PDAF-OMI: The file callback_obs_pdafomi.F90

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 canbe found in tutorial/online_2D_serialmodel_omi/.

As mentioned in the OMI introduction, the routines are mainly pass-through routines. Thus, one typically includes the observation-specific routine with ‘use’ and then calls this routine. However, the is small additional functionality in the different routines which has to be handles when implementing the routine or adding an observation type

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_f_TYPE. The sum of these individual dimension 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'
2. Declare a dimension variable dim_obs_TYPE and initialize it to 0
3. Add a call to the observation-specific routine init_dim_obs_TYPE with the condition IF (assim_TYPE)
4. add dim_obs_TYPE to the final sum computing dim_obs.

Notes:

• The variable assim_TYPE indicates whether a particular observation type is assimilated. It is usually defined in init_pdaf, or by reading from the command line or a namelist file.
• The observation-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 has to use the offset variable offset_obs. It is initialized to zero and then used as an argument in each call to the observation-specific obs_op_TYPE routine. This offset defines the order in which the observations are treated in the full observation vector.

The implementation steps are:

1. Include the observation-specific routine obs_op_TYPE from the observation-module with 'use'
2. Ensure that the integer variable offset_obs is declared and initialized to 0
3. Add a call to the observation-specific routine obs_op_TYPE

Notes:

• The order of the calls to obs_op_TYPE determine how the different observations are ordered in the full observation vector containing all observation types.

init_dim_obs_l_pdafomi

In this routine two offset variables offset_obs_f and offset_obs_l are used to ensure a consistent order of the calls.

The implementation steps are:

1. Include the observation-specific routine init_dim_obs_l_TYPE from the observation-module with 'use'
2. Ensure that the integer variables offset_obs and offset_obs_l are declared and initialized to 0
3. Add a call to the observation-specific routine init_dim_obs_l_TYPE

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
2. add a call to PDAFomi_deallocate_obs giving the observation-specific obs_TYPE as argument.
3. To perform the deallocation, insert a call to deallocate_obs_pdafomi at the end of the routine prepoststep_pdaf.