Endre søk
Begrens søket
3456789 251 - 300 of 449
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Treff pr side
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
Merk
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 251.
    Kuhn, Thomas
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Grishin, Igor
    Department of Earth and Environmental Sciences, University of Waterloo.
    Sloan, James J.
    Department of Earth and Environmental Sciences, University of Waterloo.
    Improved imaging and image analysis system for application to measurement of small ice crystals2012Inngår i: Journal of Atmospheric and Oceanic Technology, ISSN 0739-0572, E-ISSN 1520-0426, Vol. 29, nr 12, s. 1811-1824Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Accurate knowledge of ice particle size and shape distribution is required for understanding of atmospheric microphysical processes. While larger ice particles are easily measured with a variety of sensors, the measurement of small ice particles with sizes down to a few micrometers remains challenging. Here the authors report the development of a system that measures the size and shape of small ice particles using a novel combination of high-resolution imaging and high-speed automated image classification. The optical system has a pixel resolution of 0.2 μm and a resolving power of approximately 1 μm. This imaging instrument is integrated into a cryogenic flow tube that allows precise control of experimental conditions.This study also describes an automated method for the high-speed analysis of high-resolution particle images. Each particle is located in the image using a Sobel edge detector, the border is vectorized, and a polygon representing the border is found. The vertices of this polygon are expressed in complex coordinates, and an analytic implementation of Fourier shape descriptors is used for piecewise integration along the edges of the polygon.The authors demonstrate the capabilities of this system in a study of the early-stage growth of ice particles, which are grown for approximately 1 min at fixed temperature and saturated water vapor concentrations in the cryogenic flowtube. Ice particle shapes and size distributions are reported and compared with habit diagrams found in the literature. The capability of the shape recognition system is verified by comparison with manual classification.

  • 252.
    Kuhn, Thomas
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Gultepe, Ismail
    Cloud Physics and Severe Weather Research Section, Environment Canada.
    Ice Fog and Light Snow Measurements Using a High-Resolution Camera System2016Inngår i: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136, Vol. 173, nr 9, s. 3049-3064Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ice fog, diamond dust, and light snow usually form over extremely cold weather conditions, and they affect both visibility and Earth’s radiative energy budget. Prediction of these hydrometeors using models is difficult because of limited knowledge of the microphysical properties at the small size ranges due to measurement issues. These phenomena need to be better represented in forecast and climate models; therefore, in addition to remote sensing accurate measurements using ground-based instrumentation are required. An imaging instrument, aimed at measuring ice fog and light snow particles, has been built and is presented here. The ice crystal imaging (ICI) probe samples ice particles into a vertical, tapered inlet with an inlet flow rate of 11 L min−1. A laser beam across the vertical air flow containing the ice crystals allows for their detection by a photodetector collecting the scattered light. Detected particles are then imaged with high optical resolution. An illuminating LED flash and image capturing are triggered by the photodetector. In this work, ICI measurements collected during the fog remote sensing and modeling (FRAM) project, which took place during Winter of 2010–2011 in Yellowknife, NWT, Canada, are summarized and challenges related to measuring small ice particles are described. The majority of ice particles during the 2-month-long campaign had sizes between 300 and 800 μm. During ice fog events the size distribution measured had a lower mode diameter of 300 μm compared to the overall campaign average with mode at 500 μm.

  • 253.
    Kuhn, Thomas
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Heymsfield, Andrew J.
    National Center for Atmospheric Research, Boulder, Colorado.
    In Situ Balloon-Borne Ice Particle Imaging in High-Latitude Cirrus2016Inngår i: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136, Vol. 173, nr 9, s. 3065-3084Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cirrus clouds reflect incoming solar radiation, creating a cooling effect. At the same time, these clouds absorb the infrared radiation from the Earth, creating a greenhouse effect. The net effect, crucial for radiative transfer, depends on the cirrus microphysical properties, such as particle size distributions and particle shapes. Knowledge of these cloud properties is also needed for calibrating and validating passive and active remote sensors. Ice particles of sizes below 100 µm are inherently difficult to measure with aircraft-mounted probes due to issues with resolution, sizing, and size-dependent sampling volume. Furthermore, artefacts are produced by shattering of particles on the leading surfaces of the aircraft probes when particles several hundred microns or larger are present. Here, we report on a series of balloon-borne in situ measurements that were carried out at a high-latitude location, Kiruna in northern Sweden (68N 21E). The method used here avoids these issues experienced with the aircraft probes. Furthermore, with a balloon-borne instrument, data are collected as vertical profiles, more useful for calibrating or evaluating remote sensing measurements than data collected along horizontal traverses. Particles are collected on an oil-coated film at a sampling speed given directly by the ascending rate of the balloon, 4 m s−1. The collecting film is advanced uniformly inside the instrument so that an always unused section of the film is exposed to ice particles, which are measured by imaging shortly after sampling. The high optical resolution of about 4 µm together with a pixel resolution of 1.65 µm allows particle detection at sizes of 10 µm and larger. For particles that are 20 µm (12 pixel) in size or larger, the shape can be recognized. The sampling volume, 130 cm3 s−1, is well defined and independent of particle size. With the encountered number concentrations of between 4 and 400 L−1, this required about 90- to 4-s sampling times to determine particle size distributions of cloud layers. Depending on how ice particles vary through the cloud, several layers per cloud with relatively uniform properties have been analysed. Preliminary results of the balloon campaign, targeting upper tropospheric, cold cirrus clouds, are presented here. Ice particles in these clouds were predominantly very small, with a median size of measured particles of around 50 µm and about 80 % of all particles below 100 µm in size. The properties of the particle size distributions at temperatures between −36 and −67 °C have been studied, as well as particle areas, extinction coefficients, and their shapes (area ratios). Gamma and log-normal distribution functions could be fitted to all measured particle size distributions achieving very good correlation with coefficients R of up to 0.95. Each distribution features one distinct mode. With decreasing temperature, the mode diameter decreases exponentially, whereas the total number concentration increases by two orders of magnitude with decreasing temperature in the same range. The high concentrations at cold temperatures also caused larger extinction coefficients, directly determined from cross-sectional areas of single ice particles, than at warmer temperatures. The mass of particles has been estimated from area and size. Ice water content (IWC) and effective diameters are then determined from the data. IWC did vary only between 1 × 10−3 and 5 × 10−3 g m−3 at temperatures below −40 °C and did not show a clear temperature trend. These measurements are part of an ongoing study.

  • 254.
    Kuhn, Thomas
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Heymsfield, Andrew J.
    NCAR, Boulder, Colorado.
    Vertical distributions of small cirrus cloud particles from balloon-borne in-situ measurements: Oral presentation2014Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Thin and cold ice clouds are important for the radiative budget, yet they are difficult to measure. They are often high in the troposphere where they reflect incoming sunlight, creating a cooling effect. At the same time these clouds absorb longwave radiation from Earth, creating a greenhouse effect. Knowledge of the net effect is crucial and depends on the microphysical properties of the clouds, which at these altitudes and temperatures are often composed of small particles of 100 μm or less in size. Most of in-situ data reported in the literature have been sampled with aircraft probes, which have known issues with such small particles due to sizing and shattering prob- lems, in addition to having also a small and size-dependent sampling volume for these particles.A series of balloon-borne in-situ measurements, currently being carried out from a high-latitude location in north- ern Sweden (Kiruna, 68N 21E), combined with previous balloon-borne measurements from other locations, are used to study properties of small cloud ice particles at a variety of temperatures and altitudes. Among other prop- erties, size distributions and concentrations are analysed as a function of height within the cloud layer. Results are compared to literature data from aircraft probes to shed more light on the uncertainties related to the difficulties of these probes in measuring small particles.

  • 255.
    Kuhn, Thomas
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Heymsfield, Andrew J.
    National Center for Atmospheric Research, Boulder, Colorado.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Balloon-Borne Measurements of Ice Particle Shape and Ice Water Content in the Upper Troposphere over Northern Sweden2013Inngår i: 21st ESA Symposium: ESA Symposium on European Rocket and Balloon Programmes and Related Research 2013, 9–13 June 2013, Noordwijk: European Space Agency, ESA , 2013, s. 93-97Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Ice clouds play an important role in the energy budget of the atmosphere. They are at high altitudes, absorb long-wave radiation from below and, as they are cold, emit little infrared radiation. This greenhouse effect warms the Earth-atmosphere system. On the other hand, ice clouds have a cooling effect by reflecting incoming solar short wave radiation. The net effect is crucial for the atmosphere, but will depend highly on the cloud’s horizontal extent, vertical position, ice water content (IWC), and ice particle microphysical properties such as size and shape. Targeting these upper-tropospheric, cold ice clouds, a series of in-situ balloon-borne experiments has been started at Kiruna, Sweden, which is located at 68°N. Fewer mea- surements exist at these high latitudes compared to mid- or tropical latitudes. Also temperatures in the upper troposphere can be around -60 °C, a temperature range under-represented in available in-situ data. Experiments are launched from Esrange Space Center. Ice particles are collected with a balloon-borne replicator and also imaged in-situ, and measurements are complemented by a radiosonde added to the instrument. Particle shape and size as well as IWC are determined from the replicas and images. The data are analysed to reveal relationships between IWC and other measurements such as temperature and volume extinction coefficient. Such relationships can be used for validation and improvement of satellite retrievals of IWC from, for example, thin cirrus measurements with satellite-borne lidar, such as on the future EarthCARE mission.

