Many of the same commands used to display satellite images can be used with NEXRAD data as well. In this excercise, you will access real-time NEXRAD imagery, find a NEXRAD station where precipitation exists (if any) and list and display that NEXRAD station's radar image.

The DSINFO and IMGLIST commands list information about the available images. Once located, you can display the images using the IMGDISP command. You can display images one at a time or in a sequence. An entire set of images can be loaded chronologically using one IMGDISP command.

1. List all datasets from RTNEXRAD of type IMAGE in your routing table.

   Type: DSINFO IMAGE RTNEXRAD

           Dataset Names of Type: IMAGE in Group: RTNEXRAD
   
   Name         NumPos   Content
   ------------ ------   --------------------------------------
   N0R           9999    Base Reflectivity Tilt 1
   N0S           9999    Storm-Rel Mean Vel Tilt 1
   N0V           9999    Radial Velocity Tilt 1
   N0Z           9999    248 nm Base Reflectifity
   N1P           9999    1-hour Surface Rainfall
   N1R           9999    Base Reflectivity Tilt 2
   N1S           9999    Storm-Rel Mean Vel Tilt 2
   N1V           9999    Radial Velocity Tilt 2
   N2R           9999    Base Reflectivity Tilt 3
   N2S           9999    Storm-Rel Mean Vel Tilt 3
   N3R           9999    Base Reflectivity Tilt 4
   N3S           9999    Storm-Rel Mean Vel Tilt 4
   NCR           9999    Composite Reflectivity
   NET           9999    Echo Tops
   NTP           9999    Storm Total Rainfall
   NVL           9999    Vertical Liquid H2O
   
   DSINFO -- done
   

2. Erase frames 1 through 6.

   Type: ERASE F 1 6

3. Display a map of the United States on frame 1 and show the current weather conditions by displaying weather symbols.

   Type: SF 1;MAP USA;SFCPLOT WXS

   The parameter WXS displays weather symbols of the current weather conditions.

4. Choose a station in which rain, snow, or some other type of precipitation is occuring and place the cursor over the symbol.

5. Find any nearby NEXRAD stations using the STNLIST command.

   Type: STNLIST TYPE=N

   The TYPE keyword allows you to search for specific types of stations. In this example, you are only searching for NEXRAD stations (N) in the surrounding area.

   You should see an output similar to this:

   Center Lat/Lon: 43:08:38 84:36:00                                                      
   IDN   ID     Station Name         Data Types        ST CO DIST[KM]   LAT         LON       ELE
   ----- -----  -------------------- ----------------- -- -- ---------- ----------  --------- ----
    ---  GRR    GRAND RAPIDS                 NW        MI US    81.7     42:53:38   85:32:41   299
    ---  DTX    DETROIT                      N         MI US   104.3     42:41:59   83:28:18   412
   Number of stations listed: 2                                                           
   

6. Choose a station ID and display the base reflectivity (tilt 1, 124 nmi range) image from that station (in this case, DTX, Detroit, Michigan) with a red map on frame 2.

   Type: SF 2;IMGDISP RTNEXRAD/N0R ID=DTX;MAP X 5

7. One can use predefined product aliases found in IMGDISP.*, where * is CORE, SITE, or USER. Display the IMGDISP.CORE context file.

   Type: SEE IMGDISP.CORE

   After the comments section of the IMGDISP.CORE file, you will see predefined products in sections like this:

     # Products for NEXRAD Base Reflectivity, tilt 1 (0.50 deg), 124 nmi                  
   NEXRAD/BREF1  DATASET=NEXRAD/BREF1 EU=BREF REQUIRE=ID                                  
   MKX_BREF1  DATASET=NEXRAD/BREF1 EU=BREF ID=MKX \
              REFRESH='BAR (IMA) GRA=(GRA); \
              EU MAKE 1 1 55 55 75 75 85 85 (IMA) (IMA); \
              MAP X -8 DASH=1 X 4 COUNTY=ALL GRA=(GRA) IMA=(IMA); \
              MAP VH 7 GRA=(GRA) IMA=(IMA); \
              STNPLOT TYPE=FOUS COLOR=7 FONT=HELMO GRA=(GRA) NAV=(IMA); \
              FRMLABEL LEV=232 2 IMA=(IMA) \
              "(ID) RADAR - BASE REFLECTIVITY TILT 1 AT (HHMM) ON (DAY)'                  
   

8. Take a closer look at each individual line of the MKX_BREF1 predefined product, to see exactly what it does.
   • DATASET=NEXRAD/BREF1 EU=BREF ID=MKX \
     The DATASET= keyword defines the ADDE dataset to use, EU= defines the enhancement file to use, and the ID= keyword defines the default station to display. The "\" is the continuation line used by the context file.

   • REFRESH='BAR (IMA) GRA=(GRA); \
     The REFRESH= keyword runs the remaining commands on each frame after the image is displayed. (IMA) and (GRA) are used to specify the current image and graphics frame. The BAR command creates and displays a grayscale bar, which turns into a color bar with the effects of the enhancements.

   • EU MAKE 1 1 55 55 75 75 85 85 (IMA) (IMA); \
     The EU command changes the BREF image enhancement to have a different background color.

   • MAP X -8 DASH=1 X 4 COUNTY=ALL GRA=(GRA) IMA=(IMA); \
     The MAP command displays a map of gray dashed county lines using the current frame's navigation.

   • MAP VH 7 GRA=(GRA) IMA=(IMA); \
     The second MAP command displays a high resolution map using the current frame's navigation.

   • STNPLOT TYPE=FOUS COLOR=7 FONT=HELMO GRA=(GRA) NAV=(IMA); \
     The STNPLOT command plots all FOUS14 stations in white with a font of HELMO, using the current frame's navigation.

   • FRMLABEL LEV=232 2 IMA=(IMA) \
     "(ID) RADAR - BASE REFLECTIVITY TILT 1 AT (HHMM) ON (DAY)'
     

     The FRMLABEL adds a label to the frame, with the (ID), day (DAY), and time (HHMM) of the image.

9. If you had access to a server that allowed you access to the NEXRAD dataset, you could display the same station's three most recent NEXRAD images on frame 3-5, using the predefined product, MKX_BREF1, and the station you chose in step 6 (in this case, DTX). If MKX is the station you chose, you do not need to specify ID=, since ID=MKX is the default.

   Type: IMGDISP MKX_BREF1 ID=DTX ALL=3 5

10. Loop the images to see the movement of the storm.

    Type: LB 3 5

    Press:ALT-L

    Press:ALT-L

11. Display the total surface rainfall accumulation using the predefined PRECIPTOT product on frame 6.

    Type: SF 6;IMGDISP MKX_PRECIPTOT ID=DTX

12. Place the cursor over different areas of precipitation and use IMGPROBE to determine the total amount of precipitation over those selected ares.

    Type: IMGPROBE

    Press: ALT-G

    Repeat this as many times as you like.

13. Exit IMGPROBE using ALT-Q.

    Press: ALT-Q