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  • 11
    Online-Ressource
    Online-Ressource
    Schlagwort(e): Hochschulschrift
    Materialart: Online-Ressource
    Seiten: Online-Ressource
    DDC: 550
    Sprache: Englisch
    Anmerkung: Kiel, Univ., Diss., 2012
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 12
    Publikationsdatum: 2021-12-22
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev
    Format: application/pdf
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 13
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    Copernicus Publications (EGU)
    In:  Geoscientific Model Development, 9 (10). pp. 3729-3750.
    Publikationsdatum: 2019-09-24
    Beschreibung: We designed and implemented a modular software framework for the offline simulation of steady cycles of 3-D marine ecosystem models based on the transport matrix approach. It is intended for parameter optimization and model assessment experiments. We defined a software interface for the coupling of a general class of water column-based biogeochemical models, with six models being part of the package. The framework offers both spin-up/fixed-point iteration and a Jacobian-free Newton method for the computation of steady states. The simulation package has been tested with all six models. The Newton method converged for four models when using standard settings, and for two more complex models after alteration of a solver parameter or the initial guess. Both methods delivered the same steady states (within a reasonable precision) on convergence for all models employed, with the Newton iteration generally operating 6 times faster. The effects on performance of both the biogeochemical and the Newton solver parameters were investigated for one model. A profiling analysis was performed for all models used in this work, demonstrating that the number of tracers had a dominant impact on overall performance. We also implemented a geometry-adapted load balancing procedure which showed close to optimal scalability up to a high number of parallel processors.
    Materialart: Article , PeerReviewed
    Format: text
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 14
    Publikationsdatum: 2019-09-23
    Beschreibung: This paper presents the application of the Linear Quadratic Optimal Control (LQOC) method to a parameter optimization problem for a one-dimensional marine ecosystem model of NPZD (N for dissolved inorganic nitrogen, P for phytoplankton, Z for zooplankton and D for detritus) type. This ecosystem model, developed by Oschlies and Garcon, simulates the distribution of nitrogen, phytoplankton, zooplankton and detritus in a water column and is driven by ocean circulation data. The LQOC method is used to introduce annually periodic model parameters in a linearized version of the model. We show that the obtained version of the model gives a significant reduction of the model-data misfit, compared to the one obtained for the original model with optimized constant parameters. The found inner-annual variability of the optimized parameters provides hints for improvement of the original model. We use the obtained optimal periodic parameters also in validation and prediction experiments with the original non-linear version of the model. In both cases, the results are significantly better than those obtained with optimized constant parameters.
    Materialart: Article , PeerReviewed
    Format: text
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  • 15
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    Elsevier
    In:  Journal of Computational Science, 4 (5). pp. 423-437.
    Publikationsdatum: 2019-09-23
    Beschreibung: We have already shown in a previous methodological work that the surrogate-based optimization (SBO) approach can be successful and computationally very efficient when reconstructing parameters in a typical nonlinear, time-dependent marine ecosystem model, where a one-dimensional application has been considered to test the method's functionality in a first step. The application on real (measurement) data is covered in this paper. Essential here are a special model data treatment and further methodological enhancements which allow us to improve the robustness of the algorithm and the accuracy of the solution. By numerical experiments, we demonstrate that SBO is able to yield a solution close to the original model's optimum while time savings are again up to 85% when compared to a conventional direct optimization of the original model.
