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  • 151.
    Earle, M.E.
    et al.
    Department of Earth and Environmental Sciences, University of Waterloo.
    Kuhn, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Khalizov, A.F.
    Department of Earth and Environmental Sciences, University of Waterloo.
    Sloan, J.J.
    Department of Earth and Environmental Sciences, University of Waterloo.
    Volume nucleation rates for homogeneous freezing in supercooled water microdroplets: results from a combined experimental and modelling approach2009In: Atmospheric Chemistry and Physics Discussions, ISSN 1680-7367, E-ISSN 1680-7375, Vol. 9, no 5, p. 22883-22927Article in journal (Refereed)
    Abstract [en]

    Temperature-dependent volume nucleation rate coefficients for supercooled water droplets, JV(T), are derived from infrared extinction measurements in a cryogenic laminar aerosol flow tube using a microphysical model. The model inverts water and ice aerosol size distributions retrieved from experimental extinction spectra by considering the evolution of a measured initial droplet distribution via homogeneous nucleation and the exchange of vapour-phase water along a well-defined temperature profile. Experiment and model results are reported for supercooled water droplets with mode radii of 1.0, 1.7, and 2.9 α1/4m. Values of mass accommodation coefficients for evaporation of water droplets and vapour deposition on ice particles are also determined from the model simulations. The coefficient for ice deposition was found to be approximately 0.031, while that for water evaporation was 0.054. Results are considered in terms of the applicability of classical nucleation theory to the freezing of micrometre-sized droplets in cirrus clouds, with implications for the parameterization of homogeneous ice nucleation in numerical models.

  • 152.
    Earle, M.E.
    et al.
    Department of Earth and Environmental Sciences, University of Waterloo.
    Kuhn, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Khalizov, A.F.
    Department of Earth and Environmental Sciences, University of Waterloo.
    Sloan, J.J.
    Department of Earth and Environmental Sciences, University of Waterloo.
    Volume nucleation rates for homogeneous freezing in supercooled water microdroplets: results from a combined experimental and modelling approach2010In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, no 16, p. 7945-7961Article in journal (Refereed)
    Abstract [en]

    Temperature-dependent volume nucleation rate coefficients for supercooled water droplets, JV(T), are derived from infrared extinction measurements in a cryogenic laminar aerosol flow tube using a microphysical model. The model inverts water and ice aerosol size distributions retrieved from experimental extinction spectra by considering the evolution of a measured initial droplet distribution via homogeneous nucleation and the exchange of vapour-phase water along a well-defined temperature profile. Experiment and model results are reported for supercooled water droplets with mean radii of 1.0, 1.7, and 2.9 μ1/4m. Values of mass accommodation coefficients for evaporation of water droplets and vapour deposition on ice particles are also determined from the model simulations. The coefficient for ice deposition was found to be 0.031 ± 0.001, while that for water evaporation was 0.054 ± 0.012. Results are considered in terms of the applicability of classical nucleation theory to the freezing of micrometre-sized droplets in cirrus clouds, with implications for the parameterization of homogeneous ice nucleation in numerical models.

  • 153.
    Echle, Georg
    et al.
    Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe.
    Clarmann, Thomas von
    Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe.
    Dudhia, Anu
    Atmospheric, Oceanic, and Planetary Physics, Oxford University.
    Flaud, Jean-Marie
    Laboratoire de Photophysique Moléculaire, CNRS, Université Paris-Sud, Orsay.
    Funke, Bernd
    Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe.
    Glatthor, Norbert
    Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe.
    Kerridge, Brian
    Rutherford Appleton Laboratory, Oxfordshire.
    López-Puertas, Manuel
    Instituto de Astrofísica de Andalucía CSIC, Granada.
    Martin-Torres, Javier
    Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe.
    Stiller, Gabriele P.
    Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe.
    Optimized spectral microwindows for data analysis of the Michelson Interferometer for Passive Atmospheric Sounding on the Environmental Satellite2000In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 39, no 30, p. 5531-Article in journal (Refereed)
    Abstract [en]

    For data analysis of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) atmospheric limb emission spectroscopic experiment on Environmental Satellite microwindows, i.e., small spectral regions for data analysis, have been defined and optimized. A novel optimization scheme has been developed for this purpose that adjusts microwindow boundaries such that the total retrieval error with respect to measurement noise, parameter uncertainties, and systematic errors is minimized. Dedicated databases that contain optimized microwindows for retrieval of vertical profiles of pressure and temperature, H2O, O3, HNO3, CH4, N2O, and NO2 have been generated. Furthermore, a tool for optimal selection of subsets of predefined microwindows for specific retrieval situations has been provided. This tool can be used further for estimating total retrieval errors for a selected microwindow subset. It has been shown by use of this tool that an altitude-dependent definition of microwindows is superior to an altitude-independent definition. For computational efficiency a dedicated microwindow-related list of spectral lines has been defined that contains only those spectral lines that are of relevance for MIPAS limb sounding observations.

  • 154.
    Edberg, Niklas J. T.
    et al.
    Swedish Institute of Space Physics, Uppsala, Sweden.
    Eriksson, Anders I.
    Swedish Institute of Space Physics, Uppsala, Sweden.
    Vigren, Erik
    Swedish Institute of Space Physics, Uppsala, Sweden.
    Johansson, Fredrik L.
    Swedish Institute of Space Physics, Uppsala, Sweden.
    Goetz, Charlotte
    Institut für Geophysik und extraterrestrische Physik, Technische Universität Braunschweig, Germany.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna, Sweden.
    Gilet, Nicolas
    Laboratoire de Physique et Chimie de l’Environnement et de l’Espace (LPC2E), CNRS, Orléans, France.
    Henri, Pierre
    Laboratoire de Physique et Chimie de l’Environnement et de l’Espace (LPC2E), CNRS, Orléans, France.
    The Convective Electric Field Influence on the Cold Plasma and Diamagnetic Cavity of Comet 67P2019In: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 158, no 2, article id 71Article in journal (Refereed)
    Abstract [en]

    We studied the distribution of cold electrons (<1 eV) around comet 67P/Churyumov–Gerasimenko with respect to the solar wind convective electric field direction. The cold plasma was measured by the Langmuir Probe instrument and the direction of the convective electric field  conv = − ×  was determined from magnetic field () measurements inside the coma combined with an assumption of a purely radial solar wind velocity . We found that the cold plasma is twice as likely to be observed when the convective electric field at Rosetta's position is directed toward the nucleus (in the − convhemisphere) compared to when it is away from the nucleus (in the + conv hemisphere). Similarly, the diamagnetic cavity, in which previous studies have shown that cold plasma is always present, was also found to be observed twice as often when in the − conv hemisphere, linking its existence circumstantially to the presence of cold electrons. The results are consistent with hybrid and Hall magnetohydrodynamic simulations as well as measurements of the ion distribution around the diamagnetic cavity.

  • 155.
    Ehlers, Dennis
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Aalto University, School of Electrical Engineering.
    Learning Search Strategies from Human Demonstration for Robotic Assembly Tasks2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Learning from Demonstration (LfD) has been used in robotics research for the last decades to solve issues pertaining to conventional programming of robots. This framework enables a robot to learn a task simply from a human demonstration. However, it is unfeasible to teach a robot all possible scenarios, which may lead to e.g. the robot getting stuck. In order to solve this, a search is necessary. However, no current work is able to provide a search approach that is both simple and general. This thesis develops and evaluates a new framework based on LfD that combines both of these aspects. A single demonstration of a human search is made and a model of it is learned. From this model a search trajectory is sampled and optimized. Based on that trajectory, a prediction of the encountered environmental forces is made. An impedance controller with feed-forward of the predicted forces is then used to evaluate the algorithm on a Peg-in-Hole task. The final results show that the framework is able to successfully learn and reproduce a search from just one single human demonstration. Ultimately some suggestions are made for further benchmarks and development.

