Nearshore hydrodynamics and morphology derived from video imagery

Detalhes bibliográficos
Autor(a) principal: Andriolo, Umberto
Data de Publicação: 2018
Idioma: eng
Título da fonte: Repositórios Científicos de Acesso Aberto de Portugal (RCAAP)
Texto Completo: http://hdl.handle.net/10451/35191
Resumo: Tese de doutoramento, Geologia (Geodinâmica Externa), Universidade de Lisboa, Faculdade de Ciências, 2018
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spelling Nearshore hydrodynamics and morphology derived from video imageryTeses de doutoramento - 2018OndasMorfodinâmicaErosão costeiraDomínio/Área Científica::Ciências Naturais::Ciências da Terra e do AmbienteTese de doutoramento, Geologia (Geodinâmica Externa), Universidade de Lisboa, Faculdade de Ciências, 2018The 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 parameter. A first approach coupled 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 /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. The techniques herein developed allow to extract from video images some of the key drivers of nearshore morphodynamics, such as wave breaking height and wave period, as well as the main morphological features, namely subtidal bathymetry and intertidal beach topography. The combination of the methodologies presented in this thesis provides a comprehensive coverage of nearshore processes, enabling a synoptic representation of hydrodynamics and morphology. These methodologies may foster the implementation of new video-based operational systems and support the quasi-real time determination of coastal indicators and early warning systems for coastal hazards.Fundação para a Ciência e a Tecnologia (FCT), SFRH/BD/52558/2014Taborda, Rui, 1966-Lira, Fátima Cristina Gomes PonteRepositório da Universidade de LisboaAndriolo, Umberto2018-10-22T14:47:45Z201820182018-01-01T00:00:00Zdoctoral thesisinfo:eu-repo/semantics/publishedVersionapplication/pdfhttp://hdl.handle.net/10451/35191TID:101487533enginfo:eu-repo/semantics/openAccessreponame:Repositórios Científicos de Acesso Aberto de Portugal (RCAAP)instname:FCCN, serviços digitais da FCT – Fundação para a Ciência e a Tecnologiainstacron:RCAAP2025-03-17T13:58:24Zoai:repositorio.ulisboa.pt:10451/35191Portal AgregadorONGhttps://www.rcaap.pt/oai/openaireinfo@rcaap.ptopendoar:https://opendoar.ac.uk/repository/71602025-05-29T02:59:42.398271Repositórios Científicos de Acesso Aberto de Portugal (RCAAP) - FCCN, serviços digitais da FCT – Fundação para a Ciência e a Tecnologiafalse
dc.title.none.fl_str_mv Nearshore hydrodynamics and morphology derived from video imagery
title Nearshore hydrodynamics and morphology derived from video imagery
spellingShingle Nearshore hydrodynamics and morphology derived from video imagery
Andriolo, Umberto
Teses de doutoramento - 2018
Ondas
Morfodinâmica
Erosão costeira
Domínio/Área Científica::Ciências Naturais::Ciências da Terra e do Ambiente
title_short Nearshore hydrodynamics and morphology derived from video imagery
title_full Nearshore hydrodynamics and morphology derived from video imagery
title_fullStr Nearshore hydrodynamics and morphology derived from video imagery
title_full_unstemmed Nearshore hydrodynamics and morphology derived from video imagery
title_sort Nearshore hydrodynamics and morphology derived from video imagery
author Andriolo, Umberto
author_facet Andriolo, Umberto
author_role author
dc.contributor.none.fl_str_mv Taborda, Rui, 1966-
Lira, Fátima Cristina Gomes Ponte
Repositório da Universidade de Lisboa
dc.contributor.author.fl_str_mv Andriolo, Umberto
dc.subject.por.fl_str_mv Teses de doutoramento - 2018
Ondas
Morfodinâmica
Erosão costeira
Domínio/Área Científica::Ciências Naturais::Ciências da Terra e do Ambiente
topic Teses de doutoramento - 2018
Ondas
Morfodinâmica
Erosão costeira
Domínio/Área Científica::Ciências Naturais::Ciências da Terra e do Ambiente
description Tese de doutoramento, Geologia (Geodinâmica Externa), Universidade de Lisboa, Faculdade de Ciências, 2018
publishDate 2018
dc.date.none.fl_str_mv 2018-10-22T14:47:45Z
2018
2018
2018-01-01T00:00:00Z
dc.type.driver.fl_str_mv doctoral thesis
dc.type.status.fl_str_mv info:eu-repo/semantics/publishedVersion
status_str publishedVersion
dc.identifier.uri.fl_str_mv http://hdl.handle.net/10451/35191
TID:101487533
url http://hdl.handle.net/10451/35191
identifier_str_mv TID:101487533
dc.language.iso.fl_str_mv eng
language eng
dc.rights.driver.fl_str_mv info:eu-repo/semantics/openAccess
eu_rights_str_mv openAccess
dc.format.none.fl_str_mv application/pdf
dc.source.none.fl_str_mv reponame:Repositórios Científicos de Acesso Aberto de Portugal (RCAAP)
instname:FCCN, serviços digitais da FCT – Fundação para a Ciência e a Tecnologia
instacron:RCAAP
instname_str FCCN, serviços digitais da FCT – Fundação para a Ciência e a Tecnologia
instacron_str RCAAP
institution RCAAP
reponame_str Repositórios Científicos de Acesso Aberto de Portugal (RCAAP)
collection Repositórios Científicos de Acesso Aberto de Portugal (RCAAP)
repository.name.fl_str_mv Repositórios Científicos de Acesso Aberto de Portugal (RCAAP) - FCCN, serviços digitais da FCT – Fundação para a Ciência e a Tecnologia
repository.mail.fl_str_mv info@rcaap.pt
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