http://hdl.handle.net/10993/155 Search this channel search https://orbilu.uni.lu/simple-search http://hdl.handle.net/10993/56045 Title: Compression of Deep Neural Networks for Space Autonomous Systems <br/> <br/>Author, co-author: Shneider, Carl; Sinha, Nilotpal; Jamrozik, Michele Lynn; Astrid, Marcella; Rostami Abendansari, Peyman; Kacem, Anis; Shabayek, Abd El Rahman; Aouada, Djamila <br/> <br/>Abstract: Efficient compression techniques are required to deploy deep neural networks (DNNs) on edge devices for space resource utilization tasks. Two approaches are investigated. Mon, 02 Oct 2023 03:30:30 GMT http://hdl.handle.net/10993/55718 Title: Directional Statistics and Machine Learning for crater detection in Space <br/> <br/>Author, co-author: Palmirotta, Guendalina; Loizidou, Sophia; Nagarajan, Senthil Murugan <br/> <br/>Abstract: Craters are distinctive features on the surfaces of most terrestrial planets such as Mars and Venus. The distribution of craters reveals the relative ages of surface units and provides information on surface geology. Extracting craters is one of the fundamental tasks in planetary research. Although many automated crater detection algorithms have been developed to extract craters from image or topographic data, most of them are applicable only in particular regions, and only a few can be widely used, especially in complex surface settings. On the other side, once we have a reasonable craters data, statistics play an important role in better understanding their features, in particular their distribution. In this workshop, we will demonstrate to participants how basic methodologies with directional statistics and machine learning/deep learning models help in the detection and analysis of craters in our Universe. Wed, 02 Aug 2023 13:09:41 GMT http://hdl.handle.net/10993/54945 Title: Understanding our Universe thanks to mathematics <br/> <br/>Author, co-author: Palmirotta, Guendalina Sat, 29 Apr 2023 12:12:00 GMT http://hdl.handle.net/10993/54755 Title: La conquête de l'espace grâce aux statistiques appliquées <br/> <br/>Author, co-author: Palmirotta, Guendalina; Ley, Christophe <br/> <br/>Abstract: Notre espace est rempli de mystères et secrets que nous devons encore découvrir et déchiffrer. L’analyse de données spatiales figure parmi les pistes les plus prometteuses dans notre conquête de l’espace. Mais comment s’y prendre? Les statistiques appliquées permettent d’analyser les multiples données spatiales dont nous disposons de nos jours. Contrairement à ce qu’on pourrait être amené à penser, le domaine des statistiques appliquées s’apparente davantage à l’Intelligence Artificielle qu’à des calculs stérils sur des tableurs Excel. Pendant votre conférence, on vous donnera un aperçu des possibilités et défis. Mon, 03 Apr 2023 09:01:56 GMT http://hdl.handle.net/10993/54429 Title: On the Impact of GPS Multipath Correction Maps and Post-Fit Residuals on Slant Wet Delays for Tracking Severe Weather Events <br/> <br/>Author, co-author: Hunegnaw, Addisu; Duman, Huseyin; Ejigu, Yohannes G.; Baltaci, Hakki; Dousa, Jan; Teferle, Felix Norman <br/> <br/>Abstract: Climate change has increased the frequency and intensity of weather events with heavy precipitation, making communities worldwide more vulnerable to flash flooding. As a result, accurate fore- and nowcasting of impending excessive rainfall is crucial for warning and mitigating these hydro-meteorological hazards. The measurement of integrated water vapour along slant paths is made possible by ground-based global positioning system (GPS) receiver networks, delivering three-dimensional (3D) water vapour distributions at low cost and in real-time. As a result, these data are an invaluable supplementary source of knowledge for monitoring storm events and determining their paths. However, it is generally known that multipath effects at GPS stations have an influence on incoming signals, particularly at low elevations. Although estimates of zenith total delay and horizontal linear gradients make up the majority of the GPS products for meteorology to date, these products are not sufficient for understanding the full 3D distribution of water vapour above a