Pitch-based carbon/nano-silicon composite, an efficient anode for Li-ion batteries

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The high-resolution map of Oxia Planum, Mars; the landing site of the ExoMars Rosalind Franklin rover mission

This 1:30,000 scale geological map describes Oxia Planum, Mars, the landing site for the ExoMars Rosalind Franklin rover mission. The map represents our current understanding of bedrock units and their relationships prior to Rosalind Franklin’s exploration of this location. The map details 15 bedrock units organised into 6 groups and 7 textural and surficial units. The bedrock units were identified using visible and near-infrared remote sensing datasets. The objectives of this map are (i) to identify where the most astrobiologically relevant rocks are likely to be found, (ii) to show where hypotheses about their geological context (within Oxia Planum and in the wider geological history of Mars) can be tested, (iii) to inform both the long-term (hundreds of metres to ∼1 km) and the short-term (tens of metres) activity planning for rover exploration, and (iv) to allow the samples analysed by the rover to be interpreted within their regional geological context

PyBWE: Python tools for Bandwidth Extrapolation of planetary radar signals

International audiencePyBWE is a Python library containing radar super-resolution methods known as "Bandwidth Extrapolation" (BWE). Range resolution enhancement is one of the main challenges in radar signal processing. It is driven by the time resolution of radar soundings, and the speed of electromagnetic waves in the sounded material. Time resolution being limited by the frequency bandwidth of the instrument, the same applies to range resolution: the larger the bandwidth, the better the resolution

Évaluation d’outils de traitement et d’interprétation en prévision des opérations Martiennes du Radar à Pénétration de Sol WISDOM/ExoMars

