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  • 1.
    Abudayyeh, H.A.
    et al.
    Department of Physics, Al-Quds University, Jerusalem.
    Barghouthi, I.A.
    Department of Physics, Al-Quds University, Jerusalem.
    Slapak, Rikard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Nilsson, Hans
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Centrifugal acceleration at high altitudes above the polar cap: A Monte Carlo simulation2015Inngår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, nr 8, 6409-6426 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A Monte Carlo simulation was used to study the outflow of O+ and H+ ions along three flight trajectories above the polar cap up to altitudes of about 15 RE. Barghouthi (2008) developed a model on the basis of altitude and velocity-dependent wave-particle interactions and a radial geomagnetic field which includes the effects of ambipolar electric field and gravitational and mirror forces. In the present work we improve this model to include the effect of the centrifugal force, with the use of relevant boundary conditions. In addition, the magnetic field and flight trajectories, namely, the central polar cap (CPC), nightside polar cap (NPC), and cusp, were calculated using the Tsyganenko T96 model. To simulate wave-particle interactions, the perpendicular velocity diffusion coefficients for O+ ions in each region were determined such that the simulation results fit the observations. For H+ ions, a constant perpendicular velocity diffusion coefficient was assumed for all altitudes in all regions as recommended by Nilsson et al. (2013). The effect of centrifugal acceleration was simulated by considering three values for the ionospheric electric field: 0 (no centrifugal acceleration), 50, and 100 mV/m. It was found that the centrifugal acceleration increases the parallel bulk velocity and decreases the parallel and perpendicular temperatures of both ion species at altitudes above about 4 RE. Centrifugal acceleration also increases the temperature anisotropy at high altitudes. At a given altitude, centrifugal acceleration decreases the density of H+ ions while it increases the density of O+ ions. This implies that with higher centrifugal acceleration more O+ ions overcome the potential barrier. It was also found that aside from two exceptions centrifugal acceleration has the same effect on the velocities of both ions. This implies that the centrifugal acceleration is universal for all particles. The parallel bulk velocities at a given value of ionospheric electric field were highest in the cusp followed by the CPC followed by the NPC. In this study a region of no wave-particle interaction was assumed in the CPC and NPC between 3.7 and 7.5 RE. In this region the perpendicular temperature was found to decrease with altitude due to perpendicular adiabatic cooling.

  • 2.
    Aires, Filipe
    et al.
    Estellus, Paris.
    Prigent, Catherine
    Estellus, Paris.
    Orlandi, Emiliano
    Cologne university.
    Milz, Mathias
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Eriksson, Patrick
    Chalmers University of Technology.
    Crewell, Susanne
    Cologne university.
    Lin, Chung-Chi
    ESA, ESTEC.
    Kangas, Ville
    ESA, ESTEC.
    Microwave hyperspectral measurements for temperature and humidity atmospheric profiling from satellite: The clear-sky case2015Inngår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 120, nr 21, 11334-11351 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study investigates the benefits of a satellite HYper-spectral Microwave Sensor (HYMS) for the retrieval of atmospheric temperature and humidity profiles, in the context of Numerical Weather Prediction (NWP). In the infrared, hyper-spectral instruments have already improved the accuracy of NWP forecasts. Microwave instruments so far only provide observations for a limited number of carefully selected channels. An information content analysis is conducted here to assess the impact of hyper-spectral microwave measurements on the retrieval of temperature and water vapor profiles under clear-sky conditions. It uses radiative transfer simulations over a large variety of atmospheric situations. It accounts for realistic observation (instrument and radiative transfer) noise and for a priori information assumptions compatible with NWP practices. The estimated retrieval performance of the HYMS instrument is compared to those of the microwave instruments to be deployed on board the future generation of European operational meteorological satellites (MetOp-SG). The results confirm the positive impact of a HYMS instrument on the atmospheric profiling capabilities compared to MetOp-SG. Temperature retrieval uncertainty, compared to a priori information, is reduced by 2 to 10%, depending on the atmospheric height, and improvement rates are much higher than what will be obtained with MetOp-SG. For humidity sounding these improvements can reach 30%, a significant benefit as compared to MetOp-SG results especially below 250 hPa. The results are not very sensitive to the instrument noise, under our assumptions. The main impact provided by the hyper-spectral information originates from the higher resolution in the O2 band around 60 GHz. The results are presented over ocean at nadir but similar conclusions are obtained for other incidence angles and over land

  • 3.
    Alepuz, Javier Pérez
    et al.
    University of Alicante.
    Emami, Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Pomares, Jorge
    University of Alicante.
    Direct image-based visual servoing of free-floating space manipulators2016Inngår i: Aerospace Science and Technology, ISSN 1270-9638, E-ISSN 1626-3219, Vol. 55, 1-9 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents an image-based controller to perform the guidance of a free-floating robot manipulator. The manipulator has an eye-in-hand camera system, and is attached to a base satellite. The base is completely free and floating in space with no attitude control, and thus, freely reacting to the movements of the robot manipulator attached to it. The proposed image-based approach uses the system's kinematics and dynamics model, not only to achieve a desired location with respect to an observed object in space, but also to follow a desired trajectory with respect to the object. To do this, the paper presents an optimal control approach to guiding the free-floating satellite-mounted robot, using visual information and considering the optimization of the motor commands with respect to a specified metric along with chaos compensation. The proposed controller is applied to the visual control of a four-degree-of-freedom robot manipulator in different scenarios.

  • 4.
    Andersen, Torben
    et al.
    Lunds universitet.
    Enmark, Anita
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Integrated Modeling of Telescopes2011Bok (Annet vitenskapelig)
  • 5.
    Auenmüller, Christoph
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Automated Controller Design for a Missile Using Convex Optimization2016Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The focus of the present master thesis is the automation of an existing controllerdesign for a missile using two aerodynamic actuating systems. The motivation isto evaluate more missile concepts in a shorter period of time.The option used is trimming and linearization of a highly nonlinear missile at specic conditions. According to these conditions, either a two-dimensional operatingpoint grid dened by Mach number and height or three-dimensional operatingpoint grid dened by Mach number, height and angle of attack is generated forthe whole operating range of the missile. The controllers are designed at thesepoints using convex optimization. The convex set denes the pole placement areawhich is constrained by linear matrix inequalities according to the dynamic behaviorof the missile at the operating point conditions. These controllers describea validity area where the missile can be stabilized. This area consists all neighboringoperating points and denes therefore the grid density which can dier atspecic regions of the operating range. Controlling the missile to the target makesit necessary to apply gain-scheduling in order to get the manipulated variable byinterpolation of adjacent operating points. During this blending of the controllersa problem called windup can occur when an actuator is saturated. This mightlead to instability in worst case but can be counteracted by a model-recovery antiwindupnetwork which guarantees stability in the presence of saturation. Thisanti-windup design is automated by an ane linear parameter dependency of thegrid parameters and has the same validity area like the controllers.The whole design was successfully developed and tested in MATLAB/Simulink onmissiles using one or two aerodynamic actuating systems. The controllers have agood performance at small and high acceleration steps and the anti-windup keepsthe missile stable even though the actuators are saturated. Stability and robustnessof the controllers and anti-windup networks was veried as well as an airdefense maneuver where the missile starts at the ground and intercepts a targetat high altitude was successfully simulated for dierent grids and missiles.

  • 6.
    Avasak, Kalyani
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Institute of Space Systems, University of Stuttgart.
    Mission Analysis and Trajectory optimisation for project CAPE2016Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Atmospheric reentry is a challenging part of human space ight and planetary entry missions.At the Institute of Space Systems in University of Stuttgart the idea of projectCAPE was conceived in 2012. Project Cubesat Atmospheric Probe for Education aimsto demonstrate the capability of miniaturised technologies of the micro electric plasmathruster, reentry vehicle design and ablative shielding material developed in this institute.The mission scenario is such that the CAPE is being deployed from the InternationalSpace Station and needs to complete the de-orbit of the Service and deorbit module andre-entry of the Atmospheric entry module in less than 1 year. The Cube satellite weighs3.0 kg consisting of a 2+1 unit service design module with solar panels, pulsed plasmapropulsion system of the university of Stuttgart (PETRUS) and a micro atmosphericreentry module (MIRKA-2). This reentry vehicle is unique in its size and weighs 0.5kg. During its reentry phase, it will be subjected to the intense aero-thermal loads at theThermal Protection System front which are absorbed by its ablative heat shield. But thecharacteristics of the re-entry trajectory like the ight path angle, entry velocity and entrypoint greatly determine the survivability against the integral heat load for this ballisticreentry vehicle. Although the success of the mission is considerably higher when having acontrolled reentry, in case of ballistic vehicles it is solely determined by the mission design.The main task is to investigate and develop the optimal re-entry trajectories in thedesign-time phase of mission development for MIRKA-2 vehicle that satises the objectiveof minimizing heat loads and adhering to operational constraints. Thus, the aimof this thesis is to provide a novel solution and optimum trajectory of the de-orbit andre-entry ight to maximize the survivability of the reentry module. The con icting parametersin this mission would be the operational limit of the pulsed plasma thruster andminimum heat loads during reentry ight. The simulation of these trajectories is carriedout in MATLAB using the REENT software developed in the Institute of Space Systems,University of Stuttgart. Its source code is composed in Fortran 77 which is integratedinto MATLAB. A careful mission analysis with the constraints of the capacity of pulsedplasma thruster, impulse provided by the separation mechanism and survivability of thereentry vehicle is carried out to prove the feasibility of this mission. In order to accomplishthe survivability during re-entry the aspects that have been modelled are the ight dynamicsof the satellite, aerodynamic and aero-thermal loads, spacecraft behaviour underthe external loads and local heating process.

