Extracting Bathemetry Data from the<BR>ETOPO5 Database

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Extracting Bathemetry Data from the
ETOPO5 Database

Create file etopo5.par, containing values of the west longitude, east longitude, south latitude, north latititude, and SPACE (in that order, all on the same line).

If the geographical region straddles the Prime Meridian, specify the western boundary with a negative longitude. (Otherwise, longitude should always be positive, in the range 0-360.) Use negative latitudes for regions in the southern hemisphere.

Use a value of 12 for SPACE in etopo5.par, if you wish to extract and plot the data at 5 minute intervals (i.e., if you wish to simply copy the ocean depth values for this geographic region from etopo5.earth.bat). If you wish to construct a grid of ocean depths that is courser than the five minute resolution in the ETOPO5 database, you should specify a value for SPACE that is the reciprocal of the new grid spacing in degrees. For example, for 1/5 degree spacing (12 minute), set SPACE = 5; for 1/4 degree spacing (15 minute), set SPACE = 4.

Execute the shell script Etopo5.

This script compiles etopo5prep.f and runs etopo5prep, which writes the output files bathlru40 and bathmdl.gmt. These files contain the bathemetry data extracted for this geographic region. The former can be used as input to some ocean model codes. The latter consists of lines giving the longitude, latitude, and ocean depth at a grid point. If etopo5.par assigns a value of 12 to the SPACE variable, the output files will contain ocean depth values for a grid of five minute resolution in longitude and latitude. If SPACE is assigned a value less than twelve, the input depths are averaged before the output files are written. If SPACE is assigned a value greater than twelve, etopo5prep exits with an error message (the program can average, but not interpolate, values from the database).

Note that the ETOPO5 database contains land elevations as positive, and ocean depths as negative, values. The etopo5prep program sets all land values to 1.0 so that ocean depths are emphasized, and writes the absolute values of the depths to the files bathmdl.gmt and bathlru40.