This thesis investigates the capabilities of the Ocean Color Instrument (OCI) aboard the PACE satellite for methane enhancement retrievals, and explores the potential of a new methane reference band centered at 2.13 μm. We assess the performance of this band relative to the commonly used 1.61 μm band, and study how the existing multi-band–multi-pass (MBMP) method can be generalized to use more than two spectral bands.We apply existing matched filter (MF) methods to multispectral OCI data, and extend them by including the usage of a methane-free reference day. In addition, we develop a new retrieval method based on generalized least squares (GLS) which does not require linearization and which is the generalization of the MBMP method to ≥2 spectral bands. Retrieval performance is evaluated using a set of 17 real-world case studies and a roundtrip simulation framework in which synthetic methane plume absorptions are injected into observed backgrounds, allowing for controlled comparisons of retrieval accuracy and precision.Using the new 2.13 μm band instead of the 1.61 μm band with the MBMP method resulted in a factor 4 reduction in background variability averaged over all tested scenes. The GLS method consistently outperformed the standard MBMP approach in terms of both accuracy and precision. When using the H and I bands for both methods, GLS showed a background variability which was 7.2% lower compared to MBMP. When using all three methane-sensitive bands, the relative reduction was 8.8%.The new GLS method can be readily applied to existing multispectral instruments, and is likely to reduce background variability and increase retrieval precision. The method is of special interest for (future) missions which have multiple methane-sensitive bands, such as WorldView-3 and Sentinel-2 Next Generation. ... Read more

Methane (CH₄) is a key greenhouse gas for which accurate source estimation is crucial for climate action. This study evaluates divergence-based (DIV) methods: physics-based, training-free techniques that estimate pixel-wise methane emissions based wind and methane concentration fields. We conducted a systematic search and evaluation into parametrisation and method variations across idealized and simulated cases to find which combination yields the most accurate emission estimations when using observations from the TROPOMI instrument aboard Sentinel-5P. This study confirmed the choice of a pressure-based background correction combined with monthly flux-averaging on synthetic cases. This was followed by a case study of the Permian basin using TROPOMI data which was consistent with studies using divergence and inversion methods on the 2018-2021 period. Finally, an increase of 154% was revealed over the sparsely studied 2022-2024 period which may be attributed to the development of the oil and gas industry in the region. ... Read more

In the past, the Earth has been subject to various ice sheet growth and melt events. The ice exerts a pressure on the Earth’s surface, depressing the ground below it. Whenever the ice melts, the Earth responds by raising its surface level again. This process is called postglacial rebound. Glacial Isostatic Adjustment (GIA) is considered to be a broader and more general term, namely the solid Earth response to land ice and surface water redistribution following continental ice growth or melt, which thus includes postglacial rebound.

Today, uplift of up to 13mma°1 is recorded around theHudson Bay area inNorthAmerica, due to the last ice sheets that have melted roughly between eighteen and six thousand years ago. Even higher uplift rates of 30 mm a°1 have been recorded in Southeast Alaska as a response to ice melt that only started 250 years ago. Part of the reason why these uplift rates differ is due to the underlying mantle viscosity. Mantle viscosity determines how fast material in the Earth’s mantle is allowed to flow. A high mantle viscosity implies a mantle in which flow is slow, and a low mantle viscosity implies a weak mantle in which flow occurs easily. The viscosity of the mantle below Hudson Bay is expected to be around the global average value of 1021 Pa s, while the mantle viscosity in Southeast Alaska is expected to be a few orders of magnitude lower. GIA research is performed to infer structural parameters such as its mantle viscosity. Moreover, with more knowledge of GIA we are able to more accurately correct measurements for the effect of GIA. The goal of this thesis is to improve the numerical model setups, contributing to these two goals…
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Glacial isostatic adjustment (GIA) is the phenomenon where the solid Earth responds to ice shelves that grow or shrink. As the weight of an ice shelf on the Earth reduces, the Earth rebounds in that location and gravity increases. This rebound process has an instant component, elastic rebound, but also a delayed component as the mantle material slowly flows to a new equilibrium position with timescale determined by the mantle viscosity. GIA affects both the vertical land motion (VLM) and therefore relative sea level (RSL). When predicting sea-level change in the near-future ice mass and sea level changes need to be monitored. However, measurements of current ice mass change are obscured by uplift and gravity changes due to GIA. With a large portion of the world population and economic activity located in coastal areas it is important to monitor sealevel rise and therefore to understand the GIA contribution to sea level rise itself and measurements of the processes.... ... Read more