  • 256.
    Kuhn, Thomas
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Heymsfield, Andrew J.
    National Center for Atmospheric Research, Boulder, Colorado.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    In-situ ice particle measurements over northern Sweden2012Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    ce clouds play an important role in the energy budget of the atmosphere. They are at high altitudes, absorb longwave radiation from below and, as they are cold, emit little infrared radiation. This greenhouse effect warms the Earth-atmosphere system. On the other hand, ice clouds have a cooling effect by reflecting incoming solar short wave radiation. The net effect is crucial for the atmosphere, but will depend highly on the cloud’s horizontal extent, vertical position, ice water content (IWC), and ice particle microphysical properties such as size and shape. A series of in-situ balloon measurements has been started at Kiruna, Sweden, which is located at 68°N. Fewer in- situ ice cloud measurements exist at these high latitudes compared to mid- or tropical latitudes. Also temperatures in the upper troposphere can be around -60 °C, a temperature range under-represented in available in-situ data. Ice particles are collected with a balloon-borne replicator launched from Esrange Space Center (near Kiruna, Sweden). Measurements are complemented by a radiosonde added to the instrument. The shape and size as well as IWC are determined from the replicas. The data are analyzed to reveal relationships between IWC and other measurements such as temperature and volume extinction coefficient. Such relationships can be used for validation and improvement of satellite retrievals of IWC from, for example, thin cirrus measurements with satellite-borne lidar.

  • 257.
    Kuhn, Thomas
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Wolf, Veronika
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Völger, Peter
    The Swedish Institute of Space Physics (IRF).
    Stanev, Marin
    Stockholm University, Department of Meteorology (MISU).
    Gumbel, Jörg
    Stockholm University, Department of Meteorology (MISU).
    Comparison of In-Situ Balloon-Borne and Lidar Measurement of Cirrus Clouds2017Inngår i: Proceedings of the 23rd ESA Symposium on European Rocket and Balloon Programmes and Related Research, Noordwijk, The Netherlands, 2017, artikkel-id A-091kuhnKonferansepaper (Annet vitenskapelig)
    Abstract [en]

    A series of in-situ balloon-borne experiments con- ducted at Kiruna, Sweden (68°N), is studying upper- tropospheric, cold ice clouds in arctic latitudes. Ex- periments are launched from Esrange Space Center and collect ice particles with an in-situ imaging instrument. One of the aims with these measurements is to improve satellite remote sensing of cold ice clouds. Such clouds can be observed by lidar. Therefore, when possible, concurrent ground-based lidar measurements have been carried out with two available lidar systems to accom- pany the balloon-borne measurements. The Esrange lidar is located at Esrange Space Center, approximately 500 m from the in-situ launch site on the balloon pad; the IRF lidar is located about 29 km to the west of Esrange Space Center (operated by the Swedish Institute of Space Physics, IRF). Here we present results from these lidar measurements and compare them to ice particle proper- ties determined during the in-situ measurements. 

  • 258.
    Kumar, Rajesh
    et al.
    Department of Environmental Science, Sharda University, Greater Noida.
    Kumar, Ramesh
    Department of Environmental Science, Sharda University, Greater Noida.
    Singh, Shaktiman
    Department of Environmental Science, Sharda University, Greater Noida.
    Singh, Atar
    Department of Environmental Science, Sharda University, Greater Noida.
    Bhardwaj, Anshuman
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Kumari, Anupma
    Environmental Biology Laboratory, Department of Zoology, Patna University.
    Randhawa, S.S.
    State Council for Science, Technology and Environment, Shimla.
    Saha, Ashok
    Ministry of Earth Science, New Delhi.
    Dynamics of suspended sediment load with respect to summer discharge and temperatures in Shaune Garang glacierized catchment, Western Himalaya2018Inngår i: Acta Geophysica, ISSN 1895-6572, E-ISSN 1895-7455Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The observed and predicted rise in temperature will have deleterious impact on melting of snow and ice and form of precipitation which is already evident in Indian Himalayan Region. The temperature-dependent entities like discharge and sediment load will also vary with the observed and predicted rise posing environmental, social and economic threat in the region. There is little known about sediment load transport in relation to temperature and discharge in glacierized catchments in Himalaya mainly due to the scarcity of ground-based observation. The present study is an attempt to understand the suspended sediment load and transportation in relation to variation in discharge and temperature in the Shaune Garang catchment. The result shows strong dependence of sediment concentration primarily on discharge (R2 = 0.84) and then on temperature (R2 = 0.79). The catchments with similar geological and climate setting were observed to have comparatively close weathering rate. The sediment load was found to be higher in the catchments in eastern and central part of Indian Himalayan Region in comparison with western part due to dominance of Indian Summer Monsoon leading to high discharge. The annual physical weathering rate in Shaune Garang catchment was found to be 411 t km−2 year−1 which has increased from 327 t km−2 year−1 in around three decades due to rise in temperature causing increase in discharge and proportion of debris-covered glacierized area.

  • 259.
    Kumar, Rajesh
    et al.
    Department of Environmental Science, School of Basic Sciences and Research, Sharda University, Greater Noida.
    Singh, Shaktiman
    Department of Environmental Science, School of Basic Sciences and Research, Sharda University, Greater Noida.
    Kumar, Ramesh
    Department of Environmental Science, School of Basic Sciences and Research, Sharda University, Greater Noida.
    Singh, Atar
    Department of Environmental Science, School of Basic Sciences and Research, Sharda University, Greater Noida.
    Bhardwaj, Anshuman
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Sam, Lydia
    Department of Environmental Science, Sharda University, Department of Environmental Science, School of Basic Sciences and Research, Sharda University, Greater Noida.
    Randhawa, Surjeet Singh
    State Council for Science, Technology. & Environment, Shimla.
    Gupta, Akhilesh
    Department of Science and Technology, Technology Bhavan, New Delhi.
    Development of a Glacio-hydrological Model for Discharge and Mass Balance Reconstruction2016Inngår i: Water resources management, ISSN 0920-4741, E-ISSN 1573-1650, Vol. 30, nr 10, s. 3475-3492Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The reconstruction of glacio-hydrological records for the data deficient Himalayan catchments is needed in order to study the past and future water availability. The study provides outcomes of a glacio-hydrological model based on the degree-day approach. The model simulates the discharge and mass balance for glacierised Shaune Garang catchment. The degree-day factors for different land covers, used in the model, were estimated using daily stake measurements on Shaune Garang glacier and they were found to be varying between 2.6 ± 0.4 and 9.3 ± 0.3 mm °C−1day−1. The model is validated using observed discharge during ablation season of 2014 with coefficient of determination (R2) 0.90 and root mean square error (RMSE) 1.05 m3 sec−1. The model is used to simulate discharge from 1985 to 2008 and mass balance from 2001 to 2008. The model results show significant contribution of seasonal snow and ice melt in total discharge of the catchment, especially during summer. We observe the maximum discharge in July having maximum contribution from snow and ice melt. The annual melt season discharge shows following a decreasing trend in the simulation period. The reconstructed mass balance shows mass loss of 0.89 m we per year between 2001 and 2008 with slight mass gain during 2000/01 and 2004/05 hydrological years.

  • 260.
    Kunicka, Beata Iwona
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Spacecraft dynamic analysis and correlation with test results: Shock environment analysis of LISA Pathfinder at VESTA test bed2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The particular study case in this thesis is the shock test performed on the LISA Pathfinder satellite conducted in a laboratory environment on a dedicated test bed: Vega Shock Test Apparatus (VESTA). This test is considered fully representative to study shock levels produced by fairing jettisoning event at Vega Launcher Vehicle, which induces high shock loads towards the satellite.

    In the frame of this thesis, some transient response analyses have been conducted in MSC Nastran, and a shock simulation tool for the VESTA test configuration has been developed. The simulation tool is based on Nastran Direct Transient Response Analysis solver (SOL 109), and is representative of the upper composite of Vega with the LISA Pathfinder coupled to it. Post-processing routines of transient response signals were conducted in Dynaworks which served to calculate Shock Response Spectra (SRS).

    The simulation tool is a model of forcing function parameters for transient analysis which adequately correlates with the shock real test data, in order to understand how the effect of shock generated by the launcher is seen in the satellite and its sub-systems. Since available computation resources are limited the parameters for analysis were optimised for computation time, file size, memory capacity,  and model complexity. The forcing function represents a release of the HSS clamp band which is responsible for fairing jettisoning, thus the parameters which were studied are mostly concerning the modelling of this event. Among many investigated, those which visibly improved SRS correlation are radial forcing function shape, implementation of axial impulse, clamp band loading geometry and refined loading scheme. Integration time step duration and analysis duration were also studied and found to improve correlation.  From each analysis, the qualifying shock environment was then derived by linear scaling in proportion of the applied preload, and considering a qualification margin of 3dB.

    Consecutive tracking of structural responses along shock propagation path exposed gradual changes in responses pattern and revealed an important property that a breathing mode (n = 0) at the base of a conical Adapter translates into an axial input to the spacecraft. The parametrisation itself was based on responses registered at interfaces located in near-field (where the clamp band is located and forcing function is applied) and medium-field with respect to the shock event location. Following shock propagation path, the final step was the analysis of shock responses inside the satellite located in a far-field region, which still revealed a very good correlation of results. Thus, it can be said that parametrisation process was adequate, and the developed shock simulation tool can be qualified. However, due to the nature of shock, the tool cannot fully replace VESTA laboratory test, but can support shock assessment process and preparation to such test.

    In the last part of the thesis, the implementation of some finite element model improvements is investigated. Majority of the panels in spacecraft interior exhibited shock over-prediction due to finite element model limitation. Equipment units modelled as lump masses rigidly attached with RBE2 elements to the panel surface are a source of such local over-predictions. Thus, some of the units were remodelled and transient responses were reinvestigated. It was found that remodelling with either solid elements, or lump mass connected to RBE3 element and reinforced by RBE2 element, can significantly improve local transient responses. This conclusion is in line with conclusions found in ECSS Shock Handbook.

