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Modelação de dados batimétricos com estimação de incerteza
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A evolução dos sondadores acústicos impôs aos Serviços Hidrográficos novas metodologias na interpretação, manuseamento e aplicação da informação hidrográfica. Considerando a elevada densidade de dados adquiridos pelos sondadores multifeixe, alguns Serviços foram impelidos a uma redefinição do produto final de um levantamento hidrográfico. Este foi definido, em 2010, pela National Oceanic and Atmospheric Administration (NOAA) como uma superfície batimétrica construída a partir do algoritmo Combined Uncertainty Bathymetry Estimator (CUBE), onde a estimação de profundidade toma em consideração a incerteza das medições observadas. Actualmente, no Instituto Hidrográfico (IH), o produto final de um levantamento hidrográfico é constituído por um subconjunto discreto de sondas mínimas espaçadas de forma irregular, extraído do conjunto total de sondas validadas, seguindo recomendações e requisitos definidos pela Organização Hidrográfica Internacional (OHI). De modo a avaliar o processamento efectuado com recurso ao CUBE para efeitos da cartografia náutica, foram analisados diferentes levantamentos hidrográficos. As sondas mínimas validadas pelo hidrógrafo foram comparadas com as profundidades estimadas pelo CUBE. O objectivo principal foi o de quantificar a diferença entre as sondas validadas e os modelos batimétricos gerados com o CUBE e avaliar a viabilidade de utilização do CUBE para a cartografia náutica. O processamento dos dados foi executado de forma tradicional e, paralelamente, foi utilizado o CUBE para processar e gerar modelos batimétricos com as especificações da NOAA. Com excepção das áreas de declive acentuado, as diferenças encontradas entre as sondas validadas e as profundidades estimadas pelo CUBE têm uma grandeza inferior a metade da incerteza vertical requerida pela OHI. As potencialidades do CUBE minimizam a subjectividade inerente ao processamento tradicional e tornam o processamento de dados cerca de 33% mais rápido em fundos irregulares e cerca de 67% em fundos regulares. O fluxograma de processamento de dados hidrográficos proposto pretende constituir, actualmente, a abordagem mais eficiente para a criação de produtos de base cartográfica, mantendo, no entanto, sob a responsabilidade do hidrógrafo a designação de sondas mínimas de objectos, ou outras estruturas relevantes para a segurança da navegação, em casos excepcionais em que a modelação batimétrica não garanta os requisitos da cartografia náutica.
The evolution of acoustic sounding systems imposed on Hydrographic Services new methodologies for interpretation, handling and application of hydrographic information. Taking into account the high data density acquired by multibeam echosounders, some Services were driven to a redefinition of the final product of a hydrographic survey. The National Oceanic and Atmospheric Administration (NOAA) defined, in 2010, the final product of a hydrographic survey as a bathymetric surface generated from the Combined Uncertainty Bathymetry Estimator (CUBE) algorithm, where depth estimation takes into account observed measurement uncertainties. Currently, at Instituto Hidrográfico (IH), the final product of a hydrographic survey consists of a discrete subset of irregularly spaced minimum soundings (shoals), selected from the full set of validated soundings, as required by the International Hydrographic Organization (IHO). In order to evaluate CUBE processing for nautical cartography purposes, different hydrographic surveys were analyzed. Shoals validated by hydrographers were compared with estimated depths by CUBE. The main objective is to quantify the difference between validated soundings and bathymetric models generated by CUBE and evaluate the feasibility of using CUBE for nautical cartography. Data processing was performed with the traditional methodology and, at the same time, CUBE was used for processing and generating bathymetric models using the NOAA specifications. Except in areas of steep slopes, differences between traditional shoals and CUBE estimated depths are less than half of the vertical uncertainty required by IHO. CUBE capabilities minimize inherent subjectivity in traditional processing, reducing processing times up to 33% on irregular seafloor and about 67% on regular seafloor. The proposed hydrographic data processing flowchart is intended to be the most efficient approach for the creation of cartographic products. Nevertheless, in exceptional cases where bathymetric modeling does not guarantee the requirements for nautical cartography, the responsibility to designate specific minimum soundings or other relevant structures for safety of navigation still rests on the hydrographer.
The evolution of acoustic sounding systems imposed on Hydrographic Services new methodologies for interpretation, handling and application of hydrographic information. Taking into account the high data density acquired by multibeam echosounders, some Services were driven to a redefinition of the final product of a hydrographic survey. The National Oceanic and Atmospheric Administration (NOAA) defined, in 2010, the final product of a hydrographic survey as a bathymetric surface generated from the Combined Uncertainty Bathymetry Estimator (CUBE) algorithm, where depth estimation takes into account observed measurement uncertainties. Currently, at Instituto Hidrográfico (IH), the final product of a hydrographic survey consists of a discrete subset of irregularly spaced minimum soundings (shoals), selected from the full set of validated soundings, as required by the International Hydrographic Organization (IHO). In order to evaluate CUBE processing for nautical cartography purposes, different hydrographic surveys were analyzed. Shoals validated by hydrographers were compared with estimated depths by CUBE. The main objective is to quantify the difference between validated soundings and bathymetric models generated by CUBE and evaluate the feasibility of using CUBE for nautical cartography. Data processing was performed with the traditional methodology and, at the same time, CUBE was used for processing and generating bathymetric models using the NOAA specifications. Except in areas of steep slopes, differences between traditional shoals and CUBE estimated depths are less than half of the vertical uncertainty required by IHO. CUBE capabilities minimize inherent subjectivity in traditional processing, reducing processing times up to 33% on irregular seafloor and about 67% on regular seafloor. The proposed hydrographic data processing flowchart is intended to be the most efficient approach for the creation of cartographic products. Nevertheless, in exceptional cases where bathymetric modeling does not guarantee the requirements for nautical cartography, the responsibility to designate specific minimum soundings or other relevant structures for safety of navigation still rests on the hydrographer.
Descrição
Tese de mestrado em Sistemas de Informação Geográfica (Tecnologias e Aplicações), apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2011
Palavras-chave
Modelação batimétrica CUBE Sondadores multifeixe Incerteza batimétrica Cartografia náutica Teses de mestrado - 2011