For this Thesis a weighted spherical harmonic analysis is performed on the intensity distribution of Io's hotspots to find potential long wavelength patterns. Unfortunately, no definitive conclusion can be drawn as to whether the primary signal (Loki Patera) is caused by a long wavelength signal originating from deep within Io, or whether it is caused by a local phenomenon. This is because the spectral power associated with the analysis does not just have significant power in one or a few degrees. Instead all harmonic degrees return a strong signal. This has been checked up to at least degree 30 which is well into the shorter wavelengths.

Comparing the weighted spherical harmonic analysis of Io’s hotspot intensity distribution to an unweighted spherical harmonic analysis of the hotspot distribution (so without intensities), the location of the primary signal(s) is different between the two analyses, but both still point towards the asthenospheric heating model or magma ocean heating model as the explanation for Io’s heat flow pattern. ... Read more

Railway transportation is crucial to reducing greenhouse gas emissions and meeting increasing global demand for passenger and freight transport. To maintain a reliable, high-capacity railway infrastructure, regular and accurate maintenance is necessary. The recent development of a Rail-based Track
Surveying System that can be mounted on any operational train, presents a comprehensive solution to acquire track geometry measurements while limiting track unavailability. The system is able to simultaneously acquire measurements of both the absolute- and relative track geometry using a combination of a GNSS / INS integrated navigation system and a laser ranging sensor. The measurement unit is able to obtain consistently accurate absolute track geometry measurements (σ2D = 8 [mm] (Wang et al.2019)) in areas with good GNSS signal reception. However, in areas with limited GNSS coverage, the accuracy of these measurements can fall below the requirements for rapid track inventory acquisition (3 [cm], p = 0.95 (Specht et al. 2016)). This thesis, developed and conducted in lose collaboration with Fugro, aims to improve the accuracy of the trajectory solution for rail-based track surveying systems in such limited GNSS environments.

At the time this research was performed, there was no ground truth or reference trajectory available to assess the accuracy of a trajectory solution. Therefore, the research first establishes quality metrics to provide a measure of the accuracy and certainty of the integrated GNSS/INS estimated trajectory solution. By nature of the data acquisition process of the RTSS, multiple runs, or trajectory estimates, are available of an arbitrary track segment. The observed cross-track trajectory spread (precision) provides a qualitative metric to assess the level of accuracy of multiple passes over the same track segment, given that the
individual measurements are unbiased. To quantify the cross-track trajectory
spread, the standard deviation and smallest circle radius are selected as statistical and absolute metrics.

Next, the research identifies the existence of unreliable or inaccurate GNSS positioning updates in the integrated trajectory solution by linking the cross-track trajectory spread to the Quality Control metrics of individual runs. The level of accuracy of the GNSS / IMU integrated trajectory solution was found to be decreased at track segments where one (or multiple) runs showed sustained periods of high (> 5) PDOP values. A decreased accuracy in the order of 10 [cm] was observed for the high PDOP GNSS positioning updates. Furthermore, these inaccurate position updates were weighted too heavily in the Loosely Coupled integration scheme, reducing the accuracy of the integrated GNSS/IMU
trajectory solution. To improve the accuracy and certainty of the integrated trajectory solution, the GNSS positioning updates in segments with sustained high PDOP values can be inactivated. Inactivating these high PDOP GNSS positioning updates, reduced the observed cross-track trajectory spread by
as much as c.50%.

