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  • 101.
    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 tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    On cloud ice induced absorption and polarisation effects in microwave limb sounding2011Inngår i: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 4, nr 6, 1305-1318 s.Artikkel i tidsskrift (Fagfellevurdert)
    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

  • 102.
    Fatemi, Shahab
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    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 wake2012Inngår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, nr 10Artikkel i tidsskrift (Fagfellevurdert)
    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

  • 103.
    Fatemi, Shahab
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Holmström, Mats
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Futaana, Yoshifumi
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Barabash, Stas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Lue, Charles
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    The lunar wake current systems2013Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40, nr 1, 17-21 s.Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 104.
    Fatemi, Shahab
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    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 tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. 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 environment2014Inngår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 119, nr 8, 6095-6105 s.Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 105.
    Felicetti, Leonard
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    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 Sail2016Inngår i: Journal of Guidance Control and Dynamics, ISSN 0731-5090, E-ISSN 1533-3884, Vol. 39, nr 9, 2112-2126 s.Artikkel i tidsskrift (Fagfellevurdert)
    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

  • 106.
    Felicetti, Leonard
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Emami, Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    A multi-spacecraft formation approach to space debris surveillance2016Inngår i: Acta Astronautica, ISSN 0094-5765, E-ISSN 1879-2030, Vol. 127, 491-504 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper proposes a new mission concept devoted to the identification and tracking of space debris through observations made by multiple spacecraft. Specifically, a formation of spacecraft has been designed taking into account the characteristics and requirements of the utilized optical sensors as well as the constraints imposed by sun illumination and visibility conditions. The debris observations are then shared among the team of spacecraft, and processed onboard of a “hosting leader” to estimate the debris motion by means of Kalman filtering techniques. The primary contribution of this paper resides on the application of a distributed coordination architecture, which provides an autonomous and robust ability to dynamically form spacecraft teams once the target has been detected, and to dynamically build a processing network for the orbit determination of space debris. The team performance, in terms of accuracy, readiness and number of the detected objects, is discussed through numerical simulations.

  • 107.
    Felicetti, Leonard
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Emami, Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Attitude Coordination of Multiple Spacecraft for Space Debris Surveillance2017Inngår i: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 59, nr 5, 1270-1288 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper discusses the attitude coordination of a formation of multiple spacecraft for space debris surveillance. Off-the-shelf optical sensors and reaction wheels, with limited field of view and control torque, respectively, are considered to be used onboard the spacecraft for performing the required attitude maneuvers to detect and track space debris. The sequence of attitude commands are planned by a proposed algorithm, which allows for a dynamic team formation, as well as performing suitable maneuvers to eventually point towards the same debris. A control scheme based on the nonlinear state dependent Riccati equation is designed and applied to the space debris surveillance mission scenario, and its performance is compared with those of the classic linear quadratic regulator and quaternion feedback proportional derivative controllers. The viability and performance of the coordination algorithm and the controllers are validated through numerical simulations.

  • 108.
    Felicetti, Leonard
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Emami, Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Spacecraft formation for debris surveillance2017Inngår i: IEEE Aerospace Conference Proceedings, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2017, 7943750Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper explores the viability and performance of a new algorithm for in-orbit space debris surveillance, which utilizes a network of distributed optical sensors carried onboard multiple spacecraft flying in formation. The resulting network of spacecraft is able to autonomously detect unknown debris, as well as track the existing ones, estimate their trajectories, and send the estimation results directly to the mission control centers for planning the required collision avoidance maneuvers. The proposed concept includes (a) an estimation algorithm that allows for sharing observations of common debris objects among spacecraft; (b) a coordination algorithm for the re-orientation of an ad hoc team of spacecraft to align their onboard optical sensors towards common targets; and (c) a control algorithm for the detection and tracking of the debris which uses vision-based attitude maneuvers.

  • 109.
    Felicetti, Leonard
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Palmerini, Giovanni B.
    Sapienza Università di Roma, Dipartimento di Ingegneria Astronautica Elettrica Ed Energetica (DIAEE), Scuola di Ingegneria Aerospaziale, Università di Roma La Sapienza.
    Analytical and numerical investigations on spacecraft formation control by using electrostatic forces2016Inngår i: Acta Astronautica, ISSN 0094-5765, E-ISSN 1879-2030, Vol. 123, 455-469 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The paper investigates some analytical and numerical aspects of the formation control exploited by means of inter-spacecraft electrostatic actions. The analysis is based on the evaluation and check of the stability issues by using a sequence of purposely defined Lyapunov functions. The same Lyapunov approach can also define a specific under-actuate control strategy for controlling selected “virtual links” of the formation. Two different selection criteria for these links are then discussed, showing the implications on the control chain. An optimal charge distribution strategy, which assigns univocally the charges to all the spacecraft starting from the charge products computed by the control, is also presented and discussed. Numerical simulations prove the suitability of the proposed approach to a formation of 4 satellites.

  • 110.
    Felicetti, Leonard
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Palmerini, Giovanni B.
    Sapienza Università di Roma, Dipartimento di Ingegneria Astronautica Elettrica Ed Energetica (DIAEE).
    Three spacecraft formation control by means of electrostatic forces2016Inngår i: Aerospace Science and Technology, ISSN 1270-9638, E-ISSN 1626-3219, Vol. 48, 261-271 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper focuses on electrostatic orbital control in formation flying by using switching strategies for charge distribution. Natural and artificial charging effects are taken into account, and limits in charging technology and in power requirements are also considered. The case of three spacecraft formation, which is intrinsically different and more difficult than the two spacecraft problem often analyzed in literature, has been investigated. A Lyapunov based global control strategy is presented and applied to perform formation acquisition and maintenance maneuvers, producing as output the required overall charge. Then, a selective and optimized charge distribution process among the satellites is discussed for avoiding charge breakdowns to surrounding plasma, for reducing the power requirements and the number of charge switches. The results of numerical simulations show the advantages and drawbacks of the selected control technique

  • 111.
    Flores Garcia, Erick
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Simulation of attitude and orbital disturbances acting on ASPECT satellite in the vicinity of the binary asteroid Didymos2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Asteroid missions are gaining interest from the scientific community and many new missions are planned. The Didymos binary asteroid is a Near-Earth Object and the target of the Asteroid Impact and Deflection Assessment (AIDA). This joint mission, developed by NASA and ESA, brings the possibility to build one of the first CubeSats for deep space missions: the ASPECT satellite. Navigation systems of a deep space satellite di er greatly from the common planetary missions. Orbital environment close to an asteroid requires a case-by-case analysis. In order to develop the Attitude Determination Control System (ADCS) for the mission, one needs detailed information about orbital disturbances in the vicinity of the asteroid.

    This work focuses on the development of a simulator that characterises the orbital disturbances a ecting the ASPECT satellite in the space environment near the Didymos asteroid. In this work, a model of orbital conditions and disturbances near the Didymos system was defined. The model integrates several classical and modern models of spacecraft motion and disturbance. An existing Low Earth Orbit (LEO) simulator was modified and updated accordingly to the ASPECT mission scenario. The developed simulator can be used to analyse the disturbances to be counteracted by the ADCS of the ASPECT satellite. The objective of the study was to quantify the e ect of both non-gravitational and gravitational disturbances. The simulator was used to analyse di erent orbit scenarios related to the period of the mission and to the relative distance between the spacecraft and the asteroid system. In every scenario, the solar radiation pressure was found to be the strongest of the disturbance forces. With the developed simulator, suitable spacecraft configurations and control systems can be chosen to mitigate the e ect of the disturbances on the attitude and orbit of the ASPECT satellite. 