  • 7.
    Axelsson, Katarina
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Studies of auroral processes using optical methods2013Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The Aurora is a visual manifestation of the complex plasma processes that occur as the solar wind interacts with the Earth’s magnetosphere and ionosphere. Therefore, studies of the aurora can lead to better understanding of the near-Earth space environment and of fundamental physical processes.This thesis focuses on optical studies of the aurora, both ground-based observations using the Auroral Large Imaging System (ALIS) and measurements from instruments onboard the Japanese micro-satellite Reimei. Various properties of the aurora are studied, such as the characteristic energy of precipitating electrons and scale sizes of diffuse auroral structures. Our understanding of the ionospheric physical processes involved in a particular auroral emission is improved using conjugate particle and optical data.Auroral light is a result of radiative transitions between excited states of the ionospheric gases. These excited states are formed either by direct electron impact or by a series of more complicated processes, involving chemical reactions, where part of the energy is converted into auroral light. Studies of auroral emissions can therefore give information about primary particle fluxes, ionospheric composition, and the magnetospheric and ionospheric processes leading to auroral precipitation. One way of deducing the characteristic energy of the precipitating particles is by using intensity ratios of auroral emissions. To be reliable, this method requires a good understanding of the processes involved in the auroral emissions used. The method works well if the measurements are made along the geomagnetic field lines. Using data from ALIS, both in magnetic zenith and off magnetic zenith, this method is tested for angles further away from the direction of the magnetic field lines. The result shows that it is possible to use this technique to deduce the characteristic energy for angles up to 35 degrees away from magnetic zenith.Using ALIS we have also been able to study structures and variations in diffuse aurora. When mapped to the magnetosphere, this provides information about the characteristics of the modulating wave activity in the magnetospheric source region. A statistical study of the scale sizes of diffuse auroral structures was made and the result shows widths and separation between structures of the order of 13-14 km. When mapped to the magnetosphere, this corresponds to 3-4 ion gyro radii for protons with a typical energy of 7 keV. Magnetometer data show that the structures move southward with a speed close to zero in the plasma convection frame. Stationary mirror mode structures in the magnetospheric equatorial plane are a likely explanation for these diffuse auroral structures. In another study we use measured precipitating electron energy spectra to improve our understanding of how the auroral process itself relates to the 427.8 nm auroral emission, which is often used when studying intensity ratios between different emission lines. The 427.8 nm emission is a fairly simple emission to model, with only a few processes involved, but still has some uncertainties, mostly due to the excitation cross section. Simultaneous measurements of the intensity of this emission from ALIS and the intensity and electron flux from Reimei provide a way to evaluate different sets of cross sections in order to find the best fit to the experimental data. It also allows a comparison of the absolute calibration of ALIS and Reimei imagers, improving the possibility to use the space-borne data for other detailed quantitative studies.In order to compare absolute measurements of aurora using different imagers, optical instruments are usually absolute calibrated by exposing them to a calibration light source. In 2011 an intercalibration workshop was held in Sodankylä, Finland, where nine low light sources were compared to the radioactive Fritz Peak reference source. The results were compared with earlier calibration workshop results and show that the sources are fairly stable. Two sources were also calibrated with the calibration standard source at UNIS, Svalbard, and the results show agreement with the calibration workshop in Sodankylä within 15 to 25%. This confirms the quality of the measurements with ALIS and in turn also of the the Reimei imagers.

  • 8.
    Axelsson, Katarina
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Sergienko, T.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Nilsson, H.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Brändström, U.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Ebihara, Y.
    Research Institute for Sustainable Humanosphere, Kyoto University.
    Asamura, K.
    Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara.
    Hirahara, M.
    Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo.
    Spatial characteristics of wave-like structures in diffuse aurora obtained using optical observations2012Inngår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 30, nr 12, 1693-1701 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present the results of a statistical study using optical images from ALIS (Auroral Large Imaging System) to investigate the spatial and temporal variations of structures in diffuse aurora. Analysis of conjugate Reimei data shows that such fine structures are a result of modulation of high-energy precipitating electrons. Pitch angle diffusion into the loss cone due to interaction of whistler mode waves with plasma sheet electrons is the most feasible mechanism leading to high-energy electron precipitation. This suggests that the fine structure is an indication of modulations of the efficiency of the wave-particle interaction. The scale sizes and variations of these structures, mapped to the magnetosphere, can give us information about the characteristics of the modulating wave activity. We found the scale size of the auroral stripes and the spacing between them to be on average 13-14 km, which corresponds to 3-4 ion gyro radii for protons with an energy of 7 keV. The structures move southward with a speed close to zero in the plasma convection frame.

  • 9.
    Baker, Niklas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Feasibility and design of miniaturized Control Moment Gyroscope for a 3-axis stabilized Micro Satellite2016Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    In this thesis, a feasibility study will be conducted in order to determine if the usage of acontrol moment gyroscope is a possibility for a micro satellite as its attitude control. Thegoal is to conclude if gyroscopes are suitable replacements for the current reaction wheelswhich are acting as the attitude control for the satellite. In the first part of the thesis thegeneral function of the control moment gyroscope and three different types of arrangementsare displayed with all their respective advantages and disadvantages. Then one ofthem will be designed to fit within the restrictions of 1U. The full design of the pyramidconfiguration was chosen due to its compact size and spherical angular momentum envelope.The full design contains all the components such as motors, flywheels, mounts,frame, screws etc. which provide a cost estimate which is a huge input in determiningthe feasibility of this thesis. In the future the manufacture of the pyramid configurablecontrol moment gyroscopes shall be tested in the future with a more advanced steeringlaw in order to determine the full potential of the attitude control system.

  • 10.
    Barabash, Victoria
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Ejemalm, Johnny
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Kuhn, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Milz, Mathias
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Molin, Sven
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Johansson, Jonny
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Westerberg, Lars-Göran
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Masters Programs in Space Science and Engineering in Northern Sweden2017Konferansepaper (Fagfellevurdert)
  • 11.
    Barabash, Victoria
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Osepian, A.
    Polar Geophysical Institute.
    Dalin, P.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Kirkwood, S.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Electron density profiles in the quiet lower ionosphere based on the results of modeling and experimental data2012Inngår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 30, nr 9, 1345-1360 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The theoretical PGI (Polar Geophysical Institute) model for the quiet lower ionosphere has been applied for computing the ionization rate and electron density profiles in the summer and winter D-region at solar zenith angles less than 80° and larger than 99° under steady state conditions. In order to minimize possible errors in estimation of ionization rates provided by solar electromagnetic radiation and to obtain the most exact values of electron density, each wavelength range of the solar spectrum has been divided into several intervals and the relations between the solar radiation intensity at these wavelengths and the solar activity index F10.7 have been incorporated into the model. Influence of minor neutral species (NO, H2O, O, O3) concentrations on the electron number density at different altitudes of the sunlit quiet D-region has been examined. The results demonstrate that at altitudes above 70 km, the modeled electron density is most sensitive to variations of nitric oxide concentration. Changes of water vapor concentration in the whole altitude range of the mesosphere influence the electron density only in the narrow height interval 73-85 km. The effect of the change of atomic oxygen and ozone concentration is the least significant and takes place only below 70 km.