From summer 2023, the Rosalind Franklin rover of the ExoMars 2022 mission (ESA/ROSCOSMOS) will seek out past or present traces of life down to 2 m in the Martian subsurface with a drill, where collected samples could have been shielded from the harsh conditions of the surface. In order to give an insight into the structure and composition of the shallow subsurface prior to any drilling operations, and to provide clues on the geological context of the rover landing site, one of the 9 instruments onboard Rosalind Franklin is a Ground Penetrating Radar (GPR): WISDOM (Water Ice and Subsurface Deposits Observation on Mars). WISDOM will sound the first meters of the Martian shallow subsurface with a vertical resolution of a few cm. This thesis was dedicated to the assessment and implementation of new and sophisticated tools in the processing and interpretation chain of the WISDOM data, enhancing the quality and readability of future Martian observations.Data acquired by WISDOM consist in“radargrams”, displaying the amplitude of received signals (after reflection/scattering on subsurface structures) as a function of their time delays. Converting these time delays into distances requires the knowledge of the propagation speed of electromagnetic waves in the subsurface, which is linked to the dielectric permittivity of this subsurface. In the case of WISDOM, this property can be estimated from the surface echo intensity or from the shape of diffraction curves from scatter points buried in the subsurface. Since, unlike most GPR, WISDOM antennas are not directly on the ground, the latter method must account for the refraction of radar signals at the surface, which impacts the shape of the curves and thus the permittivity estimation. During this thesis, an automated tool of detection and characterization of diffraction curves was developed and validated, guarantying the display of radargrams as a function of distance.This thesis also focused on the enhancement of the vertical resolution (in range/depth) of WISDOM radargrams. The instrument operating on a large frequency bandwidth, a resolution of a few cm in the subsurface is already assured. A super-resolution technique based on the “Bandwidth Extrapolation” (BWE) was tested and implemented to the WISDOM data processing chain. This resulted in an improvement of the range resolution by a factor of 3. Such improvement has numerous positive implications on the interpretation of future WISDOM radargrams; echoes before impossible to separate can be now discriminated. Potential improvements of the BWE, exploiting for instance the polarimetric capabilities of WISDOM were also explored.Tools implemented during this thesis were systematically validated on both synthetic (analytical or simulated) and experimental data acquired on Earth with replicas of WISDOM instrument (in laboratory or natural environments). Two field campaigns were organised in the frame of this thesis (in the Desert of Atacama and at the Technical University of Dresden (TUD)), providing interesting datasets to validate the WISDOM processing and interpretation chains on, in preparation of future Martian operations.A partir de l’été 2023, le rover Rosalind Franklin de la mission ExoMars 2022 (ESA/ROSCOSMOS) recherchera à l’aide d’une foreuse de potentielles traces de vie, passées ou présentes, dans les 2 premiers mètres du sous-sol martien, là où les échantillons collectés pourraient avoir été protégés des conditions inhospitalières de la surface. Dans le but d’offrir un aperçu de la structure et de la composition de la proche sous-surface avant toute opération de forage et d’aider à reconstituer le contexte géologique du site d’atterrissage du rover, l’un des 9 instruments à bord de Rosalind Franklin est un radar à pénétration de sol (ou GPR pour Ground Penetrating Radar) : WISDOM (Water Ice and Subsurface Deposits Observation on Mars). WISDOM sondera les premiers mètres du sous-sol martien avec une résolution verticale centimétrique. Cette thèse a été dédiée à la mise en place d’une chaine de traitement et d’interprétation des données de WISDOM destinée à optimiser la qualité et lisibilité de ses futures observations sur Mars.Les données de WISDOM se présentent sous forme de « radargrammes » qui donnent l’amplitude des signaux reçus (après réflexion/diffusion sur des structures enfouies) en fonction de leur temps d’arrivée. La conversion de ces temps d’arrivée en distances requiert la connaissance de la vitesse de propagation des ondes électromagnétiques dans le sous-sol, qui elle-même est liée à la permittivité diélectrique du sol. Dans le cas de WISDOM, cette dernière peut être estimée à partir de l’intensité de l’écho de surface ou de la forme des courbes de diffraction provenant de réflecteurs ponctuels enfouis. Les antennes de WISDOM n’étant pas plaquées au sol (contrairement à celles de la majorité des GPR), cette seconde méthode d’estimation doit tenir compte de la réfraction des signaux du radar à la surface, qui a un impact sur la forme des courbes et donc l’estimation de la permittivité. Durant cette thèse, une chaîne automatique de détection et de caractérisation des courbes de diffraction tenant compte de la réfraction à la surface, a été développée et validée, garantissant la possibilité d’exprimer les radargrammes WISDOM en fonction de la distance.Cette thèse s’est aussi attachée à améliorer la résolution verticale (en distance/profondeur) des radargrammes de WISDOM. L’instrument opère sur une large bande de fréquences, ce qui lui assure déjà une résolution en distance de quelques cm dans le sous-sol. Une technique dite de super-résolution, fondée sur l’« Extrapolation de largeur de bande » (BWE), a été testée et implémentée dans la chaîne de traitement des données WISDOM. Il a été montré que cette technique permet d’améliorer la résolution en distance d’un facteur 3. Une telle amélioration de la résolution revêt un intérêt évident pour l’interprétation des futurs radargrammes WISDOM ; des échos avant impossible à séparer le sont à présent. De potentielles améliorations de la BWE, tirant par exemple partie des capacité polarimétriques de WISDOM, ont aussi été explorées.Les outils mis en place pendant cette thèse ont été systématique validés sur des données aussi bien synthétiques (analytiques ou numériques) qu’expérimentales acquises sur Terre avec des répliques de l’instrument (en laboratoire ou sur site naturel). Deux campagnes de mesures ont d’ailleurs été organisées durant cette thèse (dans le désert d’Atacama au Chili et à l’Université Technique de Dresden (TUD)), fournissant des observations sur lesquelles tester les chaînes de traitement et d’interprétation WISDOM pour préparer au mieux les futures opérations martiennes

Assessment of processing and interpretation tools in preparation of the WISDOM/ExoMars Ground Penetrating Radar operations on Mars

