S. Paardekooper
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5 records found
1
Uncovering Peculiar Rainbows
Automated Detection and Characterisation of Luminous Bands in Saturn's E Ring
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.
...
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.
Master thesis
(2026)
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J.R. Gerritsen, Tobias Arie de Jong, Bram Maasakkers, W. van der Wal, E.J.O. Schrama, S. Paardekooper
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.
...
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.
Nowadays, space-based systems for navigation, communication, Earth observation, meteorology and many other applications are indispensable for services critical for society. In order to preserve these vital applications among the increased risks in space, the Space Surveillance and Tracking segment of the Space Situational Awareness program has been set up in the last decade by the European Space Agency. This segment is occupied with one core activity: maintaining and building up a space object catalog. The object states within it can be used for conjunction assessment, collision avoidance and fragmentation event detection, allowing active satellites to be protected.
For objects in Low Earth Orbit, the Space Surveillance and Tracking segment primarily employs radar, which uses active signals, whose signal strength degrades with the fourth power of the distance. Beyond this orbit regime, passive optical sensors are primarily used, because they do not require an active signal and are therefore able to observe beyond Low Earth Orbit without large power requirements. As a consequence of the sparse optical sensors which have to track the large population of space objects, the optical observing arcs are typically very short: minutes at most. These short optical arcs are called tracklets.
Determining an orbit from a short arc is a challenging problem and is commonly referred to as the too short arc problem. Specifically, this problem entails that a single short arc tracklet is insufficient to construct an orbit with realistic state estimates. In order to obtain accurate state estimates, the object corresponding to the tracklet must be re-observed during a later pass to obtain six independent parameters of high quality. The initial problem to solve, however, is to identify which tracklets are correlated and thus associated with the same object. Thus, tracklet correlation is a critical step in the cataloging of objects. Evaluating and improving the performance of tracklet correlation methods is the key subject of this thesis. The performance is assessed on three key metrics: the association accuracy, the computational efficiency and the robustness.
In the first part of this thesis, tracklet correlation methods are evaluated. The most promising ones have been identified to be the Adapted Gooding method, the BVP optimization and IVP optimization. The performance of these methods is evaluated for different data distribution characteristics and orbit regimes, first without incorporating perturbations in the tracklet correlation methods.
In the second part, the tracklet correlation methods are modified to improve the performance. A major gap in the state of the art has been successfully addressed, namely to incorporate perturbations in the tracklet correlation methods. Results have shown a significant increase in association accuracy. Specifically, tracklet pairs with arbitrary time gap can be associated with the same true positive rate. Moreover, tracklet pairs from different orbit regimes can be associated with a similar true positive rate if the most important perturbations are incorporated.
Finally, the BVP and IVP optimization are found to be robust to noise, while the Adapted Gooding method severely suffers from the perfect measurement assumption. The performance of the latter has been improved by improving the accuracy of the angles through a Least Squares fit. Although the BVP and IVP optimization are robust to noise, the performance is limited by the accuracy of the angle rates, according to the Chi-squared distribution. A novel tracklet correlation method called the BVP-DC2-DC3 is developed to overcome this limitation, achieving an excellent TPR of 100% and a TNR of 99% for the analyzed objects in GEO for tracklets with a measurement noise of one arcsecond. This accuracy is superior to literature. Moreover, the computational efficiency is superior or comparable to literature. Additionally, the BVP-DC2-DC3 has a high robustness, because for the analyzed GEO tracklets with a measurement noise of five arcseconds, a TPR of 100% and a TNR of 95% can still be achieved. ...
For objects in Low Earth Orbit, the Space Surveillance and Tracking segment primarily employs radar, which uses active signals, whose signal strength degrades with the fourth power of the distance. Beyond this orbit regime, passive optical sensors are primarily used, because they do not require an active signal and are therefore able to observe beyond Low Earth Orbit without large power requirements. As a consequence of the sparse optical sensors which have to track the large population of space objects, the optical observing arcs are typically very short: minutes at most. These short optical arcs are called tracklets.
