Re: [ferret_users] fine-resolution bathymetry for small regions

["Paulo B. Oliveira" <pbo@xxxxxxxxx>]

Hi Billy,

Thank you for sharing the info on fine-resolution bathymetry and
script. 

Unfortunately my region of interest (W.Iberia) is not listed
specifically and the bathymetry provided is not the finest resolution
available. 

GEBCO (http://www.gebco.net/data_and_products/gridded_bathymetry_data/)
provides a 30 arc-second grid which is, to my knowledge, the best
resolution available for the region.

Paulo
------------------------------------------------------------
On Mon, 2011-05-09 at 14:37 -0700, William S. Kessler wrote:
> Hi Ferreters -
> 
> Here's a source of fine-resolution bathymetry, perhaps 10s of meters  
> horizontally in some areas. In any case, it is probably the finest  
> resolution available. Brief instructions below, then a Ferret script  
> to read the files.
> 
> These are GMT-format netcdf files with the extension *.grd; Ferret  
> will read and convert them using the attached script. However, the  
> native way to read them is with a program called grdcontour (a whole  
> set of grd* routines are available on the web). But if you want to use  
> these files in Ferret, read on:
> 
> http://www.marine-geo.org/tools/maps_grids.php
> 
> Pull down the "Focus/Study Site" menu. If you are lucky your region  
> will be listed specifically, otherwise pick "World".
> 
> Enter the coordinates of your region, Click "View Created Map" .
> 
> You will get a map, and set of links to download the data. The  
> appearance of the map is an indication of the location of truly high- 
> resolution data (perhaps 10s of meters horizontal, from side-scan  
> sonar).
> 
> As far as I can tell, the most realistic choice is "masked" at the  
> same resolution as the map. But experiment with the options and write  
> back, please.
> This will produce a file with a long numerical name (GMT format = *.grd)
> 
> Then bring this file into Ferret and rewrite using the attached script  
> (with Ansley's help).
> 
> In Ferret:
> yes? go grd_to_netcdf_convert.jnlb 1304975255453   ! the argument is  
> an example of the filename
> 
> Billy K
> 
> ------------------------
> ! read and convert grd format files to Ferret-usable netcdf
> ! read-write-read-write to fix problem of reversing latitudes:
> ! the 1-d array Z contains the 2-d grid listed in north-to-south order
> ! (despite the apparent south-to-north order of Y_RANGE):
> ! first ($dimx) values are W-E along the northern edge
> ! next ($dimx) values are 1 gridpoint south of the northern edge
> ! ...
> ! last ($dimx) values are along the southern edge
> 
> ! arg1 = grd file name
> 
> use $1.grd
> set var/bad=nan 'Z'
> 
> ! define the lat/lon grid using the file variables
> def sym dimx `dimension[i=1]`
> def sym dimy `dimension[i=2]`
> define axis/x=`x_range[i=1]`:`x_range[i=2]`/npoints=($dimx)/unit=lon  
> xlon
> define axis/y=`y_range[i=1]`:`y_range[i=2]`/npoints=($dimy)/unit=lat  
> ylat
> 
> ! RESHAPE the input 1-d vector Z to a 2-d grid (but reversed south-to- 
> north)
> let zz = reshape('Z',x[gx=xlon]+y[gy=ylat])
> 
> save/file=$1_a.cdf zz     ! write an intermediate file
> 
> ! read it back
> can var zz
> use/order=x-y $1_a.cdf             ! per Ansley, reverse the order
> let bathy = zz[gx=xlon,gy=ylat]    ! regrid on correct lat/lon axis
> 
> save/file=$1.cdf bathy
> 
> sp rm $1_a.cdf              ! remove the intermediate file
> --------------------------