Modelling the Eddy Pattern in the harbour of Zeebrugge

Hydrodynamic

Fluvio-morphological processes of meander bends - Combining conventional field measurements, close-range remote sensing and computational modelling

Meandering rivers have been perceived to evolve rather similarly around the world independently of the location or size of the river. Despite the many consistent processes and characteristics they have also been noted to show complex and unique sets of fluviomorphological processes in which local factors play important role. These complex interactions of flow and morphology affect notably the development of the river. Comprehensive and fundamental field, flume and theoretically based studies of fluviomorphological processes in meandering rivers have been carried out especially during the latter part of the 20th century. However, as these studies have been carried out with traditional field measurements techniques their spatial and temporal resolution is not competitive to the level achievable today. The hypothesis of this study is that, by exploiting e increased spatial and temporal resolution of the data, achieved by combining conventional field measurements with a range of modern technologies, will provide new insights to the spatial patterns of the flow-sediment interaction in meandering streams, which have perceived to show notable variation in space and time. This thesis shows how the modern technologies can be combined to derive very high spatial and temporal resolution data on fluvio-morphological processes over meander bends. The flow structure over the bends is recorded in situ using acoustic Doppler current profiler (ADCP) and the spatial and temporal resolution of the flow data is enhanced using 2D and 3D CFD over various meander bends. The CFD are also exploited to simulate sediment transport. Multi-temporal terrestrial laser scanning (TLS), mobile laser scanning (MLS) and echo sounding data are used to measure the flow-based changes and formations over meander bends and to build the computational models. The spatial patterns of erosion and deposition over meander bends are analysed relative to the measured and modelled flow field and sediment transport. The results are compared with the classic theories of the processes in meander bends. Mainly, the results of this study follow well the existing theories and results of previous studies. However, some new insights regarding to the spatial and temporal patterns of the flow-sediment interaction in a natural sand-bed meander bend are provided. The results of this study show the advantages of the rapid and detailed measurements techniques and the achieved spatial and temporal resolution provided by CFD, unachievable with field measurements. The thesis also discusses the limitations which remain in the measurement and modelling methods and in understanding of fluvial geomorphology of meander bends. Further, the hydro- and morphodynamic models’ sensitivity to user-defined parameters is tested, and the modelling results are assessed against detailed field measurement. The study is implemented in the meandering sub-Arctic Pulmanki River in Finland. The river is unregulated and sand-bed and major morphological changes occur annually on the meander point bars, which are inundated only during the snow-melt-induced spring floods. The outcome of this study applies to sandbed meandering rivers in regions where normally one significant flood event occurs annually, such as Arctic areas with snow-melt induced spring floods, and where the point bars of the meander bends are inundated only during the flood events.Siirretty Doriast

ACOUSTIC METHODS FOR MAPPING AND CHARACTERIZING SUBMERGED AQUATIC VEGETATION USING A MULTIBEAM ECHOSOUNDER

Submerged aquatic vegetation (SAV) is an important component of many temperate global coastal ecosystems. SAV monitoring programs using optical remote sensing are limited by water clarity and attenuation with depth. Here underwater acoustics is used to analyze the water volume above the bottom to detect, map and characterize SAV. In particular, this dissertation developed and applied new methods for analyzing the full time series of acoustic intensity data (e.g., water column data) collected by a multibeam echosounder. This dissertation is composed of three separate but related studies. In the first study, novel methods for detecting and measuring the canopy height of eelgrass beds are developed and used to map eelgrass in a range of different environments throughout the Great Bay Estuary, New Hampshire, and Cape Cod Bay, Massachusetts. The results of this study validated these methods by showing agreement between boundaries of eelgrass beds in acoustic and aerial datasets more in shallow water than at the deeper edges, where the acoustics were able to detect eelgrass more easily and at lower densities. In the second study, the methods developed for measuring canopy height in the first study are used to delineate between kelp-dominated and non-kelp-dominated habitat at several shallow rocky subtidal sites on the Maine and New Hampshire coast. The kelp detection abilities of these methods are first tested and confirmed at a pilot site with detailed diver quadrat macroalgae data, and then these methods are used to successfully extrapolate kelp- and non-kelp-dominated percent coverages derived from video photomosaic data. The third study examines the variability of the acoustic signature and acoustically-derived canopy height under different tidal currents. Submerged aquatic canopies are known to bend to accommodate the drag they generate in response to hydrodynamic forcing, and, in turn, the canopy height measured by acoustics will not be a perfect representation of canopy height as defined by common seagrass monitoring protocols, which is usually measured as the length of the blade of seagrass. Additionally, the bending of the canopy affects how the blades of seagrass are distributed within the footprint of the sonar, changing the acoustic signature of the seagrass canopy. For this study, a multibeam echosounder, a current profiler and an HD video camera were deployed on a stationary frame in a single eelgrass bed over 2 tidal cycles. Acoustic canopy heights varied by as much as 30 cm over the experiment, and although acoustic canopy height was correlated to current magnitude, the relationship did not follow the predictive flexible vegetation reconfiguration model of Luhar and Nepf (2011). Results indicate that there are significant differences in the shape of the return from a deflected (i.e., bent-over) canopy and an upright canopy, and that these differences in shape have implications for the accuracy of bottom detection using the maximum amplitude of a beam time series. These three studies clearly show the potential for using multibeam water column backscatter data for mapping coastal submerged aquatic vegetation while also testing the natural variability in acoustic canopy height measurements in the field

