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Nearshore Hydrodynamics and Morphology Derived from Video Imagery.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Nearshore Hydrodynamics and Morphology Derived from Video Imagery./
作者:	Andriolo, Umberto.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2018,
面頁冊數:	228 p.
附註:	Source: Dissertations Abstracts International, Volume: 80-12, Section: C.
Contained By:	Dissertations Abstracts International80-12C.
標題:	Geographic information science. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=13916307
ISBN:	9781083637482

Nearshore Hydrodynamics and Morphology Derived from Video Imagery.
Andriolo, Umberto.

Nearshore Hydrodynamics and Morphology Derived from Video Imagery. - Ann Arbor : ProQuest Dissertations & Theses, 2018 - 228 p.

Source: Dissertations Abstracts International, Volume: 80-12, Section: C.

Thesis (Ph.D.)--Universidade de Lisboa (Portugal), 2018.

This item must not be sold to any third party vendors.

The coastal zone is the dynamic interface between the land and the ocean. Natural processes, including wave action, flooding and coastal erosion, often endanger human occupation and the use of the littoral. It is therefore essential to improve our understanding of the physical processes occurring at the coast, particularly those related with coastal morphodynamics. Due to the complexity of the coastal environment, littoral studies should be as comprehensive as possible, covering both hydrodynamic forcing and morphological response. However, conventional in-situ survey methods involve the use of instrumentation which, due to the logistical commitments, do not provide the required time-space scales. Remote sensing methods emerge in this context as an interesting alternative solution to yield simultaneous high temporal frequency and high spatial resolution observations of the nearshore processes. Among others, shore-based video remote sensing systems have been proved, over the last three decades, as a cost-efficient and high-quality tool to support coastal scientists and managers. Video monitoring installations offer excellent spatio-temporal resolutions, in combination with cost-efficient long-term data acquisition. This dissertation aims to present new conceptual models and video imagery tools to assess nearshore morphodynamics. This objective was accomplished through the development of a set of efficient computational tools to extract synoptic hydrodynamic and morphology information from video images. Data used in this work were acquired at five different study sites located worldwide. At three sites, video data were collected from dedicated video systems installed for scientific purpose. Two more additional video data sets were derived from the acquisition of online-streaming surfcams, which are camera infrastructures installed at the coast to provide remote visual information of sea state to surf users. A stand-alone set of algorithm was built to process and to geo-reference the acquired video sequence using already existing software. In addition, the automated processing is set to produce special images, namely Timex Variance and Timestack. A first video-based technique exploited the pixel intensity variation of Timestack images to characterize nearshore hydrodynamics. The standard deviation of pixel intensity was successfully related to the spatial distribution of wave transformation domains. Therefore, shoaling, surf and swash zones could be clearly identified in the nearshore profile covered by the image. This technique provides a new tool to study the nearshore dynamics, as the extent of wave domains can be related with distinctive morphodynamic behaviour. The method can be also directly applied to Variance images, hence it offers the possibility of extending such studies to the alongshore dimension. A second methodology developed in the scope of the present work exploited the use of pixel intensity average of Timestack images to estimate wave breaking height. Breakpoint locations and pixel intensity profiles were used to define the cross-shore breaking pattern length visible on a time-averaged image, here defined as the LHs parameter. A first approach coupled LHs to the available bathymetry to solve a simple conceptual model for finding breaker height. Wave breaking height estimates yield a Normalized Root Mean Square Error (NRMSE) of 14% when compared to numerical model results, for offshore wave heights ranging from 1.6 m to 3.5 m. A second approach proposed the relationship LHs/24 to replace water depth parameter on the simplest wave height calculation formula, which multiplies water depth by the breaker index. The technique can be directly applied on Timex, therefore images from four different sites were used to test its validity, obtaining an NRMSE of about 22% for a wide range of wave heights. A third methodology aimed to investigate the possibility of combining two shorebased remote sensing techniques, 2D terrestrial LiDAR and video imagery to perform detailed beach intertidal topography. 2D LiDAR provided precise shoreline elevation along a cross-shore beach transect, while shoreline contour was detected on Timex images in the alongshore dimension. The dataset from both instruments were complemented to perform 3D beach intertidal topography mapping with a Root Mean Square Error (RMSE) of approximately 0.12 m. Finally, a method to assess nearshore bathymetry was developed. The method is based on a depth inversion technique, where wave celerity was estimated using wave trajectories visible on Timestacks. The procedure differentiates the waves in the shoaling and breaking zones and then estimates local depth from shallow or intermediate water equations. In the test case, bathymetry was mapped till a depth of 11 m with relative short time observations (5 hours), registering a RMSE of about 0.46 m when compared to ground truth data.

ISBN: 9781083637482Subjects--Topical Terms:

3432445
Geographic information science.

Nearshore Hydrodynamics and Morphology Derived from Video Imagery.
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