  • 261.
    Lahoz, William A.
    et al.
    University of Reading, Data assimililation research centre.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Legras, Bernard
    Laboratoire de Météorologie Dynamique, Paris.
    The COST 723 Action2007Inngår i: Quarterly Journal of the Royal Meteorological Society, ISSN 0035-9009, E-ISSN 1477-870X, Vol. 133, nr S2, s. 99-108Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An overview is provided of the COST 723 Action, Data Exploitation and Modelling of the Upper Troposphere and Lower Stratosphere. The three working groups are introduced and a summary of Action activities within them is provided. The achievements of the Action are: three international workshops; the LAUTLOS humidity measurement campaign; dedicated meetings to discuss the quality of upper troposphere/lower stratosphere ozone and humidity measurements; two journal special issues; more than 90 papers in the peer-reviewed literature; one international summer school; and a successor COST Action which builds on COST 723. The recommendations made are: for COST to continue to support the short-term scientific missions instrument, as they are perceived to be value for money; to encourage the use of COST money to increase links between COST Actions and other scientific communities; and for the COST secretariat to recommend that Actions consider a summer school instead of a final workshop or meeting.

  • 262.
    Lanza, Nina L.
    et al.
    Los Alamos National Laboratory.
    Wiens, Roger C.
    Los Alamos National Laboratory, Space Remote Sensing, Los Alamos National Laboratory, Los Alamos, International Space and Response Division, Los Alamos National Laboratory.
    Arvidson, Ray E.
    Washington University, St. Louis.
    Clark, Benton C.
    Space Science Institute, Boulder, Colorado, Space Science Institute.
    Fischer, W.W.
    California Institute of Technology, Pasadena.
    Gellert, Ralf
    University of Guelph, Ontario, University of Guelph, Department of Physics, University of Guelph, Ontario.
    Grotzinger, John P.
    California Institute of Technology, Pasadena, Division of Geological and Planetary Sciences, California Institute of Technology, Caltech, Pasadena, Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
    Hurowitz, J.A.
    Department of Geosciences, Stony Brook University, Stony Brook University, NY, Department of Geosciences, State University of New York, Stony Brook.
    McLennan, S.M.
    Department of Geosciences, Stony Brook University, Stony Brook University, NY, Department of Geosciences, State University of New York, Stony Brook, The State University of New York, Stony Brook.
    Morris, R.V.
    NASA Johnson Space Center, NASA Johnson Space Center, Houston, Astromaterials Research and Exploration Science Directorate, NASA Johnson Space Center, Houston.
    Rice, M.S.
    California Institute of Technology, Pasadena, Division of Geological and Planetary Sciences, California Institute of Technology.
    III, J.F. Bell
    Arizona State University, School of Earth and Space Exploration, Arizona State University, School of Earth and Space Exploration, Arizona State University, Tempe.
    Berger, Jeff A.
    University of Western Ontario, London.
    Blaney, Diana L.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena, Jet Propulsion Laboratory, Pasadena, Kalifornien.
    Bridges, Nathan T.
    Johns Hopkins University Applied Physics Laboratory, Laurel, Applied Physics Laboratory, Laurel, Maryland.
    Calef, Fred
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena, Jet Propulsion Laboratory.
    Campbell, J.L.
    Department of Physics, University of Guelph, Ontario, University of Guelph, Ontario.
    Clegg, S.M.
    Los Alamos National Laboratory, Chemistry Division, Los Alamos National Laboratory.
    Cousin, A.
    Los Alamos National Laboratory, Chemistry Division, Los Alamos National Laboratory.
    Edgett, Kenneth S.
    Malin Space Science Systems, San Diego, Malin Space Science Systems.
    Fabre, Cécile
    Université de Lorraine, Nancy.
    Fisk, M.R.
    Oregon State University, Corvallis.
    Forni, Olivier
    IRAP/CNRS, Institut de Recherche en Astrophysique et Planetologie, Toulouse, Université de Toulouse, UPS-OMP, IRAP, Institut de Recherche en Astophysique et Planetologie (IRAP), Universite' Paul Sabatier, Toulouse, IRAP, CNRS/UPS, Toulouse.
    Frydenvang, J.
    Niels Bohr Institute, University of Copenhagen.
    Hardy, K.R.
    U.S. Naval Academy, Annapolis.
    Martin-Torres, Javier
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Zorzano Mier, Maria-Paz
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Oxidation of manganese in an ancient aquifer, Kimberley formation, Gale crater, Mars2016Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 14, s. 7398-7407Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Curiosity rover observed high Mn abundances (>25wt % MnO) in fracture-filling materials that crosscut sandstones in the Kimberley region of Gale crater, Mars. The correlation between Mn and trace metal abundances plus the lack of correlation between Mn and elements such as S, Cl, and C, reveals that these deposits are Mn oxides rather than evaporites or other salts. On Earth, environments that concentrate Mn and deposit Mn minerals require water and highly oxidizing conditions; hence, these findings suggest that similar processes occurred on Mars. Based on the strong association between Mn-oxide deposition and evolving atmospheric dioxygen levels on Earth, the presence of these Mn phases on Mars suggests that there was more abundant molecular oxygen within the atmosphere and some groundwaters of ancient Mars than in the present day

  • 263.
    Lanza, N.L.
    et al.
    Los Alamos National Laboratory.
    Wiens, R.C.
    Los Alamos National Laboratory.
    Arvidson, R.E.
    Washington University, St. Louis.
    Clark, B.C.
    Space Science Institute, Boulder, Colorado.
    Fischer, W.W.
    California Institute of Technology, Pasadena.
    Gellert, R.
    University of Guelph, Ontario.
    Grotzinger, J.P.
    California Institute of Technology, Pasadena.
    Hurowitz, J.A.
    Stony Brook University, NY.
    McLennan, S.M.
    Stony Brook University, NY.
    Morris, R.V.
    NASA Johnson Space Center, Houston.
    Rice, M.S.
    Western Washington University, Bellingham.
    III, J.F. Bell
    Arizona State University.
    Berger, J.A.
    University of Western Ontario, London.
    Blaney, D.L.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
    Blank, J.G.
    NASA Ames, Blue Marble Space Institute of Science, Seattle.
    Bridges, N.T.
    Johns Hopkins University Applied Physics Laboratory, Laurel.
    III, F. Calef
    Jet Propulsion Laboratory.
    Campbell, J.L.
    University of Guelph, Ontario.
    Clegg, S.M.
    Los Alamos National Laboratory.
    Cousin, A.
    Los Alamos National Laboratory.
    Edgett, K.S.
    Malin Space Science Systems.
    Fabre, C.
    Université de Lorraine, Nancy.
    Fisk, M.R.
    Oregon State University, Corvallis.
    Forni, O.
    Institut de Recherche en Astrophysique et Planetologie, Toulouse.
    Frydenvang, J.
    Niels Bohr Institute, University of Copenhagen.
    Martin-Torres, Javier
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Instituto Andaluz de Cienccias de la Tierra (CSIC-UGR), Grenada.
    Zorzano, M.-P.
    Instituto Nacional de Técnica Aeroespacial, Madrid.
    Oxidation of manganese at Kimberley, Gale Crater: More free oxygen in Mars’ past?2015Konferansepaper (Fagfellevurdert)
  • 264.
    Larsson, Richard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    A note on modelling of the oxygen spectral cross-section in the Atmospheric Radiative Transfer Simulator – Zeeman effect combined with line mixing in the Earth’s atmosphere2014Inngår i: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 35, nr 15, s. 5845-5853Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new module to the Atmospheric Radiative Transfer Simulator is presented that models the strong oxygen spectral band at 60 GHz. The module handles the line mixing effect and works with or without additionally calculating the Zeeman effect. It is shown how the module may be internally reduced to calculations of the Zeeman effect at higher altitudes, and to calculations of the line mixing effect at lower altitudes. The article ends with a short discussion on what is being done to validate the module, and what may be done to refine the theoretical description of line mixing in the simulator.

  • 265.
    Larsson, Richard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Modeling the Zeeman Effect in Planetary Atmospheric Radiative Transfer2014Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    There are special effects in spectroscopy that must be considered in order to fullyexplain how molecular oxygen interacts with radiation in planetary atmospheres.One of these, the Zeeman effect, is described in this thesis. The Zeeman effect is the theory by which energy levels of atoms and molecules are altered by magnetism, and it causes both polarization and line shape to change. The first publication attached to this thesis, Paper I, details the technical and practical implementation of the Zeeman effect in a radiative transfer model. One potential use of magnetically altered spectroscopy is to remotely measure magnetism. Paper II discuss a method for such measurements on weakly magnetized planets by measuring the polarization caused by the Zeeman effect. The article brings up Mars as one potential candidate to utilize the method. To introduce the articles properly, the thesis starts with a shortdescription of the underlying basic theory for radiative transfer and spectroscopy.After the theory chapter, a short description of input necessary to utilize the theory on operational and experimental platforms is presented.

  • 266.
    Larsson, Richard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Modeling the Zeeman Effect in Planetary Radiative Transfer and Applications2016Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Remote sensing is about retrieving distant physical properties from locally observed radiation. The first step to remote sensing is to describe, or model, the radiative transfer. Without locating the origin of the observed radiation, and without proper interpretation of what it represents, understanding and utilizing instrumental results are nearly impossible. The focus of my thesis is on how radiation interacts with a weakly magnetized medium by means of the Zeeman effect. One molecule of particular interest affected by the Zeeman effect is the oxygen molecule. The thesis work started by an implementation of a module for the Zeeman effect in an existingradiative transfer model. Later works has applied this module to Earth and Mars radiative transfer.The high relative concentration of the oxygen molecule in Earth’s atmosphere, and the fact that the molecule interacts with sub-millimeter radiation, has made it a prime target for temperature retrievals using both ground- and satellite-based radiometers. The Zeeman effect is important for molecular oxygen at mesospheric altitudes on Earth, where the geometry of the magnetic field and of the observation influence the polarized absorption of radiation. Simulations of ground-based measurements by a radiometer in Bern, Switzerland, have the Zeeman module reproduce the dependency on observational geometry for the local magnetic field, partly validating the module. Simulations of satellite measurements comparing the Zeeman module to a fast, parameterized, implementation of the Zeeman effect for numerical weather predictions also indicates that the module works. There are small discrepancies between the two models but both are close to the satellite measurements given the noise of these measurements. Work to move beyond simulation space and analyze these satellite measurements to find the atmospheric temperatures at high altitudes also show promising results.Besides Earth applications, the module has been used for Mars conditions, where only trace amounts of molecular oxygen is available. Mars does not have a global magnetic field but instead have several magnetic sources scattered throughout its crust. This gives a magnetic field that is significantly weaker than on Earth and with much more structures. It is possible to utilize the Zeeman effect on molecular oxygen to measure the magnetic field of Mars. The last part of this thesis work suggests a measurement scheme for a satellite capable of retrieving the horizontal components of the Martian crustal magnetic field. It shows the expected errors associated with such a measurement scheme.