3d Seafloor Model Determination And Change Detection With Multitemporal Multi Beam Echo Sounder Bathymetry

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2017Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2017Topografya yeryüzü üzerinde ve altında bulunan çeşitli yer şekillerini detayları ile inceleyen çalışmaların tanımlanmasıdır. Yeryüzündeki hareketlerin anlaşılması için detaylı topografik bilgiye ihtiyaç vardır. Okyanuslarda deniz tabanının yapısı, taban yüzeyinin özellikleri ile doğal oluşumlar ve insan yapılarını içeren coğrafi nitelikler topoğrafyanın kapsamına girmektedir. Bu kapsamda detaylı deniz haritalarının hazırlanması, fiziksel oşinografi, biyoloji, deniz jeolojisi ve jeofiziği gibi bilimler açısından önem arz etmektedir. Bunun yanında seyir haritalarının oluşturulması, deniz ulaşımı açısından da kritik öneme sahiptir. Bu ise hidrografik ölçümlerin ve ölçüm sistemlerinin gerekliliğini vurgulamaktadır. Deniz tabanının haritalanması için birçok teknik geliştirilmiştir. En ilkel tekniklerden birisi olan bir ipin ucuna bağlanmış ağırlığın suya daldırılması yoluyla yapılan el iskandili yönteminden, uydu tabanlı altimetrik sistemlere kadar birçok yöntem kullanılmıştır. Elektronik ve bilgisayar teknolojilerinin gelişmesi ile birlikte, modern ölçüm sistemleri daha hassas ve etkin hale gelmiştir. Günümüzde deniz ölçümleri için etkin kullanılan optik ve sonar sistemler bulunmaktadır. Optik sistemler içerisinde teknolojisi hızla gelişen Lidar sistemleri yeşil lazer ışını kullanarak su içerisine gönderdiği sinyallerin saçılımlarını derinlik verisi olarak değerlendirir. Görünebilirliğin yüksek olduğu sığ sularda etkin çalışan bu sistem, derinlik arttıkça ve görünürlük azaldıkça hassasiyetini ve etkinliğini kaybeder. İskandil sistemi ‘su yüksekliği’ olarak adlandırılan derinlik verisini üretebilmek için ses dalgasını kullanan modern tekniklerden birdir. Ses dalgası ile ölçüm yapan sistemler basitçe sesin suda gidiş ve dönüş hızını hesaplayarak derinlik verisi elde ederler. İskandiller bir seferde ölçebildikleri derinlik verisi sayısına göre sınıflandırılmıştır. Tek bimli iskandil (TBİ) sistemi bir seferde aletin nadiri doğrultusunda tek bir derinlik verisi üretir. Bunun yanında, çok bimli iskandil (ÇBİ), bir seferde yüzlerce derinlik ölçümü sağlayarak deniz tabanında %100 kaplama sağlamaktadır. Deniz haritası üretimi için çok bimli iskandil sistemleri kullanan hidrografi kurumları/şirketler hidrografik ölçüm standartlarına uygun olarak ölçüm yapmalıdırlar. Bu standartlar genellikle Uluslararası Hidrografi Örgütü (IHO) standartları ile uyumludur. Bazı örgütler doğrudan bu standartları kullanırken, bazıları ise bu standartlardan daha sıkı olan standartlar geliştirilmiştir. Çok bimli iskandil sistemleri; iskandil, konumlandırma sistemi ve hareket sensörü gibi senkronize bir şekilde çalışması gereken birçok ölçüm aletini içermektedir. Bundan dolayı sistem elemanlarının iyi bir kurulum ile tekneye monteleri gerçekleştirilmeli ve ölçüm teknesinin 3B uzayı içerisinde birbiriyle olan ilişkileri tanımlanmalıdır. Ölçümler öncesinde ‘patch testi’ olarak adlandırılan kalibrasyon prosedürü, kurulum ve aletlerin senkronizasyonundan kaynaklanan hataların giderilmesi için gerekmektedir. Bu test kapsamında, sinyal gecikmesi testi (latency), Y ekseni dönüklüğü (roll), X ekseni dönüklüğü (pitch) ve Z ekseni dönüklüğü (yaw) hataları hesaplanmıştır. Bunlarla birlikte, özellikle zamansal veri analizi ve 3B yüzey modellemesi için su kolonu boyunca gerçekleştirilen ses hızı ölçümleri ve su seviyesi değişimleri göz önünde bulundurulmuştur. Bu tezde göz önüne alınan çalışma bölgesi KKTC (Kuzey Kıbrıs Türk Cumhuriyeti) ‘Su Temini Projesi’ içerisinde yer alan, Anamur – KKTC ishale boru hattı güzergâhını kapsayan alandır. Bu proje, Türkiye’den Kuzey Kıbrıs Türk Cumhuriyeti’ne, Akdeniz’de deniz altından boru hatları ile içme ve sulama suyu temini amacı ile