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Home > 9. Operational/Synoptic > 9.17 ASCAT Winds

9.17 Visualizing Satellite-Measured Winds in IDV: ASCAT

  • Exercise Title:  Visualizing Satellite-Measured Winds in IDV: ASCAT

  • Abstract:  In this exercise you'll learn how to access the ASCAT satellite winds analyses and to display them in IDV.  These grids are usually available on the same day, but you may have to accept day-old data in some cases.  THIS LESSON IS PROVIDED FOR EDUCATIONAL PURPOSES ONLY.  NO ONE SHOULD ATTEMPT TO RELY ON THESE ANALYSIS PRODUCTS FOR NAVIGATION OR FOR ANY OPERATIONAL PURPOSES AT SEA.

  • Preliminary Reading (in OceanTeacher, unless otherwise indicated):

  • Required Software:

  • Other Resources: 

  • Author:  Murray Brown

  • Version:  May 2012

IMPORTANT NEW INFORMATION:  Recently the Saga GIS software has been shown to deal quite adequately with most NetCDF (NC) data grids (and possibly also GRIB files).  This should be viewed as a useful addition to the rapid, direct NC analysis and display capabilities of IDV (see below).  If you are also interested in this route for your data, then please check Viewing and Managing Well-Formed NetCDF Grids in Saga.
1.  Run IDV.
2.  In the dashboard, select DATA CHOOSERS > CATALOGS.  Then navigate to the WIND folder shown here.
3.  Within the WIND folder, navigate to the ASCAT wind folders shown here.  Find the ASCAT MERIDIONAL 1-DAY product and the ZONAL product, and click ADD SOURCE.


NOTE:  In a recent announcement, the Netherlands Meteorological Office states they now provide an alternate source of ASCAT winds compatible with IDV: "As of today, the development status OSI SAF ASCAT winds from Metop-B are also available in NetCDF format on the KNMI FTP server. The data are available in directory /scat/netcdf/ascat_b. If you do not yet have access to our FTP server, please send a request to and we will provide you with access details."


4.  Now you have 2 sources, zonal and meridional.  Right-click on either one and select PROPERTIES.
5.  Select the TIMES tab.  [Notice that the correct ISO date/time (for file-naming purposes) would be 20120526T12.]  Uncheck USE DEFAULT, and select only the most recent file.
6.  Select the SPATIAL SUBSET tab.
7.  Use your cursor to draw a small rectangle ANYWHERE on the map (to activate the numerical boxes).  Then enter the geographic limits of your area of interest.

Then click OK.

8.  Perform the TIMES and SPATIAL SUBSET steps with the other data source.
9.  Just above the 2 data sources, find the FORMULAS control and click on it.
10.  A list of 5 main types of formulas appears:  MAPS, GRIDS, MISCELLANEOUS, EXPORT and IMAGERY.  Open the GRIDS and select the formula shown here to make flow vectors from U and V.


Then click MAKE DISPLAY.

11.  Now IDV wants to know which data source contains the U vectors and which contains the V vectors.

Examine the full names, and assign ZONAL to U, and assign MERIDIONAL to V.

Then click OK.

12.  And here are your vectors on the map.  Notice that a 1-day product does have some gaps in it, the price you pay for getting data so quickly.

Notice that the wind speed ranges from about 2 to about 11 m/sec.

13.  To make the arrows easier to view,   Go to the DISPLAYS tab in the dashboard and make some adjustments:
  • VECTORS SIZE - Use the little control to set it for 11
  • SKIP - Use the little control to set it for 2
  • COLOR - Set it to white
  • LINE WIDTH - Doesn't work, unfortunately.

Your map should be changing automatically as you make these changes.

14.  And here is a better map.

NOTE:  In IDV the arrows are clean lines, with no pixilation.  The editing needed to make this lesson Panel has caused the arrows to pixilate.

15.  To see it in Google Earth, select VIEW > CAPTURE > IMAGE
16.  Navigate to PRODUCTS > IDV and save the vectors as winds_20120526T12_ascat_motherload_idv in the KML/KMZ format.
17.  Here you discover that IDV saves images, not vectors.  The image can be made partially transparent to aid visibility, but the arrows pixilate if you change the size significantly.
18.  Also use FILE > SAVE AS to save this analysis in the IDV XIDV format with the same filename, winds_20120526T12_ascat_motherload_idv.
19.  Now for the brave souls, this exercise continues with completely optional steps to color the vector map IDV, using a speed-based color palette.
20.  With the same data sources still loaded, return to the FIELD SELECTOR tab, and select GRIDS > ONE VALUE COLORED BY ANOTHER.  [In this terminology, "one value" will be referred to below as the "data field" and "another" will be referred to below as the "color field".]



21.  Now you are being asked to specify exactly what are the DATA FIELD and the COLOR FIELD.
22.  On the data field side, click on FORMULAS and select MAKE FLOW VECTORS FROM U AND V.
23.  On the color field side,   Find and select SPEED FROM 2 COMPONENTS.

Then click OK

22.  Now we need to identify the zonal and meridional components for the VECTOR ARROWS.  Inspect the full filenames carefully, and make the proper selections.

Then click OK.

23.  Now we need to identify the zonal and meridional components for the SPEED.  Inspect the full filenames carefully, and make the proper selections.

Then click OK.

24.  The speeds are calculated for each arrow, and it is drawn using a color palette, as you see here.

Once again, the arrows are crowded and small, so you'll need to make some adjustments to suit your own taste.  The author of this exercise also made a change in the palette to COLOR TABLE > RADAR > DBZ.

25.  And here is the final figure.  If you make this figure, then save it to the same XIDV file (i.e. overwrite the previous version).