In the quest to answer the question “Are we alone in the universe?”, one of the biggest breakthroughs promises to come from detailed atmospheric characterisation of small, Earth-like exoplanets. To make such observations possible, the Large Interferometer for Exoplanets (LIFE) space mission has been proposed. This mission makes use of the nulling interferometry principle, a concept in which a null is placed on the host star, allowing for the orbiting exoplanets to be observed directly.

To achieve the required angular resolution and observational stability for the interferometric measurements, the LIFE concept would require precise control of a rotating spacecraft formation, over baselines of up to 600 meters. Four collector and one beam combiner spacecraft are arranged into a specific geometry dubbed the Emma X-array and together act as one large telescope.

This thesis, based on LIFE’s scientific requirements, presents a systems-level analysis of a future nulling interferometry formation-flying mission in the Sun-Earth L2 region. To that end, an operational phase mission simulator was developed within the circular restricted three-body problem (CR3BP) framework, with the spacecraft formation employing continuous-thrust propulsion for formation keeping, and higher-thrust impulsive propulsion for formation reconfigurations and orbital maintenance. The results show that, with this setup, a five-year mission is achievable from a ΔV perspective, requiring approximately 20 to 40 kg of propellant per collector and less than 10 kg for the beam combiner, assuming each spacecraft mass would be 1000 kg. In addition, the influence of several system characteristics on mission feasibility and ΔV requirements was quantified, with rotational speed and baseline size identified as the primary drivers of the mission propellant cost. Interestingly, the choice of reference orbit was found to have a negligible effect on the formation design. ... Read more

Polarization is an extremely elusive property of light. It is ever-present, yet completely invisible to the human eye. Until recently, precisely quantifying polarization required laboratory setups or very elaborate instrumentation. This changed with the development of polarized filter array (PFA) cameras, which can
image polarization in field conditions, and open a new area of polarization research. This work develops PolarVis, open source software for calibrating, processing and visualizing images from PFA cameras. A calibration model based on literature, as well as techniques of visualizing polarized information to humans are defined. A calibration procedure is conducted, and shows promising performance and future utility of PolarVis. ... Read more

Saturn's E ring harbours faint, quasi-periodic, inclined brightness structures called luminous bands, first characterised from Cassini VIMS and ISS observations during Enceladus flybys. We present the first automated, catalogue-scale survey of luminous bands, drawing on 23 Cassini flybys. Detection exploits the chromatic character of the bands, whose apparent position shifts with wavelength. Because these bands present a quasi-periodic inclined brightness structure, a frequency-domain search using a zero-padded two-dimensional Fourier angular spectrum is applied, with candidates assessed against a phase-randomised null ensemble. Of 573 processed images, 62 yield positive detections across eight flybys. Six of the eight carry no prior published detection, including the first ISS detection for E13, and five are non-targeted flybys, demonstrating bands are present in more ISS images than initially found. The observed band directions are compared against a diffraction model: 39 of the 62 detections agree to within 2 degrees, confirming the grating interpretation; the remaining 23 show a systematic offset whose origin is not yet explained. Band contrasts decrease with Cassini–Enceladus distance, suggesting the strongest structure near the plume source. Notably, no detections occur in the morning ansa despite comparable coverage. A complementary VIMS spectral analysis reveals selective suppression of sub-micron grains on the morning-side ring, consistent with size-selective electromagnetic clearing by Lorentz forces, explaining the asymmetric detection rate. ... Read more

The field of vegetation remote sensing has historically been dominated by radiative transfer models (RTMs) employing spectral reflectance as a means of characterising the interaction between vegetation and incident radiation. In recent years, polarimetry has received increasing attention as a complementary source of information in remote sensing, driven in part by advances in polarimetric instrumentation and the increasing availability of measurements capable of resolving the polarisation state of reflected radiation. The polarisation state of light contains information on the optical and structural properties of vegetation that is not captured by conventional radiometric measurements.

