Simulated Satellite Formation Flights for Detecting the Temporal Variations of the Earth’s Gravity Field

In this thesis, the concept of satellite formation flight (SFF) is studied by means of simulated satellite observations. With various formation types enabling inter-satellite measurements in various directions (e.g. along-track, cross-track or radial), the principal tasks in global gravity field recovery are tackled: the determination of the static gravity field and the detection of its temporal variations. The investigated formation flight types include GRACE, Pendulum, GRACE-Pendulum, Radial wheel and Inclined wheel configurations. For each formation type, appropriate orbit parameters are determined to receive homogeneous subsatellite track patterns required for a high spatial resolution. In addition, orbit designs are developed which allow an enhancement of the temporal resolution (i.e. sub-month solutions). The investigated formation flight types of this case include GRACE-24days, GRACE-12days, Multi-GRACE ΔM and Multi-GRACE ΔΩ configurations. In the static gravity field analysis, the test scenarios cover different spectral ranges of the Earth’s gravity field up to the spherical harmonics degree 180. The detection of the temporal variations is performed using physical models from ocean tides, atmosphere, ocean and continental hydrology. The numerical computations show that significant improvements are achieved from the formation flights for the recovery of the global static gravity field and the detection of its temporal variations. Thus, the study provides an outlook on the progress in the gravity field modeling that is achievable by future satellite missions.Simulierte Satellitenformationsflüge zur Bestimmung der temporalen Variationen des Erdgravitationsfeldes In der vorliegenden Arbeit wird mit Hilfe simulierter Satellitenbeobachtungen das Konzept des Satellitenformationsflugs (SFF) untersucht. Mit verschiedenen Formationstypen, mit denen Intersatellitenmessungen in verschiedenen Richtungen gesammelt werden können (z.B. along-track, cross-track oder radial), werden die beiden wesentlichen Aufgaben der globalen Gravitationsfeldbestimmung bearbeitet, die Bestimmung des statischen Gravitationsfeldes und die Bestimmung seiner zeitlichen Variationen. Die untersuchten Formationstypen umfassen GRACE, Pendulum, GRACE-Pendulum, Radial wheel and Inclined wheel Konfigurationen. Für jeden Formationstyp werden geeignete Bahnparameter ermittelt, um die für eine hohe räumliche Auflösung notwendige gleichmäßige Überdeckung der Erde mit Subsatellitenbahnen zu erreichen. Außerdem werden Formationsdesigns entworfen, die eine Verbesserung der zeitlichen Auflösung erlauben (submonatliche Lösungen). Die untersuchten Formationstypen dieses Falls umfassen GRACE-24days, GRACE-12days, Multi-GRACE ΔM und Multi-GRACE ΔΩ Konfigurationen. Bei der Bestimmung des statischen Schwerefeldes werden den Testszenarien unterschiedlich hoch aufgelöste Feldmodelle bis Grad 180 der Kugelfunktionsentwicklung zugrunde gelegt. Die Simulation der zeitlichen Variationen erfolgt mit physikalischen Modellen für die Ozeangezeiten, für die Massenverlagerungen in Atmosphäre und Ozeanen und für die kontinentale Hydrologie. Die numerischen Untersuchungen zeigen, dass signifikante Verbesserungen sind von Satellitenformationsflügen zur Bestimmung des statischen Gravitationsfeldes und der Bestimmung seiner zeitlichen Variationen erreicht. Die Arbeit liefert damit einen Ausblick auf den Fortschritt in der Gravitationsfeldbestimmung, der mit zukünftigen Satellitenmissionen möglich sein wird

Calibration of the Latest Generation Superconducting Gravimeter iGrav-043 Using the Observatory Superconducting Gravimeter OSG-CT040 and the Comparisons of Their Characteristics at the Walferdange Underground Laboratory for Geodynamics, Luxembourg

