Obs Builder

Obs builder is a framework that provides a simple and consistent way to create “mapping” files that are used to read BUFR files (when a YAML file is not enough).

As can be seen from the diagram, the ObsBuilder is the core object of the framework. The intent is for client applications to create a subclasses of the ObsBuilder and make a custom version of it by overriding the methods that are needed. This can be especially useful when you are creating a set of mapping files for a family of related observation types that have a lot of commonality.

Once the ObsBuilder is created, the framework provides a method called add_main_functions which automatically creates the main functions that are expected on a mapping file. Once executed the files can be executed via the command line (ex: python ./bufr_satwnd_amv_avhrr.py input.bufr output.nc). The add_main_functions methods creates the expected module level functions using the the class definitions for create_obs_file and create_obs_group (their signatures) as the template.

Common Overrides

The following methods are the most common methods that are overridden in the ObsBuilder class. Overriding each method is optional, as the ObsBuilder base class provides default implementations.

Here is a simple example of a class that implements the ObsBuilder class and demonstrates its intended usage:

MAPPING_PATH = map_path('bufr_satwnd.yaml')

class SatWndObsBuilder(ObsBuilder):
   def __init__(self):
      super().__init__(MAPPING_PATH, log_name=os.path.basename(__file__))

   def make_obs(self, comm,  input : Union[str, dict])
      assert isinstance(input, str), "Input must be a string"

      container = super().make_obs(comm, input)

      wdir = container.get('windDirection')
      wspd = container.get('windSpeed')

      uob, vob = self._compute_wind_components(wdir, wspd)
      paths = container.get_paths('windSpeed')

      container.add('windEastward', uob, paths)
      container.add('windNorthward', vob, paths)

      container.apply_mask(wspd > 0.0)
      return container

   def _make_description(self):
      description = super()._make_description()

      description.add_variables([
      {
         'name': 'ObsType/windEastward',
         'source': 'windEastward',
         'units': '1',
         'longName': 'Eastward Wind Component',
      },
      {
         'name': 'ObsType/windNorthward',
         'source': 'windNorthward',
         'units': '1',
         'longName': 'Northward Wind Component',
      }])

      return description

Add Main Functions

The ObsBuilder class provides a method called add_main_functions which automatically creates adds the main functions that are expected on a mapping file.

Here is a list of the functions that are created:

• if __name__ == ‘__main__’: Defenition that allows the file to be executed as a script.

• create_obs_file: Function that takes the input file and creates an output file.

• create_obs_group: Function that is used to create an IODA obsgroup object. It is used by the

  IODA script interface.

Note

The add_main_functions method will create the functions with the same signature as the overridden methods. If you do not override the methods, the default signatures will be used. The default signatures are:

• create_obs_file(input, output, type=’netcdf’, append=False, config=None):

• create_obs_group(input, env, category:list=None, cache_categories:list=None, config=None):

config is a dictionary that is used to initialize the ObsBuilder object.