A partir de l’été 2023, le rover Rosalind Franklin de la mission ExoMars 2022 (ESA/ROSCOSMOS) recherchera à l’aide d’une foreuse de potentielles traces de vie, passées ou présentes, dans les 2 premiers mètres du sous-sol martien, là où les échantillons collectés pourraient avoir été protégés des conditions inhospitalières de la surface. Dans le but d’offrir un aperçu de la structure et de la composition de la proche sous-surface avant toute opération de forage et d’aider à reconstituer le contexte géologique du site d’atterrissage du rover, l’un des 9 instruments à bord de Rosalind Franklin est un radar à pénétration de sol (ou GPR pour Ground Penetrating Radar) : WISDOM (Water Ice and Subsurface Deposits Observation on Mars). WISDOM sondera les premiers mètres du sous-sol martien avec une résolution verticale centimétrique. Cette thèse a été dédiée à la mise en place d’une chaine de traitement et d’interprétation des données de WISDOM destinée à optimiser la qualité et lisibilité de ses futures observations sur Mars.Les données de WISDOM se présentent sous forme de « radargrammes » qui donnent l’amplitude des signaux reçus (après réflexion/diffusion sur des structures enfouies) en fonction de leur temps d’arrivée. La conversion de ces temps d’arrivée en distances requiert la connaissance de la vitesse de propagation des ondes électromagnétiques dans le sous-sol, qui elle-même est liée à la permittivité diélectrique du sol. Dans le cas de WISDOM, cette dernière peut être estimée à partir de l’intensité de l’écho de surface ou de la forme des courbes de diffraction provenant de réflecteurs ponctuels enfouis. Les antennes de WISDOM n’étant pas plaquées au sol (contrairement à celles de la majorité des GPR), cette seconde méthode d’estimation doit tenir compte de la réfraction des signaux du radar à la surface, qui a un impact sur la forme des courbes et donc l’estimation de la permittivité. Durant cette thèse, une chaîne automatique de détection et de caractérisation des courbes de diffraction tenant compte de la réfraction à la surface, a été développée et validée, garantissant la possibilité d’exprimer les radargrammes WISDOM en fonction de la distance.Cette thèse s’est aussi attachée à améliorer la résolution verticale (en distance/profondeur) des radargrammes de WISDOM. L’instrument opère sur une large bande de fréquences, ce qui lui assure déjà une résolution en distance de quelques cm dans le sous-sol. Une technique dite de super-résolution, fondée sur l’« Extrapolation de largeur de bande » (BWE), a été testée et implémentée dans la chaîne de traitement des données WISDOM. Il a été montré que cette technique permet d’améliorer la résolution en distance d’un facteur 3. Une telle amélioration de la résolution revêt un intérêt évident pour l’interprétation des futurs radargrammes WISDOM ; des échos avant impossible à séparer le sont à présent. De potentielles améliorations de la BWE, tirant par exemple partie des capacité polarimétriques de WISDOM, ont aussi été explorées.Les outils mis en place pendant cette thèse ont été systématique validés sur des données aussi bien synthétiques (analytiques ou numériques) qu’expérimentales acquises sur Terre avec des répliques de l’instrument (en laboratoire ou sur site naturel). Deux campagnes de mesures ont d’ailleurs été organisées durant cette thèse (dans le désert d’Atacama au Chili et à l’Université Technique de Dresden (TUD)), fournissant des observations sur lesquelles tester les chaînes de traitement et d’interprétation WISDOM pour préparer au mieux les futures opérations martiennes.From summer 2023, the Rosalind Franklin rover of the ExoMars 2022 mission (ESA/ROSCOSMOS) will seek out past or present traces of life down to 2 m in the Martian subsurface with a drill, where collected samples could have been shielded from the harsh conditions of the surface. In order to give an insight into the structure and composition of the shallow subsurface prior to any drilling operations, and to provide clues on the geological context of the rover landing site, one of the 9 instruments onboard Rosalind Franklin is a Ground Penetrating Radar (GPR): WISDOM (Water Ice and Subsurface Deposits Observation on Mars). WISDOM will sound the first meters of the Martian shallow subsurface with a vertical resolution of a few cm. This thesis was dedicated to the assessment and implementation of new and sophisticated tools in the processing and interpretation chain of the WISDOM data, enhancing the quality and readability of future Martian observations.Data acquired by WISDOM consist in“radargrams”, displaying the amplitude of received signals (after reflection/scattering on subsurface structures) as a function of their time delays. Converting these time delays into distances requires the knowledge of the propagation speed of electromagnetic waves in the subsurface, which is linked to the dielectric permittivity of this subsurface. In the case of WISDOM, this property can be estimated from the surface echo intensity or from the shape of diffraction curves from scatter points buried in the subsurface. Since, unlike most GPR, WISDOM antennas are not directly on the ground, the latter method must account for the refraction of radar signals at the surface, which impacts the shape of the curves and thus the permittivity estimation. During this thesis, an automated tool of detection and characterization of diffraction curves was developed and validated, guarantying the display of radargrams as a function of distance.This thesis also focused on the enhancement of the vertical resolution (in range/depth) of WISDOM radargrams. The instrument operating on a large frequency bandwidth, a resolution of a few cm in the subsurface is already assured. A super-resolution technique based on the “Bandwidth Extrapolation” (BWE) was tested and implemented to the WISDOM data processing chain. This resulted in an improvement of the range resolution by a factor of 3. Such improvement has numerous positive implications on the interpretation of future WISDOM radargrams; echoes before impossible to separate can be now discriminated. Potential improvements of the BWE, exploiting for instance the polarimetric capabilities of WISDOM were also explored.Tools implemented during this thesis were systematically validated on both synthetic (analytical or simulated) and experimental data acquired on Earth with replicas of WISDOM instrument (in laboratory or natural environments). Two field campaigns were organised in the frame of this thesis (in the Desert of Atacama and at the Technical University of Dresden (TUD)), providing interesting datasets to validate the WISDOM processing and interpretation chains on, in preparation of future Martian operations

