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Dissertation zugänglich unter
Investigating the Dynamics of Suspended Particulate Matter in the North Sea Using a Hydrodynamic Transport Model and Satellite Data Assimilation
Untersuchung der Dynamik von Schwebstoff in der Nordsee mit einem hydrodynamischen Transport-Modell unter Verwendung von Satelliten-Datenassimilation
Dokument 1.pdf (4.218 KB)
Sedimenttransport , Dynamische Modellierung , Nordsee , Datenassimilation , Envisat
Freie Schlagwörter (Englisch):
SPM transport , Modeling , Assimilation , Satellite data , North Sea
Storch, Hans von (Prof. Dr.)
Tag der mündlichen Prüfung:
Kurzfassung auf Englisch:
Suspended particulate matter (SPM) changes light penetration depth in water and thus is an important component of marine ecosystems in the coastal and shallow regions of the world, i.e. the North Sea. The visible effect of SPM presence in seawater is the change of water color from blue to yellow depending on the SPM concentration under different ambient conditions. This study combines numeric modeling with satellite data assimilation in order to investigate the dynamics of SPM in the North Sea over a time period from 2002 to 2003.
First, a coupled three-dimensional Circulation and Transport Model for Suspended Particulate Matter (CTM-SPM) was designed based on the existing, improved and newly developed modeling routines. CTM-SPM was then applied to calculate the dynamics of SPM in seawater, as well as the dynamics of the fine sediment in the seabed in the southern North Sea. Modeled SPM exchange processes at the seawater-seabed interface, such as resuspension and erosion are forced by the shear stress due to currents and waves. Model results, the role of these two forcing components of the shear stress velocity is different in the shallow and deep regions, as well as during calm (from April to October) and storm (from October to April) periods. Therefore, this study investigates the relative impact of currents and waves on the horizontal and vertical distributions of SPM and its seasonality in details.
Calculated SPM concentrations in the North Sea for the years 2002 and 2003 are in good agreement with satellite and in-situ observations. The model results reveal two different patterns in the SPM dynamics typical for the calm and for the storm periods. This study explains the origin and evolution of the zones with high SPM concentration in the coastal areas and in the open North Sea. The results indicate that it is essential to use a coupled circulation and SPM transport model with realistic forcing data with a temporal resolution of <1 hour and instant values of shear stress velocity in order to resolve the SPM processes of different time scales, for example flash erosion events and long-term transport by currents. Utilization of the instant values of the shear stress velocity leads to the more realistic representation of the exchange processes at the water-seabed interface and to the more convenient comparison between the snap-shot satellite measurements and model results.
Second, newly developed and validated tool for satellite data processing and quality control based on the flags approach was applied for more than 400 ENVISAT MERIS snapshot scenes in order to provide the SPM concentration fields derived from satellite images for the assimilation into the CTM-SPM model. The satellite data was assimilated into the model using the sequential Optimum Interpolation scheme.
This thesis presents the first attempt of continuous satellite data assimilation into an SPM transport model. The results of this study indicate a great potential for the application of satellite optical data in the SPM modeling. Analyses of the model results with and without satellite data assimilation shows that assimilation effects not only SPM concentrations in the whole water column, but also the fine sediment distribution in the seabed. The data assimilation signal remains in the model for several days after assimilation. Also the seasonal averaged distributions of SPM changed due to assimilation. Satellite data assimilation improves the horizontal SPM distribution, especially its fine structures in the location of SPM fronts in the German Bight and near the English cliffs.
The concept presented in this study can be used as a basis for continuous calculations of SPM based on the modeling and satellite data assimilation. It can be used in operational purposes and in ecosystem modeling.