PROGRAM preprocess


Preprocess is a DART-supplied preprocessor program. Preprocess is used to insert observation specific code into DART at compile time.

In DART, forward operators are not specific to any one model. To achieve this separation between models and forward operators DART makes a distinction between an observation type and a physical quantity. For example, a radiosonde used to measure windspeed would be a type of observation. Zonal wind and meridional wind are quantities used to calculate windspeed. Specifying many observation types allows DART to be able to evaluate some observations and assimilate others even if the instruments measure the same quantity.

Preprocess takes user supplied observation and quantity files and combines them with template files to produce code for DART. Use the namelist option ‘obs_type_files’ to specify the input observation files and the namelist option ‘quantity_files’ to specify the input quantity files.

  • If no quantity files are given, a default list of quantities is used.

  • If no obs_type_files are given, only identity observations can be used in the filter (i.e. the state variable values are directly observed; forward operator is an identity)

The template files DEFAULT_obs_def_mod.F90 and DEFAULT_obs_kind_mod.F90 contain specially formatted comment lines. These comment lines are used as markers to insert observation specific information. Prepreocess relies these comment lines being used verbatim.

There is no need to to alter DEFAULT_obs_def_mod.F90 or DEFAULT_obs_kind_mod.F90. Detailed instructions for adding new observation types can be found in MODULE obs_def_mod. New quantities should be added to a quantity file, for example a new atmosphere quantity should be added to atmosphere_quantities_mod.f90.

Every line in a quantity file between the start and end markers must be a comment or a quantity definition (QTY_string). Multiple name-value pairs can be specified for a quantity but are not required. For example, temperature may be defined: ! QTY_TEMPERATURE units="K" minval=0.0. Comments are allowed between quantity definitions or on the same line as the definition. The code snippet below shows acceptable formats for quantity definitions

! Formats accepted:
! QTY_string
! QTY_string name=value
! QTY_string name=value name2=value2
! QTY_string ! comments
! ! comment
The output files produced by preprocess are named assimilation_code/modules/observations/obs_kind_mod.f90 and observations/forward_operators/obs_def_mod.f90, but can be renamed by namelist control if needed. Be aware that if you change the name of these output files, you will need to change the path_names files for DART executables.


When you run preprocess, the namelist is read from the file input.nml in the directory where preprocess is run.

Namelists start with an ampersand ‘&’ and terminate with a slash ‘/’. Character strings that contain a ‘/’ must be enclosed in quotes to prevent them from prematurely terminating the namelist. These are the defaults:

  overwrite_output        = .true.,
  input_obs_def_mod_file  = '../../../observations/forward_operators/DEFAULT_obs_def_mod.F90',
  output_obs_def_mod_file = '../../../observations/forward_operators/obs_def_mod.f90',
  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',
  obs_type_files          = '../../../observations/forward_operators/obs_def_reanalysis_bufr_mod.f90',






Path name of the template observation definition module to be preprocessed. The default is ../../../observations/forward_operators/DEFAULT_obs_def_mod.F90. This file must have the appropriate commented lines indicating where the different parts of the input special obs definition modules are to be inserted.



Path name of output observation definition module to be created by preprocess. The default is ../../../observations/forward_operators/obs_def_mod.f90.



Path name of input obs quantity file to be preprocessed. The default path name is ../../../assimilation_code/modules/observations/DEFAULT_obs_kind_mod.F90. This file must have the appropriate commented lines indicating where the different quantity modules are to be inserted.



Path name of output obs quantity module to be created by preprocess. The default is ../../../assimilation_code/modules/observations/obs_kind_mod.f90.



A list of files containing observation definitions for the type of observations you want to use with DART. The maximum number of files is limited to MAX_OBS_TYPE_FILES = 1000. The DART obs_def files are in observations/forward_operators/obs_def_*.mod.f90.



By default, preprocess will overwrite the existing obs_kind_mod.f90 and obs_def_mod.f90 files. Set overwrite_output = .false. if you want to preprocess to not overwrite existing files.

Modules used


Namelist interface &preprocess_nml must be read from file input.nml.


  • input_obs_def_mod_file, specified by namelist; usually DEFAULT_obs_def_mod.F90.

  • output_obs_def_mod_file, specified by namelist; usually obs_def_mod.f90.

  • input_obs_qty_mod_file, specified by namelist; usually DEFAULT_obs_kind_mod.F90.

  • output_obs_qty_mod_file, specified by namelist; usually obs_kind_mod.f90.

  • obs_type_files, specified by namelist; usually files like obs_def_reanalysis_bufr_mod.f90.

  • quantity_files, specified by namelist; usually files like atmosphere_quantities_mod.f90.

  • namelistfile; input.nml


  • none