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 > 2. Marine GIS > 2.32 EU Wave Climate

2.32 Global Wave Grids from the EU Climatology

New Version of Saga:  Usually a new version of Saga is quickly assimilated into these exercises.  The latest release, Version 2.1.2, is so radically different that it will take some time to catch up with revised exercises.  Please email me immediately whenever you find an old exercise that simply cannot be accomplished in the new Saga, due to big changes in the properties, etc.  I will try to provide fixes within about 2 days.

  • Exercise Title:  Global Wave Grids from the European Union (EU) Climatology

  • Abstract:  Explore the data product website and download appropriate data for your purposes.  Perform necessary edits and conversions on the data for use in Saga.  Visualize the data in Saga, appropriately displayed, and produce statistical tables.

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

    • N/A

  • Required Software:

  • Other Resources: 

    • Global Atlas of Ocean Waves - Based on VOS Observations - "This Atlas is the result of a co-operative project, funded by European Union (INTAS grant 96-2089) 'Intercomparison of ocean waves from in-situ measurements, voluntary observing ship data, remote sensing, and modelling'. The main goal of this project is to quantify biases between wave fields available from different sources. Project participants are P.P.Shirshov Institute of Oceanology, Russian Academy of Science (Moscow), Southampton Oceanography Centre (Southampton) and Royal Netherlands Meteorological Institute (De Bilt).  Authors: Sergey K. Gulev, Vika Grigorieva and Andreas Sterl"  [From the website]

    • World Borders Dataset, by Bjorn Sandvik (use TM_WORLD_BORDERS-0.3.zip)

  • Author:  Murray Brown

  • Version:  2-24-2014

1.  Open the Global Atlas website and take some time to read about the project and its products.
2.  Click on the MAPS tab, and you'll see this list of products.

3.  Click on CLIMATOLOGY OF WAVE PARAMETERS, and you'll see this main menu of graphical products.  There are 12 monthly and 1 annual averages for 3 wave height parameter and 3 wave period parameters.  Based on inspection, we already know that the same size scales were used for wave heights (0-7 m) and for wave periods (0-8.5 secs)  to facility easy visual comparisons.

4.  Click on the JANUARY WIND SEA control to see this graphic.
5.  Click on the JANUARY SWELL to see this graphic.
6.  Click on the JANUARY SIGNIFICANT WAVE HEIGHT to see this graphic.  It should be roughly the sum of the above 2 graphics.  This figure is exactly the same as the GIF files you can download if you want to save one for use elsewhere (but make sure to give credit to the original source).

7.  Click on ANALYZED DATA to see this matrix of values.  You can immediately see that the NO DATA VALUE is probably minus 9.90.

But we will not work from this page, so you can close this page and go back to the previous page.

8.  Go get the data, right-click on the ANALYZED DATA control, and select SAVE TARGET AS.
9.  Navigate to LIBERIA > DATA > OCEAN > EUWAVES and save the file as sig_wave_ht_jan_global_eu_climate_int.txt.  The source filename extension of INT is not familiar to the author, but it has been retained here for your information.
10.  Here is the downloaded file, viewed in a good ASCII editor.  You can see some possible problems:
  • The data columns appear to be separated by 2 spaces

  • The first column is preceded by 2 spaces

This requires careful editing to convert the double spaces to single spaces, but also to completely remove the leading 2 spaces in each row. 

11.  First, you must run Excel (or any good spreadsheet) and import the TXT file, as you see here.

It would seem to work best with DELIMITED, but the author has had better luck with FIXED WIDTH.

Click on NEXT.

12.  Do nothing, and click on NEXT.
12.  Do nothing, and click on FINISH.
13.  Now, select FILE > SAVE AS and save the file with these settings:
  • FOLDER: PRODUCTS > EXCEL

  • FILE NAME: Same name but extension CSV

  • SAVE AS TYPE:  CSV

Then click SAVE.

14.  Now check to make sure you have this file:  sig_wave_ht_jan_global_eu_climate_int.csv
15.  Here is the new file, viewed in a good ASCII editor.  There should be no spaces at this point.
16.  Now you can use the EDIT > REPLACE function of the editor to replace all commas with spaces.

Click REPLACE ALL to continue.  You should get a message telling you how many replacements were made.

17.  Now you have the file you need, as you see here in a good ASCII editor.  All of this work from Panel 10 to 17 is necessary because of the awkward original format of the data.
18.  Now, to continue with the analysis of these data, you must add these 6 lines to the beginning of the file.  These were worked out by the author, using trial-and-error, but you may want to use something different, as mentioned below.
  • NCOLS - Number of columns, counted

  • NROWS - Number of rows, counted

  • XLLCORNER - The longitude of the center of the southwestern corner cell

  • YLLCORNER - The latitude of the center of the southwestern corner cell

  • CELL SIZE - Must be 2 if only 180 columns go around the world

  • NODATA_VALUE - Discovered in the file by inspection

When these lines are added to an ASCII matrix like this, then it becomes an ArcGrid file, and should have the filename extension ASC.

19.  Navigate to PRODUCTS > EXCEL and save the file with the name sig_wave_ht_jan_global_eu_climate_int.asc
20.  Now you can run Saga.
21.  Select MODULES > IMPORT-EXPORT GRIDS > IMPORT ESRI ARC/INFO GRID.
  • FILE - Navigate to and select the new ASC file you just made
  • TARGET GRID TYPE - Floating point (4 byte)
  • NODATA VALUE - User defined (instead of the -9.0)
  • USER DEFINED NODATA VALUE -99999 (the usual Saga value)

Then click OK.

22.  In Saga, you can use ADD TO MAP to visualize the grid.  It should look like this.  The map is Pacific-centered, which is not the usual method.  We need to change it to Atlantic-centered.

 

23.  Select MODULES > PROJECTION/PROJ 4 > CHANGE LONGITUDINAL RANGE FOR GRIDS.
  • GRID SYSTEM - Select the system that has its corner at 1x -79y
  • INPUT - Select the grid name
  • DIRECTION - From 0-360 to -180-+180

Then click OK.

24.  You should now have a new grid system with its corner at -179x and -79y.

 

 

 

25.  Use ADD TO MAP and show the new grid in a new map.  This is the real final product.
26.  Here is the same map, with some improvements:
  • COLOR - Select  100-color rainbow palette
  • VALUE RANGE - Pick a good range that includes 0 for the minimum.
  • WORLD BORDERS - Add this shapefile to see how well the grid cells match up with the vector coastline.  If you like what you see here, then fine.  If you want to experiment with the settings in Panel 18, above, then please do so.
27.  If you are seriously interested in the wave statistics, then you can use the HISTOGRAM control in Saga to create value distribution graphs, like this.
28.  The HISTOGRAM control in Saga also allows you to show a table with the individual values for the wave height bins, etc.  This can be exported for use in statistical programs.
29.  Now make sure to save the final grid in the folder PRODUCTS > SAGA > GRIDS with the name sig_wave_ht_jan_global_eu_climate_int.sgrd
30.  Whatever plans you have for these great data, you must examine the original website to create an appropriate citation showing where you got the data, and include this citation in your publications or atlases.