  • 267.
    Larsson, Richard
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Eriksson, Patrick
    Chalmers University of Technology, Department of Earth and Space Sciences.
    Mendrok, Jana
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    A treatment of the Zeeman effect using Stokes formalism and its implementation in the Atmospheric Radiative Transfer Simulator ARTS2014Inngår i: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 133, s. 445-453Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This article presents the practical theory that was used to implement the Zeeman effect using Stokes formalism in the Atmospheric Radiative Transfer Simulator ARTS. ARTS now treats the Zeeman effect in a general manner for several gas species for all polarizations and takes into account variations in both magnetic and atmospheric fields along a full 3D geometry. We present how Zeeman splitting affects polarization in radiative transfer simulations and find that the effect may be large in Earth settings for polarized receivers in limb observing geometry. We find that not taking a spatially varying magnetic field into account can result in absolute errors in the measurement vector of at least 10 K in Earth magnetic field settings. The article also presents qualitative tests for O2 lines against previous models (61.15 GHz line) and satellite data from Odin-SMR (487.25 GHz line), and the overall consistency between previous models, satellite data, and the new ARTS Zeeman module seems encouraging.

  • 268.
    Larsson, Richard
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    McKay, Christopher
    NASA Ames Research Center.
    Timescale for oceans in the past of Titan2013Inngår i: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, s. 22-24Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We estimate the past extent of liquid on the surface of Titan as a function of time assuming the current rate of destruction of methane and no sources or subsurface sinks. As methane increases for increasing past time the polar lakes expand equatorward. We use a spherical harmonics model for the surface topography to compute the fraction of the surface covered as the methane inventory increases. We find that substantial parts of the equator would have been flooded by a polar ocean 300 million years ago and that the equator would have been connected to a global ocean 600 million years ago. This provides one possible explanation for the fluvial features seen at the equator on Titan.

  • 269.
    Larsson, Richard
    et al.
    National Institute of Information and Communications Technology, Tokyo, Japan.
    Milz, Mathias
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. IRV.
    Eriksson, Patrick
    Chalmers University of Technology, Göteborg.
    Mendrok, Jana
    Chalmers University of Technology, Göteborg.
    Kasai, Yasuko
    National Institute of Information and Communications Technology, Tokyo, Japan.
    Buehler, Stefan A.
    University of Hamburg.
    Diéval, Catherine
    Lancaster University.
    Brain, David
    University of Colorado, Boulder.
    Hartogh, Paul
    Max planck Institute for Solar System Research, Göttingen, Germany .
    Martian magnetism with orbiting sub-millimeter sensor: simulated retrieval system2017Inngår i: Geoscientific Instrumentation, Methods and Data Systems, ISSN 2193-0856, E-ISSN 2193-0864, Vol. 6, nr 1, s. 27-37Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A Mars-orbiting sub-millimeter sensor can be used to retrieve the magnetic field at low altitudes over large areas of significant planetary crustal magnetism of the sur- face of Mars from measurements of circularly polarized radi- ation emitted by the 368 GHz ground-state molecular oxygen absorption line. We design a full retrieval system for one ex- ample orbit to show the expected accuracies on the magnetic field components that one realization of such a Mars satellite mission could achieve. For one set of measurements around a tangent profile, we find that the two horizontal components of the magnetic field can be measured at about 200 nT error with a vertical resolution of around 4 km from 6 up to 70 km in tangent altitude. The error is similar regardless of the true strength of the magnetic field, and it can be reduced by re- peated measurements over the same area. The method and some of its potential pitfalls are described and discussed. 

  • 270.
    Larsson, Richard
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Milz, Mathias
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Rayer, P.
    UK Met Office, Exeter.
    Saunders, R.
    UK Met Office, Exeter.
    Bell, W.
    UK Met Office, Exeter.
    Booton, A.
    UK Met Office, Exeter.
    Buehler, S.A.
    Meteorological Institute, University of Hamburg, Hamburg.
    Eriksson, P.
    Chalmers University of Technology, Department of Earth and Space Sciences.
    John, V.
    EUMETSAT, Darmstadt.
    Modeling the Zeeman effect in high altitude SSMIS channels for numerical weather prediction profiles: Comparing a fast model and a line-by-line model2015Inngår i: Atmospheric Measurement Techniques Discussions, ISSN 1867-8610, E-ISSN 1867-8610, Vol. 8, nr 10, s. 10179-10211Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a comparison of a reference and a fast radiative transfer model using numerical weather prediction profiles for the Zeeman-affected high altitude Special Sensor Microwave Imager/Sounder channels 19–22. We find that the models agree well for channels 21 and 22 compared to the channels' system noise temperatures (1.9 and 1.3 K, respectively) and the expected profile errors at the affected altitudes (estimated to be around 5 K). For channel 22 there is a 0.5 K average difference between the models, with a standard deviation of 0.24 K for the full set of atmospheric profiles. Same channel, there is 1.2 K in average between the fast model and the sensor measurement, with 1.4 K standard deviation. For channel 21 there is a 0.9 K average difference between the models, with a standard deviation of 0.56 K. Same channel, there is 1.3 K in average between the fast model and the sensor measurement, with 2.4 K standard deviation. We consider the relatively small model differences as a validation of the fast Zeeman effect scheme for these channels. Both channels 19 and 20 have smaller average differences between the models (at below 0.2 K) and smaller standard deviations (at below 0.4 K) when both models use a two-dimensional magnetic field profile. However, when the reference model is switched to using a full three-dimensional magnetic field profile, the standard deviation to the fast model is increased to almost 2 K due to viewing geometry dependencies causing up to ± 7 K differences near the equator. The average differences between the two models remain small despite changing magnetic field configurations. We are unable to compare channels 19 and 20 to sensor measurements due to limited altitude range of the numerical weather prediction profiles. We recommended that numerical weather prediction software using the fast model takes the available fast Zeeman scheme into account for data assimilation of the affected sensor channels to better constrain the upper atmospheric temperatures.

  • 271.
    Larsson, Richard
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Milz, Mathias
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Rayer, Peter
    UK Met Office, Exeter.
    Saunders, Roger
    UK Met Office, Exeter.
    Bell, William
    UK Met Office, Exeter.
    Booton, Anna
    UK Met Office, Exeter.
    Buehler, Stephan A.
    Meteorological Institute, University of Hamburg, Hamburg.
    Eriksson, Patrick
    Chalmers University of Technology, Department of Earth and Space Sciences.
    John, Viju E.
    EUMETSAT, Darmstadt.
    Modeling the Zeeman effect in high altitude SSMIS channels for numerical weather prediction profiles: Comparing a fast model and a line-by-line model2016Inngår i: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 9, nr 2, s. 841-857Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a comparison of a reference and a fast radiative transfer model using numerical weather prediction profiles for the Zeeman-affected high altitude Special Sensor Microwave Imager/Sounder channels 19–22. We find that the models agree well for channels 21 and 22 compared to the channels' system noise temperatures (1.9 and 1.3 K, respectively) and the expected profile errors at the affected altitudes (estimated to be around 5 K). For channel 22 there is a 0.5 K average difference between the models, with a standard deviation of 0.24 K for the full set of atmospheric profiles. Same channel, there is 1.2 K in average between the fast model and the sensor measurement, with 1.4 K standard deviation. For channel 21 there is a 0.9 K average difference between the models, with a standard deviation of 0.56 K. Same channel, there is 1.3 K in average between the fast model and the sensor measurement, with 2.4 K standard deviation. We consider the relatively small model differences as a validation of the fast Zeeman effect scheme for these channels. Both channels 19 and 20 have smaller average differences between the models (at below 0.2 K) and smaller standard deviations (at below 0.4 K) when both models use a two-dimensional magnetic field profile. However, when the reference model is switched to using a full three-dimensional magnetic field profile, the standard deviation to the fast model is increased to almost 2 K due to viewing geometry dependencies causing up to ± 7 K differences near the equator. The average differences between the two models remain small despite changing magnetic field configurations. We are unable to compare channels 19 and 20 to sensor measurements due to limited altitude range of the numerical weather prediction profiles. We recommended that numerical weather prediction software using the fast model takes the available fast Zeeman scheme into account for data assimilation of the affected sensor channels to better constrain the upper atmospheric temperatures.

  • 272.
    Larsson, Richard
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Ramstad, Robin
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Mendrok, Jana
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Kasai, Yasuko
    National Institute of Information and Communications Technology, 4-2-1 Nukui-kitamachi, Koganei.
    A method for remote sensing of weak planetary magnetic fields: Simulated application to Mars2013Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40, nr 19, s. 5014-5018Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a method for characterizing the magnetic anomalies from the crustal fields in the lower atmosphere of Mars that requires two perpendicular linear polarization measurements of the Zeeman effect. The maximum effect of the magnetic field on the signal is found at the Doppler broadening width at low pressures rather than at the magnetically induced line frequency shift, and the effect strongly increases with increasing magnetic field strength. Based on simulations of the Zeeman-affected spectral cross section of the 119 GHz O2 line in a model Martian atmosphere at various magnetic field strengths, we conclude that it should be possible to probe the strength of the magnetic anomalies remotely with presently available technology. We discuss limitations of the method, how these results could be relevant to the interpretation of residuals in Herschel/HIFI observations of Mars, as well as the application to detection of exoplanetary magnetic fields.