    Model responses to changes of the solar zenith angle, solar activity (low-high) and season (summer-winter) have been considered. Modeled electron density profiles have been evaluated by comparison with experimental profiles available from the rocket measurements for the same conditions. It is demonstrated that the theoretical model for the quiet lower ionosphere is quite effective in describing variations in ionization rate, electron number density and effective recombination coefficient as functions of solar zenith angle, solar activity and season. The model may be used for solving inverse tasks, in particular, for estimations of nitric oxide concentration in the mesosphere

  • 12.
    Barabash, Victoria
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Osepian, A.
    Polar Geophysical Institute.
    Dalin, P.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Kirkwood, S.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Electron density profiles in the quiet lower ionosphere based on the results of modeling and experimental data2012Inngår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 30, nr 9, 1345-1360 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The theoretical PGI (Polar Geophysical Institute) model for the quiet lower ionosphere has been applied for computing the ionization rate and electron density profiles in the summer and winter D-region at solar zenith angles less than 80° and larger than 99° under steady state conditions. In order to minimize possible errors in estimation of ionization rates provided by solar electromagnetic radiation and to obtain the most exact values of electron density, each wavelength range of the solar spectrum has been divided into several intervals and the relations between the solar radiation intensity at these wavelengths and the solar activity index F10.7 have been incorporated into the model. Influence of minor neutral species (NO, H2O, O, O3) concentrations on the electron number density at different altitudes of the sunlit quiet D-region has been examined. The results demonstrate that at altitudes above 70 km, the modeled electron density is most sensitive to variations of nitric oxide concentration. Changes of water vapor concentration in the whole altitude range of the mesosphere influence the electron density only in the narrow height interval 73-85 km. The effect of the change of atomic oxygen and ozone concentration is the least significant and takes place only below 70 km. Model responses to changes of the solar zenith angle, solar activity (low-high) and season (summer-winter) have been considered. Modeled electron density profiles have been evaluated by comparison with experimental profiles available from the rocket measurements for the same conditions. It is demonstrated that the theoretical model for the quiet lower ionosphere is quite effective in describing variations in ionization rate, electron number density and effective recombination coefficient as functions of solar zenith angle, solar activity and season. The model may be used for solving inverse tasks, in particular, for estimations of nitric oxide concentration in the mesosphere

  • 13.
    Barabash, Victoria
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Osepian, Aleftina
    Polar Geophysical Institute, Murmansk.
    Dalin, Peter
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Influence of water vapour on the height distribution of positive ions, effective recombination coefficient and ionisation balance in the quiet lower ionosphere2014Inngår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 32, 207-222 s.Artikkel i tidsskrift (Fagfellevurdert)
  • 14.
    Barghouthi, Imad A.
    et al.
    Space Research Lab, Department of Physics, Al-Quds University, Jerusalem, Department of Physics, Al-Quds University, Jerusalem.
    Abudayyeh, H.A.
    Department of Physics, Al-Quds University, Jerusalem.
    Slapak, Rikard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Nilsson, Hans
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    O+ and H+ above the polar cap: Observations and semikinetic simulations2016Inngår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, nr 1, 459-474 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A 1-dimensional direct simulation Monte Carlo model is used to study the outflow of O+ and H+ ions from 1.2 RE to 15.2 RE along two flight trajectories originating from the polar cap, namely the central polar cap (CPC) and the cusp. To study the effect of varying geophysical conditions and to deduce the proper set of parameters. several parameters were varied and the results were compared to corresponding data from Cluster spacecraft. First, several sets of diffusion coefficients were considered based on using diffusion coefficients calculated by Barghouthi et al. [1998], Nilsson et al. [2013], and Abudayyeh et al. [2015b] for different altitude intervals. It was found that in the central polar cap using the diffusion coefficients reported by Barghouthi et al. [1998] for altitudes lower than 3.7 RE, zero diffusion coefficients between 3.7 and 7.5 RE and diffusion coefficients from Nilsson et al. [2013] for altitudes higher than 7.5 RE provide the best fit for O+ ions. For O+ ions in the cusp the best fit was obtained for using Barghouthi et al. [1998] diffusion coefficients for altitudes lower than 3.7 RE and Nilsson et al. [2013] diffusion coefficients for altitudes higher than that. The best fit for H+ ions in both regions was obtained by using the diffusion coefficients calculated by Abudayyeh et al. [2015b]. Also, it was found that along an ion's trajectory the most recent heating dominates. Second, the strength of centrifugal acceleration was varied by using three values for the ionospheric electric field namely: 0, 50, and 100 mV/m. It was found that the value of 50 mV/m provided the best fit for both ion species in both regions. Finally the lower altitude boundary conditions and the electron temperature were varied. Increasing the electron temperature and the lower altitude O+ parallel velocity were found to increase the access of O+ ions to higher altitudes and therefore increase the density at a given altitude. The variation of all other boundary conditions only affected the densities of the ions and not the other moments due to the overwhelming effect of wave particle interaction. Furthermore varying the parameters of one ion species has no effect on the other ion species. We also compared the energy gain per ion due to wave particle interaction, centrifugal acceleration, and ambipolar electric field and found that wave particle interaction is the most important mechanism, while ambipolar electric field is relatively unimportant especially at higher altitudes.

  • 15.
    Baron, P.
    et al.
    National Institute of Information and Communications Technology, 4-2-1 Nukui-kitamachi, Koganei.
    Urban, J.
    Chalmers University of Technology.
    Sagawa, H.
    National Institute of Information and Communications Technology, 4-2-1 Nukui-kitamachi, Koganei.
    Möller, J.
    Chalmers University of Technology.
    Mendrok, Jana
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Dupuy, E.
    Sato, T.O,
    Ochiai, Satoshi
    National Institute of Information and Communication Technology, Tokyo.
    Suzuk, K.
    Manabe, T.
    Osaka Prefecture University, Naka, Sakai.
    Nishibori, T.
    Japan Aerospace Exploration Agency (JAXA), Tsukuba.
    Kikuchi, K.
    Sato, R.
    Takayanagi, M.
    Murayama, Y.
    Shiotani, M.
    Research Institute for Sustainable Humanosphere, Kyoto University.
    Kasai, Y.
    The Level 2 research product algorithms for the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES)2011Inngår i: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 4, 2105-2124 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper describes the algorithms of the level-2 research (L2r) processing chain developed for the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES). The chain has been developed in parallel to the operational chain for conducting researches on calibration and retrieval algorithms. L2r chain products are available to the scientific community. The objective of version 2 is the retrieval of the vertical distribution of trace gases in the altitude range of 18–90 km. A theoretical error analysis is conducted to estimate the retrieval feasibility of key parameters of the processing: line-of-sight elevation tangent altitudes (or angles), temperature and ozone profiles. While pointing information is often retrieved from molecular oxygen lines, there is no oxygen line in the SMILES spectra, so the strong ozone line at 625.371 GHz has been chosen. The pointing parameters and the ozone profiles are retrieved from the line wings which are measured with high signal to noise ratio, whereas the temperature profile is retrieved from the optically thick line center. The main systematic component of the retrieval error was found to be the neglect of the non-linearity of the radiometric gain in the calibration procedure. This causes a temperature retrieval error of 5–10 K. Because of these large temperature errors, it is not possible to construct a reliable hydrostatic pressure profile. However, as a consequence of the retrieval of pointing parameters, pressure induced errors are significantly reduced if the retrieved trace gas profiles are represented on pressure levels instead of geometric altitude levels. Further, various setups of trace gas retrievals have been tested. The error analysis for the retrieved HOCl profile demonstrates that best results for inverting weak lines can be obtained by using narrow spectral windows.

