OPABAT Tool

OPABAT is a set of Fortran and IDL procedures allowing to build a bathymetry filed on the grid of OPA, the oceanic dynamic component of the NEMO system. The bathymetry's construction is an essential step when setting up an new configuration of the sydtem : the choice of the trsehholds, of the passage's width and dorsal's height, to sum up the choice of the realism of the bathymetry at the given resolution conditions at the first order the oceanic flows computed by the model. This aspect of the problem imposes a manual intervention during the construction, in order to control the precision.

However, this manual intervention is increasingly light with the raise in resolution, the limit of resolution equalizing the precision of the data. With OPA model, bathymetry is calculated in vertical levels at the point of mass T of the C-Arakawa grid, with for value, zero, for the continents, of 1 with jpk for the oceanic bottom.

The development of the field of bathymetry is carried out in two times :

• By the automatic construction of an outline through FORTRAN programs by using a bathymetric data file high resolution.
  
• In one second step by the manual correction under IDL of the field.
  

You can download the tools here:
IDL_OPABAT3

And find some documentation here (in French):
opabat_RAPPORT
opabat_ANNEXE

An example of IDL procedures can be found at the bottom of the page.

Automatic contruction of the files

The construction schedules of the outline file of bathymetry were conceived for fields of the model with relative small dimension, 100x100 with 1000x1000 points on the horizontal one, based on the handling of large data files and on expensive interpolations in computing times. These programs were initially conceived in 1993 to build the bathymetry of the first version world ocean OPA and were based on a set of FORTRAN programs and programs of layouts NCAR to validate the results. They were re-examined into 1997/98 per Anne-Marie Tréguier (LPO) within the framework of the CLIPPER project and with the LODYC for construction, inter alia, of the bathymetry for model ORCA. The graphic part and certain developments was given up or appreciably modified by the use of IDL which adds employment opportunities, in particular the use of the mouse. The programs, developed in FORTRAN 77 for an initial application, then used in several other contexts of the years afterwards, do not present the desired finished aspect and comprise sometimes abandoned developments, obsolete comments and certainly of the errors which we will perhaps have time and courage to begin again.

Up to now, two data files of bathymetry were used :

• ETOP5
  Released by the Marine Geology and Geophysics Division/National? Geophysical Dated Center, covering the sphere and 5 minutes per 5 minutes of
  

PARAMETER( JPITP5 = 4320, JPJTP5 = 2160 )

• Smith and Sandwel
  file covering the sphere of 72 S with 72 N and integrating the recent data satellitales, 2 minutes resolution per 2 minutes:
  

(David T. Sandwell, Walter H. F. Smith, Stuart M. Smith, and Christopher Small,

Institute for Geophysics and Planetary Physics, SIO, Geodynamics Laboratory, NOAA - Geological Data Center, SIO - Lamont Doherty Earth Observatory)

(look at ​http://topex.ucsd.edu/marine_topo/mar_topo.html ).

     PARAMETER( JPIBAT = 10800, JPJBAT = 6336)

Nota bene : If the field of the model covers areas in high latitudes, it is necessary to resort simultaneously to the two files.

Two methods of interpolation are employed:

A bilinear interpolation using the four points of data framing the point of grid.
Variable lopa_method=.false. in the namelist file.

An average of the data of bathymetry contained in an areaof the grid of the model.
Variable lopa_method=.true. in the namelist file.

This last method is more complex to carry out when the model uses an irregular grid with a symmetry east- west. It is recommended when the model is of weak resolution. The bilinear method is necessary when the resolution approaches the resolution of the data, the averages becoming nonsignificant.

To use IDL utility, it is necessary to build two files of outline of bathymetry, i.e. to carry out these programs twice to obtain a file with the resolution of the model, a file of highher resolution which will be used as file of control in the choices of the levels of bathymetry and will replace the use of the initial files of topography which are often difficult to handle and covering all the sphere. Typically the file of the model will be built by using an average by area, the file of control, to which the resolution is closer to the data, with a bilinear interpolation.

Example of parameters used for the construction of the bathymetry of configuration ORCA :

CC MODEL DATA SIZE

CC ---------------

CC JPI : FIRST HORIZONTAL DIMENSION

CC JPJ : SECOND

CC JPK : NUMBER OF VERTICAL LEVELS

CC

    INTEGER jpiglo,jpjglo,jpidta,jpjdta,jpi,jpj,jpk

    PARAMETER(JPIGLO = 182,JPJGLO = 149)

C

Second execution, bathymetry of finer resolution, in the case of ORCA, the precision was increased by a factor 12 in both direction of space thus a point of bathymetry is compared with a whole of 144 values :

   INTEGER NRES

     PARAMETER(NRES=12)

C si haute resolution

    PARAMETER(JPIGLO = 182*NRES,JPJGLO = 149*NRES)

    PARAMETER(JPI = jpiglo,JPJ = jpjglo )

     PARAMETER(JPIDTA = jpiglo,JPJDTA = jpjglo ).

The whole of the programs is called OPABAT :

-OPABAT : main program, reading of the file namelist, call of the routines.

-DOMHGR : programme OPA, définition de la grille horizontale et des facteurs d'échelle.

-HGRCOO : program OPA, definition of the horizontal grid and scale factors.programme OPA lecture de la grille horizontale si NTOPO=1.

-DOMZGR : program OPA, definition of the vertical grid.
-DOMMSK : programe OPA , masks computing.
-BATLEG : reading of the data file.
-BATGUE : interpolation and creation of the outline file.
-BATMOD : possible corrections of the file.
-BATWRI : saving the file.

A makefile allows to obtain a binary.

A file opabat.h allows to initialize the size of arrays.

The namelist file allows to initialize the context of the experiment and the choice of the variables.

Nota Bene :

The files of bathymetry have as a unit the levels of model, the file of outline is in whole value varying from 0 (ground) with jpk, ocean floor.
The file of control is to express in floating value between 0. and float(jpk), to see program batwri.