  • 112.
    Forsberg, Fredrik
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Providing Air Traffic Control Services for Small Unmanned Aircraft Through LTE2016Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave
  • 113.
    Freissinet, C.
    et al.
    Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, Maryland.
    Glavin, D.P.
    Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, Maryland.
    Mahaffy, P.R.
    Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, Maryland.
    Miller, K.E.
    Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge.
    Eigenbrode, J.L.
    Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, Maryland.
    Summons, R.E.
    Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge.
    Brunner, A.E.
    Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, Maryland.
    Buch, A.
    Laboratoire de Génie des Procédés et les Matériaux, Ecole Centrale Paris.
    Szopa, C.
    Laboratoire Atmosphères, Milieux, Observations Spatiales, Univ. Pierre et Marie Curie, Univ. Versailles Saint-Quentin & CNRS, Paris.
    Archer Jr., P.D.
    Jacobs Technology, NASA Johnson Space Center.
    Franz, H.B.
    Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, Maryland.
    Atreya, S.K.
    Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor.
    Brinckerhoff, E.B.
    Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, Maryland.
    Cabane, M.
    Laboratoire Atmosphères, Milieux, Observations Spatiales, Univ. Pierre et Marie Curie, Univ. Versailles Saint-Quentin & CNRS, Paris.
    Coll, P.
    Laboratoire Interuniversitaire des Systèmes Atmosphériques, Université Paris-Est Créteil, Univ. Paris Diderot and CNRS.
    Conrad, P.G.
    Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, Maryland.
    Marais, D.J. Des
    Exobiology Branch, NASA Ames Research Center, Moffett Field, Kalifornien.
    Dworkin, J.P.
    Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, Maryland.
    Fairén, A.G.
    Department of Astronomy, Cornell University, Ithaca, New York.
    François, P.
    Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor.
    Grotzinger, J.P.
    Division of Geological and Planetary Sciences, California Institute of Technology.
    Kashyap, S.
    Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, Maryland.
    Kate, I.L. ten
    Earth Sciences Department, Utrecht University.
    Leshin, L.A.
    Department of Earth and Environmental Science and School of Science, Rensselaer Polytechnic Institute, Troy, New York.
    Malespin, C.A.
    Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, Maryland.
    Martin-Torres, Javier
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Zorzano, María-Paz
    Centro de Astrobiologia, INTA-CSIC, Madrid.
    Organic molecules in the Sheepbed Mudstone, Gale Crater, Mars2015Inngår i: Journal of Geophysical Research - Planets, ISSN 2169-9097, E-ISSN 2169-9100, Vol. 120, nr 3, 495-514 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Sample Analysis at Mars (SAM) instrument [Mahaffy et al., 2012] onboard the Mars Science Laboratory (MSL) Curiosity rover is designed to conduct inorganic and organic chemical analyses of the atmosphere and the surface regolith and rocks to help evaluate the past and present habitability potential of Mars at Gale Crater [Grotzinger et al., 2012]. Central to this task is the development of an inventory of any organic molecules present to elucidate processes associated with their origin, diagenesis, concentration and long-term preservation. This will guide the future search for biosignatures [Summons et al., 2011]. Here we report the definitive identification of chlorobenzene (150–300 parts per billion by weight (ppbw)) and C2 to C4 dichloroalkanes (up to 70 ppbw) with the SAM gas chromatograph mass spectrometer (GCMS), and detection of chlorobenzene in the direct evolved gas analysis (EGA) mode, in multiple portions of the fines from the Cumberland drill hole in the Sheepbed mudstone at Yellowknife Bay. When combined with GCMS and EGA data from multiple scooped and drilled samples, blank runs and supporting laboratory analog studies, the elevated levels of chlorobenzene and the dichloroalkanes cannot be solely explained by instrument background sources known to be present in SAM. We conclude that these chlorinated hydrocarbons are the reaction products of martian chlorine and organic carbon derived from martian sources (e.g. igneous, hydrothermal, atmospheric, or biological) or exogenous sources such as meteorites, comets or interplanetary dust particles.

  • 114.
    Garcia Hernandez, Juan Camilo
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Development of a Class D motor amplifier for a next-generation mechanism control electronics2016Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This thesis was written at Airbus DS GmbH in Friedrichshafen, Germany, as part of a project which aims to develop a new generation of class-D power amplification circuits for sinusoidal commutating motors controlling the movement of different mechanisms in satellites. Currently used topologies have disadvantages such as high power loss, analog controlling and high degree of signal distortion.

    This work first simulates available topologies which were previously developed by the company in order to compare them and build a trade-off list so the most suitable circuit is selected. Then, by further simulating and analysis several improvements to the circuit are suggested and a final schematic is developed including an analogue-to-digital converter and a total of three phases to power a motor. After a demonstrator circuit was designed and built, it was tested by using an external real time target machine to generate the corresponding PWM signals in correspondence to a controlling signal generated via Simulink.

    The final product of this thesis confirmed the simulation results such as an improved signal quality at higher frequencies in comparison to an available measurement from a previous generation circuit. The flexibility of the topology as well as the possibility of implementing a digital control was also confirmed during this phase of the project. Upon further work, the dimensioning of the output low pass filter should be improved and a digital PID controller should be implemented in the controlling FPGA.

    NOTE: This version of the Master Thesis deviates from the formal original  submitted for examination in order not to disclose confidential information of Airbus DS GmbH. All positions in the document, where additional information was removed are properly identified. This document can be published according to the general rules of the Julius-Maximilians-Universität Würzburg and the Lulea University of Technology.

  • 115.
    Garg, Kanika
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. kanika.garg@ltu.se .
    Emami, Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Aerobot design for planetary explorations2016Inngår i: AIAA Space and Astronautics Forum and Exposition, SPACE 2016, American Institute of Aeronautics and Astronautics, 2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper studies the design of planetary aerobots with different types and shapes under various atmospheric conditions. The design framework and specifications are discussed. The development of a simulation tool is described, which is used for analyzing the behaviour of aerobots on Venus, Mars and Titan. The software is verified through the comparison of its performance with some experimental data as well as the state-of-the-art simulation tools. Based on the simulation results, some recommendations are made for different aerobot exploration missions

  • 116.
    Gasteiger, J.
    et al.
    Meteorologisches Institut, Ludwig-Maximilians-Universität.
    Emde, C.
    Meteorologisches Institut, Ludwig-Maximilians-Universität.
    Mayer, B.
    Meteorologisches Institut, Ludwig-Maximilians-Universität.
    Buras, R.
    Meteorologisches Institut, Ludwig-Maximilians-Universität.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Lemke, Oliver
    Representative wavelengths absorption parameterization applied to satellite channels and spectral bands2014Inngår i: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 148, 99-115 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Accurate modeling of wavelength-integrated radiative quantities, e.g. integrated over a spectral band or an instrument channel response function, requires computations for a large number of wavelengths if the radiation is affected by gas absorption which typically comprises a complex line structure. In order to increase computational speed of modeling radiation in the Earth׳s atmosphere, we parameterized wavelength-integrals as weighted means over representative wavelengths. We parameterized spectral bands of different widths (1 cm−1, 5 cm−1, and 15 cm−1) in the solar and thermal spectral range, as well as a number of instrument channels on the ADEOS, ALOS, EarthCARE, Envisat, ERS, Landsat, MSG, PARASOL, Proba, Sentinel, Seosat, and SPOT satellites. A root mean square relative deviation lower than 1% from a “training data set” was selected as the accuracy threshold for the parameterization of each band and channel. The training data set included high spectral resolution calculations of radiances at the top of atmosphere for a set of highly variable atmospheric states including clouds and aerosols. The gas absorption was calculated from the HITRAN 2004 spectroscopic data set and state-of-the-art continuum models using the ARTS radiative transfer model. Three representative wavelengths were required on average to fulfill the accuracy threshold. We implemented the parameterized spectral bands and satellite channels in the uvspec radiative transfer model which is part of the libRadtran software package. The parameterization data files, including the representative wavelengths and weights as well as lookup tables of absorption cross sections of various gases, are provided at the libRadtran webpage.In the paper we describe the parameterization approach and its application. We validate the approach by comparing modeling results of parameterized bands and channels with results from high spectral resolution calculations for atmospheric states that were not part of the training data set. Irradiances are not only compared at the top of atmosphere but also at the surface for which this parameterization approach was not optimized. It is found that the parameterized bands and channels provide a good compromise between computation time requirements and uncertainty for typical radiative transfer problems. In particular for satellite radiometer simulations the computation time requirement and the parameterization uncertainty is low. Band-integrated irradiances at any level as well as heating and cooling rates below 20 km can also be modeled with low uncertainty.