gerçekleştirilmiş olup, özellikleri bakımından dünyada benzeri bulunmayan uluslararası bir su iletim hattı projesidir. Proje 4 bölümden oluşmaktadır. Bu bölümlerden birincisi Anamur Alaköprü Barajı’ndan, Ören kasabasına kadar olan iletim hattı, ikincisi boru hatlarının kazı gemisi tarafından oluşturulmuş kanal içerisinde deniz ile buluştuğu bölüm, üçüncüsü projeyi bu boyutlarda yapılmış tek proje özelliğini kazandıran Akdeniz geçiş kısmı ve dördüncüsü ise KKTC kıyılarından Geçitköy barajına su taşınması kısmıdır. Akdeniz geçiş kısmını önemli yapan özelliği ise 500m uzunluğundaki yekpare boruların su seviyesinin 250m kadar altında askıda kalıp, çelik halatlar ile deniz tabanına monte edilmiş olmasıdır.Topography is the term that indicates the study of various landforms that exist on or below the Earth and a detailed knowledge of topography is required to understand the most Earth processes. In the oceans, sea floor topography refers the geographic features of the sea floor including the configuration of a surface and the position of its natural and man-made features; and detailed nautical charts are fundamental for many sciences such as physical oceanography, biology and marine geology. Besides, it is significant for navigational requirement. This revealed the necessity of hydrographic measurements and measurement systems. For this purpose, many techniques developed and used to create the map of the seafloor. From the first primitive technique which involved lowering a weighted line into the water to satellite derived altimetry many systems used for determination of seafloor. After the development of electronic and computer technology, the modern systems become more accurate and effective. An echo sounder system is one of the modern techniques that use the sound waves to determine the depth which is also called ‘sounding’. Echo sounders are classified with the capability of producing sounding in one time. Single beam echo sounder (SBES) system can produce single sounding in each measurement. Besides, multi beam echo sounder (MBES) system can produce hundreds of sounding in each measurement sets and provide 100% seafloor coverage. The hydrographic offices, which use the Multi Beam Echo Sounder (MBES) system for the establishment of nautical charts, have their own set of accuracy standards for hydrographic surveys, which generally comply with the standards defined by the International Hydrographic Organization (IHO). MBES systems include multiple measurement systems such as sonar head, positioning system, motion sensor that work in a synchronized manner. Therefore, the system components are installed and established to each other in 3D space of vessel. Before the measurements, the ‘Patch Test’ is required to eliminate the systematic errors due to instrumental synchronization and installation. In this test, signal delay test (latency), Y-axis rotation (roll), X-axis rotation (pitch), Z-axis rotation (yaw) errors are calculated. Besides, the effects of the sound velocity measurement through water column and the sea level changes need to be taken into consideration especially in the multi-temporal data analysis and 3D modeling. In this thesis, the seafloor of the Anamur -TRNC Drinking Water Pipeline route in the ‘Northern Cyprus Water Project’ is selected as a study area. This project, a unique in the world, is an international water diversion project designed to supply water for drinking and irrigation from southern Turkey to Northern Cyprus via pipeline under Mediterranean Sea. The dredged channels for pipe laying in the Anamur and TRNC shores are considered in this study and two MBES surveys are conducted in different periods to determine the surface differences. Multi temporal multi beam echo sounder measurements are used in the change analysis and surface modeling and the efficiency of this system is outlined together with its limitations.Yüksek LisansM.Sc

