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The fluctuation of the ocean surface caused by ocean tides is important for geophysical and societal applications. This thesis aims at the development of tide modelling for these applications, with particular emphasis on improving the understanding of tides in the coastal regions. In this thesis, multi-mission satellite altimetry is used to determine tides both globally and regionally. The models are applied to two studies, tidal corrections for satellite altimetry and model boundary forcings., Ozeangezeiten machen einen signifikanten Teil der Meeresspiegelvariationen aus und ihre Kenntnis ist wichtig für Wissenschaft und Gesellschaft. Ziel dieser Arbeit ist die Weiterentwicklung der empirischen Ozeangezeitenmodellierung mit besonderem Schwerpunkt auf Küstenregionen. Verwendet werden Messungen verschiedener Satellitenaltimetriemissionen auf deren Grundlage Ozeangezeiten sowohl global als auch regional modelliert werden. Diese Modelle werden dann sowohl zur Korrektur der Meeresspiegelmessungen als auch zur Unterstützung von Ozeanmodellen verwendet.

Vertical land motions cause regional relative sea level changes to differ substantially from climate-driven absolute sea level changes. However, assessing the impact of vertical land motion is challenging due to its sometimes large spatiotemporal variability and the inhomogeneous observation station network. This thesis presents a Bayesian approach to estimate the spatiotemporal variations and uncertainties along global coastlines. The reconstruction reveals previously neglected nonlinear variations that significantly increase uncertainties in relative sea level projections., Vertikale Landbewegungen führen dazu, dass sich regionale relative Meeresspiegeländerungen erheblich von klimabedingten absoluten Meeresspiegeländerungen unterscheiden. Die Bewertung der Auswirkungen vertikaler Landbewegungen ist jedoch aufgrund ihrer teilweise großen räumlich-zeitlichen Variabilität und des inhomogenen Beobachtungsstationsnetzes eine Herausforderung. In dieser Arbeit wird ein Bayes'scher Ansatz zur Abschätzung der räumlich-zeitlichen Variationen und Unsicherheiten entlang der globalen Küstenlinien vorgestellt. Die Rekonstruktion offenbart bisher vernachlässigte nichtlineare Veränderungen, die die Unsicherheiten bei relativen Meeresspiegelprojektionen signifikant erhöhen.

Vertical land movements can cause regional relative sea-level changes to differ substantially from climate-driven absolute sea-level changes. Whereas absolute sea level has been accurately monitored by satellite altimetry since 1992, there are limited observations of vertical land motion. Vertical land motion is generally modelled as a linear process, despite some evidence of nonlinear motion associated with tectonic activity, changes in surface loading or groundwater extraction. As a result, the temporal evolution of vertical land motion, and its contribution to projected sea-level rise and its uncertainty, remains unresolved. Here we generate a probabilistic vertical land motion reconstruction from 1995 to 2020 to determine the impact of regional-scale and nonlinear vertical land motion on relative sea-level projections up to 2150. We show that regional variations in projected coastal sea-level changes are equally influenced by vertical land motion and climate-driven processes, with vertical land motion driving relative sea-level changes of up to 50 cm by 2150. Accounting for nonlinear vertical land motion increases the uncertainty in projections by up to 1 m on a regional scale. Our results highlight the uncertainty in future coastal impacts and demonstrate the importance of including nonlinear vertical land motions in sea-level change projections.

Satellite altimetry is a spaceborne radar remote sensing technology that provides significant wave height measurements of the oceans, the quality and quantity of which degrade towards the coast. This thesis presents a novel retracking algorithm to improve the quality and validity of significant wave height estimates in the coastal zone. A coastal case study in the North Sea demonstrates the high performance of the novel algorithm in combination with the fully focused SAR processing scheme., Die Satellitenaltimetrie ist eine weltraumgestützte Radar-Fernerkundungstechnologie, die Messungen der signifikanten Wellenhöhe der Ozeane liefert, deren Qualität und Quantität zur Küste hin abnimmt. In dieser Arbeit wird ein neuartiger Retracking-Algorithmus vorgestellt, der die Qualität und Gültigkeit von Schätzungen der signifikanten Wellenhöhe in der Küstenzone verbessert. Eine Fallstudie an der Nordseeküste demonstriert die hohe Effizienz des neuen Algorithmus in Kombination mit der vollfokussierten SAR-Prozessierungsmethode.