  • 117.
    Gellert, Uwe
    et al.
    Universität Hamburg, Freie Universität Berlin.
    III, Benton Clark
    Space Science Institute, Boulder, Colorado.
    Martin-Torres, Javier
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    In Situ Compositional Measurements of Rocks and Soils with the Alpha Particle X-ray Spectrometer on NASA's Mars Rovers2015Inngår i: Elements, ISSN 1811-5209, E-ISSN 1811-5217, Vol. 11, nr 1, 39-44 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Alpha Particle X-ray Spectrometer (APXS) is a soda can–sized, arm-mounted instrument that measures the chemical composition of rocks and soils using X-ray spectroscopy. It has been part of the science payload of the four rovers that NASA has landed on Mars. It uses 244Cm sources for a combination of PIXE and XRF to quantify 16 elements. So far, about 700 Martian samples from about 50 km of combined traverses at the four landing sites have been documented. The compositions encountered range from unaltered basaltic rocks and extensive salty sandstones to nearly pure hydrated ferric sulfates and silica-rich subsurface soils. The APXS is used for geochemical reconnaissance, identification of rock and soil types, and sample triage. It provides crucial constraints for use with the mineralogical instruments. The APXS data set allows the four landing sites to be compared with each other and with Martian meteorites, and it provides ground truth measurements for comparison with orbital observations.

  • 118.
    Girard, Justin
    et al.
    Institute for Aerospace Studies, University of Toronto.
    Emami, Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    A robust approach to robot team learning2016Inngår i: Autonomous Robots, ISSN 0929-5593, E-ISSN 1573-7527, Vol. 40, nr 8, 1441-1457 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The paper achieves two outcomes. First, it summarizes previous work on concurrent Markov decision processes (CMDPs) currently demonstrated for use with multi-agent foraging problems. When using CMDPs, each agent models the environment using two Markov decision process (MDP). The two MDPs characterize a multi-agent foraging problem by modeling both a single-agent foraging problem, and multi-agent task allocation problem, for each agent. Second, the paper studies the effects of state uncertainty on a heterogeneous robot team that utilizes the aforementioned CMDP modelling approach. Furthermore, the paper presents a method to maintain performance despite state uncertainty. The resulting robust concurrent individual and social learning (RCISL) mechanism leads to an enhanced team learning behaviour despite state uncertainty. The paper analyzes the performance of the concurrent individual and social learning mechanism with and without a particle filter for a heterogeneous foraging scenario. The RCISL mechanism confers statistically significant performance improvements over the CISL mechanism

  • 119.
    Girard, Justin
    et al.
    Institute for Aerospace Studies, University of Toronto.
    Emami, Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Concurrent Markov decision processes for robot team learning2015Inngår i: Engineering applications of artificial intelligence, ISSN 0952-1976, E-ISSN 1873-6769, Vol. 39, 223-234 s., 12Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Multi-agent learning, in a decision theoretic sense, may run into deficiencies if a single Markov decision process (MDP) is used to model agent behaviour. This paper discusses an approach to overcoming such deficiencies by considering a multi-agent learning problem as a concurrence between individual learning and task allocation MDPs. This approach, called Concurrent MDP (CMDP), is contrasted with other MDP models, including decentralized MDP. The individual MDP problem is solved by a Q-Learning algorithm, guaranteed to settle on a locally optimal reward maximization policy. For the task allocation MDP, several different concurrent individual and social learning solutions are considered. Through a heterogeneous team foraging case study, it is shown that the CMDP-based learning mechanisms reduce both simulation time and total agent learning effort.

  • 120.
    Grosse, Christian
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Development of a Star Camera Algorithm for Calculating thePosition on Earth and Mars (VaMEx DLR)2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Within the scope of the Valles Marineris Explorer mission of the German Aerospace Center(DLR), the position of a ground vehicle on Mars needs to be determined. Due to the fact thatMars has no global magnetic field and no positioning system like Earth, a facility independentsystem is necessary. In this context, a star camera based positioning system shall be developed.The subject of this thesis is the development, implementation and verification of a star camerabased transformation algorithm for calculating the latitudinal and longitudinal position on Mars.In addition, an Earth based transformation algorithm is developed, implemented and evaluated fortesting purposes, that is for testing the hardware for the mission under real conditions on Earth.The thesis gives an insight into the fundamental theory of transformation algorithms commonlyused for the transformation between celestial and planet coordinate systems. A self-developedtransformation algorithm is presented which is able to transform a tilted star vector in TopocentricHorizon Coordinate System into observer longitude and latitude position. Moreover, themodular implementation in MATrix LABoratory (MATLAB) and Realtime Onboard DependableOperating System (RODOS) is described in detail. In the further course of the thesis the results ofdifferent test scenarios are outlined and evaluated. The overall results are eventually discussed regardingtheir implications for the mission and subsequently, suggestions for further improvementof the algorithm are made.

  • 121.
    Grotzinger, J.P.
    et al.
    California Institute of Technology, Pasadena, Division of Geological and Planetary Sciences, California Institute of Technology.
    Crisp, J.A.
    Indiana University, Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
    Vasavada, Ashwin
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
    Martin-Torres, Javier
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Curiosity's Mission of Exploration at Gale Crater, Mars2015Inngår i: Elements, ISSN 1811-5209, E-ISSN 1811-5217, Vol. 11, nr 1, 19-26 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Landed missions to the surface of Mars have long sought to determine the material properties of rocks and soils encountered during the course of surface exploration. Increasingly, emphasis is placed on the study of materials formed or altered in the presence of liquid water. Placed in the context of their geological environment, these materials are then used to help evaluate ancient habitability. The Mars Science Laboratory mission—with its Curiosity rover—seeks to establish the availability of elements that may have fueled microbial metabolism, including carbon, hydrogen, sulfur, nitrogen, phosphorus, and a host of others at the trace element level. These measurements are most valuable when placed in a geological framework of ancient environments as interpreted from mapping, combined with an understanding of the petrogenesis of the igneous rocks and derived sedimentary materials. In turn, the analysis of solid materials and the reconstruction of ancient environments provide the basis to assess past habitability.