  • 156.
    Ekman, Jonas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Martin-Torres, Javier
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Emami, Reza
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Törlind, Peter
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Kuhn, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nilsson, Hans
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Minami, Ichiro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Öhrwall Rönnbäck, Anna
    Gustafsson, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Zorzano Mier, María-Paz
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Milz, Mathias
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Grahn, Mattias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Parida, Vinit
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Wolf, Veronika
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Dordlofva, Christo
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Mendaza de Cal, Maria Teresa
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Jamali, Maryam
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Roos, Tobias
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Ottemark, Rikard
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nieto, Chris
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Soria Salinas, Álvaro Tomás
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Vázquez Martín, Sandra
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nyberg, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Neikter, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lindwall, Angelica
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Fakhardji, Wissam
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Projekt: Rymdforskarskolan2015Other (Other (popular science, discussion, etc.))
    Abstract [en]

    The Graduate School of Space Technology

  • 157.
    Ekström, M.
    et al.
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Eriksson, P.
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Read, W. G.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
    Milz, Mathias
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Murtagh, D. P.
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Comparison of satellite limb-sounding humidity climatologies of the uppermost tropical troposphere2008In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 8, no 2, p. 309-320Article in journal (Refereed)
    Abstract [en]

    Humidity climatologies of the tropical uppermost troposphere from satellite limb emission measurements have been compared. Four instruments are considered; UARS-MLS, Odin-SMR, and Aura-MLS operating in the microwave region, and MIPAS in the infrared region. A reference for the comparison is obtained by MOZAIC in-situ measurements. The upper tropospheric humidity products were compared on basis of their empirical probability density functions and seasonally averaged horizontal fields at two altitude layers, 12 and 15 km. The probability density functions of the microwave datasets were found to be in very good agreement with each other, and were also consistent with MOZAIC. The average seasonal humidities differ with less than 10%RHi between the instruments, indicating that stated measurement accuracies of 20–30% are conservative estimates. The systematic uncertainty in Odin-SMR data due to cloud correction was also independently estimated to be 10%RHi. MIPAS humidity profiles were found to suffer from cloud contamination, with only 30% of the measurements reaching into the upper troposphere, but under clear-sky conditions there is a good agreement between MIPAS, Odin-SMR and Aura-MLS. Odin-SMR and the two MLS datasets can be treated as independent, being based on different underlying spectroscopy and technology. The good agreement between the microwave limb-sounders, and MOZAIC, is therefore an important step towards understanding the upper tropospheric humidity. The found accuracy of 10%RHi is approaching the level required to validate climate modelling of the upper troposphere humidity. The comparison of microwave and infrared also stresses that microwave limb-sounding is necessary for a complete view of the upper troposphere.

  • 158.
    Eliasson, Salomon
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Ice clouds in satellite observations and climate models2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Ice clouds have an important role in climate. They are strong modulators of the outgoing longwave radiation and the incoming shortwave radiation and are an integral part of the hydrological cycle. However, our knowledge about them is inadequate. Climate models are far from consensus on the magnitude and spatial distribution of several cloud parameters, including the column integrated cloud ice amount, called Ice Water Path (IWP). The lack of adequate constraints from observations is a main contributor to the non-consensus. Cloud ice retrievals from satellite measurements are an important source of observations, since they are global and continuous. However, they carry large uncertainties since different sensors are sensitive to different aspects of clouds, and because clouds are largely inhomogeneous with complicated microphysical properties. Satellite observations are also notoriously difficult to use for model evaluation, due to a mismatch on how cloud parameters are defined in the models compared to what is actually observed. No satellite instrument can measure information from the entire cloud column, as desired from the model point of view. This thesis mainly concerns IWP, which is one of the key cloud parameters. By measuring clouds using different techniques at different wavelengths, the IWP retrievals are sensitive to different parts of the ice particle size distribution, and different depths in the cloud. A main aim of the PhD project is to assess the agreement of datasets based on different techniques and how they may be complementary. This investigation of IWP in observations and models starts by a comparison study of monthly averaged IWP from a climate perspective. The study shows that the differences in IWP within a group of models, and compared to observations are up to an order of magnitude. This confirmed results from previous studies, but in this study, large differences in the spatial distribution of IWP are also identified. The spatial distributions of modelled IWP indicate that they are in disagreement on where the Tropical convective regions are and how much IWP is found there in relation to the global averaged IWP. However, the observational datasets also differ by up to an order of magnitude and the uncertainties for the monthly averaged observations are almost intangibly large. This prompted a new study comparing strictly collocated observations to each other. By doing so, large uncertainties caused by spatially and temporally averaging data were removed. DARDAR, with IWP retrievals based on a combination of Radar and Lidar measurements, is regarded as the best dataset of IWP, and was therefore chosen as the reference dataset. This study determines that DARDAR has a relatively low uncertainty of between 20% to 50%. The validity ranges of the other datasets, i.e., the IWP values where data are trustworthy, are determined by comparing to DARDAR IWP. Once established for each dataset, the systematic and random errors of each dataset are quantified. It is shown that retrievals based on solar reflectance measurements are sensitive to the largest range of IWP values, from ∼30 gm-2 to ∼7000 gm-2, and have random uncertainties less than a factor of two throughout most of this range. To analyse the uncertainties further, the collocated measurements are assessed separately in different types of cloudy scenarios. It is shown that large uncertainties are attributed to the assumed cloud phase and the choice of IWP parameterisations. Further in depth studies on models were carried out using the EC-Earth climate model. A validation study of several upper tropospheric parameters showed that the model captures most large-scale features but has problems with clouds. This led to another study comparing the modelled evolution of several atmospheric variables before and after deep convection events to that of observations. A follow-up study analyses the impacts of clouds on upper tropospheric humidity (UTH) retrievals depending on if they are based on microwave or infrared measurements. By these cross-dataset comparisons we are closer to understanding how to utilise datasets that normally are not comparable due to their different sensitivities.

  • 159.
    Eliasson, Salomon
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Ice clouds in satellite observations and climate models2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis concerns the microphysical properties of clouds made up of ice particles, called ice clouds. Ice clouds are strong modulators of the outgoing longwave radiation and incoming shortwave radiation, yet our knowledge on several key ice cloud properties, which govern the magnitude and sign of the net contribution to the Earth’s atmospheric radiation budget, is inadequate. For instance, currently climate models are far from consensus on the magnitude and spatial distribution of ice water path (IWP), a vital radiative property of ice clouds, and the main property of concern in this thesis. The large spread amongst the models in terms of IWP is mostly due to the lack of constraints from observations on ice cloud properties. The lacking constraints reflect the major difficulties faced in observing global ice cloud properties.In-situ measurements provide useful sources of information on ice clouds, but are far from adequate due to the sparseness of measurements. Cloud ice observations from satellites provides a global view and is the most useful source of information. However, measurements from satellites also carry large uncertainties and are notoriously difficult to use for model evaluation, due to a mismatch on how IWP is defined in the models compared to what is actually observed. Not one satellite instrument can measure ice particle information from the entire ice cloud column, as desired from the model point of view. Satellite observations of IWP depend for the most part on the wavelength spectrum the instrument measures in, hence the instruments measure related, but different information on clouds.A study addressing the satellite observed and modeled IWP is presented in the first appended article: Eliasson et al. [2011]. Large differences between climate models are observations, especially in areas with frequent deep convection, were reported and discussed. The second appended article is a first evaluation study of cloud parameters, such as IWP, in the EC-Earth climate model using satellite A-Train observations. The model captures large-scale features for the most part but has problems related to ice water content and cloud fraction. This is strongly linked to the treatment of precipitation.The thesis contains introductory chapters on ice clouds; their formation, radiative importance, and representation in climate models. This is followed by a more in depth chapter on the observational data. The different satellite techniques are then discussed following a radiation physics and radiative transfer background section.