  • 16.
    Baron, P.
    et al.
    National Institute of Information and Communications Technology, 4-2-1 Nukui-kitamachi, Koganei.
    Urban, J.
    Chalmers University of Technology.
    Sagawa, H.
    National Institute of Information and Communications Technology, 4-2-1 Nukui-kitamachi, Koganei.
    Möller, J.
    Chalmers University of Technology.
    Murtagh, D.P.
    Chalmers University of Technology.
    Mendrok, Jana
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Dupuy, E.
    National Institute of Information and Communications Technology, 4-2-1 Nukui-kitamachi, Koganei.
    Sato, T.O.
    National Institute of Information and Communications Technology, 4-2-1 Nukui-kitamachi, Koganei.
    Ochiai, S.
    National Institute of Information and Communications Technology, 4-2-1 Nukui-kitamachi, Koganei.
    Suzuki, K.
    National Institute of Information and Communications Technology, 4-2-1 Nukui-kitamachi, Koganei.
    Manabe, T.
    Osaka Prefecture University, Naka, Sakai.
    Nishibori, T.
    Japan Aerospace Exploration Agency (JAXA), Tsukuba.
    Kikuchi, K.
    Japan Aerospace Exploration Agency (JAXA), Tsukuba.
    Sato, R.
    Japan Aerospace Exploration Agency (JAXA), Tsukuba.
    Takayanagi, M.
    Japan Aerospace Exploration Agency (JAXA), Tsukuba.
    Murayama, Y.
    National Institute of Information and Communications Technology, 4-2-1 Nukui-kitamachi, Koganei.
    Shiotani, M.
    Research Institute for Sustainable Humanosphere, Kyoto University.
    Kasai, Y.
    National Institute of Information and Communications Technology, 4-2-1 Nukui-kitamachi, Koganei.
    The level 2 research product algorithms for the superconducting submillimeter-wave limb-emission sounder (SMILES)2011Inngår i: Atmospheric Measurement Techniques Discussions, ISSN 1867-8610, E-ISSN 1867-8610, Vol. 4, nr 3, 3593-3645 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper describes the algorithms of the level-2 research (L2r) processingchain developed for the Superconducting Submillimeter-Wave Limb-EmissionSounder (SMILES). The chain has been developed in parallel to the operationalchain for conducting researches on calibration and retrieval algorithms. L2rchain products are available to the scientific community. The objective ofversion 2 is the retrieval of the vertical distribution of trace gases in thealtitude range of 18-90 km. An theoretical error analysis is conducted toestimate the retrieval feasibility of key parameters of the processing:line-of-sight elevation tangent altitudes (or angles), temperature and O3 profiles. The line-of-sight tangent altitudes are retrievedbetween 20 and 50 km from the strong ozone (O3) line at 625.371 GHz,with low correlation with the O3 volume-mixing ratio and temperatureretrieved profiles. Neglecting the non-linearity of the radiometric gain inthe calibration procedure is the main systematic error. It is large for theretrieved temperature (between 5-10 K). Therefore, atmospheric pressure cannot be derived from the retrieved temperature, and, then, in the altituderange where the line-of-sight tangent altitudes are retrieved, the retrievedtrace gases profiles are found to be better represented on pressure levelsthan on altitude levels. The error analysis for the retrieved HOCl profiledemonstrates that best results for inverting weak lines can be obtained byusing narrow spectral windows. Future versions of the L2r algorithms willimprove the temperature/pressure retrievals and also provide information inthe upper tropospheric/lower stratospheric region (e.g., water vapor, icecontent, O3) and on stratospheric and mesospheric line-of-sight winds.

  • 17.
    Bazzocchi, Michael C. F.
    et al.
    University of Toronto, Institute for Aerospace Studies.
    de Decker, Nathan
    University of Liège.
    Emami, Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Application of pseudo-equinoctial shaping to Near-Earth asteroid orbital transfer2017Inngår i: IEEE Aerospace Conference Proceedings, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2017, 7943777Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper determines the near-optimal transfer trajectory of a Near-Earth Asteroid (NEA) to an orbit in the Earth-Moon system through the use of an ion beam redirection method. The ion beam method is a hovering approach to asteroid redirection. The method operates through the use of two diametrically opposed thrusters. The redirection mission targets Arjuna-type asteroids, and uses a sample asteroid, 2013 RZ53, to demonstrate the applicability of the pseudo-equinoctial shaping to asteroid orbital transfer. The asteroid transfer from its initial orbit about the Sun to its final orbit in the Earth-Moon system is divided into two phases using a patched conics approximation. The first phase includes the transfer of the asteroid from its initial orbit to an optimized rendezvous point with Earth. The second phase begins as soon as the asteroid arrives within the Earth's sphere of influence and ends with the transfer of the asteroid into a stable orbit about Earth and Moon. The pseudo-equinoctial shaping approach is employed during each phase, and determines the near-optimal solution for the lowest combined delta-v required to complete the orbital transfer. The pseudo-equinoctial method is a shape-based approach to trajectory design which assumes the trajectory transfer can be modelled as a variation of a conic arc. The transfer considers the eccentricity, inclination, and semi-major axis, as well as optimizes several free parameters, such as the thrust, the start of transfer and the rendezvous point with Earth. The optimization is completed using a genetic algorithm, and the results of the optimization are presented in terms of time of flight, thrust, number of revolutions, and delta-v. Lastly, the results are detailed and the feasibility of a redirection mission for an Arjuna-type asteroid is discussed.

  • 18.
    Bazzocchi, Michael C.F.
    et al.
    Institute for Aerospace Studies, University of Toronto.
    Emami, Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Application of asteroid redirection methods to orbital debris removal2016Inngår i: 2016 IEEE Aerospace Conference: AERO 2016, Big Sky, United States, 5 - 12 March 2016, Piscataway, NJ: IEEE Communications Society, 2016, 7500750Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper discusses the applicability of some of the asteroid redirection methods, prominently studied in the literature, to orbital debris removal. The tasks of asteroid redirection and orbital debris removal share the common goal of controlled redirection of an uncooperative target. Three asteroid redirection methods are systematically compared and analyzed to assess their viability for an orbital debris reentry mission, i.e., ion beam shepherd, laser sublimation, and tugboat. These methods are investigated in terms of the characteristics of the orbital debris population and based on the major criteria for mission design of controlled reentry of uncooperative objects. In addition, the uncertainty intrinsic to the orbital debris population is quantified through the use of a Monte Carlo simulation, which provides insight into the robustness of the methods for various ranges of orbital debris. The Analytical Hierarchy Process will be employed to assess the viability of each method in a logically consistent fashion, namely, through aggregation of the relative preference (of each method) and relative importance (of each criterion). The advantages and drawbacks of each redirection method are discussed in light of the assessment results for orbital debris reentry

  • 19.
    Bazzocchi, Michael C.F.
    et al.
    Institute for Aerospace Studies, University of Toronto.
    Emami, Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Comparative analysis of redirection methods for asteroid resource exploitation2016Inngår i: Acta Astronautica, ISSN 0094-5765, E-ISSN 1879-2030, Vol. 120, 1-19 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An in-depth analysis and systematic comparison of asteroid redirection methods is performed within a resource exploitation framework using different assessment mechanisms. Through this framework, mission objectives and constraints are specified for the redirection of an asteroid from a near-Earth orbit to a stable orbit in the Earth-Moon system. The paper provides a detailed investigation of five redirection methods, i.e., ion beam, tugboat, gravity tractor, laser sublimation, and mass ejector, with respect to their capabilities for a redirection mission. A set of mission level criteria are utilized to assess the performance of each redirection method, and the means of assigning attributes to each criterion is discussed in detail. In addition, the uncertainty in physical characteristics of the asteroid population is quantified through the use of Monte Carlo analysis. The Monte Carlo simulation provides insight into the performance robustness of the redirection methods with respect to the targeted asteroid range. Lastly, the attributes for each redirection method are aggregated using three different multicriteria assessment approaches, i.e., the analytical hierarchy process, a utility-based approach, and a fuzzy aggregation mechanism. The results of each assessment approach as well as recommendations for further studies are discussed in detail.

  • 20.
    Behar, Etienne
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Lindkvist, Jesper
    Swedish Institute of Space Physics, Kiruna.
    Nilsson, Hans
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Holmström, Mats
    Swedish Institute of Space Physics, Kiruna.
    Stenberg-Wieser, G.
    Swedish Institute of Space Physics, Kiruna.
    Ramstad, Robin
    Swedish Institute of Space Physics, Kiruna.
    Götz, C.
    Technicsche Universitåt Braunschweig, Institute for Geophysics and Extraterrestrial Physics, Braunschweig.
    Mass-loading of the solar wind at 67P/Churyumov-Gerasimenko: Observations and modelling2016Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 596, A42Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Context. The first long-term in-situ observation of the plasma environment in the vicinity of a comet, as provided by the European Rosetta spacecraft. Aims. Here we offer characterisation of the solar wind flow near 67P/Churyumov-Gerasimenko (67P) and its long term evolution during low nucleus activity. We also aim to quantify and interpret the deflection and deceleration of the flow expected from ionization of neutral cometary particles within the undisturbed solar wind. Methods. We have analysed in situ ion and magnetic field data and combined this with hybrid modeling of the interaction between the solar wind and the comet atmosphere. Results. The solar wind deflection is increasing with decreasing heliocentric distances, and exhibits very little deceleration. This is seen both in observations and in modeled solar wind protons. According to our model, energy and momentum are transferred from the solar wind to the coma in a single region, centered on the nucleus, with a size in the order of 1000 km. This interaction affects, over larger scales, the downstream modeled solar wind flow. The energy gained by the cometary ions is a small fraction of the energy available in the solar wind. Conclusions. The deflection of the solar wind is the strongest and clearest signature of the mass-loading for a small, low-activity comet, whereas there is little deceleration of the solar wind

  • 21.
    Behar, Etienne
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Nilsson, Hans
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Wieser, Gabriella Stenberg
    Swedish Institute of Space Physics.
    Nemeth, Zoltan
    Wigner Research Centre for Physics, 1121 Konkoly Thege Street 29-33, Budapest.
    Brolles, T.W.
    Space Science and Engineering Division, Southwest Research Institute, San Antonio.
    Richter, Ingo
    Technische Universität–Braunschweig, Institute for Geophysics and Extraterrestrial Physics.
    Mass loading at 67P/Churyumov-Gerasimenko: A case study2016Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 4, 1411-1418 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the dynamics of the interaction between the solar wind ions and a partially ionized atmosphere around a comet, at a distance of 2.88 AU from the Sun during a period of low nucleus activity. Comparing particle data and magnetic field data for a case study, we highlight the prime role of the solar wind electric field in the cometary ion dynamics. Cometary ion and solar wind proton flow directions evolve in a correlated manner, as expected from the theory of mass loading. We find that the main component of the accelerated cometary ion flow direction is along the antisunward direction and not along the convective electric field direction. This is interpreted as the effect of an antisunward polarization electric field adding up to the solar wind convective electric field.

