= 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 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 the following: 
{{{
  SUBROUTINE PDAFomi_diag_obs_rmsd(nobs, rmsd_pointer, verbose)
}}}
with the following arguments:
{{{
    INTEGER, INTENT(inout) :: nobs                   !< Number of observation types
    REAL, POINTER, INTENT(inout) :: rmsd_pointer(:)  !< Vector of RMSD values
    INTEGER, INTENT(in) :: verbose                   !< Verbosity flag
}}}

**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. One can check this value before assessing the pointer array