  • 160. Eliasson, Salomon
    et al.
    Buehler, Stefan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Milz, Mathias
    A study on the ice water path descrepencies between global climate models2008Conference paper (Other academic)
  • 161.
    Eliasson, Salomon
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Buehler, Stefan
    Milz, Mathias
    Eriksson, P.
    Department of Radio and Space Science, Chalmers University of Technology.
    John, V.O.
    Met Office Hadley Centre, Exeter.
    Assessing modelled spatial distributions of ice water path using satellite data2010In: Atmospheric Chemistry and Physics Discussions, ISSN 1680-7367, E-ISSN 1680-7375, Vol. 10, no 5, p. 12185-12224Article in journal (Refereed)
    Abstract [en]

    The climate models used in the IPCC AR4 show large differences in monthly mean cloud ice. The most valuable source of information that can be used to potentially constrain the models is global satellite data. For this, the data sets must be long enough to capture the inter-annual variability of Ice Water Path (IWP). PATMOS-x was used together with ISCCP for the annual cycle evaluation in Fig. 7 while ECHAM-5 was used for the correlation with other models in Table 3. A clear distinction between ice categories in satellite retrievals, as desired from a model point of view, is currently impossible. However, long-term satellite data sets may still be used to indicate the climatology of IWP spatial distribution. We evaluated satellite data sets from CloudSat, PATMOS-x, ISCCP, MODIS and MSPPS in terms of monthly mean IWP, to determine which data sets can be used to evaluate the climate models. IWP data from CloudSat cloud profiling radar provides the most advanced data set on clouds. As CloudSat data are too short to evaluate the model data directly, it was mainly used here to evaluate IWP from the other satellite data sets. ISCCP and MSPPS were shown to have comparatively low IWP values. ISCCP shows particularly low values in the tropics, while MSPPS has particularly low values outside the tropics. MODIS and PATMOS-x were in closest agreement with CloudSat in terms of magnitude and spatial distribution, with MODIS being the best of the two. As PATMOS-x extends over more than 25 years and is in fairly close agreement with CloudSat, it was chosen as the reference data set for the model evaluation. In general there are large discrepancies between the individual climate models, and all of the models show problems in reproducing the observed spatial distribution of cloud-ice. Comparisons consistently showed that ECHAM-5 is the GCM from IPCC AR4 closest to satellite observations

  • 162.
    Eliasson, Salomon
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Buehler, Stefan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Milz, Mathias
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Eriksson, P.
    Chalmers University of Technology, Department of Earth and Space Sciences.
    John, V.O.
    Met Office Hadley Centre, Exeter.
    Assessing observed and modelled spatial distributions of ice water path using satellite data2011In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 11, no 1, p. 375-391Article in journal (Refereed)
    Abstract [en]

    The climate models used in the IPCC AR4 show large differences in monthly mean ice water path (IWP). The most valuable source of information that can be used to potentially constrain the models is global satellite data. The satellite datasets also have large differences. The retrieved IWP depends on the technique used, as retrievals based on different techniques are sensitive to different parts of the cloud column. Building on the foundation of Waliser et al. (2009), this article provides a more comprehensive comparison between satellite datasets. IWP data from the CloudSat cloud profiling radar provide the most advanced dataset on clouds. For all its unmistakable value, CloudSat data are too short and too sparse to assess climatic distributions of IWP, hence the need to also use longer datasets. We evaluate satellite datasets from CloudSat, PATMOS-x, ISCCP, MODIS and MSPPS in terms of monthly mean IWP, in order to determine the differences and relate them to the sensitivity of the instrument used in the retrievals. This information is also used to evaluate the climate models, to the extent that is possible. ISCCP and MSPPS were shown to have comparatively low IWP values. ISCCP shows particularly low values in the tropics, while MSPPS has particularly low values outside the tropics. MODIS and PATMOS-x were in closest agreement with CloudSat in terms of magnitude and spatial distribution, with MODIS being the better of the two. Additionally PATMOS-x and ISCCP, which have a temporal range long enough to capture the inter-annual variability of IWP, are used in conjunction with CloudSat IWP (after removing profiles that contain precipitation) to assess the IWP variability and mean of the climate models. In general there are large discrepancies between the individual climate models, and all of the models show problems in reproducing the observed spatial distribution of cloud-ice. Comparisons consistently showed that ECHAM-5 is probably the GCM from IPCC AR4 closest to satellite observations

  • 163.
    Eliasson, Salomon
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Holl, Gerrit
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Buehler, Stefan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Kuhn, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Stengel, M.
    Iturbe-Sanchez, F.
    Johnston, M.
    Systematic and random errors between collocated satellite ice water path observations2013In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118, no 6, p. 2629-2642Article in journal (Refereed)
    Abstract [en]

    There remains large disagreement between IWP in observational datasets, largely because the sensors observe different parts of the ice particle size distribution. A detailed comparison of retrieved IWP from satellite observations in the Tropics ({plus minus}30{degree sign} latitude) in 2007 is made using collocated measurements. The DARDAR IWP dataset, based on combined Radar/Lidar measurements, is used as a reference as it provides arguably the best estimate of the total column IWP. For each dataset, usable IWP dynamic ranges are inferred from this comparison. IWP retrievals based on solar reflectance measurements, MODIS, and AVHRR-based CMSAF, and PATMOS-x, were found to be correlated with DARDAR over a large IWP range (~20-7000 g/m-2;). The random errors of the collocated datasets have a close to log-normal distribution, and the combined random error of MODIS and DARDAR is less than a factor of 2, which also sets the upper limit for MODIS alone. In the same way the upper limit for the random error of all considered datasets is determined. Datasets based on passive microwave measurements,MSPPS, MiRS, and CMO, are largely correlated with DARDAR for IWP values larger than approximately 700 g/m². The combined uncertainty between these datasets and DARDAR in this range is slightly less MODIS-DARDAR, but the systematic bias is nearly an order of magnitude.

  • 164.
    Eliasson, Salomon
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Mendrok, Jana
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Systematic and random errors between collocated satellite ice water path observations2013Conference paper (Other academic)
    Abstract [en]

    There remains large disagreement between ice-water path (IWP) in observational data sets, largely because the sensors observe different parts of the ice particle size distribution. A detailed comparison of retrieved IWP from satellite observations in the Tropics (±30° latitude) in 2007 was made using collocated measurements. The radio detection and ranging(radar)/light detection and ranging (lidar) (DARDAR) IWP data set, based on combined radar/lidar measurements, is used as a reference because it provides arguably the best estimate of the total column IWP. For each data set, usable IWP dynamic ranges are inferred from this comparison. IWP retrievals based on solar reflectance measurements, in the moderate resolution imaging spectroradiometer (MODIS), advanced very high resolution radiometer–based Climate Monitoring Satellite Applications Facility (CMSAF), and Pathfinder Atmospheres-Extended (PATMOS-x) datasets, were found to be correlated with DARDAR over a large IWP range (~20–7000 g m-2). The random errors of the collocated data sets have a close to lognormal distribution, and the combined random error of MODIS and DARDAR is less than a factor of 2, which also sets the upper limit for MODIS alone. In the same way, the upper limit for the random error of all considered data sets is determined. Data sets based on passive microwave measurements, microwave surface and precipitation products system (MSPPS), microwave integrated retrieval system (MiRS), and collocated microwave only (CMO), are largely correlated with DARDAR for IWP values larger than approximately 700 g m-2. The combined uncertainty between these data sets and DARDAR in this range is slightly less MODIS-DARDAR, but the systematic bias is nearly an order of magnitude.

  • 165. Eliasson, Salomon
    et al.
    Tetzlaff, Anke
    Karlsson, Karl-Göran
    Prototyping an improved PPS cloud detection for the Arctic polar night2007Report (Other academic)
  • 166.
    Emde, C.
    et al.
    Universität Bremen, Institute of Environmental Physics.
    Buehler, Stefan
    Sreerekha, T.R.
    Universität Bremen, Institute of Environmental Physics.
    Modeling polarized microwave radiation in a 3D spherical cloudy atmosphere2003In: Electromagnetic and Light Scattering: Theory and applications / [ed] T. Wriedt, University of Bremen , 2003Conference paper (Refereed)
  • 167.
    Emde, Claudia
    et al.
    Universität Bremen, Institute of Environmental Physics.
    Buehler, Stefan
    Davis, C.
    University of Edinburgh, Institute of Atmospheric and Environmental Science.
    Eriksson, Patrick
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Sreerekha, T.R.
    Universität Bremen, Institute of Environmental Physics.
    Teichmann, C.
    Universität Bremen, Institute of Environmental Physics.
    A polarized discrete ordinate scattering model for simulations of limb and nadir long-wave measurements in 1-D/3-D spherical atmospheres2004In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 109, no 24, p. 24207-Article in journal (Refereed)
    Abstract [en]

    This article describes one of the scattering algorithms of the three-dimensional polarized radiative transfer model ARTS (Atmospheric Radiative Transfer Simulator) which has been implemented to study for example the influence of cirrus clouds on microwave limb sounding. The model uses the DOIT (Discrete Ordinate Iterative) method to solve the vector radiative transfer equation. The implementation of a discrete ordinate method is challenging due to the spherical geometry of the model atmosphere which is required for the simulation of limb radiances. The involved numerical issues, which are grid optimization and interpolation methods, are discussed in this paper. Scattering simulations are presented for limb- and down-looking geometries, for one-dimensional and three-dimensional spherical atmospheres. They show the impact of cloud particle size, shape, and orientation on the brightness temperatures and on the polarization of microwave radiation in the atmosphere. The cloud effect is much larger for limb radiances than for nadir radiances. Particle size is a very important parameter in all simulations. The polarization signal is negligible for simulations with completely randomly oriented particles, whereas for horizontally aligned particles with random azimuthal orientation the polarization signal is significant. Moreover, the effect of particle shape is only relevant for oriented cloud particles. The simulations show that it is essential to use a three-dimensional scattering model for inhomogeneous cloud layers.