  • 22.
    Berčič, Laura
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Swedish Institute of Space Physics.
    Instrumental and environmental effects on RPC-ICA measurements of the cometary ion dynamics at comet 67P/CG2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Observations provided from RPC-ICA in combination with the data from RPC-MAG and ROSINA-COPS show that many aspects of the time variability of the detected ions is correlated with the magnetic field or -- to a smaller extent -- with neutral atmosphere density. We also show that not all changes in the cometary ion data reflect the nature of the plasma dynamics, but are a consequence of the instrumental limitations. The main outcome of the article in Appendix 1 is that the cometary ions can be divided into two populations with distinct characteristics. One population we termed the convecting population, is accelerated to higher energies through the interaction with the solar wind. The other population we termed the expanding population is moving radially away from the nucleus in the terminator plane. Both populations exhibit a significant anti-sunward component.In addition we present in this thesis a case with observations day-side of the terminator plane. There we show how the expanding population has a sunward component, consistent with initial radial expansion of the ions from the nucleus which gradually turn into an anti-sunward flow which is then observed in the terminator plane.

  • 23.
    Bethge, Matthias
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Situation and Threat Comprehensionand Conduit of Action with particular reference to aFuture Technology Data Fusion System2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 24.
    Bhardwaj, Anshuman
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Martin-Torres, Javier
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Identification and Mapping of Glacier-Like Forms (GLFs) Near Martian Subpolar Latitudes2016Konferansepaper (Fagfellevurdert)
  • 25.
    Bhardwaj, Anshuman
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Sam, Lydia
    Department of Environmental Science, Sharda University.
    Akanksha, Akanksha
    Banaras Hindu University, Varanasi.
    Martin-Torres, Javier
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Kumar, Rejesh
    Department of Environmental Science, Sharda University.
    UAVs as remote sensing platform in glaciology: Present applications and future prospects2016Inngår i: Remote Sensing of Environment, ISSN 0034-4257, E-ISSN 1879-0704, Vol. 175, 196-204 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Satellite remote sensing is an effective way to monitor vast extents of global glaciers and snowfields. However, satellite remote sensing is limited by spatial and temporal resolutions and the high costs involved in data acquisition. Unmanned aerial vehicle (UAV)-based glaciological studies are gaining pace in recent years due to their advantages over conventional remote sensing platforms. UAVs are easy to deploy, with the option of alternating the sensors working in visible, infrared, and microwave wavelengths. The high spatial resolution remote sensing data obtained from these UAV-borne sensors are a significant improvement over the data obtained by traditional remote sensing. The cost involved in data acquisition is minimal and researchers can acquire imagery according to their schedule and convenience. We discuss significant glaciological studies involving UAV as remote sensing platforms. This is the first review work, exclusively dedicated to highlight UAV as a remote sensing platform in glaciology. We examine polar and alpine applications of UAV and their future prospects in separate sections and present an extensive reference list for the readers, so that they can delve into their topic of interest. Because the technology is still widely unexplored for snow and glaciers, we put a special emphasis on discussing the future prospects of utilising UAVs for glaciological research.

  • 26.
    Bhardwaj, Anshuman
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Sam, Lydia
    Department of Environmental Science, Sharda University.
    Bhardwaj, Akanksha
    Banaras Hindu University, Varanasi.
    Martin-Torres, Javier
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    LiDAR remote sensing of the cryosphere: Present applications and future prospects2016Inngår i: Remote Sensing of Environment, ISSN 0034-4257, E-ISSN 1879-0704, Vol. 177, 125-143 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The cryosphere consists of frozen water and includes lakes/rivers/sea ice, glaciers, ice caps/sheets, snow cover, and permafrost. Because highly reflective snow and ice are the main components of the cryosphere, it plays an important role in the global energy balance. Thus, any qualitative or quantitative change in the physical properties and extents of the cryosphere affects global air circulation, ocean and air temperatures, sea level, and ocean current patterns. Due to the hardships involved in collecting ground control points and field data for high alpine glaciers or vast polar ice sheets, several researchers are currently using remote sensing. Satellites provide an effective space-borne platform for remotely sensing frozen areas at the global and regional scales. However, satellite remote sensing has several constraints, such as limited spatial and temporal resolutions and expensive data acquisition. Therefore, aerial and terrestrial remote sensing platforms and sensors are needed to cover temporal and spatial gaps for comprehensive cryospheric research. Light Detection and Ranging (LiDAR) antennas form a group of active remote sensors that can easily be deployed on all three platforms, i.e., satellite, aerial, and terrestrial. The generation of elevation data for glacial and snow-covered terrain from photogrammetry requires high contrast amongst various reflective surfaces (ice, snow, firn, and slush). Conventional passive optical remote sensors do not provide the necessary accuracy, especially due to the unavailability of reliable ground control points. However, active LiDAR sensors can fill this research gap and provide high-resolution and accurate Digital Elevation Models (DEMs). Due to the obvious advantages of LiDAR over conventional passive remote sensors, the number of LiDAR-based cryospheric studies has increased in recent years. In this review, we highlight studies that have utilised LiDAR sensors for the cryospheric research of various features, such as snow cover, polar ice sheets and their atmospheres, alpine glaciers, and permafrost. Because this technology shows immense promise for applications in future cryospheric research, we also emphasise the prospects of utilising LiDAR sensors. In this paper, a large compilation of relevant references is presented to allow readers to explore particular topics of interest.

  • 27.
    Bhardwaj, Anshuman
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Sam, Lydia
    Institut für Kartographie, Technische Universität Dresden.
    Martin-Torres, Javier
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Rock glaciers as proxies for identifying terrestrial and analogous Martian permafrost2016Inngår i: XI. International Conference On Permafrost: Book of Abstracts / [ed] Günther, F. and Morgenstern, A., Potsdam: Bibliothek Wissenschaftspark Albert Einstein , 2016, 535-537 s.Konferansepaper (Fagfellevurdert)
  • 28.
    Bhardwaj, Anshuman
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Sam, Lydia
    Institut für Kartographie, Technische Universität Dresden.
    Martin-Torres, Javier
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Zorzano Mier, Maria-Paz
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Fonseca, Ricardo
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Martian slope streaks as plausible indicators of transient water activity2017Inngår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, nr 1, 7074Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Slope streaks have been frequently observed in the equatorial, low thermal inertia and dusty regions of Mars. The reason behind their formation remains unclear with proposed hypotheses for both dry and wet mechanisms. Here, we report an up-to-date distribution and morphometric investigation of Martian slope streaks. We find: (i) a remarkable coexistence of the slope streak distribution with the regions on Mars with high abundances of water-equivalent hydrogen, chlorine, and iron; (ii) favourable thermodynamic conditions for transient deliquescence and brine development in the slope streak regions; (iii) a significant concurrence of slope streak distribution with the regions of enhanced atmospheric water vapour concentration, thus suggestive of a present-day regolith-atmosphere water cycle; and (iv) terrain preferences and flow patterns supporting a wet mechanism for slope streaks. These results suggest a strong local regolith-atmosphere water coupling in the slope streak regions that leads to the formation of these fluidised features. Our conclusions can have profound astrobiological, habitability, environmental, and planetary protection implications

  • 29.
    Bhardwaj, Anshuman
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Singh, Shaktiman
    Institut für Kartographie, Technische Universität Dresden.
    Sam, Lydia
    Institut für Kartographie, Technische Universität Dresden.
    Bhardwaj, Akanksha
    Banaras Hindu University, Varanasi.
    Martin-Torres, Javier
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Singh, Atar
    Department of Environmental Science, Sharda University.
    Kumar, Rajesh
    Department of Environmental Science, Sharda University.
    MODIS-based estimates of strong snow surface temperature anomaly related to high altitude earthquakes of 20152017Inngår i: Remote Sensing of Environment, ISSN 0034-4257, E-ISSN 1879-0704, Vol. 188, 1-8 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The high levels of uncertainty associated with earthquake prediction render earthquakes some of the worst natural calamities. Here, we present our observations of MODerate resolution Imaging Spectroradiometer (MODIS)-derived Land Surface Temperature (LST) anomaly for earthquakes in the largest tectonically active Himalayan and Andean mountain belts. We report the appearance of fairly detectable pre-earthquake Snow Surface Temperature (SST) anomalies. We use 16 years (2000–2015) of MODIS LST time-series data to robustly conclude our findings for three of the most destructive earthquakes that occurred in 2015 in the high mountains of Nepal, Chile, and Afghanistan. We propose the physical basis behind higher sensitivity of snow towards geothermal emissions. Although the preliminary appearance of SST anomalies and their amplitudes vary, we propose employing a global-scale monitoring system for detecting and studying such spatio-temporal geophysical signals. With the advent of improved remote sensors, we anticipate that such efforts can be another step towards improved earthquake predictions.