Determining an orbit from a short arc is a challenging problem and is commonly referred to as the too short arc problem. Specifically, this problem entails that a single short arc tracklet is insufficient to construct an orbit with realistic state estimates. In order to obtain accurate state estimates, the object corresponding to the tracklet must be re-observed during a later pass to obtain six independent parameters of high quality. The initial problem to solve, however, is to identify which tracklets are correlated and thus associated with the same object. Thus, tracklet correlation is a critical step in the cataloging of objects. Evaluating and improving the performance of tracklet correlation methods is the key subject of this thesis. The performance is assessed on three key metrics: the association accuracy, the computational efficiency and the robustness.
In the first part of this thesis, tracklet correlation methods are evaluated. The most promising ones have been identified to be the Adapted Gooding method, the BVP optimization and IVP optimization. The performance of these methods is evaluated for different data distribution characteristics and orbit regimes, first without incorporating perturbations in the tracklet correlation methods.
In the second part, the tracklet correlation methods are modified to improve the performance. A major gap in the state of the art has been successfully addressed, namely to incorporate perturbations in the tracklet correlation methods. Results have shown a significant increase in association accuracy. Specifically, tracklet pairs with arbitrary time gap can be associated with the same true positive rate. Moreover, tracklet pairs from different orbit regimes can be associated with a similar true positive rate if the most important perturbations are incorporated.
Finally, the BVP and IVP optimization are found to be robust to noise, while the Adapted Gooding method severely suffers from the perfect measurement assumption. The performance of the latter has been improved by improving the accuracy of the angles through a Least Squares fit. Although the BVP and IVP optimization are robust to noise, the performance is limited by the accuracy of the angle rates, according to the Chi-squared distribution. A novel tracklet correlation method called the BVP-DC2-DC3 is developed to overcome this limitation, achieving an excellent TPR of 100% and a TNR of 99% for the analyzed objects in GEO for tracklets with a measurement noise of one arcsecond. This accuracy is superior to literature. Moreover, the computational efficiency is superior or comparable to literature. Additionally, the BVP-DC2-DC3 has a high robustness, because for the analyzed GEO tracklets with a measurement noise of five arcseconds, a TPR of 100% and a TNR of 95% can still be achieved. ...
Nowadays, space-based systems for navigation, communication, Earth observation, meteorology and many other applications are indispensable for services critical for society. In order to preserve these vital applications among the increased risks in space, the Space Surveillance and Tracking segment of the Space Situational Awareness program has been set up in the last decade by the European Space Agency. This segment is occupied with one core activity: maintaining and building up a space object catalog. The object states within it can be used for conjunction assessment, collision avoidance and fragmentation event detection, allowing active satellites to be protected.
For objects in Low Earth Orbit, the Space Surveillance and Tracking segment primarily employs radar, which uses active signals, whose signal strength degrades with the fourth power of the distance. Beyond this orbit regime, passive optical sensors are primarily used, because they do not require an active signal and are therefore able to observe beyond Low Earth Orbit without large power requirements. As a consequence of the sparse optical sensors which have to track the large population of space objects, the optical observing arcs are typically very short: minutes at most. These short optical arcs are called tracklets.
Determining an orbit from a short arc is a challenging problem and is commonly referred to as the too short arc problem. Specifically, this problem entails that a single short arc tracklet is insufficient to construct an orbit with realistic state estimates. In order to obtain accurate state estimates, the object corresponding to the tracklet must be re-observed during a later pass to obtain six independent parameters of high quality. The initial problem to solve, however, is to identify which tracklets are correlated and thus associated with the same object. Thus, tracklet correlation is a critical step in the cataloging of objects. Evaluating and improving the performance of tracklet correlation methods is the key subject of this thesis. The performance is assessed on three key metrics: the association accuracy, the computational efficiency and the robustness.
In the first part of this thesis, tracklet correlation methods are evaluated. The most promising ones have been identified to be the Adapted Gooding method, the BVP optimization and IVP optimization. The performance of these methods is evaluated for different data distribution characteristics and orbit regimes, first without incorporating perturbations in the tracklet correlation methods.