  • 168.
    Emde, Claudia
    et al.
    Universität Bremen, Institute of Environmental Physics.
    Buehler, Stefan
    Eriksson, Patrick
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Sreerekha, T. R.
    Universität Bremen, Institute of Environmental Physics.
    The effect of cirrus clouds on microwave limb radiances2004In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 72, no 1-4, p. 383-401Article in journal (Refereed)
    Abstract [en]

    This study presents and analyses the first simulations of microwave limb radiances with clouds. They are computed using the 1D unpolarized version of the Atmospheric Radiative Transfer System (ARTS). The study is meant to set a theoretical foundation for using microwave limb measurements for cloud monitoring. Information about clouds is required for the validation of climate models.Limb spectra are generated for the frequency bands of the Millimeter wave Acquisitions for Stratosphere/Troposphere Exchange Research (MASTER) instrument. For these simulations, the radiative transfer equation is solved using the Discrete Ordinate ITerative (DOIT) method, which is briefly described. Single scattering properties for the cloud particles are calculated using the T-matrix method.The impact of various cloud parameters is investigated. Simulated brightness temperatures most strongly depend on particle size, ice mass content and cloud altitude. The impact of particle shape is much smaller, but still significant. Increasing the ice mass content has a similar effect as increasing the particle size; this complicates the prediction of the impact of clouds on microwave radiances without exact knowledge of these cloud parameters.

  • 169.
    Engeln, Axel von
    et al.
    Universität Bremen.
    Brocard, E.
    Buehler, Stefan
    Eriksson, P.
    Chalmers University of Technology.
    John, V.O.
    Universität Bremen.
    Kuhn, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Universität Bremen, Institute of Environmental Physics.
    ACE+ Climate Impact Study: Radiation part2004Report (Other academic)
  • 170.
    Engeln, Axel von
    et al.
    Universität Bremen.
    Brocard, E.
    Buehler, Stefan
    Eriksson, Patrick
    Chalmers University of Technology.
    John, V.O.
    Universität Bremen.
    Kuhn, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Universität Bremen, Institute of Environmental Physics.
    ACE+ Climate Impact Study: Radiation part2004Report (Other academic)
  • 171.
    Engeln, Axel von
    et al.
    Universität Bremen.
    Buehler, Stefan
    Kirchengast, Gottfried
    University of Graz.
    Kuenzi, Klaus
    Universität Bremen.
    Temperature profile retrieval from surface to mesopause by combining GNSS radio occultation and passive microwave limb sounder data1999In: Conference on Satellite Meteorology and Oceanography, American Meteorological Society, 1999, p. 240-243Conference paper (Refereed)
  • 172.
    Engeln, Axel von
    et al.
    Universität Bremen, Institute of Environmental Physics.
    Buehler, Stefan
    Kirchengast, Gottfried
    University of Graz, Institute for Geophysics, Astrophysics and Meteorology.
    Kuenzi, Klaus
    Universität Bremen, Institute of Environmental Physics.
    Temperature profile retrieval from surface to mesopause by combining GNSS radio occultation and passive microwave limb sounder data2001In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 28, no 5, p. 775-778Article in journal (Refereed)
    Abstract [en]

    A theoretical study on the combination of a passive microwave and a GNSS radio occultation instrument, mounted on the International Space Station (ISS), was performed. Both instruments allow to deduce the atmospheric temperature profile. We combined realistically simulated data of the two highly synergistic sensors with the optimal estimation method (OEM) and retrieved single joint temperature profiles from 0 to 90 km altitude for which we found accuracies < 1 K below 35 km and < 4 K in the mesosphere, respectively. In addition, we performed simultaneous tropospheric water vapor and temperature retrievals leading to a water vapor accuracy < 10 to 20 % at altitudes below 5 to 8 km. The OEM allows to optimally exploit the synergy in the data and maximizes retrieval accuracy over the full range from surface to mesopause. It seems worthwhile to install this type of instrument combination on the ISS or other low-Earth-orbit (LEO) platforms.

  • 173.
    Engeln, Axel von
    et al.
    Naval Research Laboratory, Washington, DC.
    Nedoluha, Gerald
    Naval Research Laboratory, Washington, DC.
    Kirchengast, Gottfried
    University of Graz, Institute for Geophysics, Astrophysics and Meteorology.
    Buehler, Stefan
    One-dimensional variational (1-D Var) retrieval of temperature, water vapor, and a reference pressure from radio occultation measurements: A sensitivity analysis2003In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 108, no 11, p. 4337-Article in journal (Refereed)
    Abstract [en]

    A 1-D Var retrieval study of simulated radio occultation measurements is presented. Temperature and a water vapor profile are retrieved along with a reference pressure to generate the pressure profile by applying the hydrostatic equation. High-resolution European Center for Medium-Range Weather Forecasts (ECMWF) atmospheric fields are used by a ray tracing tool to calculate the exact positions of the tangent point. The 1-D atmospheric profiles following the calculated tangent point trajectory in the 3-D ECMWF fields are used to simulate bending angle measurements with a 1-D forward model. Assimilation of these bending angles in a 1-D Var tool employing the same 1-D forward model is performed. We analyze the sensitivity of the retrieval to changes in vertical resolution, horizontal smearing of the tangent point trajectory, and the assumption of hydrostatic equilibrium for a nonvertical atmospheric scan. We find that retrievals calculated without adequate vertical resolution can have significant errors in temperature and water vapor. Errors in the retrieval by assuming hydrostatic equilibrium for a nonvertical scan generally cause only minor errors in the retrieved profiles. A study into the occurrence of rays curving down toward the Earth surface indicates that about 5–10% of the profiles could experience so-called critical refraction at altitudes between 0.5 km and 2 km in case of the applied high-resolution ECMWF data.

  • 174.
    Engeln, Axel von
    et al.
    Universität Bremen, Institute of Environmental Physics.
    Teixeira, Joao
    UCAR/VSP at Marine meteorology division of Naval research laboratory, Monterey, CA.
    Wickert, Jens
    GeoForschungsZentrum Potsdam, Department of Geodesy and Remote Sensing, Potsdam.
    Buehler, Stefan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    CHAMP radio occultation detection of the planetary boundary layer top2006In: Atmosphere and climate: studies by occultation methods, Berlin: Encyclopedia of Global Archaeology/Springer Verlag, 2006Chapter in book (Other academic)
  • 175.
    Engeln, Axel von
    et al.
    Meteorological Division, European Organization for the Exploitation of Meteorological Satellites, Darmstadt.
    Teixeira, Joao
    NATO Undersea Research Centre, La Spezia.
    Wickert, Jens
    GeoForschungsZentrum Potsdam.
    Buehler, Stefan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Comment on "Monitoring the atmospheric boundary layer by GPS radio occultation signals recorded in the open-loop mode" by S. Sokolovskiy et al.2007In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 34, no 2, p. L02806-Article in journal (Other academic)
  • 176.
    Engeln, Axel von
    et al.
    UK Met Office, Exeter.
    Teixeira, Joao
    Marine Meteorology Division, Naval Research Laboratory, Monterey, California.
    Wickert, Jens
    GeoForschungsZentrum Potsdam, Department of Geodesy and Remote Sensing, Potsdam.
    Buehler, Stefan
    Using CHAMP radio occultation data to determine the top altitude of the planetary boundary layer2005In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 32, no 6, p. L06815-Article in journal (Refereed)
    Abstract [en]

    A simple approach to derive the Planetary Boundary Layer (PBL) top altitude from CHAMP (CHAllenging Minisatellite Payload) radio occultation (RO) data is presented. Our RO processing cuts off at an altitude, typically ≤4 km, below which the GPS signals are affected by tracking errors. This lowest processed altitude (LPA) is assumed to coincide with the PBL top. We average LPAs for the years 2001 to 2004 over 5 Degree latitude longitude boxes and compare them to ECMWF analysis data. The ECMWF PBL top was calculated from the relative humidity gradient with respect to altitude. Agreement between the data sets is good in terms of mean PBL height, especially over sea. The CHAMP data shows the major features of PBL height with a realistic transition from stratocumulus regions to shallow and deep cumulus areas. CHAMP also shows a substantial amount of PBL height variability that may prove useful to study PBL dynamics.

