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
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.
The potential examples are numerous.
Since each ‘observation quantity’ 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
For this reason, we strongly recommend that you use the DART routines to read and process DART observation sequence files.
You must actually run
preprocess before building any executables.
It is an essential part of DART that enables the same code to interface with
multiple models and observation types. For example,
DART to 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_quantity 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
The list of
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, you must rerun
preprocess and recompile the rest of your project.
As an example, if a
preprocess_nml namelist in
input.nml looks like:
&preprocess_nml input_obs_kind_mod_file = '../../../assimilation_code/modules/observations/DEFAULT_obs_kind_mod.F90' output_obs_kind_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', '../../../observations/forward_operators/obs_def_QuikSCAT_mod.f90', '../../../observations/forward_operators/obs_def_GWD_mod.f90', '../../../observations/forward_operators/obs_def_altimeter_mod.f90', '../../../observations/forward_operators/obs_def_reanalysis_bufr_mod.f90' output_obs_def_mod_file = '../../../observations/forward_operators/obs_def_mod.f90' /
preprocess will combine the following modules:
obs_def_mod.f90. This resulting module can be used by the rest of the
Building and running
preprocess is an executable, it must be compiled following the
procedure of all DART executables:
DART/build_templates/mkmf.templatemust be correct for your environment.
input.nmlmust be set properly with the modules you want to use.
If those two conditions are met, you can build and run
$ csh mkmf_preprocess $ make $ ./preprocess
The first command generates an appropriate
Makefile and the
input.nml.preprocess_default file. The second command results in the
compilation of a series of Fortran90 modules which ultimately produces the
preprocess executable file. The third command actually runs preprocess -
which builds the new
obs_def_mod.f90 source code
files. Once these source code files are created, you can now build the rest of