[ferret_users] creating a file with short integers as output

[Hein Zelle <hein.zelle@xxxxxxxxxxxxx>]

Dear ferret users / developers,


I'm having trouble trying to write a netcdf file with scaled values
using short integers.  The process (which works fine in the old
situation) I'm trying to improve is

1)  grib files on thredds (opendap)
2)  ferret loops over time steps and saves selected variables as
    netcdf
3)  catenenate netcdf files to one big file (ncrcat)

I would now like to let ferret write the data as scaled short
integers, with a fixed offset and scale factor in step 2).

After reading the documentation I have tried something like this:

let /units="degrees C" my_t2 = t2[d=1] - 272.15

define att my_t2.scale_factor = 0.01
set attribute /output my_t2.scale_factor

define att my_t2.add_offset = 0.0
set attribute /output my_t2.scale_factor

set var /outtype=short /bad=-32767 my_t2

save /clobber /file=testing.nc my_t2


Questions:

- is this the correct way?

- Does ferret automatically scale the values or do I need to do
  explicitly divide by scale_factor and subtract add_offset?

- When saving multiple scaled variables, ferret (6.8.4 and 6.8.5) gets
  confused.  The order of saving matters: a single variable works,
  saving 3 together breaks.  Message: cannot represent data in
  variable as short. 


Any help is much appreciated.
Kind regards,

     Hein


-- 

Dr. Hein Zelle
Senior consultant meteorology & oceanography
BMT ARGOSS

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