  • 122.
    Grulich, Maria
    et al.
    Technische Universität München.
    Conte, Davide
    The Pennsylvania State University.
    Borg, Kyle
    University of Colorado, Boulder.
    Burg, Alexander
    George Washington University.
    Burgoyne, Hayden
    California Institute of Technology.
    Celik, Onur
    School of Aerospace, Transport and Manufacturing, Cranfield University.
    Kraetzig, Benjamin
    Neptec Design Group, Atlas Building (R27), Harwell Campus Didcot, Fermi Avenue, Oxfordshire.
    Meskoob, Behnoosh
    Electrical and Electronics Faculty, Istanbul Technical University, Maslak.
    Tió, Meritxell Viñas
    Thales Alenia Space Cannes, 5 Allée des Gabians, Cannes.
    Yesil, Ali
    Institute of Space Systems, University of Stuttgart.
    Heizmann, Sören
    Universität Stuttgart.
    Scherrmann, Marcel
    Institute of Space Systems, University of Stuttgart.
    Laudan, Katarina
    Technical University Berlin.
    Pérez, Ana Alexandra
    Universidad Simón Bolívar, Sartenejas, Caracas.
    Roos, Tobias
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Weisser, Constantin
    Massachusetts Institute of Technology.
    Next - Exploration universal station (NEXUS)2016Inngår i: Proceedings of the International Astronautical Congress, IAC, 2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

     From July 25 to August 1, 2015 the Space Station Design Workshop (SSDW) was held at the University of Stuttgart in Germany with students coming from around the world. During the SSDW the participants where challenged to develop a concept for a new international platform like the International Space Station (ISS) for future space research. This paper discuss the Preliminary Design Document of the architectural design, deployment strategy and operational phase of NEXUS: the Next EX-ploration Universal Station, an international crewed space platform in cis-lunar space to support the current vision for future deep space exploration. This station is designed to be modular, extensible, sustainable and serves a number of novel applications, including unique research, supporting current and future robotic and human planetary exploration, and providing a platform for international cooperation and commercial development. This space station will be the center of space exploration during its operation and will dramatically enhance the opportunities for every partner to explore the unknown and new locations beyond Low Earth Orbit. The world has successfully collaborated for many years at the ISS. However, the ISS is only currently supported through mid-2020s. The next step is to further the research and exploration done in space and provide an intermediate staging location for missions beyond Earths sphere of influence. NEXUS is located in cis-lunar space, in a halo orbit around the Earth-Moon Libration Point 2 (EML2). While the priorities of potential international partners are extremely varied, NEXUS location enhances and supports the vision of nearly every international space agency and commercial companies. The station offers numerous opportunities for research and technology testing in space and on the Moon. The overall mission architecture is separated into two phases: the construction phase and the operations phase. In order to align with the end of the ISS, the construction will begin in 2024. The construction phase would last 6 years during which the various station modules are sent to EML2 using heavy lift launchers such as the SLS Block 1 and 1B through weak stability boundary trajectories. The station will become fully operational in 2030 and will receive supplies from Earth by using a solar electric tug which would taxi supplies from Earth to NEXUS. NEXUS will be used as an intermediate location for human and robotic missions to explore the Moon, Mars, and other destinations in our Solar System

  • 123.
    Guldevall, Peter
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Development of an FPGA based Trigger for Slow Moving Events for the EUSO-TA Telescope2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 124.
    Gultepe, Ismail
    et al.
    Cloud Physics and Severe Weather Research Section, Environment Canada.
    Kuhn, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Pavolonis, Michael J.
    NOAA, NESDIS, Madison, WI.
    Calvert, C.
    CIMSS, University of Wisconsin-Madison, Madison, WI.
    Gurka, James J.
    NOAA, NESDIS, Greenbelt, MD.
    Heymsfield, Andrew J.
    NCAR, Boulder, Colorado.
    Liu, P.S.K.
    Cloud Physics and Severe Weather Research Section, Environment Canada.
    Zhou, B.
    I.M. Systems Group, NOAA/NWS/NCEP, Camp Springs, MD.
    Ware, Randolph H.
    Radiometrics Corporation, CIRES, University of Colorado, Boulder, CO.
    Ferrier, Brad Schoenberg
    I.M. Systems Group, NOAA/NWS/NCEP, Camp Springs, MD.
    Milbrandt, Jason A.
    RPN, CMC, Environment Canada.
    Bernstein, Ben C.
    Leading Edge Atmospherics, Boulder, CO.
    Ice fog in arctic during fram-ice fog project aviation and nowcasting applications2014Inngår i: Bulletin of The American Meteorological Society - (BAMS), ISSN 0003-0007, E-ISSN 1520-0477, Vol. 95, nr 2, 211-226 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Increased understanding of ice fog microphysics can improve frost and ice fog prediction using forecast models and remote-sensing retrievals, thereby reducing potential hazards to aviation

  • 125.
    Gultepe, Ismail
    et al.
    Cloud Physics and Severe Weather Research Section, Environment Canada.
    Zhou, B.
    I.M. Systems Group, NOAA/NWS/NCEP, Camp Springs, MD.
    Milbrandt, Jason A.
    RPN, CMC, Environment Canada.
    Bott, A.
    Meteorolooieches lnstitut, University of Bonn.
    Li, Y.
    Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing.
    Heymsfield, Andrew J.
    National Center for Atmospheric Research, Boulder, Colorado.
    Ferrier, Brad Schoenberg
    I.M. Systems Group, NOAA/NWS/NCEP, Camp Springs, MD.
    Ware, Randolph H.
    Radiometrics Corporation, CIRES, University of Colorado, Boulder, CO.
    Pavolonis, Michael J.
    NOAA, NESDIS, Madison, WI.
    Kuhn, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Gurka, James J.
    NOAA, NESDIS, Greenbelt, MD.
    Liu, P.
    Cloud Physics and Severe Weather Research Section, Environment Canada.
    Cermak, J.
    Ruhr-Universität Bochum, Department of Geography.
    A review on ice fog measurements and modeling2015Inngår i: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 151, 2-19 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The rate of weather-related aviation accident occurrence in the northern latitudes is likely 25 times higher than the national rate of Canada. If only cases where reduced visibility was a factor are considered, the average rate of occurrence in the north is about 31 times higher than the Canadian national rate. Ice fog occurs about 25% of the time in the northern latitudes and is an important contributor to low visibility. This suggests that a better understanding of ice fog prediction and detection is required over the northern latitudes. The objectives of this review are the following: 1) to summarize the current knowledge of ice fog microphysics, as inferred from observations and numerical weather prediction (NWP) models, and 2) to describe the remaining challenges associated with measuring ice fog properties, remote sensing microphysical retrievals, and simulating/predicting ice fog within numerical models. Overall, future challenges related to ice fog microphysics and visibility are summarized and current knowledge is emphasized.

  • 126.
    Guzewich, Scott D.
    et al.
    Universities Space Research Association/NASA Goddard Space Flight Center.
    Newman, C.
    Ashima Research Inc.
    De La Torre Juárez, Manuel
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
    Mason, E.
    Texas A&M University, College Station, TX.
    Battalio, M.
    Texas A&M University, College Station, TX.
    Zorzano Mier, Maria-Paz
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Moores, John E.
    Earth and Space Science and Engineering , York University.
    Moore, C.A.
    Earth and Space Science and Engineering , York University.
    Kloos, J.L
    Earth and Space Science and Engineering , York University.
    Martinez, M.D.
    Uni-versity of Michigan, Ann Arbor.
    Smith, M.D.
    NASA Goddard Space Flight Center, Greenbelt.
    The Mars Science Laboratory dust storm campaign2017Konferansepaper (Annet vitenskapelig)
  • 127.
    Güttler, Johannes
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Field-Site Prototype for HABIT (FSP-HABIT): Characterizing Martian Salts Prior to the ExoMars 2020 Mission2016Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    One of the major remaining question about Mars is its habitability - if the requirements necessary to allow for life are presently fulfilled. One of the most relevant ingredients for life, as we know it, is water. Indirect evidence of transient liquid water on Mars has been retrieved from both rover [Martín-Torres et al., 2015] and orbiter [Ojha et al., 2015].

