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

[saurabh rathore <rohitsrb2020@xxxxxxxxx>]

Thanks Ryo for your quick reply i have through this thread and i am also agree with you that decibars are more or less same as meters. but for the sake of accuracy if some one want to do that then what is the procedure to do this. As per the previous description I coded like this  

use temp_rg.nc
use salt_rg.nc

let tm=temp[d=1]
let sl=salt[d=2]

let lat=y[gy=tm]
let pre=z[gz=tm]

let pi=4*atan(1)

let alat=abs(lat)
let a=sin(alat/(180/pi))
let xx=a*a
let gr=9.780318 * (1.0 + (5.2788E-3 + 2.36E-5 * xx) * xx) + (1.092E-6 * Pre)
let depthterm = ((((-1.82E-15 * Pre + 2.279E-10) * Pre - 2.2512E-5) * Pre) + 9.72659) * Pre
let depth=depthterm/gr

in this way i get my depth. in detail

sh gr depth
    GRID (G008)
 name       axis              # pts                 start                end                 subset
 ABSTRACT  X             99999999 r       1                    1.E+08              full
 LATITUDE  LATITUDE       130 r         64.5S                64.5N               full
 PRESSURE  DEPTH (dbar)  58 i-       2.5                  1975                full
 ABSTRACT  T             99999999 r       1                    1.E+08              full
 ABSTRACT  E             99999999 r       1                    1.E+08              full
 ABSTRACT  F             99999999 r       1                    1.E+08              full

regards, saurabh

On Fri, Mar 3, 2017 at 4:16 PM, Ryo Furue <furue@xxxxxxxxxx> wrote:

Hi Saurabh and Russ,

On Fri, Mar 3, 2017 at 11:34 AM, Russ Fiedler <russell.fiedler@xxxxxxxx> wrote:

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.

But, very often, we don't need that accuracy. Usually pressure in decibars is regarded as equivalent to depth in meters.  We had the same discussion in the mid January:

http://www.pmel.noaa.gov/maillists/tmap/ferret_users/fu_2017/msg00034.html

The thread also describes more accurate conversions.

Ryo

--

REGARDS

Saurabh Rathore

Research Scholar (PhD.)

Centre For Oceans, Rivers, Atmosphere & Land Science Technology

Indian Institute Of Technology, Kharagpur

contact :- 91- 8345984434