Marine Data Literacy 2.0

Providing instruction for managing, converting, analyzing and displaying oceanographic station data, marine meteorological data, GIS-compatible marine and coastal data or model simulations, and mapped remote sensing imagery





Home > 9. Operational/Synoptic > 9.5 GlobWaves

9.5 Visualizing Operational Satellite-Measured Wave Analyses in IDV: GlobWave

  • Exercise Title:  Visualizing Operational Satellite-Measured Wave Analyses in IDV: GlobWave

  • Abstract:  In this exercise you'll learn how to use operational satellite "overpass" data that comes in the form of Level 2 "swaths" rather than neat Level 3 grids.  These data are all from wave-sensing instruments that look downward and only "see" the significant wave heights (SWH) directly below.  The exercise is also good for showing how IDV handles NetCDF point data.  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:  7-1-2014

1.  To help you navigate below, and to understand the data products of interest. here's the "tree" of the available data products:
  • waveuser

    • globwave

      • data

        • matchup - Satellite data paired with buoy data

        • l4 - Data for exercise 2.34

        • l2p - Data for this exercise

          • altimeter

            • nrt

              • envisat

              • jason1

              • jason1_geodetic

              • jason2

              • cryosat2

          • synthetic aperture radar (sar)

            • nrt

              • envisat

2.  Use any good FTP client, plus the ID and passwords provided to you, and open the folder waveuser/globwave/data/l2p to see its contents.

We'll use the altimeter data, so click on that folder.

3.  NOTE:  You can also use your browser (e.g. Firefox) as an FTP client.  Just enter the address
4.  At this level the contents are of  two types:
  • GDR - generally means geophysical data record, and is often used for final, quality-controlled data
  • NRT - near-real-time, or quick delivery data

Click on the NRT folder.

5.  Here you see the 5 available satellites.

Navigate around in the folders to discover their structure and contents.  Very often it is up to you to learn about large collections, simply by inspection.

6.  Within all the folders, you'll see files with names such as:

These filenames are fully explained at page 17 in the Product User Guide (link above).  But here's a quick summary of the parts, in order:

  • GlobeWave
  • Processing level (2P)
  • Instrument
  • Satellite
  • Analysis type
  • Start date (yyyymmdd)
  • Start time (hhmmss)
  • End date
  • End time
  • Satellite mission cycle
  • Orbit number in cycle

You'll see that there are roughly 5 products per day, at roughly 2-hour intervals.

7.  After inspection, you should have discovered these facts about the folder contents.
  • altimeter > nrt

    • envisat - Historical only; to mid 2012

    • jason1 - Historical only; to mid 2012

    • jason1_geodetic - Historical only; to mid 2013

    • jason2 - Operational & current

    • cryosat2 - Operational & current

  • synthetic aperture radar (sar) > nrt

    • envisat - Historical only; to mid 2012

8.  Go into the JASON1_GEO folder and navigate to the latest available day.

NOTE:  Until this exercise is revised, please use CRYOSAT2 in stead of JASON1, here and in the steps that follow

9.  Download the latest 2 available files to DATA > OCEAN > GLOBWAVE with their existing long filenames.
10.  Similarly, navigate to the latest available day for the JASON2 data.
11.  Download the latest 2 available files to DATA > OCEAN > GLOBWAVE with their existing long filenames.
12.  Open IDV.
13.  Open the dashboard, and select DATA SOURCE TYPE = NETCDF/GEMPAK POINT DATA FILES.

Then navigate to the JASON1_GEO folder and select the latest file in the group.

Then click ADD SOURCE..

15.  In the lower right corner, you can see a REGION selection option.  This is mainly for global grids, and not L2 swaths.  So, for these types of data, let's ignore the REGION function for now.
16.  In the lower right corner, select LAYOUT MODEL.  This is a recipe for how IDV displays all the different types of data it can handle.

You can see that NONE is the current choice. So we must make one, and select it.