    [Martín-Torres et al., 2015] inferred the existence of an active water cycle, driven by chlorate and perchlorate salts, which are commonly found on the Martian surface, and absorb atmospheric water to form stable hydrated compounds and liquid solutions. This happens through a process called deliquescence (absorption of moisture from the atmosphere by the salts and dissolving into a liquid solution). One of the goals of HABIT is to confirm the hypothesis about the water cycle on Mars. HABIT will record the behavior of a selection of salts on Mars, and will also record Martian environmental conditions (UVdose, air and ground temperatures).

    The Field-Site Prototype for HABIT (FSP-HABIT) was the first prototype of HABIT deployed during field-site campaigns. Three campaigns took place during summer 2016: First, a short preparatory campaign in Abisko, Sweden, was carried out. The second campaign took place in Iceland, within the EU COST Action TD1308 ORIGINS (Origins and evolution of life on Earth and in the Universe), and the third campaign was conducted within the NASA Spaceward Bound India Program in Ladakh. After providing the corresponding background on the mission framework and the scientific background, this document covers the mechanical, electrical, and software design of the instrument. Afterwards, the steps taken to test the instrument and their results are covered, followed by a rating of the instrument and ideas for future improvements. Instruments like FSP-HABIT will enable the characterization of hygroscopic salts by their conductivity as liquid brines are good conductors, hydrated salts are poor conductors, and dehydrated salts are insulators. During the field-site campaigns, the measurements of FSP-HABIT were used to characterize the near surface environment by its temperature, pressure and relative humidity. Now, these measurements are available for comparison with microbiological studies of the water, ice and soils to characterize the habitability of the explored site. The lessons learned while designing and building FSP-HABIT can be used to inform the development of further prototypes for space missions such as HABIT.

  • 128.
    Hagen, Christoph
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    A Bluetooth based intra-satellite communication system2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This thesis presents a wireless communication system for intra-satellite communication based on Bluetooth Low Energy technology, which can have many benefits regarding the design and operation of satellites. The proposed design based on the nRF53832 chip from Nordic Semiconductor is described, followed by the results of several tests regarding the most important design criteria for its application in small satellites. The tested aspects include the power consumption of the wireless module in different operation modes, which is sufficiently low for the application even in small satellites. Signal strength measurements for various output power settings and obstacles show that reliable communication is possible in a satellite mockup. No packet error was detected, and latencies of less than 30 ms combined with achievable data rates between 200 and 700 kbps should be sufficient for most CubeSat satellites. Additionally, details are given to successfully integrate the chip with existing satellite subsystems. A code library is provided to simplify the communication between the modules, and a concept of a redundant system is established to increase the reliability for critical satellite subsystems. The overall assessment of the technology suggests that the presented system is suitable for in-orbit deployment with the Aalto-3 satellite (currently being developed at Aalto University), which will provide further validation of the technology. 

  • 129.
    Hagos, Tesfamichael Marikos
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Aalto University .
    Estimation of phases for compliant motion: Auto-regressive HMM, multi-class logistic regression, Learning from Demonstration (LfD), Gradient descent optimization,2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Fulltekst tilgjengelig fra 2018-01-01 08:00
  • 130.
    Hakima, Houman
    et al.
    University of Toronto Institute for Aerospace Studies, 4925 Dufferin Street, Toronto.
    Emami, Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Debris detumbler: An alternative approach to active debris removal2016Inngår i: Proceedings of the International Astronautical Congress, IAC, 2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Since the launch of the first artificial satellite, i.e., Sputnik in 1957, several thousand man-made objects have been launched into the Earth orbits, great majority of which remained in their orbit despite the termination of their mission. A number of viable solutions have been suggested in the research community for actively removing the orbital debris, some of which require the capturing of the debris, while others are contactless methods. A challenging aspect of capturing an orbital debris using any method is due to the tumbling motion of the debris. A majority of the suggested methods require zero or very low rates of debris attitude to perform successfully, or need to follow a synchronization phase with the debris before the capturing and removal operation. This is technically costly and challenging, if not infeasible. This paper proposes an alternative approach to orbital debris removal, which can make various state-of-the-art methods of active debris removal perform at lower costs and risks. The approach utilizes one or more detumbler platforms, in the form of miniaturized cubesats, which are de-signed to be lunched from the remover spacecraft, attach to the target debris, and reduce its attitude rate to zero using the onboard attitude determination sensors and control actuators. The paper outlines the operation of debris detumblers. The conceptual design of such platforms is also presented, based on the one- to three-unit cubesat bus and commercial off-the-shelf technologies. Orbital insertion, rendezvous and attachment maneuvers are also discussed. Finally, through simulations the performance of the proposed approach is compared with that of some well-studied methods in various scenarios using several catalogued debris, based on performance metrics such as delta-v, operation time, trajectory simplicity, total thrust, etc

  • 131.
    Hammarsten, Michael
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    A statistical study of incoherent scatter plasma line enhancements during the International Polar Year ’07-’08 in Svalbard2016Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    There was a large radar campaign during 2007 and 2008, the International Polar Year (IPY),and at that time the EISCAT Svalbard Radar was operated and measured the ionosphere continuouslyat most times. This report presents statistical results from an electron enhancementpoint of view. Until now there has been some research into the field and results based on theions in the ionosphere, and the enhancements we refer to as Naturally enhanced ion acousticlines (NEIALs). Plasma line data from May 2007 to February 2008 has been analysed inorder to find and classify enhancements as NEIALs have been classified but with respect tothe electron distribution instead of the ion distribution. A method of detection was developedin order to differentiate the enhancements from the background with a relation between theminimum and maximum power of each measured dump. Results show that there is a largedifference between the downshifted plasma lines and the upshifted plasma lines, both has arange distribution peak at 180 km and the upshifted plasma line has another peak at 230 kmwhich the downshifted plasma line does not. The occurrence rate of the enhancements was1.64 % for the downshifted plasma line and 4.69 % for the upshifted plasma line. Threedifferent types of enhancements are classified using the variance distribution for the peakfrequency of that detected dump, Single, Profile, and Diffuse. The Single enhancements havea bit different spectral, range, and time of day distributions than of the Profile and Diffusedistributions. The Diffuse classifications are mostly wrong classifications and aliasing and itis very similar to Profile enhancements as seen by its distribution.

  • 132.
    Hirschmüller, Korbinian
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Development and Evaluation of a 3D Point Cloud Based Attitude Determination System2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 133.
    Holl, Gerrit
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Microwave and infrared remote sensing of ice clouds: measurements and radiative transfer simulations2011Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This licentiate thesis considers the combination of multiple instruments for remote sensing of the Earth atmosphere from space. The primary focus is on remote sensing of atmospheric ice. Ice clouds are important for the Earth’s radiation budget, but their properties are difficult to measure and therefore poorly known. A better quantification of ice clouds is needed to improve global climate models. This thesis introduces the reader to the subject and describes how to combine measurements and radiative transfer simulations in an attempt to improve our understanding. A major part of this work is the development of a toolkit to find co-incident measurements, or collocations, between any pair of down-looking satellite sensors. Firstly, this toolkit is used to collocate passive microwave and thermal infrared sensors on meteorological satellites with the Cloud Profiling Radar on CloudSat. With the resulting collocated dataset, the Ice Water Path (IWP) signal in passive thermal radiation is studied and an improved IWP retrieval is presented. The toolkit is also used to better characterise the bias between different copies of passive microwave radiometers on-board polar-orbiting operational satellites. For the Atmospheric Radiative Transfer Simulator (ARTS), version 2, an optimised frequency grid for infrared broadband simulations is shown to be applicable for cloudy simulations. This frequency grid can and will be used to study the IWP signal in thermal infrared radiances. An outlook on a comparison between collocations and simulations is presented in the thesis.

