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data_assimilation.rst in NEMO/trunk/doc/rst/source – NEMO

source: NEMO/trunk/doc/rst/source/data_assimilation.rst @ 11707

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1*****************
2Data assimilation
3*****************
4
5.. contents::
6   :local:
7
8The assimilation interface to NEMO is split into three modules.
9
10- ``OBS`` for the observation operator
11- ``ASM`` for the application of increments and model bias correction
12  (based on the assimilation increments).
13- ``TAM`` the tangent linear and adjoint model.
14
15Please see |DOI man OCE|_ for more details including information about the input file formats and
16the namelist settings.
17
18Observation and model comparison (``OBS``)
19==========================================
20
21The observation and model comparison code (OBS) reads in observation files
22(profile temperature and salinity, sea surface temperature, sea level anomaly, sea ice concentration,
23and velocity) and calculates an interpolated model equivalent value at
24the observation location and nearest model timestep.
25The resulting data are saved in a feedback file (or files).
26The code was originally developed for use with the NEMOVAR data assimilation code, but
27can be used for validation or verification of model or any other data assimilation system.
28This is all controlled by the namelist.
29To build with the OBS code active ``key_diaobs`` must be set.
30
31More details in |DOI man OCE|_ "Observation and Model Comparison (``OBS``)" chapter.
32
33Standalone observation operator (``SAO``)
34-----------------------------------------
35
36The OBS code can also be run after a model run using saved NEMO model data.
37This is accomplished using the standalone observation operator (SAO)
38(previously known the offline observation operator).
39
40To build the SAO use makenemo.
41This means compiling NEMO once (in the normal way) for the chosen configuration.
42Then include ``SAO`` at the end of the relevant line in ``cfg.txt`` file.
43Then recompile with the replacement main program in ``./src/SAO``.
44This is a special version of ``nemogcm.F90`` (which doesn't run the model,
45but reads in the model fields, and observations and runs the OBS code.
46See "Standalone observation operator (``SAO``)" section in |DOI man OCE|_.
47
48Apply assimilation increments (``ASM``)
49=======================================
50
51The ASM code adds the functionality to apply increments to the model variables:
52temperature, salinity, sea surface height, velocity and sea ice concentration.
53These are read into the model from a NetCDF file which
54may be produced by separate data assimilation code.
55The code can also output model background fields which are used as an input to data assimilation code.
56This is all controlled by the namelist ``&nam_asminc``.
57To build the ASM code ``key asminc`` must be set.
58
59More details in |DOI man OCE|_ "Apply Assimilation Increments (``ASM``)" chapter.
60
61Tangent linear and adjoint (``TAM``)
62====================================
63
64This is the tangent linear and adjoint code of NEMO which is useful to 4D VAR assimilation.
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