  • 273.
    Lasue, J.
    et al.
    IRAP-OMP, CNRS-UPS, Toulouse.
    Martin-Torres, Javier
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Zorzano Mier, Maria-Paz
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    What ChemCam’s first shots tell us about martian dust?2017Konferansepaper (Annet vitenskapelig)
  • 274.
    Leblebici, Robin
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Development of an automated adjusting process for robotic end-effectors to handle dry textiles for preforming of carbon fiber reinforced plastics2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    In order to fulfill increasing production rates, new automated production technologies are required for manufacturing carbon fiber reinforced plastic components for the aerospace industry. Currently, large, double curved composite components have to be manufactured manually, which leads to high process times and poor scalability. As a consequence, a team of cooperating robots with passively adjustable end-effectors was developed, that is capable of handling dry carbon textiles and can be used for layups in double curved molds. This thesis deals with the implementation of a robot program, that performs an automated adjustment of each end-effector to the surface geometry of the manufactured part. The functional principle and the accuracy of the process are evaluated. Further, the automatically adjusted end-effectors are utilized to cooperatively layup carbon plies. The results show, that the accuracy of the automated adjusting process is sufficient to drape carbon fabrics during pick-up and automated layup is possible with this approach. In conclusion, the developed process can be integrated into a fully automated process for future experiments, but hardware inaccuracies should be improved, in order to further enhance the accuracy of the system.

  • 275.
    Li, Yuangui
    et al.
    Department of Automation, Shanghai Jiaotong University.
    Lin, Chen
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Huang, Jinjie
    Department of Automation, Shanghai Jiaotong University.
    Zhang, Weidong
    Department of Automation, Shanghai Jiaotong University.
    A new method to construct reduced vector sets for simplifying support vector machines2006Inngår i: IEEE International Conference on Engineering of Intelligent Systems, Piscataway, NJ: IEEE Communications Society, 2006Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Support vector machines (SVM) are well known to give good results on pattern recognition problems, but for large scale problems, they exhibit substantially slower classification speeds than neural networks. It has been proposed to speed the SVM classification by approximating the decision function of SVM with a reduced vector set. A new method to construct the reduced vector set is proposed in this paper, which is constructed by merging the closest support vectors in an iterative fashion. A minor modification on the proposed method also has been made in order to simplify the decision function of reduced support vector machines (RSVM). The proposed method was compared with previous study on several benchmark data sets, and the computational results indicated that our method could simplify SVMs and RSVMs effectively, which will speed the classification for large scale problems

  • 276.
    Li, Yuangui
    et al.
    Department of Automation, Shanghai Jiaotong University.
    Lin, Chen
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Zhang, Weidong
    Department of Automation, Shanghai Jiaotong University.
    Improved sparse least-squares support vector machine classifiers2006Inngår i: Neurocomputing, ISSN 0925-2312, E-ISSN 1872-8286, Vol. 69, nr 13-15, s. 1655-1658Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The least-squares support vector machines (LS-SVM) can be obtained by solving a simpler optimization problem than that in standard support vector machines (SVM). Its shortcoming is the loss of sparseness and this usually results in slow testing speed. Several pruning methods have been proposed. It is found that these methods can be further improved for classification problems. In this paper a different reduced training set is selected to re-train LS-SVM. Then a new procedure is proposed to obtain the sparseness. The performance of the proposed method is compared with other typical ones and the results indicate that it is more effective.

  • 277.
    Lidström, Viktor
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Mass Loading of Space Plasmas2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The solar wind interaction with an icy comet is studied through a model problem. A hybrid simulation is done of a box with evenly distributed water ions and protons, where initially the water ions are stationary, and protons move with the speed of the solar wind. The purpose of the thesis is to investigate the interaction between the two species through the convective electric field, and focus is on early acceleration of pick-up ions, and deflection of the solar wind. It is relevant to the cometary case, because it enables study of the physics of this interaction, without involving other mechanisms, such as bow shock, magnetic field pile-up and draping. The species are found to exchange kinetic energy similar to a damped oscillator, where the dampening is caused by kinetic energy being transferred to the magnetic field. At early times, i.e. times smaller than the gyration time for the water ions, the solar wind does not lose much speed when it is deflected. For comparable number densities, the solar wind can be deflected more than 90° at early times, and loses more speed, and water ions are picked up faster. The total kinetic energy of the system decreases when energy builds up in the magnetic field. The nature of the energy exchange is strongly dependent on the number density ratio between water ions and protons. A density instability with behaviour similar to a plasma beam instability forms as energy in the magnetic field increases, and limits the amount of time the simulation preserves total energy, for the particular hybrid solver used. There is a discussion on the structure of the density instability, and it is compared to cometary simulations.

  • 278.
    Lue, Charles
    et al.
    Luleå tekniska universitet.
    Futaana, Yoshifumi
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Barabash, Stas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Wieser, Martin
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Holmström, Mats
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Bhardwaj, Anil
    Space Physics Laboratory, Vikram Sarabhai Space Center, Trivandrum.
    Dhanya, M.B.
    Space Physics Laboratory, Vikram Sarabhai Space Center, Trivandrum.
    Wurz, Peter
    Physikalisches Institut, University of Bern.
    Strong influence of lunar crustal fields on the solar wind flow2011Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 38, nr 3Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We discuss the influence of lunar magnetic anomalies on the solar wind and on the lunar surface, based on maps of solar wind proton fluxes deflected by the magnetic anomalies. The maps are produced using data from the Solar WInd Monitor (SWIM) onboard the Chandrayaan-1 spacecraft. We find a high deflection efficiency (average ∼10%, locally ∼50%) over the large-scale (>1000 km) regions of magnetic anomalies. Deflections are also detected over weak (<3 nT at 30 km altitude) and small-scale (<100 km) magnetic anomalies, which might be explained by charge separation and the resulting electric potential. Strong deflection from a wide area implies that the magnetic anomalies act as a magnetosphere-like obstacle, affecting the upstream solar wind. It also reduces the implantation rate of the solar wind protons to the lunar surface, which may affect space weathering near the magnetic anomalies.

  • 279.
    Lukanovic, Matej
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Evaluation Analysis of the UV-detector on the Mini-EUSO Space Telescope2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Extragalactic charged particles, each with energies rising up to and beyond 1 Joule, have been studied for almost a century. Yet, no precise evidence have proven to show where they might originate from as their energy levels rise above the current familiar acceleration sources in outer space. The highly energetic particles have been given the name Ultra-High Energy Cosmic Rays (UHECR) and investigations of particle properties such as primary energy, mass composition and direction can be made through indirect measurements of the interaction between the UHECR and Earth's atmosphere. The considered interaction induces an Extensive Air Shower (EAS) which emits fluorescent light in the Ultraviolet (UV) range. The probability of detecting such events is, however, as low as a few particles per km2 per century. Making observations more sufficient therefore requires larger detection volumes.

    By introducing the Mini-EUSO instrument, a telescope of which the main purpose is to measure the UV-light radiated from the Earth in the wavelength range of 300-400 nm, allows just for this. To be accommodating the International Space Station and targeting Earth in the nadir direction, the Mini-EUSO instrument will allow for a higher exposure to the interactions than what is currently available. The use of two Fresnel lenses provides the instrument with a large field of view (±22o) and the detections are made through multiple photomultiplier tubes.

    The scope of this thesis is to evaluate the main detector of the Mini-EUSO instrument (i.e. the UV-detector) through ground-based tests. The procedures involved in the evaluation have consisted of; validating the statistical distributions of the signals, implementing dark field and flat field calibrations, and radiations measurements with three kinds of radiation sources. The data from the tests were provided during two periods and the visualization was made by adapting an already existing piece of code, using Python and ROOT Cern, to perform step by step procedures such that all operations are overlooked properly.

    The analysis showed that the implementation of the dark field and flat field procedures improved the original image significantly. It also showed that both the lower and higher photon count values in a pixel indeed gave the expected statistical behaviours, with a Poissonian distribution for low values and a Gaussian distribution for higher values. The flat fielding screen did however show unknown fluctuations in the emitted light and further tests have to be implemented to assure its functionality. Under proper covering, almost no dark current was found, however, observation tests showed that the borders of the Multi-Anode Photomultiplier Tubes (MAPMTs) gave higher photon count values than the center part even when they were emitted with Lambertian light.

  • 280.
    Mahaffy, P.R.
    et al.
    Planetary Environments Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland, NASA Goddard Space Flight Center.
    Conrad, Pamela G.
    NASA Goddard Space Flight Center.
    Martin-Torres, Javier
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Volatile and Isotopic Imprints of Ancient Mars2015Inngår i: Elements, ISSN 1811-5209, E-ISSN 1811-5217, Vol. 11, nr 1, s. 51-56Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The science investigations enabled by Curiosity rover's instruments focus on identifying and exploring the habitability of the Martian environment. Measurements of noble gases, organic and inorganic compounds, and the isotopes of light elements permit the study of the physical and chemical processes that have transformed Mars throughout its history. Samples of the atmosphere, volatiles released from soils, and rocks from the floor of Gale Crater have provided a wealth of new data and a window into conditions on ancient Mars.