  • 134.
    Holl, Gerrit
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Remote sensing of ice clouds: synergistic measurements and radiative transfer simulations2013Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis primarily considers the spaceborne remote sensing of ice clouds and frozen precipitation. Ice clouds are important for hydrology and for the Earth’s radiation budget, but many properties are difficult to measure, in particular using spaceborne instruments. A better quantification of ice clouds is needed to improve global climate models. This thesis presents steps toward such an improvement.The first part of the thesis introduces topics related to the research presented in the second part, but presents no new scientific results. It gives a brief introduction to the history of atmospheric remote sensing and describes how the different parts of the electromagnetic spectrum can be used actively or passively. Then, it describes why ice clouds are important and what microphysical, optical, and macrophysical properties are used to describe atmospheric ice. Next, it briefly introduces the relevant topics in atmospheric radiative transfer. The first part concludes with a description of various approaches to retrievals, with a particular focus on those applied in this thesis.The second part of the thesis describes new results. The bulk of the new results is described in five peer-reviewed publications, that are appended verbatim.A major part of the work builds on the development of a toolkit to easily find co-incident measurements, or collocations, between any pair of satellite sensors. Four appended articles rely on this toolkit.The first appended article uses the toolkit to obtain collocations between passive microwave and infrared on operational meteorological satellites with the Cloud Profiling Radar on CloudSat. It presents three examples. Firstly, from the collocated dataset and a dataset of synthetic profiles, the article compares the statistical relations between an official CloudSat Ice Water Path (IWP) product and microwave radiances. Secondly, it shows a point-by-point comparison between the same CloudSat IWP product, and an IWP product based on passive microwave. A more sophisticated set of systematic comparisons, including more satellites and sensors, is presented in a dedicated paper. Finally, the first paper provides a first preview of how the collocations can be used to train a new IWP retrieval from passive operational measurements. This too is the topic of a dedicated paper, where solar, terrestrial infrared, and microwave radiances are combined to obtain an improved IWP product from passive operational sensors, by training with an active combined radar-lidar product from CloudSat-CALIPSO.The second appended article also relies on the collocations toolkit. Here, collocations between different copies of identical or very similar microwave sounders are used to assess how the inter-satellite bias depends on radiance and latitude.The remaining two studies described in the thesis do not use existing measurements, but are based on radiative transfer modelling. One attached paper verifies that optimised frequency grids obtained in clear-sky simulations for terrestrial infrared instrument studies, can be applied directly for cloudy simulations. This result is relevant for future studies. Finally, the thesis includes a short study with retrieval simulations for a new sub-millimetre instrument concept.

  • 135.
    Holl, Gerrit
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Mendrok, Jana
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Kottayil, Ajil
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Optimised frequency grids for infrared radiative transfer simulations in cloudy conditions2012Inngår i: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 113, nr 16, 2124-2134 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper shows that radiometer channel radiances for cloudy atmospheric conditions can be simulated with an optimised frequency grid derived under clear-sky conditions. A new clear-sky optimised grid is derived for AVHRR channel . For HIRS channel 11 and AVHRR channel 5, radiative transfer simulations using an optimised frequency grid are compared with simulations using a reference grid, where the optimised grid has roughly 100–1000 times less frequencies than the full grid. The root mean square error between the optimised and the reference simulation is found to be less than 0.3 K for both comparisons, with the magnitude of the bias less than 0.03 K. The simulations have been carried out with the radiative transfer model Atmospheric Radiative Transfer Simulator (ARTS), version 2, using a backward Monte Carlo module for the treatment of clouds. With this module, the optimised simulations are more than 10 times faster than the reference simulations. Although the number of photons is the same, the smaller number of frequencies reduces the overhead for preparing the optical properties for each frequency. With deterministic scattering solvers, the relative decrease in runtime would be even more. The results allow for new radiative transfer applications, such as the development of new retrievals, because it becomes much quicker to carry out a large number of simulations. The conclusions are applicable to any downlooking infrared radiometer.

  • 136. Holl, Gerrit
    et al.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Rydberg, B.
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Jiménez, C.
    Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique, Centre National de la Recherche Scientifique, Observatoire de Paris.
    Collocating satellite-based radar and radiometer measurements: methodology and usage examples2010Inngår i: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 3, nr 3, 693-708 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Collocations between two satellite sensors are occasions where both sensors observe the same place at roughly the same time. We study collocations between the Microwave Humidity Sounder (MHS) on-board NOAA-18 and the Cloud Profiling Radar (CPR) on-board CloudSat. First, a simple method is presented to obtain those collocations and this method is compared with a more complicated approach found in literature. We present the statistical properties of the collocations, with particular attention to the effects of the differences in footprint size. For 2007, we find approximately two and a half million MHS measurements with CPR pixels close to their centrepoints. Most of those collocations contain at least ten CloudSat pixels and image relatively homogeneous scenes. In the second part, we present three possible applications for the collocations. Firstly, we use the collocations to validate an operational Ice Water Path (IWP) product from MHS measurements, produced by the National Environment Satellite, Data and Information System (NESDIS) in the Microwave Surface and Precipitation Products System (MSPPS). IWP values from the CloudSat CPR are found to be significantly larger than those from the MSPPS. Secondly, we compare the relation between IWP and MHS channel 5 (190.311 GHz) brightness temperature for two datasets: the collocated dataset, and an artificial dataset. We find a larger variability in the collocated dataset. Finally, we use the collocations to train an Artificial Neural Network and describe how we can use it to develop a new MHS-based IWP product. We also study the effect of adding measurements from the High Resolution Infrared Radiation Sounder (HIRS), channels 8 (11.11 mu m) and 11 (8.33 mu m). This shows a small improvement in the retrieval quality. The collocations described in the article are available for public use

  • 137.
    Holl, Gerrit
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Rydberg, Bengt
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Jiménez, Carlos
    LERMA, CNRS, Observatoire de Paris, Paris, France.
    Collocating satellite-based radar and radiometer measurements –: methodology and usage examples2010Konferansepaper (Annet vitenskapelig)
  • 138.
    Holl, Gerrit
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Rydberg, Bengt
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Jiménez, Carlos
    Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique, Centre National de la Recherche Scientifique, Observatoire de Paris.
    Collocating satellite-based radar and radiometer measurements: methodology and usage examples2011Inngår i: Proceedings of the ESA Living Planet Symposium, European Space Agency, ESA , 2011Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Collocations between two satellite sensors are occasions where both sensors observe the same place at roughly the same time. We study collocations between the Microwave Humidity Sounder (MHS) on-board NOAA-18 and the Cloud Profiling Radar (CPR) on-board CloudSat. We present some statistical properties of the collocations. For 2007, we find approximately two and a half million MHS measurements with CPR pixels close to their centrepoints. We present some possible applications. We use the collocations to validate an operational Ice Water Path (IWP) product from MHS measurements, produced by the National Environment Satellite, Data and Information System (NESDIS) in the Microwave Surface and Precipitation Products System (MSPPS). IWP values from the CloudSat CPR are found to be significantly larger than those from the MSPPS. Finally, we use the collocations to train an Artificial Neural Network and describe how we can use it to develop a new MHS-based IWP product. The collocations described in the article are available for public use.

