Module Assimilation
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Contents
Overview
Module Assimilation is responsible for handling information used in relaxation schemes. It mainly reads the reference fields and the relaxation coefficients fields used to relax the solution to the reference solution. The standard relaxation scheme implemented in MOHID follow the following equation:
where 
is the relaxed variable computed by the model, 
is the reference solution and 
relaxation coefficient.
Module Hydrodynamic and Module WaterProperties use this module to read and prepare the information. The relaxation algorithms are actually programmed in Module Hydrodynamic and Module WaterProperties, making Module Assimilation somewhat a "reading" module. This type of approach is normally used when nesting models or using a climatological reference solution.
This module relates to simplified data assimilation schemes. For information regarding advanced data assimilation in MOHID please check ModuleSequentialAssimilation.
Concepts
Property
A property consists of a reference field and a relaxation coefficients field. It can be 2D (e.g. water level) or 3D (e.g. temperature).
Reference field
The reference field is a prescribed solution which is used to force the solution computed by the model. The reference field must be given in the same units as the computed field. Examples of properties are velocity U, velocity V, water level, temperature, salinity, etc. A reference field must be defined in the U, V or Z grid, via keyword TYPE_ZUV and it can be set using Module FillMatrix.
Relaxation coefficients
The relaxation coefficients are used to define the rate at which the solution computed by the model is relaxed to the prescribed solution. The units of these coefficients are seconds.
To generate in a easy way a relaxation coefficients file use the AssimilationZones tool.
Other features
Cold relaxation period
- COLD_RELAX_PERIOD
- COLD_ORDER
Outputs
User manual
Assimilation data file
A property is identified by the keyword NAME inside a block delimited by the <beginproperty> and <endproperty> tags. The dimension of the property is specified by keyword DIMENSION (e.g. for a 3D property: DIMENSION : 3).
A reference field is defined inside a block delimited by the <<begin_field>> and <<end_field>> tags.
A relaxation coefficients field is defined inside a block delimited by the <<begin_coef>> and <<end_coef>> tags.
A relaxation coefficients and reference fields must be defined in the U, V or Z grid, via keyword TYPE_ZUV and can be set using Module FillMatrix.
<beginproperty> NAME : velocity U UNITS : m/s DIMENSION : 3 OUTPUT_HDF : 1 <<begin_field>> DEFAULTVALUE : 0 INITIALIZATION_METHOD : HDF FILE_IN_TIME : HDF FILENAME : ../../GeneralData/Reference_vel_U.hdf5 TYPE_ZUV : z <<end_field>> <<begin_coef>> DEFAULTVALUE : 1e9 TYPE_ZUV : u FILE_IN_TIME : NONE REMAIN_CONSTANT : 1 INITIALIZATION_METHOD : ASCII_FILE FILENAME : ../../GeneralData/RelaxationCoefs_U.dat <<end_coef>> <endproperty> <beginproperty> NAME : velocity V UNITS : m/s DIMENSION : 3 OUTPUT_HDF : 1 <<begin_field>> DEFAULTVALUE : 0 INITIALIZATION_METHOD : HDF FILE_IN_TIME : HDF FILENAME : ../../GeneralData/Reference_vel_V.hdf5 TYPE_ZUV : z <<end_field>> <<begin_coef>> DEFAULTVALUE : 1e9 TYPE_ZUV : v FILE_IN_TIME : NONE REMAIN_CONSTANT : 1 INITIALIZATION_METHOD : ASCII_FILE FILENAME : ./../GeneralData/RelaxationCoefs_V.dat <<end_coef>> <endproperty>
<beginproperty> NAME : temperature UNITS : ºC DIMENSION : 3D OUTPUT_HDF : 1 <<begin_field>> DEFAULTVALUE : 0 INITIALIZATION_METHOD : HDF FILE_IN_TIME : HDF FILENAME : ../../GeneralData/Reference_T.hdf5 TYPE_ZUV : z <<end_field>> <<begin_coef>> DEFAULTVALUE : 1e32 TYPE_ZUV : z FILE_IN_TIME : NONE REMAIN_CONSTANT : 1 INITIALIZATION_METHOD : ASCII_FILE FILENAME : ../../GeneralData/RelaxationCoefs_T.dat <<end_coef>> <endproperty>