The thesis provides valuable results for the improvement of the accuracy and certainty of GNSS/IMU trajectory determination in rail-based applications. Furthermore, the framework and data-analysis algorithm developed and presented in this thesis research could be used to quantify the effect of different
quality parameters and processing thresholds on the accuracy of the trajectory solution. The main conclusion and recommendation of this report - processing the trajectory against a tight PDOP constraint - leads to a trajectory estimate for a rail-based surveying application with improved accuracy and certainty. Moreover, recommendations for research implementation, further trajectory accuracy gains and continuation of this research are also presented in this report. ... Read more

This thesis introduces a new approach to Glacial Isostatic Adjustment (GIA) modeling using Machine Learning (ML) techniques. The work addresses two main challenges – uncertainty in historical ice load history and the complexity of inverse problems – by developing two ML-based surrogate models (emulators) to rapidly estimate Relative Sea-Level (RSL) history and uplift rates from varying ice load histories, given a constant Earth model. The emulators are constructed using a Convolutional Neural Network (CNN) with U-Net architecture and spherical data representation, enabling an efficient, cost-effective approach to the GIA forward model. The performance of these emulators was evaluated in two separate experiments, displaying encouraging results in efficiency, accuracy, and versatility. The prediction performance exceeded existing models in computational speed and offers accuracy comparable to other GIA studies. The successful implementation of these emulators could advance GIA modeling by integrating ML, but enhanced resolution is needed for direct scientific application. ... Read more

In the last few decades, a large increase in interest in space and particularly the Moon has taken place. The Moon is seen as a gateway to the rest of the Solar System. Missions to the Moon will inevitably lead to technological and scientific advancements. These would help in humanity’s mission to explore and develop habitats in the Solar System. Companies see economic opportunities in these places for activities such as the acquisition of rare Earth materials, as well as commercialising space travel. Furthermore, countries see these accomplishments
as a sort of international competition while also collaborating with other nations. The mission design presented here aims to facilitate these objectives by providing the necessary navigation support to any future mission on or around the Moon... ... Read more

Nowadays, Mobile Mapping Systems (MMS) have been widely used in railway, with integrated Inertial Navigation System (INS)/Global Navigation Satellite System (GNSS) system as the common approach. For environments where GNSS signals become unavailable, additional aiding sources need to be considered to preserve the quality of measurement. Typically, in most applications, a Distance Measurement Indicator (DMI) is combined with the INS/GNSS system to ensure the desired accuracy. Nevertheless, as this approach is physically less feasible for railway, alternative solutions would be preferred. To bridge this gap, we investigate the applicability of Simultaneous Localization and Mapping (SLAM) integration with INS/GNSS for the case of a railway MMS. In particular, we aim to propose a solution for adapting a Monocular Visual (Inertial) SLAM method for railway application and further evaluate our solution using real-world data based on the RILA system (Fugro’s rail MMS). Accordingly, this dissertation consists of the following three research activities.
Firstly, we have conducted a literature review on the existing monocular Visual Inertial SLAM methods to identify the technique which fulfils the key requirements of the rail application. Considering the results of the study, we selected the ORB-SLAM3 method and proposed an end-to-end pipeline that covers all the phases to adapt it for RILA system.
Secondly, the impact of adapting ORB-SLAM3 technique on performance of the trajectory estimation has been evaluated using two criteria: Absolute Position Error (APE) and Relative Position Error (RPE). Accordingly, a case study using RILA dataset was developed for the experimental evaluations. In this case study, we have simulated a scenario in which the train entered the station, stayed there stationary for 1 minute, and then left the station slowly and manually inserted GNSS blockages before and after the station. Furthermore, a ground-truth trajectory was generated to evaluate the quality of the estimated SLAM-based trajectory. The results revealed that both APE and RPE increases with significant fluctuations in the first 15 seconds due to the lack of SLAM initialization time. Therefore, we introduced an strategy for fine-tuning the accuracy by allocating sufficient time for SLAM initialization phase. The APE and RPE were significantly reduced after fine-tuning and the expected estimated error at each time was equal to 4.3% of the travelled path length.
Finally, we presented the effect of using Zero Velocity Update (ZUPT) signals as aiding information on the accuracy of the estimated trajectory in the areas with poor GNSS coverage. Consequently, we manually inserted the extracted ZUPT signals to the INS/GNSS integration process and then compared the positional accuracy of the generated trajectories with and without this information. The results show that the estimated positional accuracy was improved by 30% with only 51 seconds of stationary condition in our case study.
Overall, based on the obtained results from the evaluations, it is possible to claim that our proposed ORB-SLAM3 technique has great potential to improve the estimated positional accuracy and in particular can be used as a standalone ZUPT detector in railway application.
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Glacial Isostatic Adjustment (GIA) is a process which focuses on the deformations of the Earth due to changing ice sheets. It is an important study in Climate Sciences, gravimetric studies and Earth modelling. Studying GIA allows to contribute to a better understanding of the Earth’s composition, thanks to the testing of multiple Earth models, as well as a broader understanding of the Earth’s ice age cycles. In GIA research, spherical Earth models have been used for half a century. However, 3D Earth models distinguish themselves by using a 3D varying viscosity profile. The reason for this recent interest is that little is known with precision about the Earth’s mantle and deeper layers structure and that such a model was more difficult to create; the inclusion of three dimensional (3D) varying viscosity profiles have not yet been widely used in GIA studies in Greenland. Hence, to this day and to our knowledge, only two papers have made use of a laterally varying viscosity in order to study GIA in Greenland: Milne et al. (2018) and van der Wal and Xu, (2016).

