# Re: [ferret_users] conversion of decibars to metre depth in sea water

Dear Russ,

I tried to remap according to your command from my new variable depth which is having depth values calculated form the above method.

define axis/z/from_depth/units="meters"/depth depth_axis=depth[k=1:58]
let temp1=tm[gz=depth_axis@asn]

but it is showing the error

**ERROR: improper grid or axis definition: data for DEFINE AXIS/FROM_VARIABLE is ambiguous

I know I am not getting this thing. This definition of axis is something new to me and I used it as it is provided by you. please have a look into it.

regards, saurabh

On Fri, Mar 3, 2017 at 4:56 PM, Russ Fiedler wrote:

Hi,

Yes, that's a nice approximation. Since you probably don't need to worry about the latitude variation (it's overkill) you can just remap using  @ASN.

Say your new variable is called depth.

def axis/z/from_data/units="meters"/depth depth_axis=depth[k=1:58]
let temp_on_z = temp[gz=depth_axis@asn]

Russ

On 03/03/17 16:20, saurabh rathore wrote:
hi, Russ and ferreters

i came across with a similar post from James Orr http://www.pmel.noaa.gov/maillists/tmap/ferret_users/fu_2017/msg00042.html. i coded the way he suggested and with the reference he provided.

and this my output for depth (m) from decibars.  Now I want to use this axis in my data as the Z axis. So i need help in doing this operation.

dbars             meters
2.5     /  1:     2.480
10      /  2:     9.919
20      /  3:    19.838
30      /  4:    29.756
40      /  5:    39.673
50      /  6:    49.590
60      /  7:    59.507
70      /  8:    69.423
80      /  9:    79.339
90      / 10:    89.254
100     / 11:    99.169
110     / 12:   109.083
120     / 13:   118.997
130     / 14:   128.910
140     / 15:   138.823
150     / 16:   148.735
160     / 17:   158.647
170     / 18:   168.558
182.5   / 19:   180.947
200     / 20:   198.290
220     / 21:   218.108
240     / 22:   237.925
260     / 23:   257.739
280     / 24:   277.552
300     / 25:   297.363
320     / 26:   317.171
340     / 27:   336.978
360     / 28:   356.783
380     / 29:   376.587
400     / 30:   396.388
420     / 31:   416.187
440     / 32:   435.985
462.5   / 33:   458.255
500     / 34:   495.366
550     / 35:   544.837
600     / 36:   594.296
650     / 37:   643.743
700     / 38:   693.179
750     / 39:   742.603
800     / 40:   792.015
850     / 41:   841.415
900     / 42:   890.804
950     / 43:   940.180
1000    / 44:   989.546
1050    / 45:  1038.899
1100    / 46:  1088.241
1150    / 47:  1137.571
1200    / 48:  1186.889
1250    / 49:  1236.196
1300    / 50:  1285.492
1350    / 51:  1334.775
1412.5  / 52:  1396.364
1500    / 53:  1482.557
1600    / 54:  1581.021
1700    / 55:  1679.438
1800    / 56:  1777.810
1900    / 57:  1876.136
1975    / 58:  1949.851

regards,saurabh

On Fri, Mar 3, 2017 at 1:34 PM, Russ Fiedler wrote:
Hi Saurabh,

You'll need the density information in order to integrate 1/(g*rho) from the surface downwards and then use ZAXREPLACE to map to the z axis.
If you have the salinity information then use the function RHO_UN.

Russ

On 03/03/17 11:49, saurabh rathore wrote:
HI Ferreters

I was wondering that do ferret/pyferret is having any function to convert depth in decibars to depth in meters. As I am having ocean temperature data in decibars along Z axis i just want to convert this pressure axis to metre axis i.e. Z axis of decibars to Z axis of meters.

yes? sh da
currently SET data sets:
1> ./temp_rg.nc  (default)
name     title                                                  I         J             K         L          M         N
TEMP     TEMP_RG[L=100]                   1:360     1:130     1:58      1:152     ...       ...

yes? sh gr temp
GRID GJF1
name       axis                           # pts                     start                      end                       subset
LONGITUDE LONGITUDE      360mr                  20.5E                  19.5E(379.5)             full
LATITUDE  LATITUDE            130 r                  64.5S                     64.5N                       full
PRESSURE  DEPTH (dbar)    58 i-                      2.5                      1975                         full
TIME      TIME                          152 i   16-JAN-2004 05:14       16-AUG-2016 04:28        full
normal    E
normal    F

​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

--

REGARDS

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