  • 177. English, S.J.
    et al.
    O'Keeffe, U.
    Sreerekha, T.R.
    Buehler, Stefan
    Emde, Claudia
    Doherty, A.M.
    A comparison of RTTOVSCATT with ARTS and AMSU observations, using the Met Office mesoscale model short range forecasts of cloud ice and liquid water2003In: 13th International TOVS study conference (ITSC-XIII), 2003Conference paper (Refereed)
  • 178.
    Enmark, Anita
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab. Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Datorbaserad styrning: utveckling av datorbaserat styrsystem till hydraulisk belastningsutrustning1987Report (Other academic)
  • 179.
    Enmark, Anita
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Andersen, Torben
    Lund Observatory.
    Owner-Petersen, Mette
    Lund Observatory.
    Chakraborty, Rijuparna
    Collège de France.
    Labeyrie, Antoine
    Collège de France.
    Integrated model of the Carlina Telescope2011In: Symposium on Integrated Modeling of Complex Optomechanical Systems: 15-17 August 2011, Kiruna, Sweden / [ed] Torben Andersen; Anita Enmark, 2011Conference paper (Refereed)
    Abstract [en]

    The Carlina hypertelescope is a planned sparse aperture 100 m telescope with pupil densification. The telescope has a spherical primary with segments located in a valley between mountains, and additional optical elements in a gondola suspended in eight cables some 100 m above the primary mirror. The resolution is about 1.2×10-3 arcsec. It is imperative that the position and attitude of the gondola be maintained within tight tolerances during observation and star tracking. The present design has servo-controlled winches on the ground for control of the gondola via the cables. An integrated model of the system, including optics, cables, gondola, position and attitude control system, and wind disturbances has been set up. The structural and control models are linear. Calculations in the frequency domain and simulations in the time domain show that the performance of the telescope with the present design seems adequate for short exposures. However, for long-exposure operation, the gondola stability should be improved by about two orders of magnitude. Recommendations are given on possible approaches for performance improvement.

  • 180.
    Eriksson, David
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    A Handling Qualities Analysis of an RPM Controlled Single-Passenger Quadrotor2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    With an exponentially growing demand for Urban Air Mobility (UAM) capable vehicles directly related to traffic congestion in large cities around the world. Companies including aerospace, transportation, and others endeavour to shape the next era of public transportation. It is no longer feasible to let traffic flow on the ground level, instead technology is leading towards a network of "flying cars" that are given the name air taxis. These vehicles are capable of Vertical Take-Off and Landing (VTOL) operations. NASA, which is acting as a leader through the UAM Grand Challenge, is dedicated to conduct research facilitating the development of key areas associated with the leap of technology. This thesis article investigates controls aspects of a single-passenger quadcopter prototype by using the programs SIMPLI-FLYD (now by the name FlightCODE), and CONDUIT. FlightCODE imports sized parameters from the vehicle design and calculates a point model linear state-space matrix governing the Equation of Motion (EOM). CONDUIT is then used to optimise a control system specifically designed for two similar quadrotor, but with different control systems. One, is based on constant rotor RPM -- variable blade-pitch angle, and the other is based on variable rotor RPM -- constant blade-pitch angle. The aircraft geometries are essentially identical with the exception of propulsion method and weight. This thesis will act as a guidance on how the control system can be designed, as well as some aspects of variable RPM rotorcraft. Further more, it describes a process of designing a motor speed controller, which goes by the name Electronic Speed Controller (ESC), that connects to the Flight Control System (FCS). Lastly, the two models are compared, the variable RPM quadrotor case is considered mostly whereas the variable blade-pitch angle acts as a reference model. The results prove that the aircraft is fully controllable using a variable RPM configuration, but that it has a spin-up region that impacts the control response and manoeuvrability mainly due to rotor inertia and lagging of the controller. Also, the control axis rate command, e.g, roll [degrees/s], has a strong correlation to motor power. Controlling the aircraft through rotor RPM is slower than varying the blade-pitch angle, spinning up the rotors require more power from the motors than keeping a fixed RPM, hence the motor power determines how fast the quadrotor can respond and better cope with sudden disturbances and turbulence. It is seen that with a fast tune on the ESC the likeliness of spiking the motor voltage increases which implies that the motor power saturates. The motor limits in this thesis was set to +/- 200V which corresponds to an effect of a single electric motor of approximately 54 hp or 40kW. The ESC correlates to the general stability of the aircraft, making the ESCs aggressive enough will inherently make the aircraft unstable. There are still some unknowns on how the ESC should be considered according to general standards and aircraft standards. Lastly, comparing the RPM controlled version of the quadrotor to the contemporary blade-pitch controlled version, one can see that the latter is more inherently responsive compared to its successor.

  • 181.
    Eriksson, Oscar
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Modeling Dielectric Barrier Discharge plasma actuators to be used for active flow control2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This Master Thesis work cover the simulation of the movement of charged species exposed to a high gradient electric field, the same environment a plasma actuator produces. The final goal is to use the plasma actuator as an active flow control device to decrease the drag of a body moving in air. This report describes how the problem was set up in COMSOL Multiphysics and the resulting volume force achieved. The volume force is the force generated by the plasma actuator that is acting on the air.

    To understand the effect of a plasma actuator better experimental work was also performed. The experimental work include what effect a plasma actuator has on a wing that has stalled out and measuring the air velocity obtained from a single plasma actuator.

    The conclusion is that more work has to be performed to make the plasma actuator a more effective flow control device. This type of work is a way to understand how plasma actuators work and in extension will lead to how a plasma actuator will be used effectively.

  • 182.
    Eriksson, P.
    et al.
    Chalmers University of Technology.
    Buehler, Stefan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Davis, C.P.
    Meteorological Service of New Zealand.
    Emde, C.
    Meteorological Institute, Ludwig-Maximilians-Universität, Munchen.
    Lemke, Oliver
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    ARTS, the atmospheric radiative transfer simulator, version 22011In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 112, no 10, p. 1551-1558Article in journal (Refereed)
    Abstract [en]

    The second version of the atmospheric radiative transfer simulator, ARTS, is introduced. This is a general software package for long wavelength radiative transfer simulations, with a focus on passive microwave observations. The core part provides a workspace environment, in line with script languages. New for this version is an agenda mechanism that gives a high degree of modularity. The framework is intended to be as general as possible: the polarisation state can be fully described, the model atmosphere can be one- (1D), two- (2D) or three-dimensional (3D), a full description of geoid and surface is possible, observation geometries from the ground, from satellite, and from aeroplane or balloon are handled, and surface reflection can be treated in simple or complex manners. Remote sensing applications are supported by a comprehensive and efficient treatment of sensor characteristics. Jacobians can be calculated for the most important atmospheric variables in non-scattering conditions. Finally, the most prominent feature is the rigorous treatment of scattering that has been implemented in two modules: a discrete ordinate iterative approach mainly used for 1D atmospheres, and a Monte Carlo approach which is the preferred algorithm for 3D atmospheres. ARTS is freely available, and maintained as an open-source project.