The first novelty introduced by this Master Thesis is the use of the Olivine flow viscosity model, with a wet rheology, to study GIA in Greenland. The second main novelty in this Master Thesis, is the use of a unified ice history from 122000 years from present till 2019 in one GIA model; while using a resolution of 10 [𝑘𝑚], which is an improvement, compared to for instance Milne et al. (2018), Simpson et al. (2011) or Lecavalier et al. (2014) which use resolutions ranging from 15 to 75 [𝑘𝑚], which is found to still not be sufficient enough to properly model modern elastic and viscous deformation.

The following conclusions were made through analysing the final results. First, the simulations which use 3D viscosity models are more sensitive regionally and react, to ice load changes with larger amplitudes of solid Earth deflections in shorter time spans. Second, 3D varying viscosity models, with the same ice loads as the 1D varying viscosity models, have a pattern of deflection which is more explicitly linked to the changes in viscosity across Greenland, whereas the 1D viscosity profiles deflection rates are clearly positive in the present day on land and negative in the sea, and hence are more explicitly linked to the coastal limits of Greenland. Last, the inability of the model to properly model elastic uplifts in recent times, is made evident by the constant under estimation of total uplift rates.
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Uncertainty in ice sheet modelling affects centennial and longer time-scale projections of the Greenland Ice Sheet's (GrIS) sea level contribution. One source of this uncertainty is the interaction between the ice sheet’s evolution and the Earth’s deformation in response to changes in the applied surface loading as the ice sheet waxes and wanes. Such deformation, Glacial Isostatic Adjustment (GIA), causes a vertical displacement of the ice sheet’s surface which affects temperature dependent precipitation and ice ablation. The significance of this feedback mechanism depends on the magnitude of GIA which is dependent on the mantle’s viscosity. Studies find that the sub-Greenland mantle viscosity varies in three dimensions which leads to a spatially varying rate of GIA. Results obtained with an ice sheet model coupled with an Earth model including 3D variations in sub-Greenland viscosity illustrate its significant effect on the GrIS’ modelled evolution by affecting both elevation-melt and elevation-precipitation feedback mechanisms. ... Read more