station. Direct utilization of slant delays can address this lack of azimuthal information, although, at low elevations it is more prone to multipath (MP) errors. This study uses the convective storm event that happened on 27 July 2017 over Bulgaria, Greece, and Turkey, which caused flash floods and severe damage, to examine the effects of multipath-corrected slant wet delay (SWD) estimations on monitoring severe weather events. First, we reconstructed the one-way SWD by adding GPS post-fit phase residuals, describing the anisotropic component of the SWD. Because MP errors in the GPS phase observables can considerably impact SWD from individual satellites, we used an averaging technique to build station-specific MP correction maps by stacking the post-fit phase residuals acquired from a precise point positioning (PPP) processing strategy. The stacking was created by spatially organizing the residuals into congruent cells with an optimal resolution in terms of the elevation and azimuth at the local horizon. This enables approximately equal numbers of post-fit residuals to be distributed across each congruent cell. Finally, using these MP correction maps, the one-way SWD was improved for use in the weather event analysis. We found that the anisotropic component of the one-way SWD accounts for up to 20% of the overall SWD estimates. For a station that is strongly influenced by site-specific multipath error, the anisotropic component of SWD can reach up to 4.3 mm in equivalent precipitable water vapour. The result also showed that the spatio-temporal changes in the SWD as measured by GPS closely reflected the moisture field estimated from a numerical weather prediction model (ERA5 reanalysis) associated with this weather event. Mon, 20 Feb 2023 04:30:28 GMT http://hdl.handle.net/10993/54353 Title: Directional Statistics for Space Weather <br/> <br/>Author, co-author: Palmirotta, Guendalina Mon, 06 Feb 2023 10:00:41 GMT http://hdl.handle.net/10993/54351 Title: Machine Learning in Space Weather and how to handle it <br/> <br/>Author, co-author: Palmirotta, Guendalina <br/> <br/>Abstract: Machine leaning (ML), an imposing but not necessarily new method, is living today its golden age by achieving unforeseen results in numerous industrial applications. On the other side, Space Weather (SW), which describes changing environmental conditions in near-Earth space, is becoming more and more important to our society. But how can SW benefit from the ongoing ML revolution? In the last decade, many researchers, like E. Camporeale, showed that SW possesses all the ingredients often required for a successful ML application. Using this large and freely data set of in situ and remote observations collected over several decades of space missions, it is possible to forecast and nowcast solar activity and thus protect our increasing satellites constellations and us! In this talk, we will give a warm introduction to this field and point out a number of open challenges that we believe is worth to discuss and to undertake. Mon, 06 Feb 2023 07:51:46 GMT http://hdl.handle.net/10993/54333 Title: Breakthrough of directional statistics in space science <br/> <br/>Author, co-author: Palmirotta, Guendalina <br/> <br/>Abstract: It should be no surprise that already back in the 17-18th centuries important foundations of modern statistical theory were formulated to address astronomical problems, the astronomers were the statisticians. For instance the 'almost coincidence' in the orbits of the planets in our Solar System with the ecliptic has intrigued the scientists for a long time. Even D. Bernoulli (in the 1730's) wondered if this fact could happen 'by chance'. In a statistical framework, one could think of using a uniformity test on the sphere. Testing isotropy or, equivalently, testing uniformity on the unit hypersphere is one of the oldest as well as most fundamental problems in directional statistics and it is still much considered nowadays. Furthermore with the increasing astronomical data, innovative modern directional statistical theories and models have been proposed to deal with space science issues such as tracking space objects. In this talk, we will