Home > 7. Bathy/Topo Data > 7.4 GEBCO Online

7.4 GEBCO 2014 Global Relief Grid: Online Processing of Products

  • Exercise Title:  GEBCO 2014 Global Relief Grid: Online Processing of Products

  • Abstract:  Alongside the well-known and widely used vector contour products, the General Bathymetric Chart of the Oceans (GEBCO) project has published a new set of global gridded relief data.  [These replace an earlier not-well-received product.]  The global 30-second grid, named GEBCO 2014, synthesizes several high-quality grids and survey tracks.  [A companion 1-minute version is also available, used in this exercise for faster results.]  If you want to do the data processing locally (i.e. download the entire dataset and subset it by geographic coordinates), then go to the companion exercise GEBCO 08 Global Relief Grid: Local Processing

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

  • Required Software:

  • Other Resources: 

    • General Bathymetric Chart of the Oceans (GEBCO) Digital Atlas - "The GEBCO One Minute Grid, a global one minute interval bathymetric grid, based primarily on the bathymetric contours of the October 2002 version of the GDA. It also incorporates land elevations derived from the Global Land One-km Base Elevation (GLOBE) project data set. " [From the website]

  • Author:  Murray Brown & Lilian Krug

  • Version:  30-Jan-2019 (with SAGA 7.1.0)

1.  Open the GEBCO website, and read about the program and its products.
2.  Scroll down the page to find and click the DOWNLOAD DATA tab.
3.  Read about the gridded dataset.  This version ("GEBCO 2014") replaces a grid published in the 1990's that was essentially a gridding of all the XYZ coordinates of the vector contour lines.  This new version is a compilation of all the best available grids, and has been recommended for use by the World Data Center for Geodesy and Geophysics (NGDC in Boulder, Colorado, USA).
4.  Scroll down the page, below the map inform the coordinates for Liberia
5.  This data selection screen appears with a global map
6.  Expand the option GEBCO One Minute Grid (1 arc-minute interval) and choose the User-defined area option
7.  Click on Add data to basket and then View basket.
8. Click in Checkout your request, which will direct you to the Log in page.

 

 

 

 

note: To download the data you are required to be a registered BODC web user. If you have already registered, simply log in, alternatively register to become a new user."

9.  Once logged in, you can click on refresh and wait. When data is ready, click on Download.
10.  Unzip the folder. The documentation has lots of important information you may want to read when working with your own data. For now, rename the nc file as gebco_1min_-23_-6_-3_9.nc and save it in the folder DATA > BASEMAP > RELIEF > GEBCO
11.  Run Saga and open MODULES > IMPORT/EXPORT GDAL/OGR > IMPORT NETCDF

 

  • FILE - select the new NC file you just created. 
  • SAVE TO FILE - Unchecked
  • SILENT - Unchecked
  • TRANSFORMATION - Check this to use the correct geographic coordinates (instead of a default page coordinate grid with 0,0 at the lower left corner)
  • INTERPOLATION - The author suggests B(ICUBIC)- SPLINE INTERPOLATION, but you can experiment with other choices; this may not even be relevant for this type of grid

Then click on OK.

12.  The grid now appears in your list of objects.  Visualize it, as you see here, with ADD TO MAP.  Check the LEGEND to make sure you have the correct grid values, as you see here.
13.  Use FILE > SAVE AS to save the new Saga format grid in the folder PRODUCTS > SAGA > GRIDS with the filename relief_liberia_gebco14_online_saga_1min.sgrd.  You will need it later for other exercises.

If you need a NetCDF format grid, then follow these steps:

  • Select IMPORT/EXPORT> GDAL/OGR > EXPORT RASTER and use FORMAT = NETWORK COMMON DATA FORMAT
  • All the other default settings in this tool should be OK.
  • FILE = Navigate to LIBERIA > PRODUCTS > SAGA > GRIDS and use relief_liberia_gebco14_online_saga_1min.nc for the filename.
  • Check the new raster in ncBrowse to make sure it looks fine.
14.  The GEBCO 2014 global relief datasets will be merged into existing MDL exercises, replacing the old ETOPO1 relief grid.  This will be a gradual process, and should not change any exercises radically.  If you find ETOPO1 in an exercise, then replace it with GEBCO 08 or 14 (1 min).  If you have the 30-sec version of GEBCO 08, then ask your instructor for special steps to deal with the change in resolutions.