  • 183.
    Eriksson, Patrick
    et al.
    Chalmers University of Technology.
    Buehler, Stefan
    Engeln, Axel von
    Universität Bremen.
    ARTS: a modular public domain radiative transfer program2001In: Atmospheric millimeter and sub-millimeter radiative transfer modelling. 2, Berlin: Dialogos Förlag, 2001, p. 57-112Chapter in book (Other academic)
  • 184.
    Eriksson, Patrick E J
    et al.
    Chalmers University of Technology, Department of Earth and Space Sciences.
    Jamali, Maryam
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Mendrok, Jana
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Buehler, Stefan
    Meteorological Institute, Center for Earth System Research and Sustainability, University of Hamburg.
    On the microwave optical properties of randomly oriented ice hydrometeors2015In: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 8, no 5, p. 1913-1933Article in journal (Refereed)
    Abstract [en]

    Microwave remote sensing is important for observing the mass of ice hydrometeors. One of the main error sources of microwave ice mass retrievals is that approximations around the shape of the particles are unavoidable. One common approach to represent particles of irregular shape is the soft particle approximation (SPA). We show that it is possible to define a SPA that mimics mean optical particles of available reference data over narrow frequency ranges, considering a single observation technique at the time, but that SPA does not work in a broader context. Most critically, the required air fraction varies with frequency and application, as well as with particle size. In addition, the air fraction matching established density parameterisations results in far too soft particles, at least for frequencies above 90 GHz. That is, alternatives to SPA must be found. One alternative was recently presented by Geer and Baordo (2014). They used a subset of the same reference data and simply selected as "shape model" the particle type giving the best overall agreement with observations. We present a way to perform the same selection of a representative particle shape but without involving assumptions on particle size distribution and actual ice mass contents. Only an assumption on the occurrence frequency of different particle shapes is still required. Our analysis leads to the same selection of representative shape as found by Geer and Baordo (2014). In addition, we show that the selected particle shape has the desired properties at higher frequencies as well as for radar applications. Finally, we demonstrate that in this context the assumption on particle shape is likely less critical when using mass equivalent diameter to characterise particle size compared to using maximum dimension, but a better understanding of the variability of size distributions is required to fully characterise the advantage. Further advancements on these subjects are presently difficult to achieve due to a lack of reference data. One main problem is that most available databases of precalculated optical properties assume completely random particle orientation, while for certain conditions a horizontal alignment is expected. In addition, the only database covering frequencies above 340 GHz has a poor representation of absorption as it is based on outdated refractive index data as well as only covering particles having a maximum dimension below 2 mm and a single temperature

  • 185.
    Eriksson, Patrick
    et al.
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Ekström, Mattias
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Melsheimer, Christian
    Universität Bremen, Institute of Environmental Physics.
    Buehler, Stefan
    Efficient forward modelling by matrix representation of sensor responses2006In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 27, no 9-10, p. 1793-1808Article in journal (Refereed)
    Abstract [en]

    The polarization, frequency and spatial responses of the sensor can be considered by calculating the Stokes vector of monochromatic pencil beam radiances for a set of frequencies and viewing directions, and weight these radiances with the instrument responses. This paper presents a highly efficient solution for this calculation procedure. The basic idea is to pre-calculate a matrix that represents the mapping from polarisation, frequency and spatial values to measured data. Sensor impacts can then be included by a simple matrix multiplication. The full sensor matrix can be obtained by determining the response matrix for the sensor parts individually. Data reduction methods can also be incorporated. A simple method for optimizing the calculation grids is further presented. The described approach for sensor modeling has been implemented in two public available softwares for atmospheric radiative transfer simulations.

  • 186.
    Eriksson, Patrick
    et al.
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Jimenez, Carlos
    Universität Bremen, Institute of Environmental Physics.
    Buehler, Stefan
    Qpack: a general tool for instrument simulation and retrieval work2005In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 91, no 1, p. 47-64Article in journal (Refereed)
    Abstract [en]

    Remote sensing requires a complete observation system, consisting of the instrument, a forward model and a retrieval environment. This paper presents a software tool to complement atmospheric sensors, with focus on passive instruments operating in the mm and sub-mm wavelength regions. The tool is of general character and offers a complete, flexible and fast calculation environment, demonstrated in both preparatory instrument studies and operational inversions. Its features include a rapid approach for modelling of sensor characteristics, several types of data reduction, simple definition of covariance matrices, a large number of retrieval and error quantities, inversion characterisation and random realisation of measurements. The software is freely available for scientific use.

  • 187.
    Eriksson, Patrick
    et al.
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Jiménez, Carlos
    Universität Bremen, Institute of Environmental Physics.
    Buehler, Stefan
    Murtagh, Donal
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    A Hotelling transformation approach for rapid inversion of atmospheric spectra2002In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 73, no 6, p. 529-543Article in journal (Refereed)
    Abstract [en]

    Atmospheric observations from space often result in spectral data of large dimensions. To allow an optimal inversion of the observed spectra it can be necessary to map the data into a space of smaller dimension. Here several data reduction techniques based on eigenvector expansions of the spectral space are compared. The comparison is done by inverting simulated observations from a microwave limb sounder, the Odin-SMR. For the examples tested, reductions exceeding two orders of magnitude with no negative influence on the retrieval performance are demonstrated. The techniques compared include a novel method developed especially for atmospheric inversions, based on the weighting functions of the variables to be retrieved. The new method shows an excellent performance in practical tests and is both computationally more effective and more flexible than the standard Hotelling transformation.

  • 188.
    Eriksson, Patrick
    et al.
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Jiménez, Carlos
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Murtagh, Donal
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Elgered, Gunnar
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Kuhn, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Universität Bremen, Institute of Environmental Physics.
    Buehler, Stefan
    Measurement of tropospheric/stratospheric transmission at 10–35 GHz for H2O retrieval in low Earth orbiting satellite links2003In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 38, no 4, p. 8069-Article in journal (Refereed)
    Abstract [en]

    Active microwave limb sounding is a possible technique for measuring water vapor in the upper troposphere and lower stratosphere, and here a first assessment of the retrieval capabilities of transmission measurements in the range 10–35 GHz is presented. The proposed observing system consists of a constellation of low Earth orbiters measuring atmospheric transmission at the frequencies 10.3, 17.2, and 22.6 GHz. The use of these relatively long wavelengths guarantees a minimal, for being a remote sensing technique, influence from scattering. The original objective of the measurements was to derive water vapor profiles, but the potential to retrieve the liquid water content of clouds was also identified during the study. Retrieval errors due to thermal noise, gain instability, and spectroscopic uncertainties were considered. With the assumed instrument characteristics a measurement precision for water vapor in the upper troposphere of 5–10% is obtained, with capability to observe through ice clouds and clouds with a low water content.

  • 189.
    Eriksson, Patrick
    et al.
    Chalmers University of Technology, Department of Earth and Space Sciences.
    Rydberg, B.
    Chalmers University of Technology, Department of Earth and Space Sciences.
    Buehler, Stefan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    On cloud ice induced absorption and polarisation effects in microwave limb sounding2011In: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 4, no 6, p. 1305-1318Article in journal (Refereed)
    Abstract [en]

    Microwave limb sounding in the presence of ice clouds was studied by detailed simulations, where clouds and other atmospheric variables varied in three dimensions and the full polarisation state was considered. Scattering particles were assumed to be horizontally aligned oblate spheroids with a size distribution parameterized in terms of temperature and ice water content. A general finding was that particle absorption is significant for limb sounding, which is in contrast to the down-looking case, where it is usually insignificant. Another general finding was that single scattering can be assumed for cloud optical paths below about 0.1, which is thus an important threshold with respect to the complexity and accuracy of retrieval algorithms. The representation of particle sizes during the retrieval is also discussed. Concerning polarisation, specific findings were as follows: Firstly, no significant degree of circular polarisation was found for the considered particle type. Secondly, for the +/- 45 degrees polarisation components, differences of up to 4 K in brightness temperature were found, but differences were much smaller when single scattering conditions applied. Thirdly, the vertically polarised component has the smallest cloud extinction. An important goal of the study was to derive recommendations for future limb sounding instruments, particularly concerning their polarisation setup. If ice water content is among the retrieval targets (and not just trace gas mixing ratios), then the simulations show that it should be best to observe any of the +/- 45 degrees and circularly polarised components. These pairs of orthogonal components also make it easier to combine information measured from different positions and with different polarisations

  • 190.
    Escamilla-Roa, Elizabeth
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Cartwright, Julyan H. E.
    Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, Armilla Granada, Spain. Instituto Carlos I de Física Teórica y Computacional, Universidad de Granada, Granada, Spain.
    Sainz-Díaz, C. Ignacio
    Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, Armilla Granada, Spain.
    Chemobrionic Fabrication of Hierarchical Self‐Assembling Nanostructures of Copper Oxide and Hydroxide2019In: ChemSystemsChem, E-ISSN 2570-4206Article in journal (Refereed)
    Abstract [en]

    Copper oxide nanostructures have great potential use in a plethora of nanotechnology applications including nanoelectronics, photovoltaics, sensors, electrochemistry, and pharmacology. In the present work we show how hierarchically nano‐structured copper oxide and hydroxide may be prepared through self‐assembly from CuSO4 salt and silicate solutions using the chemobrionic growth process of a chemical garden. Procedures were explored using the cupric salt in either solid (pellet and seed growth methods) or liquid phase (fluid injection techniques). Self‐assembling nanostructures were characterized by means of environmental scanning electron microscopy (ESEM) with energy‐dispersive X‐ray spectroscopy (EDX) analysis, micro‐Raman spectroscopy and X‐ray diffraction. Our results show the formation of crystalline aggregates of copper oxide and hydroxide in complex hierarchical nanostructured forms including fans, flowers, petals, skeins, lentils, and sheaves. Analytical methods corroborate that these nanostructures may be selected in shape and chemical composition with the reaction conditions.