    Materialart: Article , PeerReviewed
    Format: text
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  • 16
    Publikationsdatum: 2019-09-23
    Beschreibung: We present the application of the Surrogate-based Optimization (SBO) method on a parameter identification problem for a 3-D biogeochemical model. SBO is a method for acceleration of optimization processes when the underlying model itself is of very high computational complexity. In these cases, coupled simulation runs require large amounts of computer time, where optimization runs may become unfeasible even with high-performance hardware. As a consequence, the key idea of SBO is to replace the original and computationally expensive (high-fidelity) model by a so-called surrogate, which is created from a less accurate but computationally cheaper (low-fidelity) model and a suitable correction approach to increase its accuracy. To date, the SBO approach has been widely and successfully used in engineering applications and also for parameter identification in a 1-D marine ecosystem model of NPZD type. In this paper, we apply the approach onto a two-component biogeochemical model. The model is spun-up into a steady seasonal cycle via the Transport Matrix Approach. The low-fidelity model we use consists of a reduced number of spin-up iterations (several decades instead of millennia used for the original model). A multiplicative correction operator is further exploited to extrapolate the rather inaccurate low-fidelity model onto the original one. This corrected model builds our surrogate. We validate this SBO method by twin-experiments that use synthetic observations generated by the original model. We motivate our choice of the low-fidelity model and the multiplicative correction and discuss the computational advantage of SBO in comparison to an expensive parameter optimization in the context of the high-fidelity model. The proposed SBO technique is shown to yield a solution close to the target at a significant gain of computational efficiency. Without further regularization techniques, the method is able to identify most model parameters. The method is simple to implement and presents a promising and pragmatic tool to calibrate biogeochemical models in a global three-dimensional setting
    Materialart: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
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  • 17
    Publikationsdatum: 2020-02-06
    Beschreibung: To describe the underlying processes involved in oceanic plankton dynamics is crucial for the determination of energy and mass flux through an ecosystem and for the estimation of biogeochemical element cycling. Many planktonic ecosystem models were developed to resolve major processes so that flux estimates can be derived from numerical simulations. These results depend on the type and number of parameterizations incorporated as model equations. Furthermore, the values assigned to respective parameters specify a model's solution. Representative model results are those that can explain data; therefore, data assimilation methods are utilized to yield optimal estimates of parameter values while fitting model results to match data. Central difficulties are (1) planktonic ecosystem models are imperfect and (2) data are often too sparse to constrain all model parameters. In this review we explore how problems in parameter identification are approached in marine planktonic ecosystem modelling. We provide background information about model uncertainties and estimation methods, and how these are considered for assessing misfits between observations and model results. We explain differences in evaluating uncertainties in parameter estimation, thereby also discussing issues of parameter identifiability. Aspects of model complexity are addressed and we describe how results from cross-validation studies provide much insight in this respect. Moreover, approaches are discussed that consider time- and space-dependent parameter values. We further discuss the use of dynamical/statistical emulator approaches, and we elucidate issues of parameter identification in global biogeochemical models. Our review discloses many facets of parameter identification, as we found many commonalities between the objectives of different approaches, but scientific insight differed between studies. To learn more from results of planktonic ecosystem models we recommend finding a good balance in the level of sophistication between mechanistic modelling and statistical data assimilation treatment for parameter estimation
    Materialart: Article , PeerReviewed
    Format: text
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  • 18
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    Christian-Albrechts-Universität zu Kiel. Institut für Informatik
    In:  Bericht / Institut für Informatik der Christian-Albrechts-Universität zu Kiel, 1013 . Christian-Albrechts-Universität zu Kiel. Institut für Informatik, Kiel, Germany, 24 pp.
    Publikationsdatum: 2020-08-05
    Beschreibung: Parameters and initial values of a one-dimensional marine ecosystemmodel are optimized using a gradient-based optimization algorithm takinginto account parameter bounds. Sensitivities of the optimized parametersw.r.t. errors in observations and initial values are studied numerically andfound to yield parameter ranges narrow relative to the a priori parameteruncertainty reflected in upper and lower bounds on the permitted pa-rameter range. This means, that optimal parameters can be determinedaccurately. We find, that optimizing for the initial values along with theparameters can greatly improve the model’s fit to the observations
    Materialart: Report , NonPeerReviewed
    Format: text
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 19
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    Springer
    In:  In: Simulation and Modeling Methodologies, Technologies and Applications. , ed. by Pina, N., Kacprzyk, J. and Filipe, J. Advances in Intelligent Systems and Computing, 197 (2). Springer, Berlin, Germany, pp. 193-208. ISBN 978-3-642-34335-3
    Publikationsdatum: 2019-09-23
    Beschreibung: Mathematical optimization of models based on simulations usually requires a substantial number of computationally expensive model evaluations and it is therefore often impractical. An improved surrogate-based optimization methodology, which addresses these issues, is developed for the optimization of a representative of the class of one-dimensional marine ecosystem models. Our technique is based upon a multiplicative response correction technique to create a computationally cheap but yet reasonably accurate surrogate from a temporarily coarser discretized physics-based coarse model. The original version of this methodology was capable of yielding about 84% computational cost savings when compared to the fine ecosystem model optimization. Here, we demonstrate that by employing relatively simple modifications, the surrogate model accuracy and the efficiency of the optimization process can be further improved. More specifically, for the considered test case, the optimization cost is reduced three times, i.e., from about 15% to only 5% of the cost of the direct fine model optimization.
    Materialart: Book chapter , PeerReviewed
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  • 20
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    In:  [Paper] In: 1. International Conference on Simulation and Modeling Methodologies, Technologies and Applications (SIMULTECH 2011), 29.-31.07.2011, Noordwijkerhout, The Netherlands .
    Publikationsdatum: 2019-09-23
    Materialart: Conference or Workshop Item , NonPeerReviewed
    Standort Signatur Einschränkungen Verfügbarkeit
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