[ferret_users] Telling Ferret How to Convert Units of "sigma_level"

[John Schattel <john.schattel@xxxxxxxx>]

Hello All,

I'm trying to use ZAXREPLACE to regrid from sigma to depth using the 
commands listed below.  But Ferret complains about an unknown variable 
SIGMA.  Is this an issue with Ferret not being able to convert the sigma 
axis because it uses units of "sigma_level"?  If so, can anyone tell me 
how to let Ferret know how to do the conversion?

Thanks,

John

use "http://205.156.4.56/cgi-bin/nph-dods/dgom/ngom311_05Nov043D.nc";
*** NOTE: Units on axis "sigma" are not recognized: sigma_level
*** NOTE: They will not be convertible:
let depthValues = sigma * ( depth + zeta )
define axis/z=1:37:1/units=meters/depth zdepth
let saltondepth = zaxreplace(salt,depthValues,z[gz=zdepth])
plot saltondepth
**ERROR: variable unknown or not in data set: SIGMA