Uebbing, Bernd: Consistently closing global and regional sea level budgets. - Bonn, 2022. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5-68773
@phdthesis{handle:20.500.11811/10452,
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5-68773,
author = {{Bernd Uebbing}},
title = {Consistently closing global and regional sea level budgets},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2022,
month = nov,

note = {Nowadays, human-induced climate change is the major driver of global and regional sea level change threatening the well-being and livelihoods of hundreds of millions of people living close to the coast. Consequently, accurate observations of global and regional down to coastal zone sea level are paramount for monitoring and understanding as well as predicting future risk scenarios. This includes studying the global and local drivers of integrated sea level change resulting from water mass fluxes into the ocean and volumetric expansion due to ocean temperature and salinity changes.
Starting in the early 1990, conventional satellite radar altimetry, for the first time, provided sea surface height observations with global coverage on a regular basis. However in coastal zones, the radar signals are perturbed by land surfaces, requiring extensive post-processing efforts in order to obtain valid sea level information. Since 2002, mass changes in the ocean have been observed from time-variable gravity obtained from the twin satellites of the Gravity Recovery And Climate Experiment (GRACE) mission. After 2005, the Argo program reached its global coverage goal, consisting of thousands of freely drifting floats that regularly measure profiles of temperature and salinity. Combination of at least two datasets from altimetry, GRACE and in-situ profiles allows for construction of a sea level budget, partitioning the total sea level change into mass and volumetric components.
The goals of this thesis are twofold. On the one hand, the development, implementation and assessment of an improved coastal reprocessing of radar signals for application to conventional altimetry observations. On the other hand, the construction of consistently closed global and regional sea level budgets by combining altimetry, gravity and volume expansion measurements in a joint inversion framework.
For the first objective, a novel post-processing or “retracking” method is designed and implemented for the application to conventional satellite altimetry. The Spatio-Temporal Altimetry Retracker (STAR) shifts the problem of finding the matching physical model for each radar signal to a later stage by first extracting hundreds of sub-signals, based on a novel approach. These are then processed by applying a simple and robust retracking model resulting in many equally likely estimation parameters at each along-track measurement location. The resulting point clouds of equally likely estimates are then further processed by means of a shortest-path algorithm to select final estimates at each position. Validation indicates that STAR, applied to conventional altimetry, provides sea level results with a quality comparable to Delay Doppler Altimetry (DDA).
For deriving sea level budgets as part of the second objective, first, different approaches for processing each dataset individually are investigated and assessed for the application of deriving consistent budgets. As part of this effort, an inconsistency in the standard processing of ocean mass change from GRACE has been discovered and the, subsequently, updated processing is now widely applied. The main focus of this thesis is on improving and extending a global fingerprint inversion approach that consistently integrates altimetry, GRACE and Argo data within a single estimation step. The fingerprints are composed of empirical spatial patterns that have been extracted from auxiliary datasets in a pre-processing step. Based on an existing framework, each processing step has been thoroughly assessed and, if necessary, modified in order to significantly improve the quality of derived budgets. By further extending the potential input datasets, it was possible to close the sea level budget on global and, for the first time, also on regional scales within less than 0.1 mm/yr of budget closure. In addition, the inversion results are directly linked to Earth Energy Imbalance (EEI) based on a novel rescaling approach, therefore, providing an independent measure for one of the key indicators of climate change.},

url = {https://hdl.handle.net/20.500.11811/10452}
}

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