PDAF-OMI Observation Modules

The implementation of the observations with OMI is done in observation modules (obs-modules). For each observation type a separate module should be created.

Each obs-module contains four routines:

• init_dim_obs initializes all variables holding the information about one observation type. The information about the observation type is stored in a data structure (Fortran derived type).
• obs_op applies the observation operator to a state vector. One can call an observation operator routine provided by PDAF, or one can to implement a new operator.
• init_dim_obs_l calls a PDAF-OMI routine to initialize the observation information corresponding to a local analysis domain. One can set localization parameters, liek the localization radius, for each observation type.
• localize_covar calls a PDAF-OMI routine to apply covariance localization. One can set localization parameters, liek the localization radius, for each observation type.

obs_f data type

To ensure the functionality within each obs-module, we rely on a derived data type called obs_f that describes the observation. One instance of this data type is allocated in each obs-module as the variable thisobs. a few of the elements of obs_f are initialized by the user when the observation information is initialized on init_dim_obs_f. Further information is set in a call to the routine PDAFomi_gather_obs. This information is then used by all other routines in the obs-module. The template file obs_TYPE_pdafomi_TEMPLATE.F90 shows the different steps needed to initialize thisobs.

! ---- Mandatory variables to be set in init_dim_obs_f ----
  INTEGER :: doassim                    ! Whether to assimilate this observation type
  INTEGER :: disttype                   ! Type of distance computation to use for localization
                                        !   (0) Cartesian, (1) Cartesian periodic
                                        !   (2) simplified geographic, (3) geographic haversine function
  INTEGER :: ncoord                     ! Number of coordinates use for distance computation
  INTEGER, ALLOCATABLE :: id_obs_p(:,:) ! Indices of observed field in state vector (process-local)