Assessment of the Polarimetric Bandwidth Extrapolation to enhance the resolution of the WISDOM/ExoMars 2022 radar soundings

International audienceThe WISDOM (CNES/DLR) Ground Penetrating Radar (GPR), onboard the ExoMars 2022 Rosalind Franklin rover (ESA/ROSCOSMOS), is designed to study the structure and provide clues on the composition of the shallow Martian subsurface prior to drilling operations (down to a 2 m depth), acquiring key information on the geological context of the samples to be collected, and potential hazards for the drill [1]. To precisely guide this sample collection, the WISDOM instrument was designed with a large bandwidth of 2.5 GHz, allowing soundings with a range resolution of a few cm only in the Martian subsurface, with usual processing (~11 cm in vacuum, the worst case). The use of the Bandwidth Extrapolation (BWE) recently enhanced the vertical resolution of WISDOM radargrams by a factor of 3 [2], reaching a new resolution limit ~3.75 cm, to be compared with the 3 cm length of the samples to be collected. The satisfying performances of the BWE in the reconstruction of radar echoes in time delays and amplitudes have been quantified [3]. The BWE relies on a simple signal model, and its performances could be improved with a more sophisticated one. Thus we studied different modified versions of the BWE, among which the promising Polarimetric Bandwidth Extrapolation (PBWE) [4]. WISDOM having the capacity to transmit and receive signals in 2 orthogonal polarizations, 4 polarimetric channels (2 co-polar and 2 cross-polar) are available when sounding the subsurface. Depending on its geometry and orientation with respect to the antenna system, one echo from a subsurface reflector may appear in different polar channels, but with different complex scattering coefficients. The idea behind the PBWE is to use data from echoes in the different polar channels to more accurately model the signals from each channel. The PBWE was previously applied with success to SAR images on Earth, with improved performances compared to the BWE [5]. We propose here the first application of the PBWE to a planetary GPR, WISDOM, assessing its performances on synthetic soundings (analytical and FDTD simulations, see the Figure) and experimental acquisitions performed in laboratory. [1] Ciarletti et al., Astrobiology, 2017 [2] Cuomo, Lincoln Lab. Report, 1992 [3] Oudart et al., Planetary and Space Science, 2021 [4] Suwa and Iwamoto., IEEE, 2003 [5] Suwa and Iwamoto., IEEE, 200

Assessment of the Polarimetric Bandwidth Extrapolation to enhance the resolution of the WISDOM/ExoMars 2022 radar soundings