During its thirteen-year long mission in the Saturnian system, the Cassini spacecraft routinely used Titan, Saturn’s largest moon, for performing its gravity assists. The problem of determining the gravity field of Titan by performing a precise fit of Cassini’s orbit to the available Doppler tracking data was reviewed in this study. The knowledge of the gravity field of Titan can be used to constrain the moon’s internal structure and composition, providing clues about its formation process and the properties of an internal ocean (Grasset et al., 2000). Previous solutions obtained by Durante et al. (2019) and van Noort (2021) were respectively found to have inconsistencies regarding the reported small uncertainties given the noise level of the Doppler measurements and the estimation of an unfeasible negative value for the second-degree Love number k₂. It was demonstrated in the present work that this last parameter should be estimable. Here, the data from the ten Titan flybys considered in those studies was analysed and emulated by using a relativistic model for Doppler measurements in search of ways of improving the accuracy of the gravity field solution. Both the GEODYN (McCarthy et al., 2015) software from NASA GSFC and Tudat libraries (see appendices in Dirkx et al., 2019) developed by the Astrodynamics and Space Missions department at TU Delft were used to investigate the nature of this gravity determination problem and compare the results against the previous solutions. A model mismatch in Doppler in the order of 10² mHz was found between the estimation setups with GEODYN and Tudat. In the search for the source of the mismodelling, it was tested that the empirical accelerations, measurement biases, measurement timing and the spherical harmonics of Saturn have a great influence on the solution and residuals. Thus, they should be reviewed with care for future estimation efforts. It was proven that the flyby geometry is not favourable for resolving the dipole field spherical harmonics coefficients, especially J₂, C₂₂ and k₂, which reveal information about the tidal interactions from Saturn on Titan. They were found to be highly correlated and, when simulating equivalent noises to those found in the previous research, presented similar uncertainties to those obtained by van Noort (2021), but large in relation to the ones determined in Durante et al. (2019). Nevertheless, there are some prospects of estimating the dipole coefficients without the need of adding constraints on the solution, although the search for well grounded constraints is recommended and necessary when pursuing a more accurate solution. The power of fully simulated gravity field estimations as a means for addressing the quality of the available real data and verifying models and constrains, has been manifested throughout this study. ... Read more

Of the four Galilean satellites the only one without ice is Io. While it is possible that Io never contained any ice the starting point of this research work is an icy Io. As present-day Io does not contain any ice, icy Io must have lost its ice through some sort of ice loss mechanism. In this work the assumed ice loss mechanism is geysers driven by tidal heating. Tidal dissipation of sufficient magnitude is able to melt part of an icy layer creating a subsurface ocean and is also able to crack the overlying icy shell. The subsurface ocean then acts as a reservoir from which water vapor molecules and icy grains accelerate upwards through the cracks and are erupted from the surface. Erupted material with a sufficient velocity is able to escape from icy Io resulting in ice loss. ... Read more

Within a Protoplanetary disk (PPD), planets form from micron sized particles, but what are the processes taken for planet formation? How does the evolution of micron sized particles via settlement and coagulation lead to the gigantic planets as the ones in our Solar System? This thesis explores the planet formation process of pebble accretion which is a planet accretion model involving the accretion of smaller bodies onto larger planetesimals. The evolution of micron sized particles into millimetre – centimetre sized pebbles are discussed. These particles will experience growth via settlement and coagulation, radial drift before acting as reservoir for planet cores to accrete and grow from. From the results, it is found that planet formation via pebble accretion is more efficient in the outer regions of the Solar System, where pebble formation was favoured and resulted in smaller inner planets and larger ice giants. ... Read more

