Assimilating Data Into A
Circulation Model
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| The
objectives are development and testing of a TUNEd NEarshore Prediction model
(NEPTUNE) that will combine a nearshore circulation model with observations of
the circulation field. The system will consist of an existing numerical model
of the depth- and phase-averaged equations of motion governing the temporal and
spatial evolution of nearshore circulation, and will utilize video observations
of quantities relevant to the circulation. Primarily, observations of surface
current patterns obtained using Particle Image Velocimetry (PIV) techniques
applied to a video system will be used, but techniques to assimilate video
observations of surf zone width, energy dissipation, or radiation stress
gradients will also be developed. |
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| Data
assimilation methods provide the formal means for combining models with
measurements to generate solutions that constitute a best fit to all relevant
data while satisfying the constraints imposed by the modeling equations. The
focus is on a thorough understanding of the assimilation techniques and their
implementation into the circulation model, and testing of the modeling scheme
as part of the Nearshore Canyon Experiment (NCEX). Two distinct strategies are
being examined: |
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· Computationally efficient
sequential estimators that correct forward model output using available data,
but do not tune model parameters (such as frictional coefficients). It is
anticipated to model a "strip" of the beach that extends alongshore for several
kilometers and is bounded by the shoreline and the 10 m contour in the
cross-shore direction
(SEE FIGURE 1). |
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FIGURE 1
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FIGURE 1:
Domain of interest for model simulations (outlined in red). The
longshore extent of the domain of interest is chosen to coincide with the area
that will be viewed with the video cameras. Note that the model domain is
bounded by curvilinear lines in the cross-shore direction. The off-shore
boundary conicides with the 10m-contour. The location of the shoreline boundary
can vary to account for the tidal elevation and any shoreline runup due to low
frequency motions. |
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| · More computationally expensive inverse
models that are used to adjust free model parameters to achieve an optimal fit
to the data. Inverse methods are based on the derivation of an adjoint
model which propagates information backwards in both space and time. The
forward and adjoint models are solved iteratively. This process is outlined
schematically in
FIGURE 2. Using this technique a portion of the
NCEX site, such as the area around Black's beach
(SEE FIGURE 3), will be modeled in
detail. |
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FIGURE
2
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FIGURE 3
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FIGURE 2:
Flowchart of an inverse modeling scheme.
FIGURE 3:
Domain of interest for model simulations around Black's beach (outlined
in red). |
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