This study explores whether polarimetric observations of leaves contain relationships between illumination geometry, viewing geometry, and leaf degree and angle of linear polarisation (DoLP, AoLP), with the broader aim of assessing if polarimetry could enhance vegetation remote sensing by revealing information on physical and environmental vegetation characteristics. Two radiative transfer models, PROPOLAR and DART, are assessed in their ability to reproduce vegetation polarisation. The modelling component further aims to assess whether current RTM approaches can provide a sufficiently accurate physical description of vegetation polarisation to support the future development of a retrieval method between polarimetric observations and vegetation physical and environmental traits.

The results show that both DART and PROPOLAR, in their current implementations, are unable to adequately reproduce the laboratory measurements, with discrepancies potentially arising from their respective implementations of leaf microfacet properties. The laboratory measurements nevertheless show the existence of systematic relationships between observation geometry, leaf ar
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In preparation of a large-scale nulling interferometry mission aiming to detect and characterize Earth-like exoplanets, it is required that key technologies are demonstrated in a space environment. Design trade-offs for a large mission have assumed long, reconfigurable baselines. However, it is uncertain that the same design performs best for a smaller mission with shorter, fixed baselines.
This research aims to compare the performance of three possible nulling configurations, a linear double Bracewell, a rectangular double Bracewell and a off-center kite shaped kernel nuller, on their ability to constrain the temperature, radius, and position of an exoplanet during the mission detection phase.
The configurations are compared by planetary signal simulations performed using the simulation software SCIFYsim. The configurations are compared based on three categories (1) performance for a single planet case, (2) the introduced correlations between planetary parameters, and (3) the performance in a two planet case.
The analysis indicates that the configurations performed similarly when modeling a single planet system, with the linear configuration showing a slight advantage. Regarding the parameter correlations, the kernel configuration exhibits the least correlations between fitted parameters. In the two-planet system, both the rectangular and kernel configurations achieve the highest accuracy in retrieving planetary parameters, though the overall performance remains relatively similar across configurations. Notably, despite the blurry signature of the two planet system in the matched filter map for the linear configuration, the fitting process is able to retrieve the planetary parameters.
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The polarization of light has become a powerful tool for scientists in recent years. Astronomy, climatology, chemistry, and medicine are just a few sectors that are turning to this characteristic of light to produce a finer description of the environment they study.
However, the complete measurement of polarization at different wavelengths remains difficult. The difficulties are even more significant when the polarization measurement occurs in space. Current technologies are bulky, mainly featuring rotating components that can bring additional risk to the space mission. In this context, the present research discusses the development of a new method for measuring light polarization compatible with use in space.
Starting from ideas already presented in the specialized literature, we have refined here a new way to access the polarization of light that promises the construction of compact, robust, and highly accurate instruments. The present research provides a detailed theoretical description of this new method's operating principle and a practical demonstration. The results confirmed the ability to translate this method into high-performing instruments capable of accessing any polarization.
In addition, this research also highlights the versatility of the new method for measuring light polarization. It can be translated into instruments intended for use in space or for other applications; it can be adapted to determine only certain types of polarization, or it can be the basis for building imaging instruments. It opens a new horizon of development in polarimetry and spectropolarimetry. ... Read more

Finding signs of life on planets outside of Earth is an ongoing challenge in astronomy. Nulling interferometry is a promising method to not only detect exoplanets, but also allow for characterization of their atmospheres. Nulling interferometry has been demonstrated on ground, but with limited success, due to atmospheric turbulence. To maximize the potential, a space-based observatory is needed. In the early 2000s, several space based missions were proposed, which marked the start of many system studies. Nonetheless, considerations on the telescope design are lacking in the literature. To gain new insights in the behavior of a space-based nulling interferometer under operational conditions, several designs were made in Code V for this study, including an off-axis Cassegrain, Ritchey-Chretien (RC) and Gregorian. By means of a numerical perturbation analysis, the RC was shown to be the most promising. ... Read more

