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Re: [ferret_users] regarding depth axis



​Dear Ansley and Dr. Abhisek,

Thank you for this quick and new way to solve such issues. Thanks again for the info that you provided regarding mask variable.​

regards, saurabh

On Wed, Apr 18, 2018 at 2:35 AM, Ansley C. Manke <ansley.b.manke@xxxxxxxx> wrote:

Hi,

The answers so far are just fine. However the file could be changed slightly so it would work as expected with no need for those definitions  Here's an ncdump output for the dataset.  You'll see that the dimensions of vo are vo(time, dep, lat, lon), listing "dep" as the z dimension, but the coordinate variable containing the z depths is named "depth"

> ncdump -h vo_oras4_1m_2017_grid_1x1.nc
netcdf vo_oras4_1m_2017_grid_1x1 {
dimensions:
        time = UNLIMITED ; // (12 currently)
        dep = 42 ;
        lat = 180 ;
        lon = 360 ;
variables:
        float vo(time, dep, lat, lon) ;
                vo:_FillValue = 9.96921e+36f ;
                vo:_CoordinateAxes = "time depth lat lon" ;
                vo:_Fillvalue = 9.96921e+36f ;
                vo:associate = "time depth lat lon" ;
                vo:coordinates = "time depth lat lon" ;
                vo:interval_write = "monthly" ;
                vo:long_name = "Meridional Current" ;
                vo:offline_operation = "time average and spatial interpolation" ;
                vo:standard_name = "northward_sea_water_velocity" ;
                vo:units = "m s**-1" ;
        float depth(dep) ;
                depth:axis = "Z" ;
                depth:standard_name = "depth" ;
                depth:units = "m" ;
                depth:positive = "down" ;
                depth:valid_min = 5.02158975601196 ;
                depth:valid_max = 5350.27197265625 ;
        float mask(dep, lat, lon) ;
                mask:_CoordinateAxes = "depth lat lon" ;
                mask:coordinates = "depth lat lon" ;
                mask:standard_name = "land_sea_mask" ;
                mask:associate = "depth lat lon" ;

The unix tool "ncrename" could be used to change the file so that the dimension  and coordinate variable have the same name.  Either rename name the dimension to depth or the coordinate variable to dep. For example, rename the dimension:


> ncrename -d dep,depth vo_oras4_1m_2017_grid_1x1.nc

> ncdump -h vo_oras4_1m_2017_grid_1x1.nc
netcdf vo_oras4_1m_2017_grid_1x1 {
dimensions:
        time = UNLIMITED ; // (12 currently)
        depth = 42 ;
        lat = 180 ;
        lon = 360 ;
variables:
        float vo(time, depth, lat, lon) ;
                vo:_FillValue = 9.96921e+36f ;
                vo:_CoordinateAxes = "time depth lat lon" ;
                vo:_Fillvalue = 9.96921e+36f ;
                vo:associate = "time depth lat lon" ;
                vo:coordinates = "time depth lat lon" ;
                vo:interval_write = "monthly" ;
                vo:long_name = "Meridional Current" ;
                vo:offline_operation = "time average and spatial interpolation" ;
                vo:standard_name = "northward_sea_water_velocity" ;
                vo:units = "m s**-1" ;
        float depth(depth) ;

> ferret
...
yes? use vo_oras4_1m_2017_grid_1x1.nc
yes? show data
currently SET data sets:
    1> ./vo_oras4_1m_2017_grid_1x1.nc  (default)
 name     title                             I         J         K         L
 VO       Meridional Current               1:360     1:180     1:42      1:12
 MASK                                      1:360     1:180     1:42      ...

yes? show grid vo
    GRID GHO1
 name       axis              # pts   start                end                 subset
 LON       LONGITUDE          360mr   0.5E                 0.5W                full
 LAT       LATITUDE           180 r   89.5S                89.5N               full
 DEPTH     DEPTH (m)           42 i-  5.0216               5350.3              full
 TIME      TIME                12 i   16-JAN-2017 00:00    16-DEC-2017 00:00   full

yes? list/l=3/x=150/y=-10 vo
             VARIABLE : Meridional Current (m s**-1)
             DATA SET : ORAS4 ocean reanalysis
             FILENAME : vo_oras4_1m_2017_grid_1x1.nc
             SUBSET   : 42 points (DEPTH (m))
             LONGITUDE: 149.5E
             LATITUDE : 10.5S
             TIME     : 16-MAR-2017 00:00
                  149.5E 
                  150
 5       /  1:  0.006617
 15.1    /  2:  0.007251
 25.2    /  3:  0.008769
 35.3    /  4:  0.006337
 45.4    /  5:  0.004724
 55.7    /  6: -0.000646
 66      /  7: -0.001031
 76.5    /  8: -0.000896
...


You also asked about the mask variable.  That just seems to be 0 where vo is missing and 1 where it's valid, so you probably don't need to use it.

Ansley


On 4/16/2018 8:53 PM, saurabh rathore wrote:
Dear Ferreters,

I am facing a problem in regarding depth axis and I also want to know that what is the use of mask variable. If anyone used ORAS 4 data, as this data is having 3 variable namely currents, mask and depth. I want to put the depth axis in the current variable and consequently want to know what is the use of mask variable.

I am attaching a sample file for this testing.

​I believe its a very simple problem and I am missing something.​

​Regards, Saurabh​

--


REGARDS

Saurabh Rathore
Research Scholar (PhD.)
Centre For Oceans, Rivers, Atmosphere & Land Science Technology
Indian Institute Of Technology, Kharagpur
contact :- 91- 8345984434




--


REGARDS

Saurabh Rathore
Research Scholar (PhD.)
Centre For Oceans, Rivers, Atmosphere & Land Science Technology
Indian Institute Of Technology, Kharagpur
contact :- 91- 8345984434

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