Detecting trend and seasonal changes in bathymetry derived from HICO imagery: A case study of Shark Bay, Western Australia

The Hyperspectral Imager for the Coastal Ocean (HICO) aboard the International Space Station has offered for the first time a dedicated space-borne hyperspectral sensor specifically designed for remote sensing of the coastal environment. However, several processing steps are required to convert calibrated top-of-atmosphere radiances to the desired geophysical parameter(s). These steps add various amounts of uncertainty that can cumulatively render the geophysical parameter imprecise and potentially unusable if the objective is to analyze trends and/or seasonal variability. This research presented here has focused on: (1) atmospheric correction of HICO imagery; (2) retrieval of bathymetry using an improved implementation of a shallow water inversion algorithm; (3) propagation of uncertainty due to environmental noise through the bathymetry retrieval process; (4) issues relating to consistent geo-location of HICO imagery necessary for time series analysis, and; (5) tide height corrections of the retrieved bathymetric dataset. The underlying question of whether a temporal change in depth is detectable above uncertainty is also addressed. To this end, nine HICO images spanning November 2011 to August 2012, over the Shark Bay World Heritage Area, Western Australia, were examined. The results presented indicate that precision of the bathymetric retrievals is dependent on the shallow water inversion algorithm used. Within this study, an average of 70% of pixels for the entire HICO-derived bathymetry dataset achieved a relative uncertainty of less than ± 20%. A per-pixel t-test analysis between derived bathymetry images at successive timestamps revealed observable changes in depth to as low as 0.4 m. However, the present geolocation accuracy of HICO is relatively poor and needs further improvements before extensive time series analysis can be performed

Observation- and Modelling of Morphodynamics in Sandy Coastal Environments

The topic of sandy coast morphodynamics involves the mutual influences of coastal topography, local sedimentology, the driving meteorological and hydrodynamic boundary conditions, flora and fauna, and the activities of human beings: The latter as direct actors through coastal constructions and other interventions, as indirect actors through possible contributions to global change, but also as receiving agents - as living individuals confronted with the forces of the sea. The general aim of coastal research is to gain an as comprehensive as possible understanding of the different systems and their interaction in order to be able to evaluate their current state, assess their stability, explain past changes (in the geological record), and predict future developments under different conditions. Such systems dynamics involve a large bandwidth of spatial and temporal scales: from the microscopic interaction of turbulent fluid motions with single particles to meso-scale tidal dynamics of subaqueous bedforms to macro-scale seasonal adaptations of beach profiles or the meandering of tidal channels, to the mega-scale evolution of shorelines and shelf systems over decades to centuries. The process of understanding involves a continuous feedback of observations, abstractions, mathematical formulations, model development (ranging from conceptual models to mathematical formulations of processes, and to complex, process-based numerical modelling systems), and the testing of models on the basis of observations, new abstractions, and so forth. In the case of the morphodynamics of sandy coasts, the interaction of the physical processes involved in hydrodynamics, sediment dynamics, and their mutual adjustment to changing bed topographies seem most relevant, although biogeochemical processes play a (commonly underrated) additional role. This discourse presents an extended summary of the current state in the continuous process of gaining knowledge on coastal morphodynamics. It focuses on the dynamics of tidal channels and their main roughness elements: subaqueous compound bedforms. Methodological approaches involved are field measurements and numerical modelling, which are introduced and discussed

Fachzeitschrift für Hydrographie und Geoinformation

Second International Issu

The Impact of Acoustic Imaging Geometry on the Fidelity of Seabed Bathymetric Models

Attributes derived from digital bathymetric models (DBM) are a powerful means of analyzing seabed characteristics. Those models however are inherently constrained by the method of seabed sampling. Most bathymetric models are derived by collating a number of discrete corridors of multibeam sonar data. Within each corridor the data are collected over a wide range of distances, azimuths and elevation angles and thus the quality varies significantly. That variability therefore becomes imprinted into the DBM. Subsequent users of the DBM, unfamiliar with the original acquisition geometry, may potentially misinterpret such variability as attributes of the seabed. This paper examines the impact on accuracy and resolution of the resultant derived model as a function of the imaging geometry. This can be broken down into the range, angle, azimuth, density and overlap attributes. These attributes in turn are impacted by the sonar configuration including beam widths, beam spacing, bottom detection algorithms, stabilization strategies, platform speed and stability. Superimposed over the imaging geometry are residual effects due to imperfect integration of ancillary sensors. As the platform (normally a surface vessel), is moving with characteristic motions resulting from the ocean wave spectrum, periodic residuals in the seafloor can become imprinted that may again be misinterpreted as geomorphological information