= PDAF-OMI: The file callback_obs_pdafomi.F90 =
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The file `callback_obs_pdafomi.F90` contains are those routines that are directly called by PDAF as call-back routines. In the example codes we use all routines with the suffix _pdafomi to distinguish them from routine from existing implementation where the suffix is typically _pdaf.
The file `templates/omi/callback_obs_pdafomi.F90` provides a template for implementing the routines. A compact example can be found in `tutorial/online_2D_serialmodel_omi/`.
The routines are mainly pass-through routines. Thus, one typically includes the observation-specific routine with ‘use’ and then calls this routine. However, there is small additional functionality in the different routines which has to be handled when implementing the routine or adding an observation type.
In the descriptions below we use 'TYPE' as a generic label for an observation type. When implemeting an observation type, one replace this by an actual name. For example for sea surface temperature (sst) observations, one could replace TYPE by 'sst' and write e.g. `init_dim_obs_sst`.
== init_dim_obs_pdafomi ==
In this routine we declare a dimension variable `dim_obs_TYPE` for each observation type. This is initialized by the corresponding routine `init_dim_obs_TYPE`. The sum of these individual dimensions yields the total number of observations, which is returned to PDAF.
The implementation steps are:
1. Include the observation-specific routine `init_dim_obs_TYPE` and the variable `assim_TYPE` from the observation-module with 'use'
1. Declare a dimension variable `dim_obs_TYPE` and initialize it to 0
1. Add a call to the observation-specific routine init_dim_obs_TYPE with the condition `IF (assim_TYPE)`
1. add `dim_obs_TYPE` to the final sum computing `dim_obs`.
As an example, in `tutorial/online_2D_serialmodel_omi/` we have three observations, named A, B, and C. In `init_dim_obs_pdafomi` we find the lines
{{{
SUBROUTINE init_dim_obs_pdafomi(step, dim_obs)
USE obs_A_pdafomi, ONLY: assim_A, init_dim_obs_A
USE obs_B_pdafomi, ONLY: assim_B, init_dim_obs_B
USE obs_C_pdafomi, ONLY: assim_C, init_dim_obs_C
INTEGER :: dim_obs_A ! Observation dimensions
INTEGER :: dim_obs_B ! Observation dimensions
INTEGER :: dim_obs_C ! Observation dimensions
dim_obs_A = 0
dim_obs_B = 0
dim_obs_C = 0
IF (assim_A) CALL init_dim_obs_A(step, dim_obs_A)
IF (assim_B) CALL init_dim_obs_B(step, dim_obs_B)
IF (assim_C) CALL init_dim_obs_C(step, dim_obs_C)
dim_obs = dim_obs_A + dim_obs_B + dim_obs_C
}}}
Notes:
- The variable `assim_TYPE` indicates whether a particular observation type is assimilated. It is usually set in `init_pdaf`, or by reading from the command line or a namelist file.
- The obs-module can have either a specific name for `init_dim_obs_TYPE` or a generic name. If the generic name `init_dim_obs` is used one can apply a name conversion `init_dim_obs_TYPE => init_dim_obs`.
== obs_op_pdafomi ==
In this routine one just calls `obs_op_TYPE` for each observation type.
The implementation steps are:
1. Include the observation-specific routine `obs_op_TYPE` from the observation-module with 'use'
1. Add a call to the observation-specific routine `obs_op_TYPEz
As an example, in `tutorial/online_2D_serialmodel_omi/` we have
{{{
SUBROUTINE obs_op_pdafomi(step, dim_p, dim_obs, state_p, ostate)
USE obs_A_pdafomi, ONLY: obs_op_A
USE obs_B_pdafomi, ONLY: obs_op_B
USE obs_C_pdafomi, ONLY: obs_op_C
CALL obs_op_A(dim_p, dim_obs, state_p, ostate)
CALL obs_op_B(dim_p, dim_obs, state_p, ostate)
CALL obs_op_C(dim_p, dim_obs, state_p, ostate)
}}}
Notes:
- The arguments in the calls to `obs_op_TYPE` are input argumnets to `obs_op_pdafomi`. They are just passed on.
- The order of the calls to `obs_op_TYPE` is not relevant because the setup of the overall full observation vector is defined by the order of the calls in init_dim_obs_pdafomi. Anyway, it's good practice to keep the order of the calls consistent.
- We don't need an IF-statement with `assim_TYPE` here. The check is done within each obs-module.
