retrieving bathymetry data of the oceans and its …...retrieving bathymetry data of the oceans and...
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Retrieving bathymetry data of the Oceans and its processing for iRIC calculation
Takaaki ABEDivision of River Engineering Research, CERI
Training Course for iRICSep.19(Thu) Nays2D Flood
Released: October 2013Modified:
GEBCO Top
• http://www.gebco.net/ 2
Click the link to bathymetry data
Gridded bathymetry data top page
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Click the link to download page
BODC top page
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For downloading GEBCO data, you need to create an account , register, and log in to the account home page
Registration
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Fill in the forms and create your account
Link to bathymetry data
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After registering and logging in, link button to download page appears
GEBCO gridded bathymetry data sets
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In the download page, you can select your region of interest in the interactive map like shown in this figure, however, several steps are needed for accessing GEBCO data.
Downloading world ocean data
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Firstly, you must download the whole data, namely, GEBCO_08 grid (30 arc‐second interval).
Leave values and characters unchanged
Downloading free software
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Secondly, for visualization of GEBCO data, a software provided in the same page is needed. Download link is just above the “Download Data” button.
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Link to GEBCO Grid display softwareis at the bottom of the download page.
Grid Viewer download
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Unzip the downloaded software file and put the gebco_08.nc file in the same directory after unzipping gebco_08.zip (1.1GB file you’ve just downloaded) file.
Execute the viewer
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Execute the GridViewer.exe
Click “Continue”
Region settings
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Input the region of interest
Aceh BODC data
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Data export
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Export this data for QGIS processingClick “Gridded Data”
Export options
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Select “ESRI raster format”Input name as “aceh.asc”
tpo file preparation for ELIMO solver (optional)
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The ELIMO solver needs longitude and latitude data in tpo file. Open aceh.asc in your text editor (or Excel), delete the header information in the file (14 lines from the top), count the number of data points, add it in the first line and save as tpo file with .tpo extension like “aceh.tpo”
Imported tpo file in ELIMO solver
Open raster layer
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Click “Add Raster Layer”and select “aceh.asc” file
If you are going to use other solvers, following procedures are needed.
Define CRS
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Define the CRS (Coordinate Reference System) as “WGS 84” (EPSG:4326 or ID:3452)
Raster layer added
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Grey square region will appearIn Layers window right click the aceh layerSelect “Properties”
Set color map
21Set Color map of the Elevation
Convert raster to vector
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In the menu bar, click Raster > Conversion > “Polygonize (Raster to vector)”Input file name for polygonsClick “OK”
Add vector layer
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Specify CRS
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Again, define the CRS (Coordinate Reference System) as “WGS 84” (EPSG:4326 or ID:3452)
Save vector layer as UTM
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New vector layer is addedRight click the layer name and click “Save as...”
Input the name for outputSelect ”Selected CRS”Browse CRS and here, you must choose “WGS 84 / UTM zone 46N”
Add vector layer
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Add vector layerin rectangular coordinates system
Convert polygon to point data
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Add geometry columns
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In the menu bar, click Vector > Geometry Tools > “Export/Add geometry columns”Select Input vector layerInput “Output shapefile name”Click “OK”
NOTE: It may take several minutes
Click OK and add the new layer
Geometry column table
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New vector layer is addedRight click the layer name and click “Open attribute table”Geometry columns are added
Copy attribute table
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Select all lines and copy them to clipboard
Convert to X[m],Y[m],Z[m] data
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Open Excel and paste the clipboard data
Delete the 1st column and change row positions like below
tpo file export
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Input the number of lines in the 1st line
Save as “aceh.tpo” and select Text (tab delimited) (*.txt)
Tpo file import to iRIC preprocessor
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Open iRIC software and import “aceh.tpo” file
End.
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