Non-tidal loading (NTL) is an effect that leads to deformations of the solid Earth due to time-varying global distributions of air and water masses. If the corresponding non-linear displacements of the reference points of the observing stations are not applied in the analysis of geodetic space observations, the resulting target parameters such as reference frame positions and Earth orientation parameters are distorted. In this thesis, we demonstrate the positive impact of the reduction of different components of NTL at distinct levels in Very Long Baseline Interferometry analyses., Nicht-gezeitenbedingte Auflasteffekte (non-tidal loading, NTL) beschreiben die Deformation der festen Erde aufgrund der veränderlichen globalen Verteilung von Luft- und Wassermassen. Wenn die zugehörigen Verschiebungen der Referenzpunkte der Beobachtungsstationen nicht in der Analyse der Messungen von geodätischen Raumverfahren berücksichtigt werden, sind die resultierenden Zielparameter wie Referenzrahmenpositionen oder Erdorientierungsparameter verzerrt. In dieser Arbeit zeigen wir die vielfältigen Vorteile der Reduktion von NTL in der Radiointerferometrie auf langen Basislinien.

Masterarbeit Universität Innsbruck 2023

Estimating the three geophysical variables significant wave height (SWH), sea surface height, and wind speed from satellite altimetry continues to be challenging in the coastal zone because the received radar echoes exhibit significant interference from strongly reflective targets such as sandbanks, sheltered bays, ships etc. Fully focused SAR (FF-SAR) processing exhibits a theoretical along-track resolution of up to less than half a metre. This suggests that the application of FF-SAR altimetry might give potential gains over unfocused SAR (UF-SAR) altimetry to resolve and mitigate small-scale interferers in the along-track direction to improve the accuracy and precision of the geophysical estimates. The objective of this study is to assess the applicability of FF-SAR-processed Sentinel-6 Michael Freilich (S6-MF) coastal altimetry data to obtain SWH estimates as close as possible to the coast. We have developed a multi-mission FF-SAR processor and applied the coastal retracking algorithm CORALv2 to estimate SWH. We assess different FF-SAR and UF-SAR processing configurations, as well as the baseline Level-2 product from EUMETSAT, by comparison with the coastal, high-resolution SWAN-Kuststrook wave model from the Deltares RWsOS North Sea operational forecasting system. This includes the evaluation of the correlation, the median offset, and the percentage of cycles with high correlation as a function of distance to the nearest coastline. Moreover, we analyse the number of valid records and the L2 noise of the records. The case study comprises five coastal crossings of S6-MF that are located along the Dutch coast and the German coast along the East Frisian Islands in the North Sea. We observe that accurate and precise SWH records can be estimated in the nearshore zone within 1–3 km from the coast using satellite SAR altimetry. We find that the FF-SAR-processed dataset with a Level-1b posting rate of 140 Hz shows the greatest similarity with the wave model. We achiev, Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Physical and Space Geodesy, Mathematical Geodesy and Positioning

With the continued rise in global mean sea level, operational predictions of tidal height and total water levels have become crucial for accurate estimations and understanding of sea level processes. The Dutch Continental Shelf Model in Delft3D Flexible Mesh (DCSM-FM) is developed at Deltares to operationally estimate the total water levels to help trigger early warning systems to mitigate against these extreme events. In this study, a regional version of the Empirical Ocean Tide model for the Northwest European Continental Sea (EOT-NECS) is developed with the aim to apply better tidal forcing along the boundary of the regional DCSM-FM. EOT-NECS is developed at DGFI-TUM by using 30 years of multi-mission along-track satellite altimetry to derive tidal constituents which are estimated both empirically and semi-empirically. Compared to the global model, EOT20, EOT-NECS showed a reduction in the root-square-sum error for the eight major tidal constituents of 0.68 cm compared to in situ tide gauges. When applying constituents from EOT-NECS at the boundaries of DCSM-FM, an overall improvement of 0.29 cm was seen in the root-mean-square error of tidal height estimations made by DCSM-FM, with some regions exceeding a 1 cm improvement. Furthermore, of the fourteen constituents tested, eleven showed a reduction of RMS when included at the boundary of DCSM-FM from EOT-NECS. The results demonstrate the importance of using the appropriate tide model(s) as boundary forcings, and in this study, the use of EOT-NECS has a positive impact on the total water level estimations made in the northwest European continental seas., Mathematical Physics

This is a data supplement to 'Vertical land motion reconstruction unveils non-linear effects on relative sea level changes from 1900-2150'. It presents a global-scale Vertical Land Motion (VLM) reconstruction that resolves height changes in the period 1995-2020. It is based on the joint probabilistic analysis of an extensive network of more than 11,000 GNSS stations, tide gauges, and satellite altimetry. The approach used to derive this reconstruction is described in the paper. The dataset variables are explained in the .pdf file.