and set the image extents to the desired view before starting the process. Choose a block of files (time frame) to be animated. Keep in mind that this can be a CPU intensive process. Depending on your system's resources, animating several hours of data can exceed system resources. When in doubt, start with a small block to see how it goes.

After highlighting the desired files, choose Load to begin the animation process. Do not be alarmed when the Viewer window vanishes as the files are processing. When the process is complete, the Viewer window will reappear, along with another window which contains the animation. By default, the animation will begin playing (continuously) immediately.

To stop the animation at any time, hit the Stop button. The current frame number is displayed above the image. The time stamp of the file will also change in the legend. Please refer to the Viewer help files for further information on the other controls.

Saving the animation

Saving Images: With the animation stopped, Save Image will save the image currently displayed in the viewer. Save All will save the whole animation as individual frames.
Export Movie: The Export Movie button will allow you to save the animation as either an animated gif or QuickTime movie. (Note: In order to export QuickTime movies, "QuickTime for Java" must be enabled during the QuickTime installation.)

Creating an Animation Directly to a File

The benefit of using this method is that it has very low memory consumption, allowing an infinite number of images to be processed. The initial process is the same. Choose the block of files you wish to animate. After choosing the files, select Export. A window will prompt for a filename and location. The default type is animated gif, though QuickTime Movie is available if QuickTime was installed with the option "QuickTime for Java" enabled at the time of QuickTime installation. After choosing, another window will appear prompting for a frame duration (in milliseconds). You may want to experiment with the time: 200 milliseconds is 5 frames per second and is probably a good starting point.

Sample animations: (Click to animate)

Unsmoothed animated gif of KAMA (691 kb)

Smoothed (by a factor of 7) animated gif of KAMA (948 kb)