  • 30.
    Bhardwaj, Anshuman
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Department of Environmental Science, Sharda University.
    Singh, Shaktiman
    Department of Environmental Science, Sharda University,.
    Sam, Lydia
    Department of Environmental Science, Sharda University,.
    Joshi, PK
    School of Environmental Sciences, Jawaharlal Nehru University, New Delhi.
    Bhardwaj, Akanksha
    Banaras Hindu University.
    Martín-Torres, Javier F.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR).
    Kumar, Rajesh
    Department of Environmental Science, Sharda University.
    A review on remotely sensed land surface temperature anomaly as an earthquake precursor2017Inngår i: International Journal of Applied Earth Observation and Geoinformation, ISSN 0303-2434, Vol. 63, 158-166 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The low predictability of earthquakes and the high uncertainty associated with their forecasts make earthquakes one of the worst natural calamities, capable of causing instant loss of life and property. Here, we discuss the studies reporting the observed anomalies in the satellite-derived Land Surface Temperature (LST) before an earthquake. We compile the conclusions of these studies and evaluate the use of remotely sensed LST anomalies as precursors of earthquakes. The arrival times and the amplitudes of the anomalies vary widely, thus making it difficult to consider them as universal markers to issue earthquake warnings. Based on the randomness in the observations of these precursors, we support employing a global-scale monitoring system to detect statistically robust anomalous geophysical signals prior to earthquakes before considering them as definite precursors.

  • 31.
    Bhattacharya, Shaondip
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Multi-agent System Distributed Sensor Fusion Algorithms2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The concept of consensus filters for sensor fusion is not an entirely new proposition but one with an internally implemented Bayesian fusion is. This work documents a novel state update algorithm for sensor fusion which works using the principle of Bayesian fusion of data with variance implemented on a single integrator consensus algorithm. Comparative demonstrations of how consensus over a pinning network is reached are presented along with a weighted Bayesian Luenberger type observer and a ’Consensus on estimates’ algorithm. This type of a filter is something that is novel and has not been encountered in previous literature related to this topic to the best of our knowledge. In this work, we also extend the proof for a distributed Luenberger type observer design to include the case where the network being considered is a strongly connected digraph.

  • 32.
    Birman, Camille
    et al.
    Météo-France-CNRS, Toulouse .
    Mahfouf, Jean-François
    Météo-France-CNRS, Toulouse.
    Milz, Mathias
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. IRV.
    Mendrok, Jana
    Chalmers University of Technology, Gothenburg, Sweden.
    Buehler, Stefan A.
    University of Hamburg, Hamburg.
    Brath, Manfred
    University of Hamburg, Hamburg .
    Information content on hydrometeors from millimeter and sub-millimeter wavelengths2017Inngår i: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 69, nr 1, 1271562Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study examines the information content on hydrometeors that could be provided by a future HYperspectralMicrowave Sensor (HYMS) with frequencies ranging from 6.9 to 874 GHz (millimeter and sub-millimeter regions). Through optimal estimation theory the information content is expressed quantitatively in terms of degrees of freedom for signal (DFS). For that purpose the Atmospheric Radiative Transfer Simulator (ARTS) and its Jacobians are used with a set of 25 cloudy and precipitating profiles and their associated errors from the European Centre for Medium-range Weather Forecasting (ECMWF) global numerical weather prediction model.

    In agreement with previous studies it is shown that frequencies between 10 and 40 GHz are the most informative ones for liquid and rain water contents. Similarly, the absorption band at 118 GHz contains significant information on liquid precipitation. A set of new window channels (15.37-, 40.25-, 101-GHz) could provide additional information on the liquid phase. The most informative channels on cloud icewater are the window channels at 664 and 874GHz and thewater vapour absorption bands at 325 and 448 GHz. Regarding snow water contents, the channels having the largest DFS values are located inwindow regions (150-, 251-, 157-, 101-GHz). However it is necessary to consider 90 channels in order to represent 90% of the DFS. The added value of HYMS has been assessed against current Special Sensor Microwave Imager/Sounder (SSMI/S) onboard the Defense Meteorological Satellite Program (DMSP) and future (Microwave Imager/Ice Cloud Imager (MWI/ICI) onboard European Polar orbiting Satellite – Second Generation (EPS-SG)) microwave sensors. It appears that with a set of 276 channels the information content on hydrometeors would be significantly enhanced: the DFS increases by 1.7 against MWI/ICI and by 3 against SSMI/S. A number of tests have been performed to examine the robustness of the above results. The most informative channels on solid hydrometeors remain the same over land and over ocean surfaces. On the other hand, the database is not large enough to produce robust results over land surfaces for liquid hydrometeors. The sensitivity of the results to the microphysical properties of frozen hydrometeors has been investigated. It appears that a change in size distribution and scattering properties can move the large information content of the channels at 664 and 874 GHz from cloud ice to solid precipitation.

  • 33.
    Blanco, Enrique
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    DESIGN OF A SCALABLE, ADAPTABLE AND RELIABLE DEORBITING MECHANISM2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 34.
    Bohra, Murtaza M.
    et al.
    Space Mechatronics Group, Institute for Aerospace Studies, University of Toronto.
    Xu, Linsen
    Space Mechatronics Group, Institute for Aerospace Studies, University of Toronto.
    Emami, Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    CPG-based online trajectory generation for quadruped rovers2016Inngår i: 2015 IEEE International Conference on Robotics and Biomimetics (ROBIO): Zhuhai, 6-9 Dec. 2015, Piscataway, NJ: IEEE Communications Society, 2016, 1053-1058 s., 7418911Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Legged rovers are often considered as viable solutions for traversing unknown terrain. A 2D sagittal plane rover model, based on a domestic cat, is considered in this paper, and an online model-free gait planning framework is implemented using Central Pattern Generators. The framework is used to generate joint trajectories for any arbitrarily varying speed profile, and regulate locomotion transition and speed modulation, both continuously and endogenously. For a continuously changing speed profile, the gait transition is continuous as well. For a discontinuously changing speed profile, a hopping motion is observed, because the rover's thrust speed cannot increase discontinuously

  • 35.
    Browne Mwakyanjala, Moses
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Emami, Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Beek, Jaap van de
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Software-defined radio transceiver for QB50 CubeSat telemetry and telecommand2016Inngår i: Proceedings of the 34th AIAA International Communications Satellite Systems Conference (ICSSC 2016), American Institute of Aeronautics and Astronautics, 2016Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper presents the development of a ground system based on software-defined radio for supporting both ground testing and space telemetry and telecommand of one of the nanosatellites in the QB50 mission. The QB50 project is an ongoing European Commission Seventh Framework initiative, which aims at launching a constellation of 50 CubeSats in the lower thermosphere to carry out in-situ scientific measurements. The paper discusses the implementation of amateur radio protocols and telecommunication modulation schemes on the ground system. The system setup, deployment and scheduling are also discussed using two separate ground stations. The use of different software for testing the system is detailed, the results show the operability of the developed ground system. © 2016, American Institute of Aeronautics and Astronautics Inc

