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Marine Data Literacy 2.0

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Home > 2. Marine GIS > 2.7 Sediment Thickness

2.7  Adding a Sediment Thickness Grid to a Project Map in Saga

  • Exercise Title:  Adding a Sediment Thickness Grid to a Project Map in Saga

  • Abstract:  A global marine sediment thickness dataset has been published as a zero-th order resource to assist coastal States make decisions about their Exclusive Economic Zone determinations.  The method to download the data, translate it to the desired longitude system, and add it to the project map is demonstrated.  The grid can be "cut down" to the project area in the related exercise 5.3 Resampling Gridded Data to the Project Map Extent with a "Dummy" Grid

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

  • Required Software:

  • Other Resources: 

  • Author:  Murray Brown

  • Version:  8-21-2014

1.  This approximately what you should be seeing in Saga now (the Liberia project map).
2.  Open the Sediment Thickness webpage and read about this product. 
3.  On the left side, you'll see this menu of file options:
  • NetCDF can be read by Saga and IDV
  • XYZ can be read (and gridded) by Saga, IDV or ODV
  • GeoTIFF can be read by Saga and any GIS
  • ArcGIS can be read by any GIS program
4.  Download the ArcGIS file to DATA > BASEMAP > GEOLOGY.  Then unzip it.

NOTE:  The author has also tried TOOLS > IMPORT/EXPORT-GDAL/OGR > IMPORT RASTER with the "GMT NETCDF" file (filename extension GRD), and it works fine also, giving the same initial grid in Saga.  You can also change the filename extension to NC and the file will open in ncBrowse and in Integrated Data Viewer.

5.  Open the ArcGIS file (extension ASC) to see this typical header.  You can see that it is cell-centered.  The blank value is not the usual Saga value of -99999.
7.  Make these choices to load the file:
  • FILE = The grid you just downloaded and unzipped
  • TARGET GRID TYPE = Leave it unchanged or maybechange to 2-byte integer (up to you)
  • NO DATA VALUE = User defined
  • USER DEFINED NODATA VALUE = Saga value of -99999

Then click OK.

8.  The new Version 2 sediment thickness grid appears.  It is centered on the Pacific.
10.  For GRID SYSTEM, select the system for the new Version 2 grid.
11.  For INPUT, click the ellipsis (...) and select the new Version 2 grid

For DIRECTION, select >> -180-180

Then click OK.


12..  This new grid object appears (the top one)
13.  You can make a new map for it, and see that it is centered on the Atlantic.
14.  Save the grid with the name sediments_global_ngdc in DATA-BASEMAP-GEOLOGY
15.  Now add this new sediment grid to the existing world borders map.  You can see that it covers up many of the shapes already on the map.

The light yellow area indicates very thick sediments.  Not all thick sediment areas in the sea contain oil, but all oil-bearing seafloor areas have thick sediments.  Hence the importance of these data.

16.  Select MAPS-TREE (at the bottom) to see this list of objects on the available maps.

On the world borders map, right-click on the graticule object, and select MOVE TO TOP.

17.  You can move things around and change the colors to suit yourself.
18.  Try to get something line this, eventually, to show the new sediments grid in your project map.

It might be a good idea to use a new, different project name for it.

19.  On your own:  In the properties window for the sediments grid, there is a setting MODE that allows you to choose a linear scale for the color palette or two logarithmic modes.  Log scaling emphasizes either small ("up') or large ("down") values in a large set of data values, such as this huge grid.  See what setting gives this much more detailed picture of sediments in the Liberia area.
20.  On your own:  Right click on the sediment thickness object, and select SHOW HISTOGRAM to see a more detailed picture of the data values in the grid.  How does this graphic relate to the logarithmic scale you selected for MODE?