The Indian Space Research Organisation(ISRO) plans to equip future satellites of its Indian Nano Satellite(INS) with COTS dual frequency receivers in order to let them contribute to various scientific research opportunities. This thesis develops a test framework for Commercial Of The Shelf (COTS) Global Navigation Satellite System (GNSS)receivers on Nano satellites of the Indian Space Research Organisation(ISRO) to be used for scientific applications. This thesis aims to provided answer to the suitability of this data for scientific application. We have analyzed that the current generation Skytraq single frequency receiver, mounted in previous INS-1A to INS-1C missions, has with an accuracy in the meters range insufficient position accuracy to be used for scientific applications. Nevertheless, based on historical mission experiences and design constraints, a receiver-antenna system selection has been executed. Using this system as an example configuration, a test framework has been setup to analyze influential design and system configuration parameters influence on the GNSS receivers for future missions. The test setup consist of a series of static tests that enable to research the hardware configuration, such as the influence of a ground plane, and the data processing options, such as filters for the data and the choice of atmospheric models. It is complemented with a dynamic analysis of the receiver simulated performance in orbit using a GNSS simulator. Multiple data series were obtained for each individual test of the framework. These data series were analyzed with a developed data handling protocol in which multiple data processing software packages were used. In order to obtain comparable results in all test series, average deviations of the position fixes in the test periods were calculated and analyzed. This leads to a number of conclusions: The current antenna mounting on INS-1C is less than optimal and a ground plane would enhance the antenna performance with 20%. The raw data are essential for scientific experiments. However, they can most likely be limited to those obtained from GPS satellites excluding GLONASS and other GNSS constellations. It does pay off to include low viewing angle measurements for optimal results. The ionospheric models are indispensable to achieve sub meter accuracy with single frequency receivers. ... Read more

The evolution of ice loads during the last Ice Age causes an ongoing Earth response with deformations and stress fields. The viscosity of the mantle depends on stresses, therefore the model stresses should be combined with ambient stresses such as due to mantle convection. This combination has been successfully simulated in the FEM software ABAQUS.

At each timestep background stresses are added to existing component and the Mises stress is recalculated to be used in a custom creep law. This leads to a new viscosity leading to different stress components, which is solved an iterative procedure.

This work shows that the initial model provided can be adapted to simulate this iterative process with a loop inside each timestep of the computation. Results show that stresses increase with time while deformations and viscosity decrease, an opposite trend compared to a non-ambient stresses case. ... Read more

It has been shown that glacially induced decompression rates under Vatnajökull cause an increase in mantle melt and enhancement in volcanic activity. Eruptions under ice can form tuyas, that can be used to constrain past ice sheet thickness. Several mountains in the Martian South Polar Region qualify as tuyas, but their exact origin is still unknown. In this study we reconstruct a palaeo ice sheet from the height and spatial distribution of these tuyas and study glacially induced decompression rates within the Martian mantle.
In a finite element model we use the reconstructed ice sheet to constrain the surface pressure load and test different lithosphere thicknesses and linear deglaciation periods. We find a general decrease in decompression rates over depth and time. Results show that a decompression rate equal to the one induced by present-day deglaciation of Vatnajökull occurs at a lower depth inside the Martian mantle. Given that the mantle temperature is close to the solidus at this depth and magma ascent velocity is sufficiently high, mantle unloading due to ice melt could have contributed to the formation of the tuyas in the Martian South Polar Region. Our study proposes present-day deglaciation of Vatnajökull as a potential analogue for processes related to deglaciation on Mars.
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By analysing spectra of meteors ablating in the atmosphere, one can infer the composition of their parent bodies (asteroids and comets). A challenge to the accurate composition inference comes from external factors: factors other than the parent body composition, which affect meteoroid-atmosphere interactions and hence influence meteor spectral appearances. External factors considered here were meteoroid entry speeds, ablation temperatures and yearly meteoroids' interaction in space. This research aimed to assess to what degree these external factors influence the appearance of meteor spectra and meteoroids’ composition retrieval from them.

The analysis revealed a strong correlation between meteors' entry speeds and elements’ number densities; number densities of meteoric elements showed a proportional decrease with speed. Moreover, the study concluded that increases of meteor spectra line intensities with height strongly correlate with increase in the ablation temperature. Finally, significant changes in meteoroid composition were seen among meteors generated from the same parent body but observed over different years. ... Read more