  • 36.
    Browne Mwakyanjala, Moses
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Emami, Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    van de Beek, Jaap
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Verication of phase and frequency modulation for software-defined radio baseband systems using field data2017Konferansepaper (Fagfellevurdert)
  • 37.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Atmospheric radiative-transfer simulator2006Inngår i: Thermal Microwave Radiation: Applications for Remote Sensing, London: Institution of Engineering and Technology, 2006, 54-56 s.Kapittel i bok, del av antologi (Annet vitenskapelig)
  • 38.
    Buehler, Stefan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    UTH-MOS: Wasserdampf und Cirren in der oberen Troposphäre aus operationellen meteorologischen Satellitendaten2006Rapport (Annet vitenskapelig)
  • 39.
    Buehler, Stefan
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Courcoux, N.
    Universität Bremen, Institute of Environmental Physics.
    John, Viju Oommen
    University of Miami, Rosenstiel School of Marine and Atmospheric Sciences, Miami.
    Radiative transfer calculations for a passive microwave satellite sensor: comparing a fast model and a line-by-line model2006Inngår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 111, nr 20, 20304- s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    [1] A comparison between the fast radiative transfer model Radiative Transfer for the TIROS Operational Vertical Sounder (RTTOV-7) and the physical radiative transfer model Atmospheric Radiative Transfer Simulator ( ARTS) was carried out. Radiances were simulated for the sounding channels of the Advanced Microwave Sounding Unit B (AMSU-B) for the whole globe for a single time of a single day ( 1 January 2000, 0000 UT). Temperature, pressure, and specific humidity profiles from the reanalysis data set ERA-40 of the European Centre for Medium-Range Weather Forecasts (ECMWF) were used as input for both models; geopotential height profiles were also used but only as input for ARTS. The simulations were made for two different surface emissivities, 0.60 and 0.95. The low surface emissivity case exhibits the larger radiance differences. Although the global values of the mean difference and standard deviation are small ( for example, the global mean difference for channel 18 is 0.014 K and the standard deviation is 0.232 K), the examination of the geographical distribution of the differences shows that large positive or negative values are observed over dry regions of high northern and southern latitudes and over dry elevated regions. The origin of these differences was found to be due to errors introduced by the transmittance parametrization used in RTTOV.

  • 40.
    Buehler, Stefan
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Defer, E.
    CNRS, Laboratoire d'Etudes du Rayonnement et de la Matière en Astrophysique, Observatoire de Paris.
    Evans, F.
    Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder.
    Eliasson, Salomon
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Mendrok, Jana
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Erikssson, P.
    Chalmers University of Technology, Department of Earth and Space Sciences.
    Lee, C.
    Met Office Hadley Centre, Exeter.
    Jimenez, C.
    CNRS, Laboratoire d'Etudes du Rayonnement et de la Matière en Astrophysique, Observatoire de Paris.
    Prigent, C.
    CNRS, Laboratoire d'Etudes du Rayonnement et de la Matière en Astrophysique, Observatoire de Paris.
    Crewell, S.
    Institute for Geophysics and Meteorology, University of Cologne.
    kasai, Y.
    National Institute of Information and Communications Technology, 4-2-1 Nukui-kitamachi, Koganei.
    Bennartz, R.
    Atmospheric and Oceanic Sciences, University of Wisconsin.
    Gasiewski, A.J.
    NOAA-CU Center for Environmental Technology (CET), Department of Electrical and Computer Engineering, University of Colorado at Boulder.
    Observing ice clouds in the submillimeter spectral range: the CloudIce mission proposal for ESA's Earth Explorer 82012Inngår i: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 5, nr 7, 1529-1549 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Passive submillimeter-wave sensors are a way to obtain urgently needed global data on ice clouds, particularly on the so far poorly characterized 'essential climate variable' ice water path (IWP) and on ice particle size. CloudIce was a mission proposal to the European Space Agency ESA in response to the call for Earth Explorer 8 (EE8), which ran in 2009/2010. It proposed a passive submillimeter-wave sensor with channels ranging from 183 GHz to 664 GHz. The article describes the CloudIce mission proposal, with particular emphasis on describing the algorithms for the data-analysis of submillimeter-wave cloud ice data (retrieval algorithms) and demonstrating their maturity. It is shown that we have a robust understanding of the radiative properties of cloud ice in the millimeter/submillimeter spectral range, and that we have a proven toolbox of retrieval algorithms to work with these data. Although the mission was not selected for EE8, the concept will be useful as a reference for other future mission proposals.

  • 41.
    Buehler, Stefan
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Eriksson, Patrick
    Chalmers University of Technology, Department of Earth and Space Sciences.
    Lemke, Oliver
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Absorption lookup tables in the radiative transfer model ARTS2011Inngår i: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 112, nr 10, 1559-1567 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We describe the lookup table approach that is used to store pre-calculated absorption data in the radiative transfer model ARTS. The table stores absorption cross sections as a function of frequency, pressure, temperature, and the water vapor volume mixing ratio, where the last dimension is only included for those gas species that require it. The table is used together with an extraction strategy, which uses polynomial interpolation, with recommended interpolation orders between five and seven. We also derived recommended default settings for grid spacings and interpolation orders, and verified that the approach gives very accurate results with these default settings. The tested instrument setups were for AMSU-B, HIRS, and Odin, three well-known satellite remote sensing instruments covering a wide range of frequencies and viewing geometries. Errors introduced by the lookup table were found to be always below a few millikelvin, in terms of the simulated brightness temperature.

  • 42.
    Buehler, Stefan
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Jimenez, C.
    Evans, K. F.
    Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder.
    Eriksson, P.
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Rydberg, B.
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Heymsfield, A.
    NCAR, Boulder, Colorado.
    Stubenrauch, C.
    CNRS/IPSL - Laboratoire de Meteorologie Dynamique, Ecole Polytechnique, Palaiseau.
    Lohmann, U.
    ETH Zurich, Institute for Atmospheric and Climate Science.
    Emde, C.
    Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Oberpfaffenhofen.
    John, V. O.
    Met Office Hadley Centre, Exeter.
    Sreerekha, T. R.
    Met Office Hadley Centre, Exeter.
    Davis, C. P.
    School of Geosciences, University of Edinburgh.
    A concept for a satellite mission to measure cloud ice water path, ice particle size, and cloud altitude2007Inngår i: Quarterly Journal of the Royal Meteorological Society, ISSN 0035-9009, E-ISSN 1477-870X, Vol. 133, nr Suppl.2, 109-128 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A passive satellite radiometer operating at submillimetre wavelengths can measure cloud ice water path (IWP), ice particle size, and cloud altitude. The paper first discusses the scientific background for such measurements. Formal scientific mission requirements are derived, based on this background and earlier assessments. The paper then presents a comprehensive prototype instrument and mission concept, and demonstrates that it meets the requirements. The instrument is a conically scanning 12-channel radiometer with channels between 183 and 664 GHz, proposed to fly in tandem with one of the Metop satellites. It can measure IWP with a relative accuracy of approximately 20% and a detection threshold of approximately 2 g m-2. The median mass equivalent sphere diameter of the ice particles can be measured with an accuracy of approximately 30 µm, and the median IWP cloud altitude can be measured with an accuracy of approximately 300 m. All the above accuracies are median absolute error values; root mean square error values are approximately twice as high, due to rare outliers.

  • 43.
    Buehler, Stefan
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    John, V.O.
    Met Office Hadley Centre, Exeter.
    Kottayil, Ajil
    Milz, Mathias
    Eriksson, P.
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Efficient radiative transfer simulations for a broadband infrared radiometer: combining a weighted mean of representative frequencies approach with frequency selection by simulated annealing2010Inngår i: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 111, nr 4, 602-615 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a method to efficiently simulate the measurements of a broadband infrared instrument. The High Resolution Infrared Radiation Sounder (HIRS) instrument is used as example to illustrate the method. The method uses two basic ideas. Firstly, the channel radiance can be approximated by a weighted mean of the radiance at some representative frequencies, where the weights can be determined by linear regression. Secondly, a near-optimal set of representative frequencies can be found by simulated annealing.The paper does not only describe and analyze the method, it also describes how the method was used to derive optimized frequency grids for the HIRS instruments on the satellites TIROS N, NOAA 6-19, and Metop A. The grids and weights, as well as the optimization algorithm itself are openly available under a GNU public license.

