1 | ***************** |
---|
2 | Data assimilation |
---|
3 | ***************** |
---|
4 | |
---|
5 | .. todo:: |
---|
6 | |
---|
7 | |
---|
8 | |
---|
9 | .. contents:: |
---|
10 | :local: |
---|
11 | |
---|
12 | The assimilation interface to NEMO is split into three modules. |
---|
13 | |
---|
14 | - ``OBS`` for the observation operator |
---|
15 | - ``ASM`` for the application of increments and model bias correction |
---|
16 | (based on the assimilation increments). |
---|
17 | - ``TAM`` the tangent linear and adjoint model. |
---|
18 | |
---|
19 | Please see :doc:`NEMO manual <cite>` for more details including |
---|
20 | information about the input file formats and the namelist settings. |
---|
21 | |
---|
22 | Observation and model comparison (``OBS``) |
---|
23 | ========================================== |
---|
24 | |
---|
25 | The observation and model comparison code (OBS) reads in observation files |
---|
26 | (profile temperature and salinity, sea surface temperature, sea level anomaly, sea ice concentration, |
---|
27 | and velocity) and calculates an interpolated model equivalent value at |
---|
28 | the observation location and nearest model timestep. |
---|
29 | The resulting data are saved in a feedback file (or files). |
---|
30 | The code was originally developed for use with the NEMOVAR data assimilation code, but |
---|
31 | can be used for validation or verification of model or any other data assimilation system. |
---|
32 | This is all controlled by the namelist. |
---|
33 | To build with the OBS code active ``key_diaobs`` must be set. |
---|
34 | |
---|
35 | More details in :manhtml:`"Observation and Model Comparison (OBS)" chapter <node83.html>`. |
---|
36 | |
---|
37 | Standalone observation operator (``SAO``) |
---|
38 | ----------------------------------------- |
---|
39 | |
---|
40 | The OBS code can also be run after a model run using saved NEMO model data. |
---|
41 | This is accomplished using the standalone observation operator (SAO) |
---|
42 | (previously known the offline observation operator). |
---|
43 | |
---|
44 | To build the SAO use :file:`makenemo`. |
---|
45 | This means compiling NEMO once (in the normal way) for the chosen configuration. |
---|
46 | Then include ``SAO`` at the end of the relevant line in :file:`cfg.txt` file. |
---|
47 | Then recompile with the replacement main program in :file:`./src/SAO`. |
---|
48 | This is a special version of :file:`nemogcm.F90` (which doesn't run the model, |
---|
49 | but reads in the model fields, and observations and runs the OBS code. |
---|
50 | See :manhtml:`"Standalone observation operator (SAO)" section <node88.html>`. |
---|
51 | |
---|
52 | Apply assimilation increments (``ASM``) |
---|
53 | ======================================= |
---|
54 | |
---|
55 | The ASM code adds the functionality to apply increments to the model variables: |
---|
56 | temperature, salinity, sea surface height, velocity and sea ice concentration. |
---|
57 | These are read into the model from a NetCDF file which |
---|
58 | may be produced by separate data assimilation code. |
---|
59 | The code can also output model background fields which are used as an input to data assimilation code. |
---|
60 | This is all controlled by the namelist ``&nam_asminc``. |
---|
61 | To build the ASM code ``key asminc`` must be set. |
---|
62 | |
---|
63 | More details in :manhtml:`"Apply Assimilation Increments (ASM)" chapter <node89.html>`. |
---|
64 | |
---|
65 | Tangent linear and adjoint (``TAM``) |
---|
66 | ==================================== |
---|
67 | |
---|
68 | This is the tangent linear and adjoint code of NEMO which is useful to 4D VAR assimilation. |
---|