  • 281.
    Mahfouf, J.-F.
    et al.
    CNRM–GAME, Météo-France and CNRS.
    Birman, C.
    CNRM–GAME, Météo-France and CNRS.
    Aires, F.
    Estellus, Paris.
    Prigent, C.
    L'Observatoire de Paris-LERMA.
    Orlandi, E.
    University of Cologne.
    Milz, Mathias
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Information content on temperature and water vapour from a hyper-spectral microwave sensor2015Inngår i: Quarterly Journal of the Royal Meteorological Society, ISSN 0035-9009, E-ISSN 1477-870X, Vol. 141, nr 693, s. 3268-3284Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study examines the information content on atmospheric temperature and humidity profiles that could be provided by a future spaceborne microwave sensor with a few hundred radiances in the millimetre and submillimetre spectral domains (ranging from 7–800 GHz). A channel selection method based on optimal estimation theory is undertaken, using a database of profiles with associated errors from the European Centre for Medium-Range Weather Forecasts (ECMWF) numerical weather prediction model and the radiative transfer model Atmospheric Radiative Transfer Simulator (ARTS) under clear-sky conditions. The main results indicate that, by increasing the number of channels within the oxygen absorption band around 60 GHz and within the water-vapour absorption band at 183 GHz, the accuracy of temperature and humidity retrievals in the troposphere and stratosphere (for temperature) would be noticeably improved compared with present and planned microwave radiometers. The channels located in the absorption lines at 118 GHz and above 200 GHz do not bring significant additional information regarding atmospheric profiles under clear-sky conditions, partly due to greater radiometric noise. With a set of 137 selected channels that contribute to 90% of the total information content (measured by the degree of freedom for signal), it is possible to achieve almost the same performance in terms of variance error reduction as with 276 candidate channels. Sensitivity studies of various prescribed quantities defining the channel selection have been undertaken, in order to check the robustness of the conclusions. They show that none of the choices modifies the above findings.

  • 282.
    Mannes, Quentin
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    ICE Cubes Mission: Design, Development and Documentation of the Cube-Zero System2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The International Space Station provides a high-quality of microgravity and extended exposure time which makes it a platform of choice for microgravity research. In order to increase accessibility of onboard experimentation, Space Applications Services will soon launch the ICE Cubes facility as part of its ICE Cubes Service. The facility is foreseen to host standardized plug-and-play payload cubes to reduce overall cost and procedure time required to install payloads on the station. To remotely support the facility it is decided to develop a utility cube named Cube-Zero that will be launched and installed with the facility on the station. This thesis work included the complete design, development and documentation of the cube.

    The thesis started by conducting a preliminary needs and market study from which two specific purposes were defined for the cube. In addition to its original function of support-utility, the cube is tasked to be a technical commercial demonstrator for the service. This led to the conceptual design of the cube as a multidisciplinary framework able to host two user-defined experiment modules. The preliminary concept was further refined in this paper and with support of prototypes, simulations and analyses led to a final functional design for the Cube-Zero.

    The work is concluded with the manufacturing of an engineering model of the cube. The model is fully operational, can support the test of the facility before launch and can demonstrate to users its versatility and ease of use in operating any kind of experiment module.

    Eventually, the information gathered in this thesis report will support future users into developing their own Cube-Zero payload module and guide Space Applications Services into manufacturing, testing and operating the Cube-Zero protoflight model.

  • 283.
    Martell, Angel Alfredo
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Benchmarking structure from motion algorithms with video footage taken from a drone against laser-scanner generated 3D models2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Structure from motion is a novel approach to generate 3D models of objects and structures. The dataset simply consists of a series of images of an object taken from different positions. The ease of the data acquisition and the wide array of available algorithms makes the technique easily accessible. The structure from motion method identifies features in all the images from the dataset, like edges with gradients in multiple directions, and tries to match these features between all the images and then computing the relative motion that the camera was subject to between any pair of images. It builds a 3D model with the correlated features. It then creates a 3D point cloud with colour information of the scanned object. There are different implementations of the structure from motion method that use different approaches to solve the feature-correlation problem between the images from the data set, different methods for detecting the features and different alternatives for sparse reconstruction and dense reconstruction as well. These differences influence variations in the final output across distinct algorithms.

    This thesis benchmarked these different algorithms in accuracy and processing time. For this purpose, a terrestrial 3D laser scanner was used to scan structures and buildings to generate a ground truth reference to which the structure from motion algorithms were compared. Then a video feed from a drone with a built-in camera was captured when flying around the structure or building to generate the input for the structure from motion algorithms. Different structures are considered taking into account how rich or poor in features they are, since this impacts the result of the structure from motion algorithms. The structure from motion algorithms generated 3D point clouds, which then are analysed with a tool like CloudCompare to benchmark how similar it is to the laser scanner generated data, and the runtime was recorded for comparing it across all algorithms. Subjective analysis has also been made, such as how easy to use the algorithm is and how complete the produced model looks in comparison to the others.

    In the comparison it was found that there is no absolute best algorithm, since every algorithm highlights in different aspects. There are algorithms that are able to generate a model very fast, managing to scale the execution time linearly in function of the size of their input, but at the expense of accuracy. There are also algorithms that take a long time for dense reconstruction, but generate almost complete models even in the presence of featureless surfaces, like COLMAP modified PatchMacht algorithm. The structure from motion methods are able to generate models with an accuracy of up to \unit[3]{cm} when scanning a simple building, where Visual Structure from Motion and Open Multi-View Environment ranked among the most accurate. It is worth highlighting that the error in accuracy grows as the complexity of the scene increases. Finally, it was found that the structure from motion method cannot reconstruct correctly structures with reflective surfaces, as well as repetitive patterns when the images are taken from mid to close range, as the produced errors can be as high as \unit[1]{m} on a large structure.

  • 284.
    Martin-Torres, Javier
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Mier, Maria-Paz Zorzano
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Vida Extraterrestre: Implicaciones2015Inngår i: Burgense, ISSN 0521-8195, Vol. 55, nr 1, s. 197-206Artikkel i tidsskrift (Fagfellevurdert)
  • 285.
    Martin-Torres, Javier
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Zorzano, María-Paz
    Centro de Astrobiologia, INTA-CSIC, Madrid , Instituto Nacional de Técnica Aeroespacial, Madrid, Centro de Astrobiologia, Madrid.
    Valentin-Serrano, Patricia
    CSIC-UGR - Instituto Andaluz de Ciencias de la Tierra (IACT), Granada.
    Harri, Ari-Matti
    Earth Observation Research Division, Finnish Meteorological Institute, Helsinki.
    Genzer, Maria
    Finnish Meteorological Institute, Earth Observation Research Division, Finnish Meteorological Institute, Helsinki.
    Kemppainen, Osku
    Finnish Meteorological Institute, Earth Observation Research Division, Finnish Meteorological Institute, Helsinki.
    Rivera-Valentin, Edgard G.
    Arecibo Observatory, Universities Space Research Association, Arecibo, Puerto Rico.
    Jun, Insoo
    California Institute of Technology, Jet Propulsion Laboratory.
    Wray, James J.
    School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta.
    Madsen, Morten B.
    Niels Bohr Institute, University of Copenhagen.
    Goetz, Walter
    Max-Planck-Institut für Solar System Research.
    McEwen, Alfred S,
    Lunar and Planetary Lab, University of Arizona, Tucson.
    Hardgrove, Craig
    Arizona State University, Department of Earth & Planetary Sciences, University of Tennessee, Knoxville, Malin Space Science Systems.
    Renno, Nilton
    University of Michigan, College of Engineering, University of Michigan, Ann Arbor.
    Chevrier, Vincent F.
    Arkansas Center for Space and Planetary Sciences, University of Arkansas, Fayetteville.
    Mischna, Michael A.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
    Navarro-Gonzalez, Rafael
    Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de Mexico, Ciudad Universitaria, Centro de Astrobiologia, INTA-CSIC, Madrid , Universidad Nacional Autónoma de México, Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Mexico D.F., Laboratorio de Química de Plasmas y Estudios Planetarios, Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México.
    Martínez-Frías, Jesús
    Centro de Astrobiologia, INTA-CSIC, Madrid , Instituto de Geociencias (CSIC-UCM), 28040 Madrid.
    Conrad, Pamela G.
    NASA Goddard Space Flight Center, Solar System Exploration Division, Goddard Space Flight Center, National Aeronautics and Space Administration, Greenbelt, Maryland.
    McConnochie, Timothy H.
    Department of Astronomy, University of Maryland, College Park.
    Cockell, Charles
    ESO, UK Centre for Astrobiology, School of Physics and Astronomy,.
    Berger, Gilles
    IRAP/CNRS, Institut de Recherche en Astrophysique et Planetologie, Toulouse, Université de Toulouse, UPS-OMP, IRAP.
    Vasavada, Ashwin
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
    Sumner, Dawn Y.
    Department of Earth and Planetary Sciences, University of California, Davis, Department of Geology, University of California, Davis.
    Vaniman, David T.
    Planetary Science Institute, Tucson.
    Transient liquid water and water activity at Gale crater on Mars2015Inngår i: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 8, nr 5, s. 357-361Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Water is a requirement for life as we know it1. Indirect evidence of transient liquid water has been observed from orbiter on equatorial Mars2, in contrast with expectations from large-scale climate models. The presence of perchlorate salts, which have been detected at Gale crater on equatorial Mars by the Curiosity rover3, 4, lowers the freezing temperature of water5. Moreover, perchlorates can form stable hydrated compounds and liquid solutions by absorbing atmospheric water vapour through deliquescence6, 7. Here we analyse relative humidity, air temperature and ground temperature data from the Curiosity rover at Gale crater and find that the observations support the formation of night-time transient liquid brines in the uppermost 5 cm of the subsurface that then evaporate after sunrise. We also find that changes in the hydration state of salts within the uppermost 15 cm of the subsurface, as measured by Curiosity, are consistent with an active exchange of water at the atmosphere–soil interface. However, the water activity and temperature are probably too low to support terrestrial organisms8. Perchlorates are widespread on the surface of Mars9 and we expect that liquid brines are abundant beyond equatorial regions where atmospheric humidity is higher and temperatures are lower.