International audienceThe WISDOM (CNES/DLR) Ground Penetrating Radar (GPR), onboard the ExoMars 2022 Rosalind Franklin rover (ESA/ROSCOSMOS), is designed to study the structure and provide clues on the composition of the shallow Martian subsurface prior to drilling operations (down to a 2 m depth), acquiring key information on the geological context of the samples to be collected, and potential hazards for the drill [1]. To precisely guide this sample collection, the WISDOM instrument was designed with a large bandwidth of 2.5 GHz, allowing soundings with a range resolution of a few cm only in the Martian subsurface, with usual processing (~11 cm in vacuum, the worst case). The use of the Bandwidth Extrapolation (BWE) recently enhanced the vertical resolution of WISDOM radargrams by a factor of 3 [2], reaching a new resolution limit ~3.75 cm, to be compared with the 3 cm length of the samples to be collected. The satisfying performances of the BWE in the reconstruction of radar echoes in time delays and amplitudes have been quantified [3]. The BWE relies on a simple signal model, and its performances could be improved with a more sophisticated one. Thus we studied different modified versions of the BWE, among which the promising Polarimetric Bandwidth Extrapolation (PBWE) [4]. WISDOM having the capacity to transmit and receive signals in 2 orthogonal polarizations, 4 polarimetric channels (2 co-polar and 2 cross-polar) are available when sounding the subsurface. Depending on its geometry and orientation with respect to the antenna system, one echo from a subsurface reflector may appear in different polar channels, but with different complex scattering coefficients. The idea behind the PBWE is to use data from echoes in the different polar channels to more accurately model the signals from each channel. The PBWE was previously applied with success to SAR images on Earth, with improved performances compared to the BWE [5]. We propose here the first application of the PBWE to a planetary GPR, WISDOM, assessing its performances on synthetic soundings (analytical and FDTD simulations, see the Figure) and experimental acquisitions performed in laboratory. [1] Ciarletti et al., Astrobiology, 2017 [2] Cuomo, Lincoln Lab. Report, 1992 [3] Oudart et al., Planetary and Space Science, 2021 [4] Suwa and Iwamoto., IEEE, 2003 [5] Suwa and Iwamoto., IEEE, 200

Automated detection and characterization of diffraction curves in WISDOM/ExoMars radargrams

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Validation of an automated detection and characterization of diffraction curves in the WISDOM/ExoMars radargrams with a Hough transform

International audienceThe WISDOM (CNES/DLR) Ground Penetrating Radar (GPR), onboard the ExoMars 2022 Rosalind Franklin rover (ESA/ROSCOSMOS), is designed to study the structure and composition of the first meters of the Martian subsurface prior to drilling operations, providing key information on the geological context of the samples to be collected (down to a 2 m depth), and the potential hazards the drill may encounter.In the inversion process of GPR data, diffraction curves corresponding to underground scatterers are commonly used to retrieve the dielectric constant of the surrounding medium. The Hough transform adapted to hyperbolic shapes has already proven its efficiency in detecting diffraction curves in terrestrial GPR acquisitions, without requiring any learning or training dataset. The method has been adapted to WISDOM radargrams.WISDOM being an air-coupled GPR, the effect of refraction at surface level on the inversion is quantified and has to be taken into account. The Hough transform process is applied to synthetic WISDOM soundings, first generated with a simple scattering model of a subsurface accounting for refraction (an example is presented in the figure), and then with more complex ground models and FDTD simulations to evaluate its performances in terms of detection and dielectric constant estimation. Eventually, the same test is performed on experimental acquisitions with different models of the instrument, in a semi-controlled environment with buried metallic targets, and in natural environments being potential Martian analogs.The Hough transform adapted to WISDOM acquisitions provides an automated detection of potential underground obstacles with objective criteria, as well as a retrieval of the dielectric constant of the subsurface, allowing an estimation of their depth. It will significantly help the interpretation of future Martian radargrams, and meet the allowed decision time requirements of the Rover Operation Control Center when selecting a safe and relevant drilling location

WISDOM/ExoMars: Towards the high resolution imaging of the Martian subsurface

International audienceThe WISDOM ground penetrating radar is one of the instruments onboard the rover of ESA and ROSCOSMOS ExoMars 2020 mission. Its objective is to seek out traces of past or present life in the shallow Martian subsurface. To achieve this goal, the rover is equipped with a 2 m long drill, able to retrieve underground samples. WISDOM will give useful insights on the structure and dielectrical properties of the subsurface to guide drilling operations. In this context, the vertical resolution of the radar is key. In order to improve this resolution, bandwidth extrapolation techniques are applied to both synthetic and experimental WISDOM data