U_obs_op_f

The page document the user-supplied call-back routine U_obs_op_f.

The routine U_obs_op_f is a call-back routine that has to be provided by the user. In the simplified interface the predefined name of the routine is obs_op_f_pdaf, but in the full interface, the user can choose the name of the routine. The routine is used with all filter algorithms using domain-localization (LSEIK, LETKF, LESTKF) and is independent of the particular algorithm. The routine is called during the analysis step, before the loop over the local analysis domain is entered. It purpose is to perform the operation of the observation operator acting on a state vector, which is provided as input argument. The observed state corresponding to the 'full' observation vector has to be returned.

The interface is the following:

SUBROUTINE U_obs_op_f(step, dim_p, dim_obs_f, state_p, m_state_f)

with

• step : integer, intent(in)
  Current time step
• dim_p : integer, intent(in)
  Size of state vector (local part in case of parallel decomposed state)
• dim_obs_f : integer, intent(in)
  Size of full observation vector
• state_p : real, intent(in), dimension(dim_p)
  Model state vector
• m_state_f : real, intent(out), dimension(dim_obs_f)
  Full observed state (i.e. the result after applying the observation operator to state_p)

Hints:

• The routine is similar to obs_op_pdaf used for the global filters. However, with a domain-decomposed model m_state_f will contain parts of the state vector from neighboring model sub-domains. To make these parts accessible, some parallel communication will be necessary (The state information for a neighboring model sub-domain will be in the memory of the process that handles that sub-domain). The example implementation in testsuite/dummymodel_1d uses the function MPI_AllGatherV for this communication.
• In case of a parallelized analysis step one has to take care that the order of observation in m_state_f is consistent with the order in the full observation vector obs_f generated by init_obs_f_pdaf.
• In case of a parallelized analysis step the full vector m_state_f can be obtained by first computing the process-local vector m_state_p from the state vector state_p and then calling the routine PDAF_gather_obs_f (introduced with PDAF V1.13). When PDAF_gather_obs_f is used in both init_dim_obs_f_pdaf and obs_op_f_pdaf it is ensured that the order of the entries in the full observation vector and m_state_f is consistent.