provide a review of the many old and recent developments of directional statistics animated by interesting applications in space science. This is a joint work with Christophe Ley. Fri, 03 Feb 2023 10:39:52 GMT http://hdl.handle.net/10993/52714 Title: Forschung in Geodäsie und Geoinformation an der Uni.lu <br/> <br/>Author, co-author: Teferle, Felix Norman <br/> <br/>Abstract: This is a summary of selected research carried out by the team GGE of the DoE in 2017-2022. Fri, 11 Nov 2022 08:14:38 GMT http://hdl.handle.net/10993/51037 Title: Lëtzebuerger Mathematikerin bei der Weltraumagence ESA <br/> <br/>Author, co-author: Palmirotta, Guendalina <br/> <br/>Abstract: Eng Lëtzebuerger Mathematikerin schafft zanter e puer Woche fir d'europäesch Weltraumagence zu Darmstadt. Déi jonk Fra entwéckelt Modeller fir d'Wieder am Weltall virauszesoen, fir esou d' Satellittesystemer viru Sonnestierm ze schützen. De Weltall passionéiert zanter, datt et d'Mënschheet gëtt. D’Dr. Guenda Palmirotta ass Mathematikerin a huet sech fréi fir dat interesséiert, wat ausserhalb vun der Äerd geschitt. Mam Job bei der Europäescher Weltraumagence geet en Dram an Erfëllung. Zu Darmstadt entwéckelt d'Lëtzebuergerin Modeller fir d’Weltraumwieder virauszesoen. Bestëmmt gëtt dëst vun der Sonn an de Sonnestierm, déi kennen entstoen, déi fir Satellittesystemer e Problem kënnen duerstellen. Ee vun den Ziler ass et, an den nächste Joren d’Previsioune méi präzis ze maachen, ma och méi wäit am viraus kënne viraussoen, wat geschitt. Konkret ginn d’Modeller elo schonn agesat, fir d’Astronauten op der Internationaler Weltraumstatioun ze schützen. Zu Darmstadt huet d'ESA een neien Iwwerwaachungszentral, wou nieft dem Weltraumwieder och aner Elementer vun der Weltraumsécherheet am A behale ginn. Esou zum Beispill de Weltraumschrott, mëttlerweil gëtt et vill Satellitten, déi net fonctionéieren a mat Aktive kéinte kollidéieren. Mat mathematesche Modeller sollen déi aktiv Satellitte gewarnt ginn a se esou hir Positioun fréizäiteg kënnen änneren. Mon, 16 May 2022 19:27:45 GMT http://hdl.handle.net/10993/50567 Title: An aspiring career in Space <br/> <br/>Author, co-author: Palmirotta, Guendalina Fri, 11 Mar 2022 16:34:53 GMT http://hdl.handle.net/10993/49270 Title: An improved accelerometer calibration model for gravity field estimates <br/> <br/>Author, co-author: Chen, Qiujie; Francis, Olivier; Shen, Yunzhong; Chen, Wu <br/> <br/>Abstract: During gravity field modelling, accelerometer measurements must be calibrated via scale and bias parameters. Klinger and Mayer-Gürr (2016) found that behaviors of both scales and biases are related to the thermal control service for the accelerometers. This finding indicates that the scales and biases may change significantly after April 2011 as the thermal control service has been switched off since then. To improve gravity field estimates, the time-related variations in either scales or biases should be better modelled. For the purpose of considering the time-dependent changes of scales and biases, we propose an improved accelerometer calibration model in this study, where the scales and biases are modelled by polynomials besides estimating the errors of attitude and accelerometer data. Detailed discussions on the selection of the optimal orders of polynomials for scales and biases, their time-dependent changes and the benefits from the improved accelerometer calibration model are given in this investigation. Compared to other accelerometer calibration models, the improved model has the comparable ability to calibrate the accelerometer measurements, while it achieves better conditioned normal equation and noticeable improvement in gravity field determination. <br/> <br/>Commentary: EGU General Assembly Conference Abstracts Wed, 05 Jan 2022 07:04:18 GMT http://hdl.handle.net/10993/49269 Title: How radar can be supported by gravimeters for estimating hail intensity <br/> <br/>Author, co-author: Van Camp, Michel; Delobbe, Laurent; Wilfert, Svenja; Watlet, Arnaud; Francis, Olivier; Delforge, Damien <br/> <br/>Commentary: EGU General Assembly Conference Abstracts Wed, 05 Jan 2022 06:51:07 GMT http://hdl.handle.net/10993/46697 Title: Towards global