In December 2019, the latest generation transportable superconducting gravimeter (SG) iGrav-043 purchased by the University of Bonn was installed in the Walferdange Underground Laboratory for Geodynamics (WULG) in the Grand Duchy of Luxembourg. In this paper, we estimate the calibration factor of the iGrav-043, which is essential for long-term gravity monitoring. We used simultaneously collected gravity data from the un-calibrated iGrav-043 and the calibrated Observatory superconducting gravimeter OSG-CT040 that operates continuously at WULG since 2002. The tidal analysis provides a simple way to transfer the calibration factor of one SG to the other. We then assess and compare tidal analyses, instrumental drifts and high frequency noises. After 20 years of continuous operation, the instrumental drift of the OSG-CT040 is almost zero. From 533 days of joint operation, we found that the instrumental drift of iGrav-043 exhibits a composite behavior: just after the setup and for two months a fast exponential decrease of 171 nm s−2, then a linear with a rate of 66 nm s−2 ± 10 nm s−2 per year. We suggest that a period of 3 months is sufficient for calibrating the iGrav. Accidental electrical power cuts triggered slight differences in the reaction and recovery of the OSG-CT040 and iGrav-043. However, it has been found that the long-term linear behavior of the drift was not affected

Simulated satellite formation flights for detecting the temporal variations of the Earth's gravity field

In this thesis, the concept of satellite formation flight (SFF) is studied by means of simulated satellite observations. With various formation types enabling inter-satellite measurements in various directions (e.g. along-track, cross-track or radial), the principal tasks in global gravity field recovery are tackled: the determination of the static gravity field and the detection of its temporal variations. The investigated formation flight types include GRACE, Pendulum, GRACE-Pendulum, Radial wheel and Inclined wheel configurations. For each formation type, appropriate orbit parameters are determined to receive homogeneous subsatellite track patterns required for a high spatial resolution. In addition, orbit designs are developed which allow an enhancement of the temporal resolution (i.e. sub-month solutions). The investigated formation flight types of this case include GRACE-24days, GRACE-12days, Multi-GRACE ΔM and Multi-GRACE ΔΩ configurations. In the static gravity field analysis, the test scenarios cover different spectral ranges of the Earth’s gravity field up to the spherical harmonics degree 180. The detection of the temporal variations is performed using physical models from ocean tides, atmosphere, ocean and continental hydrology. The numerical computations show that significant improvements are achieved from the formation flights for the recovery of the global static gravity field and the detection of its temporal variations. Thus, the study provides an outlook on the progress in the gravity field modeling that is achievable by future satellite missions.Simulierte Satellitenformationsflüge zur Bestimmung der temporalen Variationen des Erdgravitationsfeldes In der vorliegenden Arbeit wird mit Hilfe simulierter Satellitenbeobachtungen das Konzept des Satellitenformationsflugs (SFF) untersucht. Mit verschiedenen Formationstypen, mit denen Intersatellitenmessungen in verschiedenen Richtungen gesammelt werden können (z.B. along-track, cross-track oder radial), werden die beiden wesentlichen Aufgaben der globalen Gravitationsfeldbestimmung bearbeitet, die Bestimmung des statischen Gravitationsfeldes und die Bestimmung seiner zeitlichen Variationen. Die untersuchten Formationstypen umfassen GRACE, Pendulum, GRACE-Pendulum, Radial wheel and Inclined wheel Konfigurationen. Für jeden Formationstyp werden geeignete Bahnparameter ermittelt, um die für eine hohe räumliche Auflösung notwendige gleichmäßige Überdeckung der Erde mit Subsatellitenbahnen zu erreichen. Außerdem werden Formationsdesigns entworfen, die eine Verbesserung der zeitlichen Auflösung erlauben (submonatliche Lösungen). Die untersuchten Formationstypen dieses Falls umfassen GRACE-24days, GRACE-12days, Multi-GRACE ΔM und Multi-GRACE ΔΩ Konfigurationen. Bei der Bestimmung des statischen Schwerefeldes werden den Testszenarien unterschiedlich hoch aufgelöste Feldmodelle bis Grad 180 der Kugelfunktionsentwicklung zugrunde gelegt. Die Simulation der zeitlichen Variationen erfolgt mit physikalischen Modellen für die Ozeangezeiten, für die Massenverlagerungen in Atmosphäre und Ozeanen und für die kontinentale Hydrologie. Die numerischen Untersuchungen zeigen, dass signifikante Verbesserungen sind von Satellitenformationsflügen zur Bestimmung des statischen Gravitationsfeldes und der Bestimmung seiner zeitlichen Variationen erreicht. Die Arbeit liefert damit einen Ausblick auf den Fortschritt in der Gravitationsfeldbestimmung, der mit zukünftigen Satellitenmissionen möglich sein wird