This thesis describes the implementation of an innovative experimental set-up to perform simulations of laser link acquisitions between two spacecraft, in the context of laser ranging interferometry missions, which are increasingly relevant in the fields of gravimetry and gravitational waves detection. The objective of the project is to reproduce realistic laser beam characteristics, demonstrate the ability of the Optical Formation Metrology Testbed (OFMT) to perform autonomous link acquisition procedures and define requirements for the OFMT architecture based on the experimental results. To achieve the goals set, the OFMT set-up has been assembled and aligned, the relevant beam properties have been measured, the supporting experimental infrastructure to conduct the acquisition tests has been integrated, the necessary calibration procedures have been carried out and finally the acquisition tests have been defined and performed, followed by a comprehensive analysis of the results.
From the evaluation of the test runs and the measurements of the beam characteristics, it can be concluded that the OFMT set-up represents a new way of successfully recreating laser beams between spacecraft that are placed far apart from each other, following a design path that had not previously been covered by other experimental architectures of this kind. Additionally, the work outlined in this thesis demonstrates the ability of the set-up to carry out autonomous link acquisition procedures, paving the way for further developments of the instruments. ... Read more

Direct imaging of exoplanets relies on advanced post-processing techniques to differentiate planetary signals from the bright stellar point spread function (PSF) and quasi-static speckle noise. While angular-spectral differential imaging (ASDI) with integral field spectrographs has significantly enhanced the capability to induce diversity in high-contrast imaging (HCI) observations, current post-processing methods like matrix Principal Component Analysis (PCA) are limited in their ability to fully exploit the multi-modal structure of ASDI data.

This thesis introduces tensor decomposition methods as generalizations of matrix-PCA for modeling the coronagraphic PSF in ASDI observations. These methods preserve the higher-order structure of ASDI data, enabling the modeling of complex cross-modal interactions while maintaining the strengths of PCA-based approaches. By extending PCA to higher-order tensors, these methods offer a more natural representation of the multi-dimensional nature of ASDI data.

The proposed tensor methods are evaluated using both synthetic and real observations from the SPHERE instrument on the VLT. They successfully recover known exoplanets in benchmark systems like HR 8799 and $\beta$ Pictoris, and detect a new collision-induced feature in the AU Microscopii debris disk. Notably, a new sub-stellar companion candidate is identified in the HD 108767 B system. Their performance is assessed through both quantitative metrics and qualitative analysis of residual images. Results demonstrate that tensor methods are competitive with matrix-PCA, outperforming it at small angular separations where speckle noise is most problematic.

This work establishes tensor decompositions as a powerful tool for HCI post-processing, offering increased flexibility and interpretability of factorizations while building upon the established framework of PCA. Furthermore, this approach lays the groundwork for tractable deep learning techniques on HCI datasets, and more generally for higher-order tensor methods in direct exoplanet imaging. ... Read more

The miniaturization of space systems push for cheaper and more compact instruments. The use of photonic crystals as optical filters are a promising option for the miniaturization of spectrometers. This thesis is part of a project in SRON where a novel concept using photonic crystals is being investigated for Earth observation. Ways of using the transmission of photonic crystals for remote sensing of methane were explored. Later, the effects of the concentrations of other gases and the reflectance of the surface in the performance of the instrument were investigated. A method of selecting which photonic crystals to use in the instrument was developed and used to improve its performance. Finally, an optical design was made to estimate the volume of such an instrument. ... Read more

Distributed formation control has received increasing attention in multiagent systems. Maintaining certain geometry in space is advantageous in many applications such as space interferometry and underwater sensing. At present, there is a variety of distributed solutions for agents to converge to desired formations and track a series of prescribed maneuvers. They typically rely on the relative kinematics e.g., relative positions of the neighboring agents as state observations for the local controller. In harsh working environments, the acquisition of the relative kinematics is challenged and observation losses might occur, which can be detrimental to the optimality of formation.

In this work, observation losses in noisy environments are addressed under a distributed formation control framework. Three types of solutions are proposed to enhance the robustness which is evaluated through the improvements of tracking error, convergence speed, and smoothness of trajectories in both random and permanent loss settings. Firstly, a relative localization technique is proposed using formation itself as a spatial constraint. Secondly, a dynamic model is established for the agents entailed by a Kalman filter-based solution. Finally, a fusion of the previous two types is inspired and it exhibits superior performance than both aforementioned types individually.

This work not only provides means of relative localization without additional sensor data but also shares insights into coping with random or permanent graph changes for stress-based formation control systems. This could potentially lead to the exploration of formation control with subgraphs or energy-efficient sensing as future directions. ... Read more