  • 139.
    Holl, Gerrit
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Rydberg, Bengt
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Jiménez, Carlos
    LERMA, CNRS, Observatoire de Paris, Paris, France.
    Collocating satellite-based radar and radiometer measurements: methodology and usage examples2010Konferansepaper (Annet vitenskapelig)
  • 140.
    Holl, Gerrit
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Rydberg, Bengt
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Jiménez, Carlos
    LERMA, CNRS, Observatoire de Paris, Paris, France.
    Hunting ice clouds: quantifying ice from passive infrared and microwave measurements by collocating with the CloudSat radar2011Konferansepaper (Annet vitenskapelig)
  • 141.
    Holl, Gerrit
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Eliasson, Salomon
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Mendrok, Jana
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    SPARE-ICE: Synergistic ice water path from passive operational sensors2014Inngår i: Journal of Geophysical Research: Atmospheres, ISSN 2169-8996, Vol. 119, nr 3, 1504-1523 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This article presents SPARE-ICE, the Synergistic Passive Atmospheric Retrieval Experiment-ICE. SPARE-ICE is the first Ice Water Path (IWP) product combining infrared and microwave radiances. By using only passive operational sensors, the SPARE-ICE retrieval can be used to process data from at least the NOAA 15 to 19 and MetOp satellites, obtaining time series from 1998 onward. The retrieval is developed using collocations between passive operational sensors (solar, terrestrial infrared, microwave), the CloudSat radar, and the CALIPSO lidar. The collocations form a retrieval database matching measurements from passive sensors against the existing active combined radar-lidar product 2C-ICE. With this retrieval database, we train a pair of artificial neural networks to detect clouds and retrieve IWP. When considering solar, terrestrial infrared, and microwave-based measurements, we show that any combination of two techniques performs better than either single-technique retrieval. We choose not to include solar reflectances in SPARE-ICE, because the improvement is small, and so that SPARE-ICE can be retrieved both daytime and nighttime. The median fractional error between SPARE-ICE and 2C-ICE is around a factor 2, a figure similar to the random error between 2C-ICE ice water content (IWC) and in situ measurements. A comparison of SPARE-ICE with Moderate Resolution Imaging Spectroradiometer (MODIS), Pathfinder Atmospheric Extended (PATMOS-X), and Microwave Surface and Precipitation Products System (MSPPS) indicates that SPARE-ICE appears to perform well even in difficult conditions. SPARE-ICE is available for public use.

  • 142.
    Hong, Gang
    et al.
    Department of Atmospheric Sciences, Texas A&M University, College Station, Texas.
    Heygster, Georg
    Institute of Environmental Physics, University of Bremen.
    Notholt, Justus
    Institute of Environmental Physics, University of Bremen.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Interannual to diurnal variations in tropical and subtropical deep convective clouds and convective overshooting from seven years of AMSU-B measurements2008Inngår i: Journal of Climate, ISSN 0894-8755, E-ISSN 1520-0442, Vol. 21, nr 17, 4168-4189 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study surveys interannual to diurnal variations of tropical deep convective clouds and convective overshooting using the Advanced Microwave Sounding Unit B (AMSU-B) aboard the NOAA polar orbiting satellites from 1999 to 2005. The methodology used to detect tropical deep convective clouds is based on the advantage of microwave radiances to penetrate clouds. The major concentrations of tropical deep convective clouds are found over the intertropical convergence zone (ITCZ), the South Pacific convergence zone (SPCZ), tropical Africa, the Indian Ocean, the Indonesia maritime region, and tropical and South America. The geographical distributions are consistent with previous results from infrared-based measurements, but the cloud fractions present in this study are lower. Land-ocean and Northern-Southern Hemisphere (NH-SH) contrasts are found for tropical deep convective clouds. The mean tropical deep convective clouds have a slightly decreasing trend with -0.016% decade(-1) in 1999-2005 while the mean convective overshooting has a distinct decreasing trend with -0.142% decade(-1). The trends vary with the underlying surface (ocean or land) and with latitude. A secondary ITCZ occurring over the eastern Pacific between 2 degrees and 8 degrees S and only in boreal spring is predominantly found to be associated with cold sea surface temperatures in La Nina years. The seasonal cycles of deep convective cloud and convective overshooting are stronger over land than over ocean. The seasonal migration is pronounced and moves south with the sun from summer to winter and is particularly dramatic over land. The diurnal cycles of deep convective clouds and convective overshooting peak in the early evening and have their minima in the late morning over the tropical land. Over the tropical ocean the diurnal cycles peak in the morning and have their minima in the afternoon to early evening. The diurnal cycles over the NH and SH subtropical regions vary with the seasons. The local times of the maximum and minimum fractions also vary with the seasons. As the detected deep convective cloud fractions are sensitive to the algorithms and satellite sensors used and are influenced by the life cycles of deep convective clouds, the results presented in this study provide information complementary to present tropical deep convective cloud climatologies.

  • 143.
    Hong, Gang
    et al.
    Department of Atmospheric Sciences, Texas A&M University, College Station, Texas.
    Yang, Ping
    Department of Atmospheric Sciences, Texas A&M University, College Station, Texas.
    Baum, Bryan A.
    Space Science and Engineering Center, University of Wisconsin, Madison, Wisconsin.
    Heymsfield, Andrew J.
    National Center for Atmospheric Research, Boulder, Colorado.
    Weng, Fuzhong
    Satellite Meteorology and Climatology Division, Center for Satellite Applications and Research, NOAA NESDIS, Camp Springs, Maryland.
    Liu, Quanhua
    Joint Center for Satellite Data Assimilation, NOAA NESDIS, Camp Springs, Maryland.
    Heygster, Georg
    Institute of Environmental Physics, University of Bremen.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Scattering database in the millimeter and submillimeter wave range of 100-1000 GHz for nonspherical ice particles2009Inngår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 114, D06201- s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The inference of ice cloud properties from spaceborne sensors is sensitive to the retrieval algorithms and satellite sensors used. To approach a better understanding of ice cloud properties, it is necessary to combine satellite measurements from multiple platforms and sensors operating in visible, infrared, and millimeter and submillimeter-wave regions of the electromagnetic spectrum. The single-scattering properties of ice particles with consistent ice particle models are the basis for estimating the optical and microphysical properties of ice clouds from multiple satellite sensors. In this study, the single-scattering properties (extinction efficiency, absorption efficiency, single-scattering albedo, asymmetry factor, and scattering phase matrix) of nonspherical ice particles, assumed to be hexagonal solid and hollow columns, hexagonal plates, 3D bullet rosettes, aggregates, and droxtals, are computed from the discrete dipole approximation method for 21 millimeter and submillimeter-wave frequencies ranging from 100 to 1000 GHz. A database of the single-scattering properties of nonspherical ice particles are developed for 38 particle sizes ranging from 2 to 2000 μm in terms of particle maximum dimension. The bulk scattering properties of ice clouds consisting of various ice particles, which are the fundamental to the radiative transfer in ice clouds, are developed on the basis of a set of 1119 particle size distributions obtained from various field campaigns.

  • 144.
    Houman, Hakima
    et al.
    University of Toronto, Institute for Aerospace Studies.
    Emami, Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Prioritizing orbital debris for active debris removal missions2017Inngår i: IEEE Aerospace Conference Proceedings, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2017, 7943788Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper introduces a method of prioritizing orbital debris for future active debris removal missions, based on the evaluation of the total collision probability of each cataloged debris. The United States Space Surveillance Network actively monitors, tracks, and catalogs space debris orbiting Earth. The catalog is updated routinely, and is available to the public in the form of two-line element data. The total collision probability of a debris is defined as the overall probability of the debris colliding with any other debris in a given time window. The proposed method uses the two-line element data pertaining to each debris in the catalog to project the future state of the debris, i.e., the classical orbital elements, at predefined time steps for a given time window. The effects of orbital perturbations are considered wherever applicable. The relative distances between all debris are estimated in each time step, and pairwise collision probabilities are calculated for any two debris objects in the catalog. To obtain the total collision probability for a debris, the pairwise collision probabilities pertaining to the debris are summed. Further, for every debris object the trend in the total collision probability as the time window progresses is quantified, and debris objects are ranked based on their chance of collision in the time window. The outcome of the study is compared with target debris proposed in other studies.