  • 44.
    Buehler, Stefan
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Kuhn, Thomas
    Universität Bremen, Institute of Environmental Physics.
    Bauer, Agnes
    Institute of Environmental Physics, University of Bremen.
    Corrigendum to 'Water vapor continuum: Absorption measurements at 350 GHz and model calculations' [JQSRT 2002;74:545-62]2008Inngår i: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 109, nr 9, 1743-1744 s.Artikkel i tidsskrift (Annet vitenskapelig)
  • 45.
    Buehler, Stefan
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Kuvatov, M.
    Institut für Umweltphysik (Institute for Environmental Physics) (IUP), University of Bremen.
    John, V. O.
    Meteorology and Physical Oceanography, Rosenstiel School for Marine and Atmospheric Science (RSMAS), University of Miami.
    Milz, Mathias
    Soden, B.J.
    Meteorology and Physical Oceanography, Rosenstiel School for Marine and Atmospheric Science (RSMAS), University of Miami.
    Jackson, D.L.
    Cooperative Institute for Research in Environmental Science (CIRES), University of Colorado, NOAA Earth System Research Laboratory.
    Norholt, J.
    Institut für Umweltphysik (Institute for Environmental Physics) (IUP), University of Bremen.
    An upper tropospheric humidity data set from operational satellite microwave data2008Inngår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 113, nr 14, D14110- s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    183.31 GHz observations from the Advanced Microwave Sounding Unit B (AMSUB) instruments onboard the NOAA 15, 16, and 17 satellites were used to derive a new data set of Upper Tropospheric Humidity (UTH). The data set consist of monthly median and mean data on a 1.5 degrees latitude-longitude grid between 60 degrees S and 60 degrees N, and covers the time period of January 2000 to February 2007. The data from all three instruments are very consistent, with relative difference biases of less than 4% and relative difference standard deviations of 7%. Radiometric contributions by high ice clouds and by the Earth's surface affect the measurements in certain areas. The uncertainty due to clouds is estimated to be up to approximately 10%RH in areas with deep convection. The uncertainty associated with contamination from surface emission can exceed 10%RH in midlatitude winter, where the data therefore should be regarded with caution. Otherwise the surface influence appears negligible. The paper also discusses the UTH median climatology and seasonal cycle, which are found to be broadly consistent with UTH climatologies from other sensors. Finally, the paper presents an initial validation of the new data set against IR satellite data and radiosonde data. The observed biases of up to 9%RH (wet bias relative to HIRS) were found to be broadly consistent with expectations based on earlier studies. The observed standard deviations against all other data sets were below 6%RH. The UTH data are available to the scientific community on http://www.sat.ltu.se.

  • 46.
    Buehler, Stefan
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Kuvatov, Mashrab
    IUP, University of Bremen.
    Sreerekha, T. R.
    UK Met Office, Exeter.
    John, Viju Oommen
    RSMAS, University of Miami.
    Rydberg, Bengt
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Eriksson, Patrick
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Notholt, Justus
    IUP, University of Bremen.
    A cloud filtering method for microwave upper tropospheric humidity measurements2007Inngår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 7, nr 21, 5531-5542 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The paper presents a cloud filtering method for upper tropospheric humidity (UTH) measurements at 183.31±1.00 GHz. The method uses two criteria: a viewing angle dependent threshold on the brightness temperature at 183.31±1.00 GHz, and a threshold on the brightness temperature difference between another channel and 183.31±1.00 GHz. Two different alternatives, using 183.31±3.00 GHz or 183.31±7.00 GHz as the other channel, are studied. The robustness of this cloud filtering method is demonstrated by a mid-latitudes winter case study. The paper then studies different biases on UTH climatologies. Clouds are associated with high humidity, therefore the possible dry bias introduced by cloud filtering is discussed and compared to the wet biases introduced by the clouds radiative effect if no filtering is done. This is done by means of a case study, and by means of a stochastic cloud database with representative statistics for midlatitude conditions. Both studied filter alternatives perform nearly equally well, but the alternative using 183.31±3.00 GHz as other channel is preferable, because that channel is less likely to see the Earth's surface than the one at 183.31±7.00 GHz. The consistent result of all case studies and for both filter alternatives is that both cloud wet bias and cloud filtering dry bias are modest for microwave data. The recommended strategy is to use the cloud filtered data as an estimate for the true all-sky UTH value, but retain the unfiltered data to have an estimate of the cloud induced uncertainty. The focus of the paper is on midlatitude data, since atmospheric data to test the filter for that case were readily available. The filter is expected to be applicable also to subtropical and tropical data, but should be further validated with case studies similar to the one presented here for those cases.

  • 47.
    Buehler, Stefan
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Milz, Mathias
    Eliasson, Salomon
    Upper tropospheric humidity and cloud ice: comparing global climate models and satellite observations2008Inngår i: 2008 European Geosciences Union General Assembly, Austria Center Vienna, Vienna (Austria), 13-18 Apr 2008, European Geosciences Union (EGU), 2008Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Upper tropospheric humidity (UTH) and cloud ice (measured as ice water content IWC or vertically integrated ice water path IWP) are parameters of the climate system on which current global climate models do not agree well. This is illustrated by intercomparing the models in the IPCC AR4 archive. It is then discussed, to what extent different satellite measurements agree on these parameters. The focus is on passive observations from different infrared (HIRS, IASI) and microwave (AMSU-B, HSB) sensors.

  • 48.
    Buehler, Stefan
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Östman, S.
    Luleå tekniska universitet.
    Melsheimer, C.
    Institute of Environmental Physics, University of Bremen.
    Holl, Gerrit
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Eliasson, Salomon
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    John, V.O.
    Met Office Hadley Centre, Exeter.
    Blumenstock, T.
    Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe.
    Hase, F.
    Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe.
    Ekgered, G.
    Chalmers University of Technology, Department of Earth and Space Sciences.
    Raffalski, U.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Nasuno, T.
    Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, Yokohama.
    Satho, M.
    Atmosphere and Ocean Research Institute, University of Tokyo.
    Milz, Mathias
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Mendrok, Jana
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    A multi-instrument comparison of integrated water vapour measurements at a high latitude site2012Inngår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 12, nr 22, 10925-10943 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We compare measurements of integrated water vapour (IWV) over a subarctic site (Kiruna, Northern Sweden) from five different sensors and retrieval methods: Radiosondes, Global Positioning System (GPS), ground-based Fourier-transform infrared (FTIR) spectrometer, ground-based microwave radiometer, and satellite-based microwave radiometer (AMSU-B). Additionally, we compare also to ERA-Interim model reanalysis data. GPS-based IWV data have the highest temporal coverage and resolution and are chosen as reference data set. All datasets agree reasonably well, but the ground-based microwave instrument only if the data are cloud-filtered. We also address two issues that are general for such intercomparison studies, the impact of different lower altitude limits for the IWV integration, and the impact of representativeness error. We develop methods for correcting for the former, and estimating the random error contribution of the latter. A literature survey reveals that reported systematic differences between different techniques are study-dependent and show no overall consistent pattern. Further improving the absolute accuracy of IWV measurements and providing climate-quality time series therefore remain challenging problems.

  • 49.
    Carlsson, Ella
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Barabash, Stas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Cold Mars2006Konferansepaper (Annet vitenskapelig)
  • 50. Carlsson, Ella
    et al.
    Barabash, Stas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Fedorov, A.
    Centre d’Etude Spatiale des Rayonnements, Toulouse.
    Budnik, E.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Grigoriev, Alexander
    Futaana, Y.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Gunell, H.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Nilsson, H.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Lundin, R.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Analysis of the mass composition of the escaping plasma at Mars2006Inngår i: 2006 European Geosciences Union General Assembly (EGU 2006), Austria Center Vienna, Vienna (Austria), 2-7 Apr 2006, European Geosciences Union (EGU), 2006Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Results from Mars Express, Mars Exploration Rovers and Mars Global Surveyor indicate that Mars harbored large amounts of liquid water on the surface in the past. In order for the water-associated geomorphologic features to form, the pressure in the atmosphere must have been at least a hundred times higher to produce the necessary greenhouse effect required to hold liquid water stable. The present atmospheric pressure is only 6-9 mbar and moreover, the spectral imaging of Mars suggests that the amount of carbonates stored in the surface is too low in order to explain the denser atmosphere in the past. This controversy led us to investigate the escaping plasma by analyzing the data from the IMA sensor (Ion Mass Analyzer) of the ASPERA-3 instrument suite onboard Mars Express. The IMA sensor measures the differential flow of ion components in the energy range of 0.01-30 keV/q.Since the instrument design was optimized for studies of plasma dynamics, the mass resolution is not adequate enough to directly resolve CO+2 from O+2 , which is the main molecular ion composing the Mars ionosphere according to theoretical models. Therefore, a special multi-species fitting technique, using calibration and in-flight data, was developed to resolve the CO+2 peak from the neighboring and much more intense O+2 peak. This technique was applied to the observations covering the period from April 4, 2004 to October 2, 2005. The events of heavy ion escape were identified inside the induced magnetosphere boundary and the Martian eclipse. We report the results of statistical studies of these ion-beam events which permitted to determine CO+2 / O+ and the O+2 / O+ ratio of the escaping plasma at Mars.

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