  • 191.
    Escamilla-Roa, Elizabeth
    et al.
    Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR).
    Martin-Torres, Javier
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR).
    Sainz-Díaz, C. Ignacio
    Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR).
    Adsorption of methane and CO2 onto olivine surfaces in Martian dust conditions2018In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 153, p. 163-171Article in journal (Refereed)
    Abstract [en]

    Methane has been detected on all planets of our Solar System, and most of the larger moons, as well as in dwarf-planets like Pluto and Eric. The presence of this molecule in rocky planets is very interesting because its presence in the Earth's atmosphere is mainly related to biotic processes. Space instrumentation in orbiters around Mars has detected olivine on the Martian soil and dust. On the other hand the measurements of methane from the Curiosity rover report detection of background levels of atmospheric methane with abundance that is lower than model estimates of ultraviolet degradation of accreted interplanetary dust particles or carbonaceous chondrite material. Additionally, elevated levels of methane about this background have been observed implying that Mars is episodically producing methane from an additional unknown source, making the reasons of these temporal fluctuations of methane a hot topic in planetary research. The goal of this study is to investigate at atomic level the interactions during the adsorption processes of methane and other Mars atmospheric species (CO2, H2O) on forsterite surfaces, through electronic structure calculations based on the Density Functional Theory (DFT). We propose two models to simulate the interaction of adsorbates with the surface of dust mineral, such as binary mixtures (5CH4+5H2O/5CH4+5CO2) and as a semi-clathrate adsorption. We have obtained interesting results of the adsorption process in the mixture 5CH4+5CO2. Associative and dissociative adsorptions were observed for water and CO2 molecules. The methane molecules were only trapped and held by water or CO2 molecules. In the dipolar surface, the adsorption of CO2 molecules produced new species: one CO from a CO2 dissociation, and, two CO2 molecules chemisorbed to mineral surface forming a carbonate group. Our results suggest that CO2 has a strong interaction with the mineral surface when methane is present. These results could be confirmed after the analysis of the data from the upcoming remote and in-situ observations on Mars, as those to be performed by instruments on the ESA's ExoMars Trace Gas Orbiter and ExoMars rover.

  • 192.
    Escamilla-Roa, Elizabeth
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Zorzano, María-Paz
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Centro de Astrobiología (INTA-CSIC), Torrejón de Ardoz, Madrid, Spain.
    Martin-Torres, Javier
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Granada, Spain.
    Hernäandez-Laguna, Alfonso
    Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Granada, Spain.
    Sainz-Diaz, Claro
    Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Granada, Spain.
    DFT study of electronic and redox properties of TiO2 supported on olivine for modelling regolith on Moon and Mars conditions2019In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088Article in journal (Refereed)
    Abstract [en]

    Titanium dioxide TiO2 is one of the most studied oxides in photocatalysis, due to its electronic structure and its wide variety of applications, such as gas sensors and biomaterials, and especially in methane-reforming catalysis. Titanium dioxide and olivine have been detected both on Mars and our Moon. It has been postulated that on Mars photocatalytic processes may be relevant for atmospheric methane fluctuation, radicals and perchlorate productions etc. However, to date no investigation has been devoted to modelling the properties of TiO2 adsorbed on olivine surface.

    The goal of this study is to investigate at atomic level with electronic structure calculations based on the Density Functional Theory (DFT), the atomic interactions that take place during the adsorption processes for formation of a TiO regolith. This model is formed with different TiO films adsorbed on olivine (forsterite) surfaces, one of the most common minerals in Universe, Earth, Mars, cometary and interstellar dust. We propose three regolith models to simulate the principal phase of titanium oxide (TiO, Ti2O3 and TiO2). The models show different adsorption processes i.e. physisorption and chemisorption. Our results suggest that the TiO is the most reactive phase and produces a strong exothermic effect. Besides, we have detailed, from a theoretical point of view, the effect that has the adsorption process in the electronic properties such as electronic density of state (DOS) and oxide reduction process (redox). This theoretical study can be important to understand the formation of new materials (supports) that can be used as support in the catalytic processes that occur in the Earth, Mars and Moon. Also, it may be important to interpret the present day photochemistry and interaction of regolith and airborne aerosols in the atmosphere on Mars or to define possible catalytic reactions of the volatiles captured on the Moon regolith.

  • 193.
    Exposito Garcia, Adrian
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Investigation on Model Based Observers for SpaceStructure Load Characterization2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The experimental determination of dynamic characteristics of elastic structures, in particularof space flight related structures typically is performed by experimental modal analysis(EMA) or output-only modal analysis (OMA). This document is focused on the OMA methodsand state-space modelling, the motivation for this approach is the possibility to monitorthe real loading of a structure in order to provide a loading history which may be used foran assessment of safe remaining life once the dynamic characteristics has been determined. Previous work has demonstrated that Extened Kalman Filter is not sufficient in thecase when the forces are unkown and the only resource available are the responses of thestructure. In this research a new method called Unscented Kalman Filter is investigated andimplemented, proving its capability to obtain a better approximation of the elastic structurebehaviour and a correction of the modal parameters.

  • 194.
    Farley, K.A.
    et al.
    Division of Geological and Planetary Sciences, California Institute of Technology.
    Malespin, C.
    NASA Goddard Space Flight Center.
    Mahaffy, P.
    NASA Goddard Space Flight Center.
    Grotzinger, J.P.
    Division of Geological and Planetary Sciences, California Institute of Technology.
    Vasconcelos, P.M.
    School of Earth Sciences, University of Queensland, Brisbane.
    Milliken, R.E.
    Department of Geological Sciences, Brown University, Providence.
    Malin, M.
    Malin Space Science Systems.
    Edgett, K.S.
    Malin Space Science Systems.
    Pavlov, A.A.
    NASA Goddard Space Flight Center.
    Hurowitz, J.A.
    Department of Geosciences, Stony Brook University.
    Grant, J.A.
    Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, Washington.
    Miller, H.B.
    Division of Geological and Planetary Sciences, California Institute of Technology.
    Arvidson, R.
    Department of Earth and Planetary Sciences, Washington University, St. Louis.
    Beegle, L.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
    Calef, F.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
    Conrad, P.G.
    NASA Goddard Space Flight Center.
    Dietrich, W.E.
    Earth and Planetary Science Department, University of California, Berkeley.
    Eigenbrode, J.
    NASA Goddard Space Flight Center.
    Gellert, R.
    Department of Physics, University of Guelph, Ontario.
    Gupta, S.
    Department of Earth Science and Engineering, Imperial College London.
    Hamilton, V.
    Southwest Research Institute, Boulder.
    Hassler, D.M.
    Southwest Research Institute, Boulder.
    Lewis, K.W.
    Department of Geosciences, Princeton University, New Jersey.
    McLennan, S.M.
    Department of Geosciences, Stony Brook University.
    Ming, D.
    NASA Johnson Space Center, Houston.
    Wimmer-Schweingruber, R.F.
    University of Kiel.
    In situ radiometric and exposure age dating of the martian surface2014In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 343, no 6169, article id 1247166Article in journal (Refereed)
    Abstract [en]

    We determined radiogenic and cosmogenic noble gases in a mudstone on the floor of Gale Crater. A K-Ar age of 4.21 ± 0.35 billion years represents a mixture of detrital and authigenic components and confirms the expected antiquity of rocks comprising the crater rim. Cosmic-ray-produced 3He, 21Ne, and 36Ar yield concordant surface exposure ages of 78 ± 30 million years. Surface exposure occurred mainly in the present geomorphic setting rather than during primary erosion and transport. Our observations are consistent with mudstone deposition shortly after the Gale impact or possibly in a later event of rapid erosion and deposition. The mudstone remained buried until recent exposure by wind-driven scarp retreat. Sedimentary rocks exposed by this mechanism may thus offer the best potential for organic biomarker preservation against destruction by cosmic radiation.