Mass Variations in Terrestrial Water Storage over the Nile River Basin and Mega Aquifer System as Deduced from GRACE-FO Level-2 Products and Precipitation Patterns from GPCP Data

Changes in the terrestrial total water storage (TWS) have been estimated at both global and river basin scales from the Gravity Recovery and Climate Experiment (GRACE) mission and are still being detected from its GRACE Follow-On (GRACE-FO) mission. In this contribution, the sixth release of GRACE-FO (RL06) level-2 products applying DDK5 (decorrelation filter) were used to detect water mass variations for the Nile River Basin (NRB) in Africa and the Mega Aquifer System (MAS) in Asia. The following approach was implemented to detect the mass variation over the NRB and MAS: (1) TWS mass (June 2018–June 2021) was estimated by converting the spherical harmonic coefficients from the decorrelation filter DDK 5 of the GRACE-FO Level-2 RL06 products into equivalent water heights, where the TWS had been re-produced after removing the mean temporal signal (2) Precipitation data from Global Precipitation Climatology Project was used to investigate the pattern of change over the study area. Our findings include: (1) during the GRACE-FO period, the mass variations extracted from the RL06-DDK5 solutions from the three official centers—CSR, JPL, and GFZ—were found to be consistent with each other, (2) The NRB showed substantial temporal TWS variations, given a basin average of about 6 cm in 2019 and about 12 cm in 2020 between September and November and a lower basin average of about −9 cm in 2019 and −6 cm in 2020 in the wet seasons between March and May, while mass variations for the MAS had a relatively weaker temporal TWS magnitude, (3) the observed seasonal signal over the NRB was attributed to the high intensity of the precipitation events over the NRB (AAP: 1000–1800 mm yr−1), whereas the lack of the seasonal TWS signal over the MAS was due to the low intensity of the precipitation events over the MAS (AAP:180–500 mm yr−1)

Assessment of changing satellite gravity mission architectures using terrestrial gravity and GNSS-leveling data in the Kingdom of Saudi Arabia

This research investigates the effect of the ‘future’ gravity mission (FGM) architectures i.e. Bender, Helix, Pendulum, and Cartwheel up to spherical harmonics (SH) degree/order (d/o) 120/120 to improve the estimation of the gravitational field in the Saudi Arabia. For this purpose, we evaluate ground-truth gravity anomalies and GNSS/Leveling data with the satellite-based gravity models of each aforementioned FGMs. The comparison with gravity anomalies given by the FGM provides refinements of about 57 – 61 μGal with respect to (w.r.t.) those of GRACE- and GOCE-based GGMs. The comparison with GNSS/Leveling indicates that the least differences in terms of standard deviations (STD) of geoid heights are provided by the Bender-type FGM that provides the overall least STD differences of about 62.58 cm w.r.t. the GRACE- and GOCE-based GGMs, that provide STD differences of about 62.88 cm and 62.62 cm, respectively. The outcome of this study shows that implementing additional gravity information in different flight directions of the proposed FGMs (i.e along-track, cross-track, and radial) showed slight improvement (sub of a millimeter)

Applying Geostatistics to Understand Seismic Activity Patterns in the Northern Red Sea Boundary Zone

A comprehensive geostatistical analysis was conducted on a dataset comprising 24,321 seismic events in the Red Sea region, spanning from 1997 to 2020. This analysis involved the creation of a new seismic activity database, incorporating data from both Egyptian and Saudi Seismic Networks. This enriched database provided a robust foundation for a detailed examination of the seismic patterns and activities in the region. Utilizing geographic information systems and various spatial analytic methods, it identifies seismic patterns and tectonic influences. The findings reveal significant seismic clustering along the Central Red Sea axis, indicative of active rifting between the Nubian and Arabian plates. The study demonstrates spatial autocorrelation in seismic activities, with high-high clusters marking zones of elevated seismicity. Kernel Density Estimator analyses highlight concentrated seismic activity in the Gulfs of Aqaba and Suez. Higher magnitude events are shown to localize in areas of greater tectonic stress, aligning with known geological features. This research provides critical insights into the seismic dynamics of the Red Sea, showcasing the effectiveness of geostatistical techniques in analyzing seismic data in tectonically active regions