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[ferret_users] how to convert the axis from sigma coordinates to depth axis



Dear ferret users

I have a file which is the output of pom. I need to contour the temperature in it, but the file is in sigma coordinates which is not recognized by ferret. more over the xaxis and yaxis are in I,J coordinates.
i=1:41, j=1:61, k=1:16, l=1:31
but the real lat and lon are 70E-79E / 5N-14N
 and  the depth values are like this
0.,10.,20.,30.,50.,75.,100.,125.,150.,200.,250.,300.,400.,500.,600.,700


I am furnishing the details of the file here
yes? set data pom2k.nc
 *** NOTE: Units on axis "z" are not recognized: sigma_level
 *** NOTE: They will not be convertible:
yes? sh data
     currently SET data sets:
    1> ./pom2k.nc  (default)
 name     title                                             I             J         K         L
 ZZ       sigma of cell centre             ...       ...          1:16      ...
 DX       grid increment in x                       1:41      1:61      ...       ...
 DY       grid increment in y                       1:41      1:61      ...       ...
 EAST_U   easting of u-points                  1:41      1:61      ...       ...
 EAST_V   easting of v-points                  1:41      1:61      ...       ...
 EAST_E   easting of elevation points      1:41      1:61      ...       ...
 EAST_C   easting of cell corners             1:41      1:61      ...       ...
 NORTH_U  northing of u-points                1:41      1:61      ...       ...
 NORTH_V  northing of v-points                1:41      1:61      ...       ...
 NORTH_E  northing of elevation points    1:41      1:61      ...       ...
 NORTH_C  northing of cell corners          1:41      1:61      ...       ...
 ROT      Rotation angle of x-axis wrt. e    1:41      1:61      ...       ...
 H        undisturbed water depth               1:41      1:61      ...       ...
 FSM      free surface mask                       1:41      1:61      ...       ...
 DUM      u-velocity mask                         1:41      1:61      ...       ...
 DVM      v-velocity mask                         1:41      1:61      ...       ...
 RMEAN    horizontally-averaged rho       1:41      1:61      1:16      ...
 UAB      depth-averaged u                      1:41      1:61      ...           1:31
 VAB      depth-averaged v                      1:41      1:61      ...           1:31
 ELB      surface elevation                        1:41      1:61      ...           1:31
 U        x-velocity                                     1:41      1:61      1:16       1:31
 V        y-velocity                                     1:41      1:61      1:16       1:31
 W        z-velocity                                    1:41      1:61      1:16       1:31
 TEMP     potential temperature               1:41      1:61      1:16       1:31
 S        salinity x rho / rhoref                      1:41      1:61     1:16      1:31
 RHO      (density-1000)/rhoref                  1:41      1:61     1:16      1:31

 at first I tried to convert the axis (i,j) to lat and lon but couldint succeed
using the script as below
         define axis/x=70:79:0.2195/units=degrees xlat
        define axis/y=5:14:0.1475/units=degrees ylon
        define axis/t=1-jan-2000:31-jan-2000:1/units=days tax
        define grid/x=xax/y=yax/t=tax tgrid

Can anybody else help me to convert the axis from i,j to lat and lon
and also to convert the depth axis to sigma coordinates

regards
johnson
School of marine sciences
cochin univeristy of science and technology
India

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