The assimilation interface to NEMO is split into three modules.
OBSfor the observation operator
ASMfor the application of increments and model bias correction (based on the assimilation increments).
TAMthe tangent linear and adjoint model.
Please see NEMO reference manual for more details including information about the input file formats and the namelist settings.
The observation and model comparison code (OBS) reads in observation files
(profile temperature and salinity, sea surface temperature, sea level anomaly, sea ice concentration,
and velocity) and calculates an interpolated model equivalent value at
the observation location and nearest model timestep.
The resulting data are saved in a feedback file (or files).
The code was originally developed for use with the NEMOVAR data assimilation code, but
can be used for validation or verification of model or any other data assimilation system.
This is all controlled by the namelist.
To build with the OBS code active
key_diaobs must be set.
More details in “Observation and Model Comparison (OBS)” chapter.
The OBS code can also be run after a model run using saved NEMO model data. This is accomplished using the standalone observation operator (SAO) (previously known the offline observation operator).
To build the SAO use
This means compiling NEMO once (in the normal way) for the chosen configuration.
SAO at the end of the relevant line in
Then recompile with the replacement main program in
This is a special version of
nemogcm.F90 (which doesn’t run the model,
but reads in the model fields, and observations and runs the OBS code.
See “Standalone observation operator (SAO)” section.
The ASM code adds the functionality to apply increments to the model variables:
temperature, salinity, sea surface height, velocity and sea ice concentration.
These are read into the model from a NetCDF file which
may be produced by separate data assimilation code.
The code can also output model background fields which are used as an input to data assimilation code.
This is all controlled by the namelist
To build the ASM code
key asminc must be set.
More details in “Apply Assimilation Increments (ASM)” chapter.
This is the tangent linear and adjoint code of NEMO which is useful to 4D VAR assimilation.