Porting an Existing Implementation to OMI

If you have an implementation of the data assimilation with PDAF without OMI, you can port it to OMI with the following steps:

1. Install the current PDAF version which includes the OMI functionality (V1.16 or later)
2. In mod_assimilation declare an array coords_l for the coordinates of the local analysis domain. Then fill coords_l in init_dim_l_pdaf. These coordinates are later used in init_dim_obs_l_pdafomi.
3. Copy the template file callback_obs_pdafomi.F90 to your code directory.
4. In assimilate_pdaf replace the call(s) to PDAF_put_state_X or PDAF_assimilate_X by the calls to PDAFomi_put_state_local/global or PDAFomi_assimilate_local/global (You can copy this from the template files in templates/)
5. In assimilate_pdaf further replace the declaration of the 'EXTERNAL' subroutines following the template (several of the routines are no longer present with PDAF-OMI, while those that remain now have the suffix _pdafomi (like init_dim_obs_pdafomi)
6. For each observation type implement an obs-module as described in the documention on the observation modules
7. Add a call to deallocate_obs_pdafomi() are the end of your routine prepoststep.
8. Adapt the compilation to also compile callback_obs_pdafomi.F90 and the obs-modules.
9. Modify the compilation such that the include-directory of your PDAF installation is defined as an include directory (i.e. specify -IPDAF_ROOT/include where PDAF_ROOT is the root directory of your PDAF installation.)

Notes:

• In the classical implementation variant one had to code separate routines for observation handling in global and local filters (e.g. init_dim_obs and init_dim_obs_f_pdaf. With OMI is it longer necessary to distinguish, as OMI takes case of the different operations in case of global or local filters.
• With OMI we recommend to define the observation errors (rms_obs_TYPE) within each observation module instead of using the general module mod_assimilation.
• While it is not done in the template and tutorial codes, one can move the localization parameters (locweight, local_range, srange) into each observation module. This allos to easily define separate localization values for each observation type.