  • 195.
    Fatemi, Shahab
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Kinetic Modeling of the Solar Wind Plasma Interaction with the Moon2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The main purpose of this research is to understand various aspects of the solar wind plasma interaction with the Earth's Moon by the means of kinetic computer simulations. The Moon is essentially a non-conducting object, that has a tenuous atmosphere and no global magnetic field. Then the solar wind plasma impacts the lunar surface, where it is absorbed or neutralized for the most part. On average about 10% of the solar wind protons reflect in charge form from lunar crustal magnetization and up to 20% reflect from the lunar surface as neutral atoms.First we consider the Moon to be a perfect plasma absorber and we study the global effects of the solar wind plasma interaction with the Moon using a three-dimensional self-consistent hybrid model. We show that due to the plasma absorption in the lunar dayside, a void region forms behind the Moon and a plasma wake forms downstream. Then we study different parameters that control the lunar wake, discuss various mechanisms that fill in the wake, and compare our simulations with observations. We also discuss the effects of lunar surface plasma absorption on the solar wind proton velocity space distribution at close distances to the Moon in the lunar wake. Moreover, we show that three current systems form in the wake that enhance the magnetic fields in the central wake, depress the fields in the surrounding areas, and confine the fields and plasma perturbations within a Mach cone. Finally we study the effects of protons reflected from lunar crustal magnetic fields on the global lunar plasma environment. We show that the reflected protons interact with the solar wind plasma, compress the fields and plasma upstream in the lunar dayside and downstream outside the Mach cone. The conclusion of this thesis work is that the solar wind plasma interaction with the Moon is dynamic and complex. This is, however, due to the kinetic nature of this interaction because of the scales of the interaction regions where the Magnetohydrodynamics (fluid) approach cannot address the detailed physics. This reveals the importance of kinetic modeling to understand this interaction. The results of this study will feed forward to human space exploration, kinetic theories of plasma interaction with airless bodies, and fundamental plasma physics processes.

  • 196.
    Fatemi, Shahab
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Modeling the Lunar plasma wake2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis discusses the solar wind interaction with the Moon and the formation of the lunar plasma wake from a kinetic perspective. The Moon is essentially a non-conducting body which has a tenuous atmosphere and no global magnetic fields. The solar wind plasma impacts directly the lunar day-side and is absorbed by the lunar surface. This creates a plasma void and forms a wake at the night side of the Moon.We study the properties and structure of the lunar wake for typical solar wind conditions using a three-dimensional hybrid plasma solver. Also, we study the solar wind proton velocity space distribution functions at close distances to the Moon in the lunar wake and investigate the effects of lunar surface plasma absorption and non-isothermal solar wind velocity space distribution functions on the solar wind protons there.Finally, we compare the simulation results with the observations and show that a hybrid model of plasma can explain the kinetic aspects of the lunar wake and we investigate the effects of the lunar surface plasma absorption and non-isothermal solar wind velocity distribution on the solar wind proton properties there.

  • 197.
    Fatemi, Shahab
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Holmström, Mats
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Futaana, Yoshifumi
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    The effects of lunar surface plasma absorption and solar wind temperature anisotropies on the solar wind proton velocity space distributions in the low-altitude lunar plasma wake2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, no 10Article in journal (Refereed)
    Abstract [en]

    We study the solar wind proton velocity space distribution functions on the lunar nightside at low altitudes (∼100 km) above the lunar surface using a three-dimensional hybrid plasma solver, when the Moon is in the unperturbed solar wind. When the solar wind encounters a passive obstacle, such as the Moon, without any strong magnetic field and no atmosphere, solar wind protons that impact the obstacle's surface are absorbed and removed from the velocity space distribution functions. We show first that a hybrid model of plasma is applicable to study the low-altitude lunar plasma wake by comparing the simulation results with observations. Then we examine the effects of a solar wind bi-Maxwellian velocity space distribution function and the lunar surface plasma absorption on the solar wind protons' velocity space distribution functions and their entry in the direction parallel to the interplanetary magnetic field lines into the low-altitude lunar wake. We present a backward Liouville method for particle-in-cell solvers that improves velocity space resolution. The results show that the lunar surface plasma absorption and anisotropic solar wind velocity space distributions result in substantial changes in the solar wind proton distribution functions in the low-altitude lunar plasma wake, modifying proton number density, velocity, and temperature there. Additionally, a large temperature anisotropy is found at close distances to the Moon on the lunar nightside as a consequence of the lunar surface plasma absorption effect

  • 198.
    Fatemi, Shahab
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Holmström, Mats
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Futaana, Yoshifumi
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Barabash, Stas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Lue, Charles
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    The lunar wake current systems2013In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40, no 1, p. 17-21Article in journal (Refereed)
    Abstract [en]

    We present the lunar wake current systems when the Moon is assumed to be a non-conductive body, absorbing the solar wind plasma. We show that in the transition regions between the plasma void, the expanding rarefaction region, and the interplanetary plasma, there are three main currents flowing around these regions in the lunar wake. The generated currents induce magnetic fields within these regions and perturb the field lines there. We use a three-dimensional, self-consistent hybrid model of plasma (particle ions and fluid electrons) to show the flow of these three currents. First, we identify the different plasma regions, separated by the currents, and then we show how the currents depend on the interplanetary magnetic field direction. Finally, we discuss the current closures in the lunar wake.

  • 199.
    Fatemi, Shahab
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Holmström, Mats
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Futaana, Yoshifumi
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Lue, Charles
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Collier, Michael R.
    NASA Goddard Space Flight Center.
    Barabash, Stas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics / Institutet för rymdfysik.
    Stenberg, Gabriella
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Effects of protons deflected by lunar crustal magnetic fields on the global lunar plasma environment2014In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 119, no 8, p. 6095-6105Article in journal (Refereed)
    Abstract [en]

    Solar wind plasma interaction with lunar crustal magnetic fields is different than that of magnetized bodies like the Earth. Lunar crustal fields are, for typical solar wind conditions, not strong enough to form a (bow)shock upstream but rather deflect and perturb plasma and fields. Here we study the global effects of protons reflected from lunar crustal magnetic fields on the lunar plasma environment when the Moon is in the unperturbed solar wind. We employ a three-dimensional hybrid model of plasma and an observed map of reflected protons from lunar magnetic anomalies over the lunar farside. We observe that magnetic fields and plasma upstream over the lunar crustal fields compress to nearly 120% and 160% of the solar wind, respectively. We find that these disturbances convect downstream in the vicinity of the lunar wake, while their relative magnitudes decrease. In addition, solar wind protons are disturbed and heated at compression regions and their velocity distribution changes from Maxwellian to a non-Maxwellian. Finally, we show that these features persists, independent of the details of the ion reflection by the magnetic fields.

  • 200.
    Felicetti, Leonard
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Ceriotti, Matteo
    University of Glasgow, School of Engineering, James Watt Building South .
    Harkness, Patrick
    University of Glasgow, School of Engineering, James Watt Building South .
    Attitude Stability and Altitude Control of a Variable-Geometry Earth-Orbiting Solar Sail2016In: Journal of Guidance Control and Dynamics, ISSN 0731-5090, E-ISSN 1533-3884, Vol. 39, no 9, p. 2112-2126Article in journal (Refereed)
    Abstract [en]

    A variable-geometry solar sail for on-orbit altitude control is investigated. It is shown that, by adjusting the effective area of the sail at favorable times, it is possible to influence the length of the semimajor axis over an extended period of time. This solution can be implemented by adopting a spinning quasi-rhombic pyramidal solar sail that provides the heliostability needed to maintain a passive sun-pointing attitude and the freedom to modify the shape of the sail at any time. In particular, this paper investigates the variable-geometry concept through both theoretical and numerical analyses. Stability bounds on the sail design are calculated by means of a first-order analysis, producing conditions on the opening angles of the sail, while gravity gradient torques and solar eclipses are introduced to test the robustness of the concept. The concept targets equatorial orbits above approximately 5000km. Numerical results characterize the expected performance, leading to (for example) an increase of 2200km/yr for a small device at geostationary Earth orbit

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