17.  In the main menu, select TOOLS > LAYOUT MODEL EDITOR.  This is the utility to make the various symbols that IDV uses on data maps.  You can see all kind of (mainly) meteorological symbols.
18.  Right-click the little symbol in the cross-hairs, and select PROPERTIES.
19.  In the DISPLAY TAB:
20.  In the COLOR BY tab:
  • Set DATA RANGE to a reasonable range for marine winds, such as 0 to 6 m/sec
21.  In the COLOR BY tab:
22.  In the COLOR BY tab:
  • Click the 2 small down arrows beside the MAP VALUE OF field.
  • You need to find and select the SWH (SIGNIFICANT WAVE HEIGHT) parameter.  Navigate through all the lists to find it and select it.
  • Before you close this table, notice that there is a SWH_QUALITY parameter.  This is important to know, and we'll use it later in the exercise.


24.  This means that the color palette you picked in Panel 21 will be mapped to the parameter value range 0-6 picked in Panel 23.
25.  Now you should have all these properties set for the colored circles in the layout.

Click OK..

26.  Now you're back to the layout editor itself, where you can save your work.


27.  Enter a permanent name for this layout, such as GLOBWAVE L2 and click OK.
28.  You can close the layout editor.  Now you're back to the FIELDS and DISPLAYS panels.

In the lower-right corner, open the menu beside LAYOUT MODEL and select the new model you just made, GLOBWAVE L2.

Now, with these preparations (which you never need to repeat) you can click CREATE DISPLAY.

29.  You must answer YES to this question.
30.  Now you have the DISPLAYS settings to make.  In the LAYOUT tab:
  • Check DECLUTTER, and set the density to a medium level.  You can adjust this later.
  • Change the SCALE to 0.25 (to adjust the size of the filled circules).  You can adjust this later.
31.  In the TIMES tab:
  • Change SHOW to MULTIPLE
32.  In the FILTERS tab, you'll see various ways to limit the data according to your needs.

We need this capability, because we want to filter out (i.e not display) any values that are identified in the dataset as "bad" or "unreliable".  You'll do this in the next Panel.

33.  Make these selections, by using the drop-down menus:
  • Set the boolean symbol to != (which means does not equal or <>)
  • Set the VALUE to 2 (the value for bad or unreliable data from the User's Guide)

You must click on APPLY FILTERS.

34.  All these display settings have been applied while you were working.  You can see them now in the data map, below.



36.  Select FILE > SAVE AS to save this data product in the folder PRODUCTS > IDV with the filename swh_l2_globewave_template.xidv
37.  Now to see how to use this "template", close IDV and restart it with no data.
38.  Select FILE > OPEN and navigate to the XIDV file you just made above, and click on OPEN.  This very important little window opens.
  • REMOVE ALL - Start fresh with new data
  • TRY TO ADD - Keep existing work, and add to it
  • CHANGE DATA PATHS - Use all the settings in the XIDV file, but go to a completely new data file

For now, we'll go with REMOVE ALL and click OK.

39.  You chose the existing product, and it re-appears looking exactly the same.
40.  Now we're going to add new data to the same analysis, using the TRY TO ADD and CHANGE DATA PATHS options.
42.  Select FILE > OPEN and navigate to the XIDV file you just made above, and click on OPEN.

But this time, make these choices.  Then click OK.


43.  You'll see this new window below, which lets you change from the data file you used above to one of the other files.  Click on CHANGE DATA.
45.  Navigate to any one of the other files, such as the latest file in the JASON2 folder.  Then click ADD SOURCE.

Click on OK, when you see the CHANGE DATA? panel again.

46.  With no other work, IDV applies all the properties and settings you selected before and displays the new file on the same map.
47.  If you wish, of course, you can use FILE > SAVE AS to save this compilation product, with any appropriate name.  Just don't overwrite your template XIDV file, which you'll need many more times.
48.  A final word of caution.  This work with Level 2 data will quickly show you the reason why so many marine scientists choose to target Level 3 data products.  As you learned above in Panel 23, the file contains many fields related to data quality, 38 in fact.  This means that each file takes up a lot of computer memory, and as a practical matter you will begin to see slowing down after only the 2 swaths that you see above.  This author's relatively average laptop computer cannot reliably handle 3.  This means that either one of 2 possible solutions must be undertaken, if these L2 data can be easily plotted as multi-swath aggregates:
  • Rewrite IDV to allow subsampling at the parameter level
  • Issue a Globwave "light" product that contains only a small subset of the 38 variables.