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Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
COSTA
An Introduction
Nils van Velzen email: c.vanvelzen@tudelft.nl
www.costapse.org
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
Outline
• Data assimilation and calibration• Existing software and programming issues• COSTA• Application of COSTA with
WAQUA/TRIWAQ• Conclusions
www.costapse.org
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
Data assimilation and calibration
• (Dynamic) simulation models– Weather forecast– Air quality– Shallow water (storm surge)– Ocean modelling– Reservoir
• Predictions are not perfect!
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
Data assimilation and calibration
• Measurements:– Satellites– Buoy– Radar– Weather stations
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
Data assimilation and calibration
– Make model perform better using the available observations:
• Calibration: change model parameters in order to reduce the difference between the model predictions and observations
• Data assimilation: combine the model forecast and observations into a mixed forecast
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
Existing software and programming issues
• Simulation software is complex• More complex is combined with Data
assimilation and/or Calibration methods• Expensive to develop and maintain• Splitting up software is in general a
good idea– Less complex– Possible to reuse (parts of) the code
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
Existing software and programming issues
• Why people think they have to develop a custom implementation of a DA method:– Computational efficient– Need to handle model specific issues
• Are these assumptions correct? Issues are:– Which method to implement?– Expensive– Incompatible– Potentially full of bugs
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
COSTA• A problem solving environment for data
assimilation and calibration– Components and their interface– Data assimilation methods– Platform for exchanging models and methods
• Free software (LGPL)
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
Steps to prepare model codes for implementing data assimilation
• Identify the state-vector of your model and those parameters and forcing (you think) you want to use
• Isolate the model time step--This is 90% of the work and has to be done
for a custom data assimilation implementation as well
--COSTA provides tools to simplify this work
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
COSTA• A generic environment where user can
easily try out different DA-methods to their models
• A generic environment where method developers can easily implement their method to different models
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
COSTA• Most data assimilation actually only requires
information about model state and observation at the same time.
• This makes it possible to implement model, observation and data assimilation methods separately as independent components.
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
COSTA componentsModel, observations and DA-method
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
Model Component
• Model component in COSTA (formal)
• State of a model instance• Methods to get or change the state of
model instance
, , ,d t
M t t tdt
x
x p u w
, , , , tx u p w
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
Model Component• Propagate the model state-vector
• Get, set, axpy for
• GetObsValues:
, , ,t t
t
t M t t t dt
x x p u w
y t H t x
, , ,t t tx p u w
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
Using COSTA
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
Using COSTA
• Use the “costawb” program to combine a model with a DA-method without any programming
• Model components are dynamic libraries and are linked to the “costawb” program
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
WAQUA/TRIWAQ
• Simulation model for shallow water• Used operational by the Dutch
Rijkswaterstaat• Long history of data assimilation
– Too expensive– Inflexible
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
WAQUA/TRIWAQ
• Domain decomposition and parallel computing
• COSTAmodel component
• RRSQRTFilter
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
The WAQUA/TRIWAQ model Deterministic model:
Stochastic model:
or
φ ti+ 1=A [ φ t i ,u t i ,g ]
φt t i+1 pu t i+ 1p A t i+ 1 = A [ φ t t i ,u f t i +W u pu t i ,g ]+W A p A t i
diag α A p A t i diag α u pu t i 0
η u t i η A t i
x t t i+1 =M i [ x t i ]+η t i
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
Deterministic and Stochastic We want a separation between
deterministic and stochastic model Use deterministic model for other applications Play with alternative
noise models
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
Deterministic and Stochastic WAQUA/TRIWAQ uses ADI-scheme:
One time step consist of two half time steps Time correlation applied each half time step
New approach: Time correlation
each whole time step
Different results!
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
Challenge Can we:
Separate filter and method Method?
have same results? Similar performance?
Is the COSTA modelinterface sufficientfor this task?
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
Conclusions
• COSTA offers a flexible framework for using and developing data assimilation methods.
• Successful coupling with “real” models:– WAQUA/TRIWAQ– Lotos-Euros– Chimere
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
Conclusions
• Easy to use• Complete basic functionality available:
– Implementation available for all basic building blocks
– Growing number of available methods• Support for parallel computing
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
Thank you!
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
Existing software and programming issues
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
Tools for creating COSTA models
• Simple model builder– Handles the “object oriented” aspects of the model– You only need to implement 4 functions
• Model combiner– Combine multiple COSTA models in one composite
model– Create a stochastic model from a deterministic model
• Black Box model builder– Create a COSTA component for a model without
changing the model code
• Support for parallel models
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
Automatic parallelization
Data Assimilation Summer School, Sibiu, 6th August 2009
Common Set of Tools for Assimilation of DataCOSTA
Using parallel models