flood mapping onboard low cost satellites with machine learning <br/> <br/>Author, co-author: Mateo‑Garcia, Gonzalo; Veitch‑Michaelis, Joshua; Smith, Lewis; Oprea, Silviu; Schumann, Guy; Gal, Yarin; Baydin, Atılım Güneş; Backes, Dietmar <br/> <br/>Abstract: Spaceborne Earth observation is a key technology for flood response, offering valuable information to decision makers on the ground. Very large constellations of small, nano satellites— ’CubeSats’ are a promising solution to reduce revisit time in disaster areas from days to hours. However, data transmission to ground receivers is limited by constraints on power and bandwidth of CubeSats. Onboard processing offers a solution to decrease the amount of data to transmit by reducing large sensor images to smaller data products. The ESA’s recent PhiSat-1 mission aims to facilitate the demonstration of this concept, providing the hardware capability to perform onboard processing by including a power-constrained machine learning accelerator and the software to run custom applications. This work demonstrates a flood segmentation algorithm that produces flood masks to be transmitted instead of the raw images, while running efficiently on the accelerator aboard the PhiSat-1. Our models are trained on WorldFloods: a newly compiled dataset of 119 globally verified flooding events from disaster response organizations, which we make available in a common format. We test the system on independent locations, demonstrating that it produces fast and accurate segmentation masks on the hardware accelerator, acting as a proof of concept for this approach. Wed, 31 Mar 2021 20:03:51 GMT http://hdl.handle.net/10993/44612 Title: Can GNSS-R Detect Abrupt Water Level Changes? <br/> <br/>Author, co-author: Tabibi, Sajad; Francis, Olivier <br/> <br/>Abstract: Global navigation satellite system reflectometry (GNSS-R) uses signals of opportunity in a bi-static configuration of L-band microwave radar to retrieve environmental variables such as water level. The line-of-sight signal and its coherent surface reflection signal are not separate observables in geodetic GNSS-R. The temporally constructive and destructive oscillations in the recorded signal-to-noise ratio (SNR) observations can be used to retrieve water-surface levels at intermediate spatial scales that are proportional to the height of the GNSS antenna above the water surface. In this contribution, SNR observations are used to retrieve water levels at the Vianden Pumped Storage Plant (VPSP) in Luxembourg, where the water-surface level abruptly changes up to 17 m every 4-8 h to generate a peak current when the energy demand increases. The GNSS-R water level retrievals are corrected for the vertical velocity and acceleration of the water surface. The vertical velocity and acceleration corrections are important corrections that mitigate systematic errors in the estimated water level, especially for VPSP with such large water-surface changes. The root mean square error (RMSE) between the 10-min multi-GNSS water level time series and water level gauge records is 7.0 cm for a one-year period, with a 0.999 correlation coefficient. Our results demonstrate that GNSS-R can be used as a new complementary approach to study hurricanes or storm surges that cause abnormal rises of water levels. Wed, 04 Nov 2020 09:52:22 GMT http://hdl.handle.net/10993/43863 Title: Tidal analysis of GNSS reflectometry applied for coastal sea level sensing in Antarctica and Greenland <br/> <br/>Author, co-author: Tabibi, Sajad; Geremia-Nievinski, Felipe; Francis, Olivier; van Dam, Tonie <br/> <br/>Abstract: We retrieve sea levels in polar regions via GNSS reflectometry (GNSS-R), using signal-to-noise ratio (SNR) observations from eight POLENET GNSS stations. Although geodetic-quality antennas are designed to boost the direct reception from GNSS satellites and to suppress indirect reflections from natural surfaces, the latter can still be used to estimate the sea level in a stable terrestrial reference frame. Here, typical GNSS-R retrieval methodology is improved in two ways, 1) constraining phase-shifts to yield more precise reflector heights and 2) employing an extended