  • 145.
    Höpfner, M.
    et al.
    Karlsruhe Institute of Technology.
    Milz, Mathias
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Orphal, J.
    Karlsruhe Institute of Technology.
    Stiller, G.
    Karlsruhe Institute of Technology.
    The natural greenhouse effect of atmospheric oxygen (O2) and nitrogen (N2)2012Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 39, L10706- s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of collision-induced absorption by molecular oxygen (O 2) and nitrogen (N 2) on the outgoing longwave radiation (OLR) of the Earth's atmosphere has been quantified. We have found that on global average under clear-sky conditions the OLR is reduced due to O 2 by 0.11 Wm -2 and due to N 2 by 0.17 Wm -2. Together this amounts to 15% of the OLR-reduction caused by CH 4 at present atmospheric concentrations. Over Antarctica the combined effect of O 2 and N 2 increases on average to about 38% of CH 4 with single values reaching up to 80%. This is explained by less interference of H 2O spectral bands on the absorption features of O 2 and N 2 for dry atmospheric conditions

  • 146.
    Ishtiaq, Shehryar
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Optimization of a Laser Coarse Pointing Assembly for Low Earth Orbit Satellite Missions2016Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    A laser communications terminal was developed by the Deutsches Zentrum für Luft- und Raumfahrt and is already being flown over the BIROS satellite, however it is desired to improvepointing performance with the utilization of a coarse pointing assembly. This study presents theseries of optimizations towards space applicability performed on an existing coarse pointingassembly for such a laser communications terminal. This module was initially built for airborneapplications and tested upon the tornado aircraft. The idea was to use this existing flight performanceproven system and with the help of commercial off the shelf components providebetter structural stability and tolerance to the Low Earth Orbit space environment. Criticalpoints were highlighted and the scope of the study was defined to provide reliable modal andthermal analysis results for its performance under the specified mission design parameters. Acircular low earth orbit of 450 km altitude with an inclination similar to that of the BIROS satellitewas chosen to simulate the space environmental effects for this analysis. A preliminary designreview highlighted the need to increase the link budget, which brought down the beamdivergence to 50 μrad from a previous 100 μrad. This made the entire system sensitive andmore susceptible to environmental factors requiring a more rigid and deformation tolerantstructure. In this study the effect of thermal loadings in worst-case scenarios were analysed.Aside from the optimization changes, the results of the analysis pointed out the need to utilizethermal control measures for optimum performance. Therefore, some passive thermal controlmeasures are also presented in this study, which are necessary to meet the requirements.

  • 147.
    Isoz, Oscar
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Estimation of the Impact on GNSS Receivers From Hall Thruster Engines2014Rapport (Fagfellevurdert)
  • 148.
    Isoz, Oscar
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Interference in Global Positioning System Signals and its Effect on Positioning and Remote Sensing2015Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    GPS and the other GNSS systems (GLONASS, Galileo and Beidou-2/COMPASS) is used to position billions of devices and is saving lives, the environment and money on a daily basis. GNSS enables anyone to determine their own unique global location. But the system can be fragile, it can easily be disabled or manipulated so that the calculated position from the receivers becomes incorrect. This can be done either intenionally or unintentionally. Further, many GNSS signals are located in shared frequency bands where other transmitters are allowed to broadcast as well. These transmitters can forexample be long range radars or distance montitoring equipment for aviation.In this thesis, it is demonstrated how one such radar can be detected and localized using data collected by the GNSS receiver for atmospheric sounding (GRAS). It is shown that the detected radar did not cause any measurable degradation of the temperature profiles generated from the collected data. Measurements from the GRAS sensor is also used as a reference to compare temperature soundings from the passive Advanced MicrowaveSounding Unit-A (AMSU-A) sensors that measures emission from Oxygen around 56 GHz.Further, work focusing on the detection of ground based interference is presented. It is shown how low cost independent units can be used for long term montitoring of the interference environment at key locations. Using collected data from the measurements at an area closed to the public, it is further shown how these units can be used to localize sources of broadband interference. Interference can also be generated from certain types of engines. One of the included contributions presents a theoretical analysis of the impact on GPS from an electrical engine intended for satellite propulsion. Even if the engine generates powerful broadband emission, since it is pulsed, the impact on the GPS receiver will most likely be minimal.

  • 149.
    Isoz, Oscar
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Eriksson, Per
    Chalmers University of Technology, Department of Earth and Space Sciences.
    Intercalibration of microwave temperature sounders using radio occultation measurements2015Inngår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 120, nr 9, 3758-3773 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This is a study of the usefulness of radio occultation (RO) data for intercomparing different microwave temperature (MWT) sounding instruments. The RO data used are from the Global Navigational Satellite System Receiver for Atmospheric Sounding on the Metop-A and B satellites. The MWT sounders investigated are the Advanced Microwave Sounding Unit-A instruments on the satellites NOAA 15, 16, and 18 and Metop-A. We collocate RO and MWT data and then use these collocations to study various aspects of the MWT instruments. In addition, two different versions of the MWT data are compared: standard operational data (OPR) and the NOAA Integrated Microwave Intercalibration Approach data (IMICA). The time series of monthly mean differences shows that there are robust patterns for each satellite and data version, which mostly drift only slowly over time. The intersatellite spread, measured by the standard deviation of the yearly mean values by all satellites, is between 0.1 and 0.4 K, depending on channel, with no significant differences between OPR and IMICA data. The only notable exception is Channel 8 of NOAA 16, which appears to have a time-varying offset of 0.5–1 K relative to the other instruments. At this point it is not clear whether this deviation is real or a sampling artifact, so further study is needed. Due to the large number of collocations used, it is possible to also investigate the scene brightness and scan angle dependence of the MWT bias (relative to RO). First results of such an analysis are presented and discussed. Particularly, the investigation of the scan angle dependence is novel, since this bias pattern is difficult to assess without RO data. Further work is needed on these angular dependences, before conclusions are robust enough to include in data recalibration efforts, but our overall conclusion is that RO collocations are a powerful tool for intercomparing MWT sounders.

  • 150.
    Isoz, Oscar
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Kinch, Kjartan
    Niels Bohr Institute, Copenhagen University.
    Bonnedal, Magnus
    RUAG Space, Gothenburg.
    Akos, Dennis
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Interference from terrestrial sources and its impact on the GRAS GPS radio occultation receiver2014Inngår i: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 49, nr 1, 1-6 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    [1] It is well known that terrestrial GPS/Global Navigation Satellite Systems (GNSS) receivers are vulnerable and have suffered from intentional and unintentional interference sources. Unfortunately, space-based GPS/GNSS receivers are not exempt from radio frequency interference originating from the Earth. This paper explores data recorded by the GNSS Receiver for Atmospheric Sounding (GRAS) instrument onboard MetOp-A in September 2007, which is assumed to be representative of the typical environment for GPS/GNSS instrumentation in LEO orbit. Within these data it is possible to detect both pulsed interference and variations in the background noise. One plausible source of the pulsed interference is identified. We also show that neither the pulsed interference nor the variations in the background noise degrades the performance of the higher level products from GRAS

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