In the second part, the tracklet correlation methods are modified to improve the performance. A major gap in the state of the art has been successfully addressed, namely to incorporate perturbations in the tracklet correlation methods. Results have shown a significant increase in association accuracy. Specifically, tracklet pairs with arbitrary time gap can be associated with the same true positive rate. Moreover, tracklet pairs from different orbit regimes can be associated with a similar true positive rate if the most important perturbations are incorporated.
Finally, the BVP and IVP optimization are found to be robust to noise, while the Adapted Gooding method severely suffers from the perfect measurement assumption. The performance of the latter has been improved by improving the accuracy of the angles through a Least Squares fit. Although the BVP and IVP optimization are robust to noise, the performance is limited by the accuracy of the angle rates, according to the Chi-squared distribution. A novel tracklet correlation method called the BVP-DC2-DC3 is developed to overcome this limitation, achieving an excellent TPR of 100% and a TNR of 99% for the analyzed objects in GEO for tracklets with a measurement noise of one arcsecond. This accuracy is superior to literature. Moreover, the computational efficiency is superior or comparable to literature. Additionally, the BVP-DC2-DC3 has a high robustness, because for the analyzed GEO tracklets with a measurement noise of five arcseconds, a TPR of 100% and a TNR of 95% can still be achieved.
For objects in Low Earth Orbit, the Space Surveillance and Tracking segment primarily employs radar, which uses active signals, whose signal strength degrades with the fourth power of the distance. Beyond this orbit regime, passive optical sensors are primarily used, because they do not require an active signal and are therefore able to observe beyond Low Earth Orbit without large power requirements. As a consequence of the sparse optical sensors which have to track the large population of space objects, the optical observing arcs are typically very short: minutes at most. These short optical arcs are called tracklets.
Determining an orbit from a short arc is a challenging problem and is commonly referred to as the too short arc problem. Specifically, this problem entails that a single short arc tracklet is insufficient to construct an orbit with realistic state estimates. In order to obtain accurate state estimates, the object corresponding to the tracklet must be re-observed during a later pass to obtain six independent parameters of high quality. The initial problem to solve, however, is to identify which tracklets are correlated and thus associated with the same object. Thus, tracklet correlation is a critical step in the cataloging of objects. Evaluating and improving the performance of tracklet correlation methods is the key subject of this thesis. The performance is assessed on three key metrics: the association accuracy, the computational efficiency and the robustness.
In the first part of this thesis, tracklet correlation methods are evaluated. The most promising ones have been identified to be the Adapted Gooding method, the BVP optimization and IVP optimization. The performance of these methods is evaluated for different data distribution characteristics and orbit regimes, first without incorporating perturbations in the tracklet correlation methods.
In the second part, the tracklet correlation methods are modified to improve the performance. A major gap in the state of the art has been successfully addressed, namely to incorporate perturbations in the tracklet correlation methods. Results have shown a significant increase in association accuracy. Specifically, tracklet pairs with arbitrary time gap can be associated with the same true positive rate. Moreover, tracklet pairs from different orbit regimes can be associated with a similar true positive rate if the most important perturbations are incorporated.
Finally, the BVP and IVP optimization are found to be robust to noise, while the Adapted Gooding method severely suffers from the perfect measurement assumption. The performance of the latter has been improved by improving the accuracy of the angles through a Least Squares fit. Although the BVP and IVP optimization are robust to noise, the performance is limited by the accuracy of the angle rates, according to the Chi-squared distribution. A novel tracklet correlation method called the BVP-DC2-DC3 is developed to overcome this limitation, achieving an excellent TPR of 100% and a TNR of 99% for the analyzed objects in GEO for tracklets with a measurement noise of one arcsecond. This accuracy is superior to literature. Moreover, the computational efficiency is superior or comparable to literature. Additionally, the BVP-DC2-DC3 has a high robustness, because for the analyzed GEO tracklets with a measurement noise of five arcseconds, a TPR of 100% and a TNR of 95% can still be achieved.
Constraining exoplanet parameters in nulling interferometry
A configuration comparison study for a single spacecraft mission
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.
...
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.
...
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.
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.
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. ...
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. ...
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.
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.