= PDAFomi_diag_obs_rmsd = 

This page documents the routine `PDAFomi_diag_obs_rmsd` of PDAF, which was introduced with PDAF V3.0. This is part of the [wiki:PDAFomi_observation_diagnostics PDAF-OMI observation diagnostics module].

The routine returns a pointer to a vector of the root-mean square difference (RMSD) between the observations and the observed ensemble mean for each observation type. 

Usually all PDAFomi_diag routines are called in `prepoststep_pdaf` where the observation information can be retrieved and analyzed.

The interface is: 
{{{
  SUBROUTINE PDAFomi_diag_obs_rmsd(nobs, rmsd_pointer, verbose)

    INTEGER, INTENT(inout) :: nobs                   ! Number of observation types
    REAL, POINTER, INTENT(inout) :: rmsd_pointer(:)  ! Vector of RMSD values
    INTEGER, INTENT(in) :: verbose                   ! Verbosity flag; >0 for screen output
}}}

For verbose>0 a list of the RMSD for each observation type is printed like
{{{
PDAFomi   obs-ID      RMSD   
PDAFomi      1      7.097E-01
PDAFomi      2      1.312E-02
}}}

**Note:**
 * The computed RMSD is for the global model domain. Thus, in case of a parallelized model, all process sub-domains are taken into account and calling `PDAFomi_diag_obs_rmsd` will return the same value for all processes.
 * In Fortran user code the pointer should be declared in the form[[BR]] `REAL, POINTER :: rmsd_ptr(:)`[[BR]] It does not need to be allocated. The target vector has the length `nobs`.
 * If the observation diagnostics have not be activated by using [wiki:PDAFomi_set_obs_diag] the pointer array will not be set and `nobs=0` is returned. One can check this value before assessing the pointer array.
 * A more extensive set of statistics can be obtained using the routine [wiki:PDAFomi_diag_stats].