Re: Masking fields by topography

[David Oxilia <oxilia@xxxxxxxxxxxx>]

Thanks for the ferret script. I received it from pmel a little
while ago. I'm not sure what you mean by a "horizontal section"
(all sections are vertical to my mind), but it seems to me that
your script produces geographical land maps suitable for masking
fields that are plotted at various depths. Also, a variant of
this approach would require me to build a data file (your 
levitus_mask.nc) for all possible sections; a real chore indeed!

Ferret does provide 3D global topography (etopo*). This could 
in principle be used to overlay topography roughly corresponding
to the section at hand (provided it is reasonably zonal or
meridional). However, this is not as satisfactory (definitely not
for publication purposes) as actually plotting a "filled curve"
which delineates the bottom topography.

The inherent problem with this is that ferret doesn't handle too
well a mix of gridded data plots and line plots. The only 
(somewhat satisfactory) solution is to "grid" one's data (hence,
uniformly discretizing it from the non-uniform data points) and
overlay this topography mask. The net effect is that of a 
staircased topography whose coarseness is dictated by that of 
the grid resolution. A 0-6000 m depth axis in steps of 5 m creates
a rather large final grid!

Perhaps Steve Hankin has better insight to this problem. It
would surprise me if this question hasn't been raised before.
After all ferret is an oceanographers package!

David.

*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*
David Oxilia			Tel: (541) 737-2368
COAS:Oregon State University	Fax: (541) 737-2064
Ocean Admin. Bldg. 104		WWW: http://www.oce.orst.edu/po
Corvallis, OR 97331-5503	Email: oxilia@kundun.oce.orst.edu
*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*