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Marine Data Literacy 2.0

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3.4 Managing Standard-Depth Analyzed Parameters from the World Ocean Atlas 2009

  • Exercise Title:  Managing Standard-Depth Analyzed Parameters from the World Ocean Atlas 2009

  • Abstract:  Although there are many sources of World Ocean Atlas products on the web, many are still limited to WOA05 (or earlier!), or they are not flexible enough to smoothly provide datasets that overlap either the prime meridian or the international dateline.  In this exercise you'll learn about the Ingrid server at the Lamont-Doherty Environmental Observatory (LDEO) which is arguably one of the very best data servers on the planet, easily capable of providing WOA09 products for any region.

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

  • Required Software:

    • Saga GIS and IDV are recommended for further visualization of the products, but they are not strictly required here

  • Other Resources: 

    • IRI/LDEO Climate Data Library - Contains over 300 datasets from a variety of earth science disciplines and climate-related topics. It is a powerful tool that offers the following capabilities at no cost to the user

  • Author:  Murray Brown

  • Version:  May 2012

1.  Open the IRI/LDEO Climate Data Library.  Take a few minutes to read more about it, and about the datasets it contains.

On the left menu, select BY SOURCES.

2.  Here is the list of all sources.  Scroll down to find and select NOAA.
3.  In the NOAA menu, select NODC (National Oceanographic Data Center).
4.  This is the NODC menu.
5.  Skip over the DOCUMENTS.  Select DATASETS & VARIABLES > WOA09 > GRID-1X1 > MONTHLY > TEMPERATURE > SEA WATER TEMPERATURE (going through several different pages).
  • NOTE:  In the above steps you will pass by many interesting other variables, settings and statistics.  We don't have time now to go into these, but you should return later to the IRI-LDEO server to explore the many possibilities.
6.  Now you are at the actual data selection page for the temperature data.  Notice that some new options are available, including DATA SELECTION, FILTERS, DATA TABLES, and TABLES.

At the bottom of the page, you can see the "independent variables" that can be used to select data; they include DEPTH, LATITUDE, LONGITUDE and TIME.

7.  Click on DATA SELECTION to see this control screen.
8.  At the bottom of the page are these important HINTS.  They are especially important for longitude values, if your area of interest crosses the prime meridian or the international dataline.
  • longitude is best specified as west to east, two east values or two west values, otherwise you can end up with the wrong half of the world (e.g. 0.5E to 355.5E will work much better than 0.5E to 0.5W).

  • order matters: reversing values will reverse the grid.

  • when specifying time, some seasonal patterns work, i.e. Jan-Mar will select Jan-Mar of all years in the dataset, and Jan 1980-1990 will select Jan 1980, Jan 1981 through Jan 1990 (if those years exist in the dataset).

  • a blank entry will get you back to the full grid.


9.  Make these changes to specify Liberia, then click on RESTRICT RANGES.
10.  Your changes will appear in the CURRENT SETTINGS.  Click on STOP SELECTING.
11.  This screen appears, similar to Panel 6, but selection criteria are now in effect.

NOTE:  "t_an" means "analyzed temperature"

Click on DATA FILES.

12.  A long list of formats appears, with similar formats in groups.  You can study this on your own later, because right now we only want to find the ASC format (compatible with all GIS programs).  [Other formats include NetCDF, for use in IDV.]
13.  In the "GIS-Compatible Formats" you can find the 2-Dimensional Table, which is the familiar ESRI ASCII grid format.
14.  If you click on 2-Dimensional Table, you'll see this huge list of grids.  Each grid is a separate standard depth and month.

Select the very first one (Jan/0.0m) and save it in the folder DATA > OCEAN as temp_grid_jan_0m_liberia_woa09_irildeo.asc

15.  Here's the contents of  temp_grid_jan_0m_liberia_woa09_irildeo.asc.

NOTE:  The very strange nodata_value, 9.96920997E36 is clearly a mistake.  The actual value in the file is 9.96921e+36.

16.  Use any good ASCII text editor to change the NODATA_value to read exactly the same as the values appearing in the datagrid, then save the file.
17.  To open temp_grid_jan_0m_liberia_woa09_irildeo.asc in Saga, use  IMPORT/EXPORT GRIDS > IMPORT ESRI ARC/INFO GRID.

Make sure you use these settings.  [The 8-byte size is needed to accommodate the very large exponent of the no data value.]

18.  And the grid looks fine.