[Thread Prev][Thread Next][Index]

Re: [ferret_users] FILL w/o interpolation at coast line?

On Fri, 27 Jun 2008, martin.schmidt@xxxxxxxxxxxxxxxxx wrote:

Hi Steve,

guess your problem is, that you have zero and not missing values in your
land points? Then you may want to replace such data with missing values
before you
make a plot. Possibly this helps.

Hi Martin,

The land values are not zeroes. The metadata for this variable is:

	short temp(time, zpos, ypos, xpos) ;
		temp:valid_range = -5.f, 30.f ;
		temp:long_name = "Temperature" ;
		temp:units = "Celsius" ;
		temp:scale_factor = 0.0005340739f ;
		temp:add_offset = 12.5f ;
		temp:missing_value = -99999.f ;

After the scale factor, offset and short integer modulo arithmetic the missing value in the file becomes -25184 which translates back to -0.950117.

Another hint - there is a function fill_xy, which extrapolates data as
smooth as possible. It fills missing values with average values from
valid neighbour points.
It is of some help, if you want to interpolate and extrapolate data and
have some of your interpolation grid points near land.

use coads_climatology
fill/l=10 sst[d=1]
go fland 5

You will see some white areas near land.

Now define a field of ones, needed for fill_xy

let mask=0*missing(sst[l=1],1)+1
let sst_fill=fill_xy(sst,mask,2)

fill_xy fills missings, if the mask is 1 and does nothing, if mask is 0.
"2" is the number of
nearest neighbour filling cycles.

Enhancing this value defines SST also around Antarctica. So be carefull.

set win 2
fill/l=10 sst_fill[d=1]
go fland 5

If you have zeros at land, you may proceed in two steps. First replace
zeros by missings. Then you
may extrapolate as described here.

Please note, a nearest neighbour filler does about the same here. But
again, first you should
replace zeros (valid data) with missing values.

Does this solve your problem?

I see no difference between the FILL TEMP and the FILL SST_FILL:


However, what is the purpose of fland here? I tried it but it complained about not having etopo5:

yes? go fland 5
 **TMAP ERR: non-existent or not on line
             Searched $FER_DESCR and $FER_DATA for etopo5(.des,.cdf,.nc)
set data etopo5
Command file, command group, or REPEAT execution aborted

Was this part of fill_xy technique you were describing or just an example.

Thanks for your help.


[Thread Prev][Thread Next][Index]

Contact Us
Dept of Commerce / NOAA / OAR / PMEL / TMAP

Privacy Policy | Disclaimer | Accessibility Statement