Coastal environment monitoring through satellite, terrestrial, and airborne remote sensing
(English) Coastal areas are increasingly threatened by sea-level rise due to climate change and anthropogenic pressures, calling for robust and scalable monitoring tools. The first phase of this thesis implements a comprehensive methodology for semi-automatic shoreline extraction through the use of...
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| Formato: | tesis doctoral |
| Fecha de publicación: | 2025 |
| País: | España |
| Recursos: | Universitat Politècnica de Catalunya (UPC) |
| Repositorio: | UPCommons. Portal del coneixement obert de la UPC |
| Idioma: | inglés |
| OAI Identifier: | oai:upcommons.upc.edu:2117/449713 |
| Acesso em linha: | https://hdl.handle.net/2117/449713 https://dx.doi.org/10.5821/dissertation-2117-449713 |
| Access Level: | acceso abierto |
| Palavra-chave: | Shoreline extraction Remote sensing Satellita platform Multispectral imagery SAR imagery 627 - Enginyeria de ports i costes Àrees temàtiques de la UPC::Enginyeria civil |
| Resumo: | (English) Coastal areas are increasingly threatened by sea-level rise due to climate change and anthropogenic pressures, calling for robust and scalable monitoring tools. The first phase of this thesis implements a comprehensive methodology for semi-automatic shoreline extraction through the use of multispectral satellite imagery (Sentinel-2 and PlanetScope). The extracted shorelines are validated using in situ GNSS surveys and high-resolution orthomosaics along three Mediterranean sandy beaches. The shoreline extraction tool works with several spectral indices tested with thresholding and unsupervised clustering segmentation methods. A high coastline extraction performance is achieved using Sentinel-2, with an average sub-pixel accuracy of 4 m (Mean Absolute Deviation, MAD) obtained from a 10 m pixel. A MAD of 2 m is achieved from imagery at 3 m pixel resolution of PlanetScope. In the second phase, the obtained multispectral satellite shorelines are used to characterize megacusps shoreline undulations with alongshore wavelengths of hundreds of meters and cross-shore amplitudes up to a few tens of meters that can significantly affect beach usability. Subsequent validation with reference data proves satellite-derived shorelines can robustly and accurately describe megacusp parameters such as amplitude and wavelength. Moreover, megacusp evolution can be effectively characterized by combining different types of satellite imagery (Sentinel-2 and PlanetScope), enabling the identification of periods of growth, decay, and migration, even at weekly timescales. This can be a useful tool to manage the impact of these features on Mediterranean beaches. Another phase involves evaluating and correcting the extracted shorelines to tide excursions and wave setup. Corrections based on tide gauge and buoy data show that although absolute displacements are limited, assessing them helps eliminate a potential source of error, justifying their integration into high-accuracy workflows. This would also allow applying the developed methodology to meso- or macro-tidal beaches. Finally, the research incorporates Synthetic Aperture Radar (SAR) imagery (Sentinel-1 and TerraSAR-X) to expand the shoreline extraction tool to periods without light or with clouds, including two other Mediterranean beaches characterized by gravel sediment. The SAR-based shoreline extraction module includes advanced extra-denoising filtering and an outlier detection module, but it maintains the core methodology used in the first phase, demonstrating the flexibility of the developed approach. The results demonstrate unprecedented accuracy and stability for gravel beaches (approximately 6 m of MAD), and for sandy beaches (approximately 7 m of MAD), starting from a 10 m pixel size. In a comparative assessment between the two TerraSAR-X images available and the closest Sentinel-1 in terms of time, the first achieves higher accuracy in terms of MAD (2.5 m) compared to the second one (6.5 m), but only in the image with good meteorological conditions (no differences are obtained in the other date). The study also investigates the influence of radar parameters, such as polarization, wavelength, acquisition geometry, and environmental conditions, on SAR shoreline accuracy. The results show that higher land–sea backscatter contrast, typical of gravel beaches, and moderate wind conditions enhance detection reliability. Conversely, high wind and wave activity reduce contrast and increase errors. Overall, this work offers robust, scalable tools for high-resolution coastal morphology monitoring in Mediterranean beaches using satellite data. These methodologies could be extended to beaches with significant tides and other related fields such as flood mapping. The developed algorithms could be incorporated into operational platforms like early warning systems or interactive WebGIS applications, potentially significantly contributing to local authorities' adaptive coastal zone management. |
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