341 research outputs found

    A geostationary orbit microwave multi-channel radiometer

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    The geostationary orbit microwave multi-channel radiometer has the advantages of high real-time performance and large coverage, which plays an important role in typhoon, strong precipitation detection, and medium-to-short-term meteorological/oceanic forecasting. However, due to the difficulty in engineering development of the payload, its application on-orbit has not yet been achieved at present. To satisfy the requirements of fine and quantitative application of satellite observation data, a geostationary orbit microwave multi-channel radiometer with a 10-m-caliber is developed, in which the spatial resolution at horizontal polarization is better than 24 km at 54 GHz. In geostationary orbit microwave multi-channel radiometer, a quasi-optical feed network covering nearly 28 frequency octave bands and ranging from 23.8 to 664 GHz is proposed to solve the technical problem of multi-frequency sharing in the system. Meanwhile, a high-precision reflector preparation method and a high-precision unfolding scheme are proposed, which are considered as a solution for the large-diameter reflector with a high maintaining surface accuracy. A high-precision antenna prototype with 0.54-m is developed, and the tests are performed to verify the key technologies, such as the preparation of high-precision grating reflectors at the micron level, high surface accuracy detection, and sub-millimeter wave antenna electrical performance testing. The results indicate that measured main beam efficiency of the 664 GHz antenna is better than 95.5%. In addition, the system sensitivity is greater than 1.5 K, and the calibration accuracy is better than 1.8 K, according to the results of an analysis of the multi-channel radiometer’s essential parameters and calibration errors

    TriHex: combining formation flying, general circular orbits and alias-free imaging, for high resolution L-band aperture synthesis

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    The Soil Moisture and Ocean Salinity (SMOS) mission of the European Space Agency (ESA), together with NASA’s Soil Moisture Active Passive (SMAP) mission, is providing a wealth of information to the user community for a wide range of applications. Although both missions are still operational, they have significantly exceeded their design life time. For this reason, ESA is looking at future mission concepts, which would adequately address the requirements of the passive L-band community beyond SMOS and SMAP. This article proposes one mission concept, TriHex, which has been found capable of achieving high spatial resolution, radiometric resolution, and accuracy, approaching the user needs. This is possible by the combination of aperture synthesis, formation flying, the use of general circular orbits, and alias-free imaging.Peer ReviewedPostprint (author's final draft

    Roadmap on Label-Free Super-resolution Imaging

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    Label-free super-resolution (LFSR) imaging relies on light-scattering processes in nanoscale objects without a need for fluorescent (FL) staining required in super-resolved FL microscopy. The objectives of this Roadmap are to present a comprehensive vision of the developments, the state-of-the-art in this field, and to discuss the resolution boundaries and hurdles that need to be overcome to break the classical diffraction limit of the label-free imaging. The scope of this Roadmap spans from the advanced interference detection techniques, where the diffraction-limited lateral resolution is combined with unsurpassed axial and temporal resolution, to techniques with true lateral super-resolution capability that are based on understanding resolution as an information science problem, on using novel structured illumination, near-field scanning, and nonlinear optics approaches, and on designing superlenses based on nanoplasmonics, metamaterials, transformation optics, and microsphere-assisted approaches. To this end, this Roadmap brings under the same umbrella researchers from the physics and biomedical optics communities in which such studies have often been developing separately. The ultimate intent of this paper is to create a vision for the current and future developments of LFSR imaging based on its physical mechanisms and to create a great opening for the series of articles in this field.Peer reviewe

