PDAF_generate_obs

This page documents the routine PDAF_generate_obs of PDAF.

The routine is typically called in assimilate_pdaf or directly in the model code.

This routine is used to generate synthetic observations. It bases on the usual implementation strategy for PDAF which is described on the page Modification of the model code for the ensemble integration and its sub-page on inserting the analysis step. The routine is used in the fully-parallel implementation variant of the data assimilation system. When the 'flexible' implementation variant, the routine `PDAF_put_state_generate_obs' is used.

The interface is the following:

  SUBROUTINE PDAF_generate_obs(U_collect_state, U_distribute_state, &
                                  U_init_dim_obs_f, U_obs_op_f, U_get_obs_f, U_init_obserr_f, &
                                  U_prepoststep, U_next_observation, status_pdaf)

with the following arguments:

• U_collect_state: The name of the user-supplied routine that initializes a state vector from the array holding the ensemble of model states from the model fields. This is basically the inverse operation to U_distribute_state used in PDAF_get_state
• U_distribute_state: The name of a user supplied routine that initializes the model fields from the array holding the ensemble of model state vectors.
• U_init_dim_obs_f: The name of the user-supplied routine that provides the size of the full observation vector
• U_obs_op_f: The name of the user-supplied routine that acts as the full observation operator on some state vector
• U_get_obs_f: The name of the user-supplied routine that receives the full vector of generated synthetic observations from PDAF
• U_init_obserr_f: The name of the user-supplied routine that initializes the vector of observations error standard deviations for for full observation vector
• U_prepoststep: The name of the pre/poststep routine as in PDAF_get_state
• U_next_observation: The name of a user supplied routine that initializes the variables nsteps, timenow, and doexit. The same routine is also used in PDAF_get_state.
• status_pdaf: The integer status flag. It is zero, if PDAF_generate_obs is exited without errors.

The user-supplied call-back routines are described on the page on implementing the generation of synthetic observations.

It is recommended that the value of status_pdaf is checked in the program after PDAF_generate_obs is executed. Only if its value is 0 the initialization was successful.

PDAF also has a Simplified Interface providing the routine PDAF_generate_obs_si. In the simplified interface, the name of the user-supplied routines have predefined names and do not appear in the call to PDAF_generate_obs_si.