How DART supports different types of observations: the preprocess program

DART’s preprocess program actually writes the source code that supports observations. This source code is then used by other modules.

The rationale for preprocess

Certain types of data require additional metadata in order to be assimilated. For example, while radiosondes only require the observation location in order to be assimilated, radar observations need extra metadata to specify the location of the radar in addition to the location of the observation. GPS occultations need the locations of the two satellites so the forward operator can integrate along the raypath. Cosmic ray soil moisture sensors have forward operators that require site-specific calibration parameters that are not part of the model and must be included in the observation metadata.

Since each observation type may require different amounts of metadata to be read or written, any routine to read or write an observation sequence must be compiled with support for those particular observations. This is the rationale for the inclusion of preprocess in DART. The supported observations are listed in the obs_kind_nml namelist in input.nml.

For this reason, we strongly recommend that you use the DART routines to read and process DART observation sequence files.


Preprocess is built and run when you run

Preprocess is used to insert observation specific code into DART at compile time. This compile time choice is how DART can assimilate synthetic observations for the Lorenz_63 model and real radar reflectivities for WRF without needing to specify a set of radar operators for the Lorenz_63 model.

preprocess combines multiple obs_def modules into one obs_def_mod.f90 that is then used by the rest of DART. Additionally, a new obs_kind_mod.f90 is built that will provide support for associating the specific observation TYPES with corresponding (generic) observation QUANTITIES.

The list of obs_def and obs_quantity module source codes are contained in the &preprocess_nml namelist in input.nml. These modules determine what observations and operators are supported.


If you want to add another obs_def module or quantity file, you must rerun preprocess and recompile the rest of your project.

Example preprocess namelist

As an example, if a preprocess_nml namelist in input.nml looks like:

    input_obs_qty_mod_file  = '../../../assimilation_code/modules/observations/DEFAULT_obs_kind_mod.F90'
    output_obs_qty_mod_file = '../../../assimilation_code/modules/observations/obs_kind_mod.f90'
    quantity_files           = '../../../assimilation_code/modules/observations/atmosphere_quantities_mod.f90',
    input_obs_def_mod_file   = '../../../observations/forward_operators/DEFAULT_obs_def_mod.F90'
    obs_type_files           = '../../../observations/forward_operators/obs_def_gps_mod.f90',
    output_obs_def_mod_file  = '../../../observations/forward_operators/obs_def_mod.f90'

preprocess will combine the following modules:

  • DEFAULT_obs_def_mod.F90

  • obs_def_gps_mod.f90

  • obs_def_QuikSCAT_mod.f90

  • obs_def_GWD_mod.f90

  • obs_def_altimeter_mod.f90

  • and obs_def_reanalysis_bufr_mod.f90

into obs_def_mod.f90. This resulting module can be used by the rest of the project.