    Advanced VLBI Imaging

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    Very Long Baseline Interferometry (VLBI) is an observational technique developed in astronomy for combining multiple radio telescopes into a single virtual instrument with an effective aperture reaching up to many thousand kilometers and enabling measurements at highest angular resolutions. The celebrated examples of applying VLBI to astrophysical studies include detailed, high-resolution images of the innermost parts of relativistic outflows (jets) in active galactic nuclei (AGN) and recent pioneering observations of the shadows of supermassive black holes (SMBH) in the center of our Galaxy and in the galaxy M87. Despite these and many other proven successes of VLBI, analysis and imaging of VLBI data still remain difficult, owing in part to the fact that VLBI imaging inherently constitutes an ill-posed inverse problem. Historically, this problem has been addressed in radio interferometry by the CLEAN algorithm, a matching-pursuit inverse modeling method developed in the early 1970-s and since then established as a de-facto standard approach for imaging VLBI data. In recent years, the constantly increasing demand for improving quality and fidelity of interferometric image reconstruction has resulted in several attempts to employ new approaches, such as forward modeling and Bayesian estimation, for application to VLBI imaging. While the current state-of-the-art forward modeling and Bayesian techniques may outperform CLEAN in terms of accuracy, resolution, robustness, and adaptability, they also tend to require more complex structure and longer computation times, and rely on extensive finetuning of a larger number of non-trivial hyperparameters. This leaves an ample room for further searches for potentially more effective imaging approaches and provides the main motivation for this dissertation and its particular focusing on the need to unify algorithmic frameworks and to study VLBI imaging from the perspective of inverse problems in general. In pursuit of this goal, and based on an extensive qualitative comparison of the existing methods, this dissertation comprises the development, testing, and first implementations of two novel concepts for improved interferometric image reconstruction. The concepts combine the known benefits of current forward modeling techniques, develop more automatic and less supervised algorithms for image reconstruction, and realize them within two different frameworks. The first framework unites multiscale imaging algorithms in the spirit of compressive sensing with a dictionary adapted to the uv-coverage and its defects (DoG-HiT, DoB-CLEAN). We extend this approach to dynamical imaging and polarimetric imaging. The core components of this framework are realized in a multidisciplinary and multipurpose software MrBeam, developed as part of this dissertation. The second framework employs a multiobjective genetic evolutionary algorithm (MOEA/D) for the purpose of achieving fully unsupervised image reconstruction and hyperparameter optimization. These new methods are shown to outperform the existing methods in various metrics such as angular resolution, structural sensitivity, and degree of supervision. We demonstrate the great potential of these new techniques with selected applications to frontline VLBI observations of AGN jets and SMBH. In addition to improving the quality and robustness of image reconstruction, DoG-HiT, DoB-CLEAN and MOEA/D also provide such novel capabilities as dynamic reconstruction of polarimetric images on minute time-scales, or near-real time and unsupervised data analysis (useful in particular for application to large imaging surveys). The techniques and software developed in this dissertation are of interest for a wider range of inverse problems as well. This includes such versatile fields such as Ly-alpha tomography (where we improve estimates of the thermal state of the intergalactic medium), the cosmographic search for dark matter (where we improve forecasted bounds on ultralight dilatons), medical imaging, and solar spectroscopy

    Land Use and Land Cover Mapping in a Changing World

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    It is increasingly being recognized that land use and land cover changes driven by anthropogenic pressures are impacting terrestrial and aquatic ecosystems and their services, human society, and human livelihoods and well-being. This Special Issue contains 12 original papers covering various issues related to land use and land use changes in various parts of the world (see references), with the purpose of providing a forum to exchange ideas and progress in related areas. Research topics include land use targets, dynamic modelling and mapping using satellite images, pressures from energy production, deforestation, impacts on ecosystem services, aboveground biomass evaluation, and investigations on libraries of legends and classification systems

    Geologic controls on fluid flow and seismic imaging of faults in carbonate rocks : Insights from quantitative outcrop analysis and reflection seismic modeling

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    Utforsking av undergrunnen har historisk sett hovudsakleg vore drive av økonomiske insentiv gjennom leiting etter hydrokarbon og andre geologiske ressursar. I nyare tid, derimot, har geologiens rolle i det grøne skiftet fått aukande fokus. Undergrunnen er svært viktig for blant anna CO2- og hydrogenlagring, grunnvassressursar og geotermisk energi, og avgjerande for alle disse bruksområda er strukturar som forkastingar og sprekkenettverk, og deira kontroll på væskestraum i undergrunnen. Hovudfokuset i denne avhandlinga er å forbetre forståinga av undergrunnen gjennom to overordna tema; (i) kontrollen forkastings- og sprekkenettverk har på væskestraum og reaksjonar mellom væsker og bergartar, og (ii) seismisk avbilding av slike forkastingar og deira væske-bergart reaksjonsprodukt i undergrunnen. Sjølv om det er generell einigheit i at geologiske strukturer utøver sterk kontroll på væskestraum, har få forsøkt å kvantifisere dette forholdet. I samsvar med tema (i) ovanfor byrjar denne avhandlinga difor med å kvantifisere og visualisere forholdet mellom væskestraum og strukturell kompleksitet (Artikkel 1). Ved hjelp av sementerte haugar med lav porøsitet som bevis for paleo-væskestraum, nyttast topologi for å karakterisere og visualisere strukturell kompleksitet i lokaliserte område, og kvantitativt dokumentere deira korrelasjon med områder for lokalisert paleo-væskestraum. Artikkel 2 gir ei oversikt over geologiske kontrollar på væskestraum i sedimentære bergartar, basert på ein kombinasjon av litteraturanalyse og studie av eksempel frå felt der jernoksidutfelling blir brukt som bevis for paleo-væskestraum. Artikkelen dokumenterer eit vidt spenn av kontrollar på væskestraum og inkluderer alt frå enkle geologiske heterogeniteter til meir komplekse nettverk av strukturar, og dokumenterer og kvantifiserer topologien til både sprekkenettverk og hybridnettverk beståande av ein kombinasjon av sprekker og sedimentære avsetningsstrukturar som fungerer som leiarar for væskestraum. Eit viktig verktøy for kartlegging av slike væskeleiande strukturar i undergrunnen er seismiske refleksjonsdata. I tråd med Tema (ii), undersøkjer Artikkel 3 effekten av småskala forkastingar (nær eller under seismisk oppløysing) på seismiske bilde ved hjelp av seismisk modellering. Hovudmålet i denne artikkelen er å dokumentere effekten som forkastingar under- eller på grensa til seismisk oppløysing kan ha på seismiske data. For eksempel illustrerer artikkelen korleis subtile forandringar i ein refleksjon kan vere resultat av små forkastingar i undergrunnen, noko som er viktig ny innsikt og som mogleg kan bidra til å forbetre tolking av strukturar i seismikk. I tillegg til avbilding av forkastingar i seg sjølv, er også produkta av væske-bergart interaksjon av interesse, og det er derfor viktig å også forstå deira seismiske signatur. Ved hjelp av seismisk modellering av forkastingskontrollerte dolomittar i ei kalksteinsdominert sone i Suezbukta, blir seismisk avbilding av både massive og stratigrafisk kontrollerte dolomittkroppar undersøkt med varierande geologiske og geofysiske parametrar i Artikkel 4. Resultata i denne artikkelen gir ny innsikt i korleis forkastingskontrollerte hydrotermale dolomittkroppar blir avbilda i seismiske data; artikkelen dokumenterer at dei generelle trendane og nærværet av dolomitt i undergrunnen er mogleg å slutte frå seismiske data, men identifisering av individuelle, stratigrafisk kontrollerte dolomittkroppar er ikkje stadfesta mogleg. Funna frå denne avhandlinga fremjar den grunnleggande forståinga av sentrale geologiske kontrollar på væskestraum i undergrunnen, og avbilding av potensielt strøymingskontrollerande forkastingar og deira bergreaktive produkt i refleksjonsseismiske data. Den nye innsikta presentert i avhandlinga har eit breitt spekter av implikasjonar og nytteområde, for eksempel for lokalisering av økonomisk betydelege førekomstar av nyttige mineral, i risikovurdering for CO2- og hydrogenlagring, grunnvasshandtering, lokalisering av forureining, og meir.Exploration of the sub-surface has historically largely been driven by economic incentives through potential hydrocarbon recovery, but more recently the role of subsurface geology in the green shift has gained more focus. The subsurface are highly important for CO2- and hydrogen storage, freshwater resources, and geothermal energy to name a few, and crucial for all these are structures such as faults and their conjugate damage zones, veins, joints, and deformation bands, as well as the depositional architecture of the host rock. This thesis aim to improve our understanding of the sub-surface through two overarching themes, (i) fault and fracture networks and their controls on fluid flow and fluid-rock interaction, and (ii) the seismic imaging of such faults and their fluid-rock reactive products in the subsurface. Despite the consensus that structures exert strong control on fluid flow, few have attempted to quantify this relationship. In accordance with theme (i) above, this thesis therefore starts by quantifying and visualizing the relationship between fluid flow and structural complexity; using low-porosity cemented mounds as a record of paleo-fluid flow and topological characterization, zones of past fluid flow and areas of structural complexity are correlated and documented. Further, an overview of controls on fluid flow is given through literature review and documentation of outcrops using iron oxide precipitates as proxy for paleo-fluid flow; the fluid flow controls are ranging from simple geological heterogeneities to more complex networks of structures, and through topological characterization, the connectivity of fracture networks and hybrid networks are documented. The structures controlling flow can be found at all scales, but as the most commonly used tool for subsurface investigation is seismic imaging many of these will fall below seismic resolution. Following theme (ii), we investigate the effect of sub-seismic faults on seismic imaging using synthetic seismic from outcrop analogues and prove that under the right conditions, faults with throw as low as 5 m still produce distortion of reflections. But not only fault and fractures but also the products of fluid-rock interaction are of interest to explore in the subsurface, and hence it is important to understand their seismic signature. Using seismic modelling of fault-controlled dolomites in a limestone-dominated succession in the Golf of Suez it is found that the presence of both stratabound and massive dolomite bodies can be inferred, although only the massive dolomite can be distinguished individually. The findings form this thesis have implications for the fundamental understanding of how fluids are controlled in the subsurface, and present examples of how these controls might be imaged in reflection seismic data. This is in turn critical for a variety of processes and areas such as locating economically significant ore deposits, hydrocarbon seal risk assessment, prediction of earthquakes, groundwater management, and more. Due to the vast number of processes that are controlled by sub-surface fluid flow it is of both environmental, societal, and economic interest to be able to predict and understand fluid flow pathways, how they interact to form networks, and how they and their fluid-rock interactive products might be portrayed in reflection seismic data.Doktorgradsavhandlin

    The Development and Performance of the First BICEP Array Receiver at 30 and 40 GHz for Measuring the Polarized Synchrotron Foreground

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    The existence of the CMB marks a big success of the lambda cold dark matter standard model, which describes the universe’s evolution with six free parameters. The inflationary theory was added to the picture in the ’80s to explain the initial conditions of the universe. Scalar perturbations from inflation seeded the formation of the large-scale structure and produced the curl-free E-mode polarization pattern in the CMB. On the other hand, tensor fluctuations sourced primordial gravitational waves (PGW), which could leave unique imprints in the CMB polarization: the gradient-free B-mode pattern. The amplitude of B modes is directly related to the tensor-to-scalar ratio r of the primordial fluctuations, which indicates the energy scale of inflation. The detection of the primordial B modes will be strong supporting evidence of inflation and give us opportunities to study physics at energy scales far beyond what can ever be accessed in laboratory experiments on the Earth. Currently, the main challenge for the B-mode experiments is to separate the primordial B modes from those sourced by matter between us and the last scattering surface: the galactic foregrounds and the gravitational lensing effect. The two most important foregrounds are thermal dust and synchrotron, which have very different spectral properties from the CMB. Thus the key to foreground cleaning is the high sensitivity data at multiple frequency bands and the accurate modeling of the foregrounds in data analyses and simulations. In this dissertation, I present my work on ISM and dust property studies which enriched our understanding of the foregrounds. The BICEP/Keck (BK) experiments build a series of polarization-sensitive microwave telescopes targeting degree-scale B-modes from the early universe. The latest publication from the collaboration with data taken through 2018 reported tensor-to-scalar ratio r0.05 &#60; 0.036 at 95% C.L., providing the tightest constraint on the primordial tensor mode. BICEP Array is the latest generation of the series experiments. The final configuration of the BICEP Array has four BICEP3-class receivers spanning six frequency bands, aiming to achieve σ(r) ≾ 0.003. The first receiver of the BICEP Array is at 30 and 40 GHz, constraining the synchrotron foregrounds. In this dissertation, I cover the development of this new receiver focusing on the design and performance of the detectors. I report on the characterizing and diagnosing tests for the receiver during its first few observing seasons.</p

    ATHENA Research Book, Volume 2

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    ATHENA European University is an association of nine higher education institutions with the mission of promoting excellence in research and innovation by enabling international cooperation. The acronym ATHENA stands for Association of Advanced Technologies in Higher Education. Partner institutions are from France, Germany, Greece, Italy, Lithuania, Portugal and Slovenia: University of Orléans, University of Siegen, Hellenic Mediterranean University, Niccolò Cusano University, Vilnius Gediminas Technical University, Polytechnic Institute of Porto and University of Maribor. In 2022, two institutions joined the alliance: the Maria Curie-Skłodowska University from Poland and the University of Vigo from Spain. Also in 2022, an institution from Austria joined the alliance as an associate member: Carinthia University of Applied Sciences. This research book presents a selection of the research activities of ATHENA University's partners. It contains an overview of the research activities of individual members, a selection of the most important bibliographic works of members, peer-reviewed student theses, a descriptive list of ATHENA lectures and reports from individual working sections of the ATHENA project. The ATHENA Research Book provides a platform that encourages collaborative and interdisciplinary research projects by advanced and early career researchers

    Classification and alignment of DRAGNs

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    The study of Active Galactic Nuclei formation and evolution is important in modern astronomy, as they represent an evolutionary stage in every galaxy, and thus are important to understand the formation and evolution of galaxies. However, there is not yet a full understanding of the physics and evolution of the population that emit brightly at radio wavelengths. In order to properly compare observations with theory, a large survey of radio-loud galaxies is required. In this project, I will be studying Double Radio sources Associated with Galactic Nuclei, as I wanted to learn more about them. I will be focusing on the Fanaroff-Riley types I and II in particular. I study their luminosities and find a large overlap between the two classes, moreso than previous studies, with no obvious ‘break’. I also study their alignment in the sky, and find significant alignment up to 4 degrees. This is to test claims that the position angles of radio galaxies are aligned over cosmic distances. Such an alignment could only have arisen at the time of formation which would perhaps be able to provide some insight into early formation of supermassive black holes. I will be using data from the Evolutionary Map of the Universe pilot survey that was obtained with CSIRO’s Australian Square Kilometre Array Pathfinder, as well as GAMA-23 Early Science. A survey of this size will allow study of a large sample of sources that are free from selection effects and biases of previous and older studies and will be a valuable training set for my colleagues who are developing machine learning algorithms to find and classify radio sources

    Land Use and Land Cover Mapping in a Changing World

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    It is increasingly being recognized that land use and land cover changes driven by anthropogenic pressures are impacting terrestrial and aquatic ecosystems and their services, human society, and human livelihoods and well-being. This Special Issue contains 12 original papers covering various issues related to land use and land use changes in various parts of the world (see references), with the purpose of providing a forum to exchange ideas and progress in related areas. Research topics include land use targets, dynamic modelling and mapping using satellite images, pressures from energy production, deforestation, impacts on ecosystem services, aboveground biomass evaluation, and investigations on libraries of legends and classification systems
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