  • 286.
    Martín-Torres, Javier
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    A space rose by another name smells sweeter2017Inngår i: New scientist (1971), ISSN 0262-4079, Vol. 233, nr 3116, s. 52-54Artikkel i tidsskrift (Fagfellevurdert)
  • 287.
    Martín-Torres, Javier
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Zorzano Mier, Maria-Paz
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Should We Invest in Martian Brine Research to Reduce Mars Exploration Costs?2017Inngår i: Astrobiology, ISSN 1531-1074, E-ISSN 1557-8070, Vol. 17, nr 1, s. 3-7Artikkel i tidsskrift (Fagfellevurdert)
  • 288.
    Mendaza de Cal, Maria Teresa
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Blanco-Ávalos, J.J.
    Universidad Alcalá de Henares (UAH) Dpto. Física y Matemáticas, Campus Científico-Tecnológico (Externo) Alcalá de Henares (Madrid).
    Martin-Torres, Javier
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Instituto Andaluz de Ciencias de la Tierra (UGR-CSIC), Avenida de las Palmeras 4, Armilla, Granada, Spain.
    Interplanetary Coronal Mass Ejection effects on thermospheric density as inferred from International Space Station orbital data2017Inngår i: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 60, nr 10, s. 2233-2251Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The solar activity induces long term and short term periodical variations in the dynamics and composition of Earth’s atmosphere. The Sun also shows non periodical (i.e., impulsive) activity that reaches the planets orbiting around it. In particular, Interplanetary Coronal Mass Ejections (ICMEs) reach Earth and interact with its magnetosphere and upper neutral atmosphere. Nevertheless, the interaction with the upper atmosphere is not well characterized because of the absence of regular and dedicated in situ measurements at high altitudes; thus, current descriptions of the thermosphere are based on semi empirical models.

    In this paper, we present the total neutral mass densities of the thermosphere retrieved from the orbital data of the International Space Station (ISS) using the General Perturbation Method, and we applied these densities to routinely compiled trajectories of the ISS in low Earth orbit (LEO). These data are explicitly independent of any atmospheric model. Our density values are consistent with atmospheric models, which demonstrates that our method is reliable for the inference of thermospheric density. We have inferred the thermospheric total neutral density response to impulsive solar activity forcing from 2001 to the end of 2006 and determined how solar events affect this response. Our results reveal that the ISS orbital parameters can be used to infer the thermospheric density and analyze solar effects on the thermosphere.

  • 289.
    Mendrok, Jana
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Eriksson, Patrick
    Chalmers University of Technology.
    PERRIN, Agnes
    LISA, CNRS.
    HARTOGH, Paul
    Max-Planck-Institut für Solar System Research.
    REZAC, Ladislav
    Max-Planck-Institut für Solar System Research.
    Lemke, Oliver
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    ARTS+ - A toolbox for microwave atmospheric radiative transfer in solar system planets2013Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Microwave and (sub)millimetre-wave frequencies have long been of interest for remote sensing of the Earth and space objects. They suffer less from interference by small particles (dust, clouds), hence penetrate deeper into atmospheres revealing their deeper structures hidden to shorter wavelengths, and possess characteristic line absorption features of many gaseous species, which are of interest for the understanding of atmospheric chemistry and dynamics.Models simulating radiative transfer and wave propagation (RT/WP) have been developed by many institutions. Most of them are designed for a particular, narrow region of the electromagnetic spectrum, certain instrument types or missions, and specific atmospheric conditions. In particular, they are usually set up for a specific planetary body. This high level of specialisation allows for accurate modelling results. However, it also limits the flexibility of those models and comparability between them.For various applications there is a demand on easy and quick calculations of propagation characteristics, like feasibility estimates of missions proposed to space agencies and performance estimates of radiocommunication links between satellites or orbiter and lander.Within an ESA study we have developed a toolbox for microwave RT/WP in planetary atmospheres. The toolbox consists of the RT/WP model and a data package. The RT/WP model is a largely revised and extended version of ARTS, a sophisticated, flexible RT model for Earth atmosphere (3D spherical geometry, diverse absorption models, scattering, polarization, Jacobians). Focus has been on creating a consistent, physics-based model. Several features have been added (radio link and cloud radar modes, zeeman splitting, doppler shifts). A new spectroscopic approach has been implemented considering effects of a range of broadening/pressure-shifting/refracting species, a corresponding spectroscopic line catalogue designed and prepared. At the current state, the data package contains atmospheric and surface data for Earth and the planets Venus, Mars, and Jupiter, but is easily extendable.We will illustrate the capabilities of the toolbox introducing several example cases and presenting results from the toolbox validation.

  • 290.
    Mendrok, Jana
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Wu, Dong L.
    Jet Propulsion Laboratory.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Jimenez, Carlos
    Observatoire de Paris.
    Kasai, Yasuko
    National Institute of Information and Communications Technology, 4-2-1 Nukui-kitamachi, Koganei.
    Sub-millimeter wave radiometer for observation of cloud ice: a proposal for Japanese mission2009Inngår i: Sensors, Systems, and Next-Generation Satellites XIII: 31 August - 3 September 2009, Berlin, Germany / [ed] Roland Meynart, Bellingham, Wash: SPIE - International Society for Optical Engineering, 2009Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Ice clouds play an important role in the energy budget of the atmosphere as well as in the hydrological cycle. Currently cloud ice is one of the largest remaining uncertainties in climate models. Large discrepancies arise from different assumptions on ice cloud properties, in particular on microphysics, which are not sufficiently constrained by measurements. Passive sub-millimeter wave (SMM) techniques have the potential of providing direct information on ice content and particle sizes with daily global coverage. Here we introduce a concept for a compact 2-receiver SMM sensor and demonstrate its capabilities on measurements of ice content, mean particle size, and cloud altitude.

  • 291.
    Menzel Barbara, Antara
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Investigation of low-energy PPT's for CubeSat's2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The Pulsed Plasma Thruster (PPT) is the oldest type of electric propulsion, as the first was sent into spacein 1964. However, this technology was mostly abandoned in the subsequent decades, with more efficient electric propulsion technologies having been developed. In parallel with the rise in popularity of nanosatellites, the last two decades have sparked a growing interest for this type of propulsion due to its apparent simplicity, low cost and easy-scalability in terms of size and power. This work offers a preliminary investigation of a low-energy PPT for an eventual integration in a CubeSat. A comprehensive literature review on PPT’s provides an overview over the wealth of information that has been gathered over the past five decades. A short literature review of CubeSat’s, their history, advantages, limitations and subsystems introduces the subject to allow for a design process tailored on CubeSat’s needs. A subsequent market analysis of Attitude Control Systems (ACS) and already designed PPT’s for CubeSat allows to envision apotential future PPT for attitude control and drag compensation that could be marketable. After an overview of past PPT research done at the National Cheng Kung University in Taiwan, experiments were conductedon sub-1J PPT’s. Long term tests were performed and allowed to see the limitations of the design of the sparkplug. Measurements of the eroded mass to determine the eroded mass per discharge were attempted but were unsuccessful due to insufficient resolution of the balance. A new set of electrodes was designed and the Impulse-bit, analogous to thrust-per-pulse, of all set electrodes were measured using a semi-empirical formula. A significant novelty was the attempted use of Quartz instead of PTFE between theelectrodes, which resulted in successful discharges without performance decrease compared to the equivalent PTFE PPT. This yields the promise to mitigate the problem of carbon-coating in the discharge chamber. However, it remains unclear if the presence of PTFE in the sparkplug may have been a significant source of the plasma and thus would have compensated for the lack of PTFE in-between the electrodes. Future research will have to determine if similar performance figures can be achieved even without the presence of PTFE in the sparkplug, as well as investigate if the erosion rate of the sparkplug is higher when Quartz is used.

  • 292.
    Mignard, F.
    et al.
    Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange.
    Granvik, Mikael
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Department of Physics, University of Helsinki.
    Zwitter, T.
    University of Ljubljana, Faculty of Mathematics & Physics.
    Gaia Data Release 2: The celestial reference frame (Gaia-CRF2)2018Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 16, nr A14Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Context. The second release of Gaia data (Gaia DR2) contains the astrometric parameters for more than half a million quasars. This set defines a kinematically non-rotating reference frame in the optical domain. A subset of these quasars have accurate VLBI positions that allow the axes of the reference frame to be aligned with the International Celestial Reference System (ICRF) radio frame. Aims. We describe the astrometric and photometric properties of the quasars that were selected to represent the celestial reference frame of Gaia DR2 (Gaia-CRF2), and to compare the optical and radio positions for sources with accurate VLBI positions. Methods. Descriptive statistics are used to characterise the overall properties of the quasar sample. Residual rotation and orientation errors and large-scale systematics are quantified by means of expansions in vector spherical harmonics. Positional differences are calculated relative to a prototype version of the forthcoming ICRF3. Results. Gaia-CRF2 consists of the positions of a sample of 556 869 sources in Gaia DR2, obtained from a positional cross-match with the ICRF3-prototype and AllWISE AGN catalogues. The sample constitutes a clean, dense, and homogeneous set of extragalactic point sources in the magnitude range G similar or equal to 16 to 21 mag with accurately known optical positions. The median positional uncertainty is 0.12 mas for G < 18 mag and 0.5 mas at G = 20 mag. Large-scale systematics are estimated to be in the range 20 to 30 mu as. The accuracy claims are supported by the parallaxes and proper motions of the quasars in Gaia DR2. The optical positions for a subset of 2820 sources in common with the ICRF3-prototype show very good overall agreement with the radio positions, but several tens of sources have significantly discrepant positions. Conclusions. Based on less than 40% of the data expected from the nominal Gaia mission, Gaia-CRF2 is the first realisation of a non-rotating global optical reference frame that meets the ICRS prescriptions, meaning that it is built only on extragalactic sources. Its accuracy matches the current radio frame of the ICRF, but the density of sources in all parts of the sky is much higher, except along the Galactic equator.