== init_dim_obs_l_pdafomi ==
In this routine one just calls `init_dim_obs_l_TYPE` for each observation type. The routine is only required for domain-localized filters (like LESTKF, LETKF, LNETF).
The implementation steps are:
1. Include the observation-specific routine `init_dim_obs_l_TYPE` from the observation-module with 'use'
1. Add a call to the observation-specific routine init_dim_obs_l_TYPE
As an example, in `tutorial/online_2D_serialmodel_omi/` we have
{{{
SUBROUTINE init_dim_obs_l_pdafomi(domain_p, step, dim_obs, dim_obs_l)
USE obs_A_pdafomi, ONLY: init_dim_obs_l_A
USE obs_B_pdafomi, ONLY: init_dim_obs_l_B
USE obs_C_pdafomi, ONLY: init_dim_obs_l_C
CALL init_dim_obs_l_A(domain_p, step, dim_obs, dim_obs_l)
CALL init_dim_obs_l_B(domain_p, step, dim_obs, dim_obs_l)
CALL init_dim_obs_l_C(domain_p, step, dim_obs, dim_obs_l)
}}}
Notes:
- The order of the calls to `init_dim_obs_l_TYPE` defines the order in which the observations are stored in the local observation vector. The calling order does not need to be the same as in the other routines, but it's good practive to keep the order of the calls consistent.
== localize_covar_pdafomi ==
In this routine one calls `localize_covar_TYPE` for each observation type. The routine is only required for the localized EnKF and performs covariance localization.
The implementation steps are:
1. Include the observation-specific routine `localize_covar_TYPE` from the observation-module with 'use'
1. Initialize the array `coords` which holds the coordinates of all elements of the state vector for the current process domain
1. Add a call to the observation-specific routine localize_covar_TYPE
As an example, in `tutorial/online_2D_serialmodel_omi/` we have
{{{
SUBROUTINE localize_covar_pdafomi(dim_p, dim_obs, HP_p, HPH)
USE obs_A_pdafomi, ONLY: localize_covar_A
USE obs_B_pdafomi, ONLY: localize_covar_B
USE obs_C_pdafomi, ONLY: localize_covar_C
REAL, ALLOCATABLE :: coords_p(:,:) ! Coordinates of PE-local state vector entries
ALLOCATE(coords_p(2, dim_p))
coords_p = ... ! Initialize coords_p
CALL localize_covar_A(dim_p, dim_obs, HP_p, HPH, coords_p)
CALL localize_covar_B(dim_p, dim_obs, HP_p, HPH, coords_p)
CALL localize_covar_C(dim_p, dim_obs, HP_p, HPH, coords_p)
DEALLOCATE(coords_p)
}}}
Notes:
- Instead of allocating and filling the coordinate array `coords_p` in this routine one could also do it once in `init_pdaf` and declare the array in the module `mod_assimilation`.
- The order of the calls to `obs_op_TYPE` is not relevant because the setup of the overall full observation vector is defined by the order of the calls in init_dim_obs_pdafomi. Anyway, it's good practice to keep the order of the calls consistent.
== deallocate_obs_pdafomi ==
The file callback_obs_pdafomi.F90 also contains a routine deallocate_obs_pdafomi. Each obs-module allocates arrays in the observation type `obs_f` and `deallocate_obs_pdafomi` is used to deallocate the different observation-specific arrays after the analysis step.
The implementation steps are:
1. Include the observation-specific type `thisobs` from the observation-module with 'use' apply a name conversion like `obs_TYPE => thisobs`
1. add a call to `PDAFomi_deallocate_obs` giving the observation-specific `obs_TYPE` as argument.
1. To perform the deallocation, insert a call to deallocate_obs_pdafomi at the end of the routine `prepoststep_pdaf`.
As an example, in `tutorial/online_2D_serialmodel_omi/` we have
{{{
SUBROUTINE deallocate_obs_pdafomi(step)
USE PDAFomi, ONLY: PDAFomi_deallocate_obs
USE obs_A_pdafomi, ONLY: obs_A => thisobs
USE obs_B_pdafomi, ONLY: obs_B => thisobs
USE obs_C_pdafomi, ONLY: obs_C => thisobs
CALL PDAFomi_deallocate_obs(obs_A)
CALL PDAFomi_deallocate_obs(obs_B)
CALL PDAFomi_deallocate_obs(obs_C)
}}}