dynamic filter to account for the second-order height rate of change (vertical acceleration). We validate retrievals over a 4-year period at Palmer Station (Antarctica), where there is a co-located tide gauge (TG). Because ice contaminates the long-period tidal constituents, we focus on the main tidal species (daily and subdaily), by employing a deseasonalization filter. The difference between sub-hourly GNSS-R retrievals of the ocean surface and TG records has a root-mean-square error (RMSE) of 15.4 cm and a correlation of 0.903, while the tidal prediction has a RMSE of 1.9 cm and a correlation of 0.998. There is excellent millimetric agreement between the two sensors for most eight major tidal constituents, with the exception of luni-solar diurnal (K1), principal solar (S2), and luni-solar semidiurnal (K2) components, which are biased in GNSS-R due to the leakage of the GPS orbital period. We also compare the GNSS-R tidal constituents from seven additional POLENET sites, without co-located TG, to global and local ocean tide models. We find that the root-sum-square-error (RSSE) of eight major constituents varies between 26.0 cm and 56.9 cm for different models. Given that the agreement in tidal constituents between the TG and GNSS-R was better at Palmer Station, we conclude that assimilating the GNSS-R retrievals into tidal models would improve their accuracy in Antarctica and Greenland, provided that care is exercised to avoid the orbital period overtones and also sea ice. Fri, 17 Jul 2020 08:00:27 GMT http://hdl.handle.net/10993/41893 Title: Scratch testing for micro- and nanoscale evaluation of tribocharging in DLC films containing silver nanoparticles using AFM and KPFM techniques <br/> <br/>Author, co-author: Vieira, L.; Lucas, Francis; Fisssmer, S. F.; dos Santos, L. C. D.; Massi, M.; Leite, P. M. S. C. M.; Costa, C. A. R.; Martin Lanzoni, Evandro; Pessoa, R. S.; Maciel, H. S. <br/> <br/>Abstract: Scratch testing is a fast and effective method for the measurement of critical loads in order to determine the adhesion properties of coatings and their behavior in tribological applications. Kelvin probe force microscopy (KPFM) provides a means of monitoring electrostatic charging on the surfaces of materials. In this paper, we describe the use of a combination of scratch testing and KPFM analysis to evaluate the electrostatic effect induced by silver nanoparticles incorporated as clusters in diamond-like carbon (DLC) films, as well as its correlation with the rubbing process. KPFM was used for mapping of the potentials on the surfaces of DLC–Ag films subjected to nanoscale scratching. The procedure was also conducted at the microscale in order to analyze the way in which silver nanoparticles were spread in the track. After scratching, the track was analyzed using backscattered electrons (BSE) and energy dispersive X-ray diffraction (EDX). The BSE images highlighted bright domains of metallic nanoparticles dispersed in the amorphous coating and EDX confirmed the presence of silver nanoparticles in the scratched track. Micro Raman spectroscopy was used to check the DLC signature. The electric potentials of DLC films with and without silver nanoparticles were also analyzed. The results indicated that the incorporation of silver nanoparticles in amorphous materials could offer new option for electrostatic energy storage on the surfaces of materials. <br/> <br/>Commentary: The 41st International Conference on Metallurgical Coatings and Thin Films Wed, 22 Jan 2020 09:52:51 GMT http://hdl.handle.net/10993/41859 Title: Conventional EO Satellites vs. CubeSats; FDL - AI flood detection onboard a Nano Satellite <br/> <br/>Author, co-author: Backes, Dietmar; Schumann, Guy; Teferle, Felix Norman Tue, 21 Jan 2020 17:26:14 GMT http://hdl.handle.net/10993/40339 Title: A comparison between conventional Earth Observation Satellites and CubeSats; Requirements, Capabilities and Data Quality <br/> <br/>Author, co-author: Backes, Dietmar; Hassani, Saif Alislam; Teferle, Felix Norman; Schumann, Guy <br/> <br/>Abstract: From its early beginning as an educational tool in 1999, cubesats have evolved into a popular platform for technology demonstrations and scientific instruments. Ideas and innovations sparked from an enthusiastic community led to the development of new Earth Observation (EO) technology concepts based on large constellations of satellites with high-resolution optical imagers previously considered as infeasible. Probably the most significant constellation today is deployed by Planet who are currently operating a fleet larger than 120 3U Dove satellites, which provide an imaging service with up to 3m Ground Sample Distance (GSD). The number of low-cost EO Cubesat systems is constantly increasing. However, for a number of reasons there still seems to be a reluctance to use such data for many EO applications. A better understanding of the capabilities of the current generation of small Cubesats compared to the traditional well-established bigger operational missions of high and medium resolution EO satellites is required. What are the critical capabilities and quality indicators? Due to the limited size and weight of Cubesats, critical system components, e.g. for navigation and communication, always compete with operational payloads such as optical camera/sensor systems. A functional EO system requires balanced payload, which provides adequate navigational capabilities, that match the requirements of the optical imagers (camera) deployed with the system. This study reviews the current performance and capabilities of Cubesats for optical EO and compares them to the capabilities of conventional, dedicated high and medium resolution EO systems. We summarise key performance parameters and quality indicators to evaluate the difference between the systems. An empirical study compares recent very high-resolution (VHR) imagery from big EO satellite missions with available images from Cubesats for the use case in disaster monitoring. Small and agile Nanosatellites or Cubesats already show remarkable performance. Although it is not expected that their performance and capability will match those of current bigger EO satellite missions, they are expected to provide a valuable tool for EO and remote sensing, in particular for downstream industry applications. Thu, 12 Sep 2019 16:15:44 GMT http://hdl.handle.net/10993/39859 Title: Recent Advances on GNSS Multipath Reflectometry (GNSS-MR) for Sea and Lake Level Studies <br/> <br/>Author, co-author: van Dam, Tonie; Tabibi, Sajad; Geremia-Nievinski, F.; Francis, Olivier <br/> <br/>Abstract: Global navigation satellite system multipath reflectometry (GNSS-MR) has been used to exploit signals of opportunity at L-band for ground-based sea and lake level studies at several locations in the last few years. Although geodetic-quality antennas are designed to boost the direct transmission from the satellite and to suppress indirect surface reflections, the delay of reflections with respect to the line-of-sight propagation can be used to estimate the water-surface level in a stable terrestrial reference frame. In this contribution, signal-to-noise ratio (SNR) observations from commercial off-the-shelf systems are used to retrieve water level at multiple constellations and modulations. We constrained phase-shifts so as yield more precise reflector heights and further corrected for the tropospheric propagation delays for greater accuracy. We assess GNSS-MR accuracy and precision in two cases. In the first one, using the inversion formal uncertainty and modulation-specific variance factors, reflector heights are combined and converted to water level at hourly epoch spacing and eight-hourly averaging window length. The RMSE between GNSS-MR and tide gauge (TG) records for a single station in the Great Lakes is 1.93 cm for a 12-year period. In the second case, we employ an extended dynamic model, taking tidal velocity and acceleration into account, which is applied for ten stations worldwide. Regression slope between GNSS-MR and TG exhibits a smaller deviation from the ideal 1:1 relationship, compared to the conventional dynamic model (with no acceleration). The RMSE between sub-hourly GNSS-MR and TG is 1.98 cm, with 0.998 correlation coefficient. Tidal constituents agree at the sub-mm level between GNSS-MR and TG. Mon, 08 Jul 2019 11:41:32 GMT