  • 293.
    Mihalikova, Maria
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Mesoscale processes in the polar atmosphere: radar remote sensing, balloon-borne in situ measurements and modelling2013Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Mesoscale processes (atmospheric phenomena with horizontal scales ranging from a few tens to several hundred kilometres and lasting from a few tens of minutes to a few days) have the potential to influence the chemical composition of the troposphere. Tropopause folds and mountain waves are two important types of mesoscale processes. Concentrations and gradients of trace gases like ozone (O3) can be influenced by these processes. Tropopause folds bring ozone-rich stratospheric air to lower altitudes. Mountain waves and turbulence associated with them influence O3 gradients in the troposphere. Tropospheric O3 is a toxic pollutant and a short-lived greenhouse gas with an influence on the lifetime of many other trace gases. Understanding of its long-term development and budgets are important. For this, better understanding, generalization and representation of mesoscale processes are necessary. Observations made by the 52MHz wind-profiler radar ESRAD (ESrange RADar) and the 54.5MHz wind-profiler radar MARA (Movable Atmospheric Radar for Antarctica) served as the basis for this study. ESRAD is located close to Kiruna in arctic Sweden and has been in operation since July 1996. This is a site with frequent mountain wave activity. By analysis of ESRAD and sonde data we have studied vertical mixing and turbulence associated with mountain waves. An attempt was made to show the influence of these processes on relaxation of the O3 gradient in the lower troposphere. Additional balloon-borne in situ measurements of vertical profiles of atmospheric characteristics (temperature, humidity, O3 mixing ratio) complement the radar measurements and aid in correct identification and improved understanding of the observed processes as well as of the radar backscatter signal itself. MARA was operated at the Swedish summer station Wasa (73°S, 13.5°W) during austral summer 2010/2011 and at the Norwegian year-round station Troll (72°S, 2.5°E) nonstop since December 2011. During its operation at the Wasa station, ozonesonde measurements were successfully undertaken during the passage of a tropopause fold. These provided validity to the radar measurements and proved them to be a useful tool for tropopause fold studies, for the first time at Antarctic latitudes. Data gathered at the Troll station exhibit signs of an annual cycle of tropopause folds with winter maximum and summer minimum in their occurrence rate which is similar to the observed behaviour in the northern hemisphere. Comparisons with ECMWF (European Centre for Medium-Range Weather Forecasts) model data and the WRF model (Advanced Research and Weather Forecasting) show that higher resolution models such as WRF are needed for more adequate representation of these processes. High resolution models can in return serve as a basis for studies of areas that are not at all or only partially covered by measurement networks, as well as for global studies. Thus they can provide useful information about atmospheric transport and the state of trace gases like O3.

  • 294.
    Mihalikova, Maria
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Kirkwood, Sheila
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Tropopause fold occurrence rates over the Antarctic station Troll (72 degrees S, 2.5 degrees E)2013Inngår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 31, nr 4, s. 591-598Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    One of the important mechanisms of stratosphere-troposphere exchange, which brings ozone-rich stratospheric air to low altitudes in extratropical regions, is transport related to tropopause folds. The climatology of folds has been studied at high latitudes of the Northern Hemisphere with the help of radars and global models. Global models supply information about fold occurrence rates at high latitudes of the Southern Hemisphere as well, but so far comparisons with direct measurements are rare. The Moveable Atmospheric Radar for Antarctica (MARA), a 54.5 MHz wind-profiler radar, has been operated at the Norwegian year-round station Troll, Antarctica (72 degrees S, 2.5 degrees E) since December 2011. Frequent tropopause fold signatures have been observed. In this study, based on MARA observations, an occurrence rate statistics of tropopause folds from December 2011 until November 2012 has been made, and radar data have been compared with the analysis from the European Center for Medium-Range Weather Forecasting (ECMWF). The fold occurrence rates exhibit an annual cycle with winter maximum and summer minimum and suggest significantly higher occurrence rates for the given location than those obtained previously by global model studies.

  • 295.
    Mihalikova, Maria
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Kirkwood, Sheila
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Vertical mixing in the lower troposphere by mountain waves over Arctic Scandinavia2011Inngår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 11, s. 31475-31493Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Measurements made by ozonesondes and by a 52 MHz wind-profiling radar during February and March 1997 are studied. The radar is located at Esrange, near Kiruna in Arctic Sweden, on the eastern flank of the Scandinavian mountains. Daily ozonesondes were launched from the same site. The radar vertical and horizontal wind measurements are used to identify times when mountain waves were present. Mean vertical gradients in ozone mixing ratio in the lower troposphere are determined in conditions with mountain waves present and when they were absent. Back-trajectories were calculated so that only air-masses with their origin to the west of the mountains were included in the final averages. The vertical gradient in ozone mixing ratio is found to be about twice as steep outside wave conditions as it is during mountain waves. This suggests a very high rate of vertical mixing, with an average eddy diffusivity of order 5000 m2 s−1. This is consistent with an earlier estimate of the occurrence rate of complete mixing by wave breaking over the mountain range.

  • 296.
    Mihalikova, Maria
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Kirkwood, Sheila
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Arnault, J.
    Polar Atmospheric Research, Swedish Institute of Space Physics, Box 812, 98128, Kiruna.
    Mikhaylova, D.
    Polar Atmospheric Research, Swedish Institute of Space Physics, Box 812, 98128, Kiruna.
    Observation of a tropopause fold by MARA VHF wind-profiler radar and ozonesonde at Wasa, Antarctica: Comparison with ECMWF analysis and a WRF model simulation2012Inngår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 30, nr 9, s. 1411-1421Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Tropopause folds are one of the mechanisms of stratosphere-troposphere exchange, which can bring ozone rich stratospheric air to low altitudes in the extra-tropical regions. They have been widely studied at northern mid-or high latitudes, but so far almost no studies have been made at mid-or high southern latitudes. The Moveable Atmospheric Radar for Antarctica (MARA), a 54.5 MHz wind-profiler radar, has operated at the Swedish summer station Wasa, Antarctica (73° S, 13.5° W) during austral summer seasons from 2007 to 2011 and has observed on several occasions signatures similar to those caused by tropopause folds at comparable Arctic latitudes. Here a case study is presented of one of these events when an ozonesonde successfully sampled the fold. Analysis from European Center for Medium Range Weather Forecasting (ECMWF) is used to study the circumstances surrounding the event, and as boundary co

  • 297.
    Mikael, Hedberg
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    CFD simulations of Luleälven: An examination of CFD as a tool forevaluating restoration possibilities of regulated dredgedrivers2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Dredged rivers remain from when lumber was floated downriver for processing and shipping purposes. This has left parts of some rivers in Sweden with shallow rocky beaches and deep central furrows. Restoration efforts of dredged unregulated rivers has shown positive results for fish populations. This report compares, by use of CFD two regulated parts of Luleälven, one dredged and one natural. The report looks at habitats where the Riverine Grayling prefers to lay its eggs and evaluates whether velocity and depth conditions could give an explanation for the lower population of the Riverine Grayling in the dredged river. For the water levels tested, usable areas exist for all cases, but the dredged river has substantially smaller areas suitable as a habitat. The river geometry seems to be the large issue for Mattisudden as its shallow wide riverbanks are not conducive to habitats for the Riverine Grayling. Surprisingly the "lower" test case for the dredged river showed a larger usable area than for the "higher" water level, for the same river and higher usable area than the natural river. For this case the water level is now so low that the shallow wide riverbanks are above the water level and only the central furrow is filled with water. This shows two avenues that can be used to improve the habitats for the Riverine Grayling, lower the water level, or raise the riverbanks.

  • 298.
    Millán, L.
    et al.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
    Read, W.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
    Kasai, Y.
    National Institute of Information and Communications Technology, 4-2-1 Nukui-kitamachi, Koganei.
    Lambert, A.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
    Livesey, N.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
    Mendrok, Jana
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Sagawa, H.
    National Institute of Information and Communications Technology, 4-2-1 Nukui-kitamachi, Koganei.
    Sano, T.
    Japanese Aerospace Exploration Agency, Cho-fu, Tokyo.
    Shiotani, M.
    Kyoto University.
    Wu, D.L.
    NASA Goddard Space Flight Center.
    SMILES ice cloud products2013Inngår i: Journal of Geophysical Research: Atmospheres, ISSN 2169-8996, Vol. 118, nr 12, s. 6468-6477Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Upper tropospheric water vapor and clouds play an important role in Earth's climate, but knowledge of them, in particular diurnal variation in deep convective clouds, is limited. An essential variable to understand them is cloud ice water content. The Japanese Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) on board the International Space Station (ISS) samples the atmosphere at different local times allowing the study of diurnal variability of atmospheric parameters. We describe a new ice cloud data set consisting of partial Ice Water Path and Ice Water Content. Preliminary comparisons with EOS-MLS, CloudSat-CPR and CALIOP-CALIPSO are presented. Then, the diurnal variation over land and over open ocean for partial ice water path is reported. Over land, a pronounced diurnal variation peaking strongly in the afternoon/early evening was found. Over the open ocean, little temporal dependence was encountered. This data set is publicly available for download in HDF5 format.

  • 299.
    Milz, Mathias
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Study on forest fire detection with satellite data2013Rapport (Annet vitenskapelig)
  • 300. Milz, Mathias
    et al.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    John, V.O.
    Met Office Hadley Centre, Exeter.
    Comparison of AIRS and AMSU-B monthly mean estimates of upper tropospheric humidity2009Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 36, nr L10804Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Satellite-borne measurements provide valuable information on the global distribution of upper tropospheric humidity (UTH), which represents the mean relative humidity in a layer approximately enclosed by the atmospheric pressure levels 500 and 200 hPa. Monthly mean distributions of microwave observations of UTH obtained from the Advanced Microwave Sounding Unit-B (AMSU-B) and the Humidity Sounder for Brazil (HSB) are compared to infrared observations of UTH from the Atmospheric Infrared Sounder (AIRS). All data sets for January 2003 show distributions as expected from climatologies. Data of AIRS and AMSU-B averaged on 1.5° × 1.5° lat-lon bins for January 2003 show good overall agreement. However, with 2.7%RH AIRS shows an unexpected wet mean bias, especially for regions where the influence of clouds is small or cloud affected measurements are excluded for both sensors. In regions where AIRS is sensitive to cloud affected measurements but not AMSU-B, the bias is reduced and partly negative.

3456789 251 - 300 of 449
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf