Endre søk
Begrens søket
678910 401 - 450 of 476
Referera
Referensformat
• apa
• ieee
• modern-language-association-8th-edition
• vancouver
• Annet format
Fler format
Språk
• de-DE
• en-GB
• en-US
• fi-FI
• nn-NO
• nn-NB
• sv-SE
• Annet språk
Fler språk
Utmatningsformat
• html
• text
• asciidoc
• rtf
Treff pr side
• 5
• 10
• 20
• 50
• 100
• 250
Sortering
• Standard (Relevans)
• Forfatter A-Ø
• Forfatter Ø-A
• Tittel A-Ø
• Tittel Ø-A
• Type publikasjon A-Ø
• Type publikasjon Ø-A
• Eldste først
• Nyeste først
• Disputationsdatum (tidligste først)
• Disputationsdatum (siste først)
• Standard (Relevans)
• Forfatter A-Ø
• Forfatter Ø-A
• Tittel A-Ø
• Tittel Ø-A
• Type publikasjon A-Ø
• Type publikasjon Ø-A
• Eldste først
• Nyeste først
• Disputationsdatum (tidligste først)
• Disputationsdatum (siste først)
Merk
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
• 401.
Institute of Astronomy, Russian Academy of Sciences, Moscow.
Institute of Astronomy, Russian Academy of Sciences, Moscow. Swedish Institute of Space Physics / Institutet för rymdfysik. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Luleå tekniska universitet, Institutionen för system- och rymdteknik. LPAP, Université de Liège.
He2+ transport in the Martian upper atmosphere with an induced magnetic field2013Inngår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118, nr 3, s. 1231-1242Artikkel i tidsskrift (Fagfellevurdert)

Solar wind helium may be a significant source of neutral helium in the Martian atmosphere. The precipitating particles also transfer mass, energy, and momentum. To investigate the transport of He2+ in the upper atmosphere of Mars, we have applied the direct simulation Monte Carlo method to solve the kinetic equation. We calculate the upward He, He+, and He2+ fluxes, resulting from energy spectra of the downgoing He2+ observed below 500 km altitude by the Analyzer of Space Plasmas and Energetic Atoms 3 instrument onboard Mars Express. The particle flux of the downward moving He2+ ions was 1–2 × 106 cm–2 s–1, and the energy flux is equal to 9–10 × 10–3 erg cm–2 s–1. The calculations of the upward flux have been made for the Martian atmosphere during solar minimum. It was found, that if the induced magnetic field is not introduced in the simulations the precipitating He2+ ions are not backscattered at all by the Martian upper atmosphere. If we include a 20 nT horizontal magnetic field, a typical field measured by Mars Global Surveyor in the altitude range of 85–500 km, we find that up to 30%–40% of the energy flux of the precipitating He2+ ions is backscattered depending on the velocity distribution of the precipitating particles. We thus conclude that the induced magnetic field plays a crucial role in the transport of charged particles in the upper atmosphere of Mars and, therefore, that it determines the energy deposition of the solar wind.

• 402.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Upgrading a groundbased 142 GHz microwave radiometer to higher sensitivity2016Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave

The accuracy of ozone measurements in the middle atmosphere is of great importance when determining its diurnal variation. A high time resolution of the measured data is desirable and depends on the sensitivity of the receiver used to detect the ozone. This thesis aims to improve the sensitivity of a groundbased 142 GHz microwave radiometer used for measuring atmospheric ozone data. This is done by replacing the previous receiver components with a series of new components and arranging them in different setups for comparison purposes. Mechanics and wiring were changed in order to install the setups along with changes in the optics. Each test setup could be implemented as a first step towards improving the sensitivity of the radiometer. The result show that the optics contribute with an unexpected addition of noise to the measurements and hence the overall performance and improvement of the radiometer could not be determined. Suggestions are made for further work which include improving the optics and performing cryo-measurements.

• 403.
Department of Environmental Science, Sharda University, India; Institut für Kartographie, Technische Universität Dresden, Germany.
Department of Environmental Science, Sharda University, India . Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Department of Environmental Science, Sharda University, India . Department of Environmental Science, Sharda University, India.
Changing climate and glacio-hydrology: a case study of Shaune Garang basin, Himachal Pradesh2018Inngår i: International Journal of Hydrology Science and Technology, ISSN 2042-7808, E-ISSN 2042-7816, Vol. 8, nr 3, s. 258-272Artikkel i tidsskrift (Fagfellevurdert)

The rise in temperature is already evident in Himalaya with rate of increase varying seasonally and spatially. Changes in precipitation are also evident with no clear trend. Several studies in different parts of Himalayas suggest that the glaciers are retreating in general with few exceptions as response to changes in temperature and precipitation. The stream flow in river basins in Indian Himalayan region (IHR) is already showing changes in studies undertaken in the last few decades. Use of glacio-hydrological models gives opportunity to estimate stream flow in glaciated river basins and understand the changes. The present study deals with estimation of discharge in Shaune Garang Basin, Himachal Pradesh using a glacio-hydrological model based on degree day factors. The model was used to estimate long term average of melt season discharge (1985-2007) in the basin. The modelled discharge shows good correlation with measured discharge for simulation period except for first year of comparison.

• 404.
Department of Environmental Science, School of Basic Sciences and Research, Sharda University, Greater Noida.
Department of Environmental Science, School of Basic Sciences and Research, Sharda University, Greater Noida. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Department of Environmental Science, Sharda University, Department of Environmental Science, School of Basic Sciences and Research, Sharda University, Greater Noida. Birbal Sahni Institute of Palaeobotany, Lucknow. Department of Environmental Science, School of Basic Sciences and Research, Sharda University, Greater Noida. Department of Environmental Science, School of Basic Sciences and Research, Sharda University, Greater Noida. Department of Science and Technology, Technology Bhavan, New Delhi.
Changing climate and glacio-hydrology in Indian Himalayan Region: a review2016Inngår i: Wiley Interdisciplinary Reviews: Climate Change, ISSN 1757-7780, E-ISSN 1757-7799, Vol. 7, nr 3, s. 393-410Artikkel i tidsskrift (Fagfellevurdert)

This study presents a comprehensive review of the published literature on the evidences of a changing climate in the Indian Himalayan Region (IHR) and its impacts on the glacio-hydrology of the region. The IHR serves as an important source of fresh water for the densely populated areas downstream. It is evident from the available studies that temperature is significantly increasing in all parts of the IHR, whereas precipitation is not indicative of any particular spatiotemporal trend. Glacio-hydrological proxies for changing climate, such as, terminus and areal changes of the glaciers, glacier mass balance, and streamflow in downstream areas, highlight changes more evidently in recent decades. On an average, studies have predicted an increase in temperature and precipitation in the region, along with increase in streamflow of major rivers. Such trends are already apparent in some sub-basins of the western IHR. The region is particularly vulnerable to changing climate as it is highly dependent on snow and glacier melt run-off to meet its freshwater demands. We present a systematic review of key papers dealing with changing temperature, precipitation, glaciers, and streamflow in the IHR. We discuss these interdisciplinary themes in relation to each other, in order to establish the present and future impacts of climatic, glaciological, and hydrological changes in the region.

• 405.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
O⁺ heating in the high altitude cusp and mantle due to wave-particle interaction2011Licentiatavhandling, med artikler (Annet vitenskapelig)

This thesis is composed of three articles, which have the common denominator that they are studies of heating of oxygen ions in the high altitude cusp and mantle in the terrestrial magnetosphere. All data analysis are based on observational data from the Cluster satellites. Oxygen ions originate in the ionosphere, from where they flow up along open cusp field lines. This upflowing ionospheric plasma is generally gravitationally bound and will return as ionospheric downflow. However, if the plasma is sufficiently energized it may overcome gravity and reach the magnetosphere. Further energization is able to put the plasma on trajectories leading downstream along the magnetotail, which may cause the plasma to escape into the magnetosheath. This thesis considers energization of oxygen ions through wave-particle interactions. We show that the average electric spectral densities in the altitude range of 8-15 Earth radii are able to explain the average perpendicular temperatures, using a simple gyroresonance model and 50% of the observed spectral density at the O+ gyrofrequency. We also show that the phase velocities derived from the observed low frequency electric and magnetic fields are consistent with Alfvén waves. Strong heating is sporadic and spatially limited. For three case studies of strong heating, we show that the regions of enhanced wave activity are at least one order of magnitude larger than the gyroradius of the ions, which is a condition for the gyroresonance model to be valid. An analysis indicates that enhanced perpendicular temperatures can be observed over several Earth radii after heating has ceased, suggesting that high perpendicular-to-parallel temperature ratio is not necessarily a sign of local heating. This also explains why we sometimes observe enhanced temperatures and low spectral densities. Three events of very high temperatures and simultaneously observed high spectral densities were studied, and we showed that the temperatures could be explained with the simple gyrofrequency model. We have also provided average diffusion coefficients at different altitudes, which can be used for ion heating and outflow modeling.

• 406.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
O+ heating, outflow and escape in the high altitude cusp and mantle2013Doktoravhandling, med artikler (Annet vitenskapelig)

The Earth and its atmosphere are embedded in the magnetosphere, a region in space dominated by the geomagnetic field, shielding our planet as it acts to deflect the energetic solar wind. Even though the atmosphere is protected from direct interaction with the solar wind it is indirectly affected by significant magnetosphere-solar wind interaction processes, causing constituents of the upper atmosphere to flow up into the magnetosphere. The fate of the atmospheric originating ions is interesting from a planetary evolution point of view. If the upflowing ions in the magnetosphere are to escape into the solar wind they need to not only overcome gravity, but also the magnetic forces, and therefore need to be energized and accelerated significantly. The subject of this thesis is analysis of oxygen ions (O+) and wave field observations in the high altitude cusp/mantle and in the high latitude dayside magnetosheath of Earth, investigating magnetospheric processes behind ion heating, outflow and escape. Most data analysis is based on observational data from the Cluster satellites, orbiting the Earth and altitudes corresponding to different key regions of the magnetosphere and the immediate solar wind environment. The mechanism behind O+ heating mainly discussed in this thesis is energization through interactions between the ions and low-frequency waves. The average electric spectral densities in the altitude range of 8-15 Earth radii are able to explain the average perpendicular temperatures, using a gyroresonance model and 50% of the observed spectral density at the O+ gyrofrequency. Strong heating is sporadic and spatially limited. The regions of enhanced wave activity are at least one order of magnitude larger than the local gyroradius of the ions, which is a necessary condition for the gyroresonance model to be valid. An analysis indicates that enhanced perpendicular temperatures can be observed over several Earth radii after heating has ceased, suggesting that high perpendicular-to-parallel temperature ratio is not necessarily a sign of local heating. This also explains why we sometimes observe enhanced temperatures and low spectral densities. We also show that the phase velocities derived from the observed low frequency electric and magnetic fields are consistent with Alfvén waves. Outflowing ions flow along magnetic field lines leading downstream in the magnetotail, where the ions may convect into the plasma sheet and be brought back toward Earth. However, the effective heating in the cusp and mantle provides a majority of the O+ enough acceleration to escape into the solar wind and be lost, rather than entering the plasma sheet. The heating can actually be effective enough to allow outflowing cusp O+ to escape immediately from the high altitude cusp and mantle along recently opened magnetic field lines, facilitating a direct coupling between the magnetospheric plasma and interplanetary space. Observations in the shocked and turbulent solar wind (the magnetosheath) reveals hot O+ flowing downstream and approximately tangentially to the magnetopause and often close to it. An estimated total flux of O+ in the high-latitude magnetosheath of 0.7 ·1025 s-1 is significant in relation to the observed cusp outflows at lower altitudes, pointing to that escape of hot O+ from the cusp and mantle into the dayside magnetosheath being an important loss route.

• 407.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Belgian Institute for Space Aeronomy, Avenue Circulaire, Brussels. Department of Physics, Umeå University.
Observations of multiharmonic ion-cyclotron waves due to inverse ion-cyclotron damping in the northern magnetospheric cusp2017Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, nr 1, s. 22-29Artikkel i tidsskrift (Fagfellevurdert)

We present a case study of inverse ion-cyclotron damping taking place in the northern terrestrial magnetospheric cusp, exciting waves at the ion-cyclotron frequency and its harmonics. The ion-cyclotron waves are primarily seen as peaks in the magnetic-field spectral densities. The corresponding peaks in the electric-field spectral densities are not as profound, suggesting a background electric field noise or other processes of wave generation causing the electric spectral densities to smoothen out more compared to the magnetic counterpart. The required condition for inverse ion-cyclotron damping is a velocity shear in the magnetic field-aligned ion-bulk flow, and this condition is often naturally met for magnetosheath influx in the northern magnetospheric cusp, just as in the presented case. We note that some ion-cyclotron wave activity is present in a few similar shear events in the southern cusp, which indicates that other mechanisms generating ion-cyclotron waves may also be present during such conditions.

• 408.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Department of Physics, Umeä University. Department of Physics, Umeä University. Swedish Institute of Space Physics, Kiruna. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Space and Plasma Physics, School of Electrical Engineering, Royal Institute of Technology, Stockholm. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Quantification of the total ion transport in the near-Earth plasma sheet2017Inngår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 35, nr 4, s. 869-877Artikkel i tidsskrift (Fagfellevurdert)

Recent studies strongly suggest that a majority of the observed O+ cusp outflows will eventually escape into the solar wind, rather than be transported to the plasma sheet. Therefore, an investigation of plasma sheet flows will add to these studies and give a more complete picture of magnetospheric ion dynamics. Specifically, it will provide a greater understanding of atmospheric loss. We have used Cluster spacecraft 4 to quantify the H+ and O+ total transports in the near-Earth plasma sheet, using data covering 2001-2005. The results show that both H+ and O+ have earthward net fluxes of the orders of 1026 and 1024 s -1, respectively. The O+ plasma sheet return flux is 1 order of magnitude smaller than the O+ outflows observed in the cusps, strengthening the view that most ionospheric O+ outflows do escape. The H+ return flux is approximately the same as the ionospheric outflow, suggesting a stable budget of H+ in the magnetosphere. However, low-energy H+, not detectable by the ion spectrometer, is not considered in our study, leaving the complete magnetospheric H+ circulation an open question. Studying tailward flows separately reveals a total tailward O+ flux of about 0. 5 × 1025 s -1, which can be considered as a lower limit of the nightside auroral region O+ outflow. Lower velocity flows ( < 100kms -1) contribute most to the total transports, whereas the high-velocity flows contribute very little, suggesting that bursty bulk flows are not dominant in plasma sheet mass transport.

• 409.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Swedish Institute of Space Physics, Kiruna. Swedish Institute of Space Physics, Kiruna. Swedish Institute of Space Physics, Kiruna. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. CNSR, Institut de Recherche en Astrophysique et Planetologie, Toulouse.
Atmospheric outflow from the terrestrial magnetosphere: implications forescape on evolutionary time scales2017Konferansepaper (Fagfellevurdert)
• 410.
Luleå tekniska universitet, Institutionen för system- och rymdteknik.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
A statistical study on O+ flux in the dayside magnetosheath2013Inngår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 31, s. 1005-1010Artikkel i tidsskrift (Fagfellevurdert)

Studies on terrestrial oxygen ion (O+) escape into the interplanetary space have considered a number of different escape paths. Recent observations however suggest a yet insufficiently investigated additional escape route for hot O+: along open magnetic field lines in the high altitude cusp and mantle. Here we present a statistical study on O+ flux in the high-latitude dayside magnetosheath. The O+ is generally seen relatively close to the magnetopause, consistent with observations of O+ flowing primarily tangentially to the magnetopause. We estimate the total escape flux in this region to be ~ 7 × 1024 s−1, implying this escape route to significantly contribute to the overall total O+ loss into interplanetary space.

• 411.
Luleå tekniska universitet, Institutionen för system- och rymdteknik.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Swedish Institute of Space Physics / Institutet för rymdfysik.
Observations of oxygen ions in the dayside magnetosheath associated with southward IMF2012Inngår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117Artikkel i tidsskrift (Fagfellevurdert)

We present a case study of high energy oxygen ions (O+) observed in the dayside terrestrial magnetosheath, in the southern hemisphere. It is shown that the presence of O+ is strongly correlated to the IMF direction: O+ is observed only for Bz<0. Three satellites observe O\$^+ immediately at both sides of the magnetopause and about 2 RE outside the magnetopause. These conditions indicate escape along open magnetic field lines. We show that if outflowing O+ is heated and accelerated sufficiently in the cusp, it takes 15-20 minutes for it to reach the magnetopause, allowing the ions to escape along newly opened field lines on the dayside. Earlier studies show evidence of strong heating and high velocities in the cusp and mantle at high altitudes, strengthening our interpretation. The observed magnetosheath O+ fluxes are of the same order as measured in the ionospheric upflow, which indicates that this loss mechanism is significant when it takes place.

• 412.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
O+ transport in the dayside magnetosheath and its dependence on the IMF direction2015Inngår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 33, s. 301-307Artikkel i tidsskrift (Fagfellevurdert)

Recent studies have shown that the escape of oxygen ions (O+) into the magnetosheath along open magnetic field lines from the terrestrial cusp and mantle is significant. We present a study of how O+ transport in the dayside magnetosheath depends on the interplanetary magnetic field (IMF) direction. There are clear asymmetries in the O+ flows for southward and northward IMF. The asymmetries can be understood in terms of the different magnetic topologies that arise due to differences in the location of the reconnection site, which depends on the IMF direction. During southward IMF, most of the observed magnetosheath O+ is transported downstream. In contrast, for northward IMF we observe O+ flowing both downstream and equatorward towards the opposite hemisphere. We observe evidence of dual-lobe reconnection occasionally taking place during strong northward IMF conditions, a mechanism that may trap O+ and bring it back into the magnetosphere. Its effect on the overall escape is however small: we estimate the upper limit of trapped O+ to be 5%, a small number considering that ion flux calculations are rough estimates. The total O+ escape flux is higher by about a factor of 2 during times of southward IMF, in agreement with earlier studies of O+ cusp outflow.

• 413.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Swedish Institute of Space Physics, Kiruna. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Atmospheric loss from the dayside open polar region and its dependence on geomagnetic activity: Implications for atmospheric escape on evolutionary time scales2017Inngår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 35, nr 3, s. 721-731Artikkel i tidsskrift (Fagfellevurdert)
• 414.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Swedish Institute of Space Physics, Kiruna. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Corrigendum to Atmospheric loss from the dayside open polar region and its dependence on geomagnetic activity: Implications for atmospheric escape on evolutionary time scales, published in Ann. Geophys., 35, 721–731,20172018Inngår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576Artikkel i tidsskrift (Fagfellevurdert)
• 415.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Long-term observations of polar mesosphere summer echoes using the ESRAD MST radar2011Doktoravhandling, med artikler (Annet vitenskapelig)

Polar Mesosphere Summer Echoes (PMSE) are strong radar echoes observed from altitudes of 80-90 km in polar regions, during summer time. PMSE are closely related to the fascinating atmospheric phenomenon known as noctilucent clouds (NLC). Since it has been suspected that NLC could respond to climate change in the mesosphere, they have attracted considerable interest in the scientific community during recent years. However, continuous visual or photographic NLC observations suffer from weather restrictions and the human factor. In contrast, PMSE radar measurements can easily be made over a long interval and are very attractive for long-term studies of the atmospheric parameters at the polar mesopause. This thesis uses the world’s longest data set of PMSE observations made by the same radar at the same place. Since 1997 these measurements have been carried out with the 52 MHz ESRAD MST radar located near Kiruna in Northern Sweden. The data set for 1997-2008 has been used for studies of diurnal, day-to-day and year-to-year variations of PMSE. We showed that PMSE occurrence rate and volume reflectivity on a daily scale show predominantly semidiurnal variations with the shape of the diurnal curves remaining consistent from year to year. We found that day-to-day and inter-annual variations of PMSE correlate with geomagnetic activity while they do not correlate with mesopause temperature or solar activity. We did not find any statistically significant trends in PMSE occurrence rate and length of PMSE season over 1997-2008. The thesis also presents also a new, independent calibration method, which can be used to estimate changes in transmitter output and antenna feed losses from year to year (for example due to changes of antenna configuration) and allows making accurate calculations of PMSE strength. This method is based on radar-radiosonde comparisons in the upper troposphere/lower stratosphere region simultaneously with PMSE observations. Using this calibration we calculated the distribution of PMSE strength over magnitudes; it varies from year to year with the peak of the distribution varying from 2×10−15 to 3×10−14 m−1. We found that inter-annual variations of PMSE volume reflectivity strongly correlate with the local geomagnetic k-index and anticorrelate with solar 10.7 cm flux. We did not identify any significant trend in PMSE volume reflectivity over 1997–2009. Finally, using 11 years of measurements, we calculated in-beam the PMSE aspect sensitivities using the FCA technique. We showed that half of PMSE detected each year cannot be explained by isotropic turbulence since they are highly aspect sensitive echoes. The distribution of these echoes remains consistent from year to year with median values of aspect sensitivity from 2.9 to 3.7°. The remaining half of the PMSE have aspect sensitivity parameters larger than 9-11°. We found that PMSE aspect sensitivity has altitude dependence: the scatter becomes more isotropic with increasing height. We did not identify any dependence of PMSE aspect sensitivity on backscattered power for any year. We analysed limitations of the in-beam and off-zenith beam methods and concluded that the former is suitable for highly aspect sensitive echoes while the latter is needed for more isotropic scatterers.

• 416.
NASA Goddard Space Flight Center, Greenbelt.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Department of Atmospheric Sciences , Texas A&M University. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Aerosol optical depth as observed by the Mars Science Laboratory REMS UV photodiodes2017Konferansepaper (Annet vitenskapelig)
• 417.
NASA Goddard Space Flight Center.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Department of Atmospheric Sciences, Texas A&M University, Texas A&M University, College Station. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Aerosol optical depth as observed by the Mars Science Laboratory REMS UV photodiodes2016Inngår i: Icarus (New York, N.Y. 1962), ISSN 0019-1035, E-ISSN 1090-2643, Vol. 280, s. 234-248Artikkel i tidsskrift (Fagfellevurdert)

Systematic observations taken by the REMS UV photodiodes on a daily basis throughout the landed Mars Science Laboratory mission provide a highly useful tool for characterizing aerosols above Gale Crater. Radiative transfer modeling is used to model the approximately 1.75 Mars Years of observations taken to date taking into account multiple scattering from aerosols and the extended field of view of the REMS UV photodiodes. The retrievals show in detail the annual cycle of aerosol optical depth, which is punctuated with numerous short timescale events of increased optical depth. Dust deposition onto the photodiodes is accounted for by comparison with aerosol optical depth derived from direct imaging of the Sun by Mastcam. The effect of dust on the photodiodes is noticeable, but does not dominate the signal. Cleaning of dust from the photodiodes was observed in the season around Ls=270°, but not during other seasons. Systematic deviations in the residuals from the retrieval fit are indicative of changes in aerosol effective particle size, with larger particles present during periods of increased optical depth. This seasonal dependence of aerosol particle size is expected as dust activity injects larger particles into the air, while larger aerosols settle out of the atmosphere more quickly leading to a smaller average particle size over time.

• 418.
Department of Physics, University of Helsinki, Helsinki, Finland.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Department of Physics, University of Helsinki, Helsinki, Finland.
Monitoring near-Earth-object discoveries for imminent impactors2018Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 616, artikkel-id A176Artikkel i tidsskrift (Fagfellevurdert)

Aims. We present an automated system called NEORANGER that regularly computes asteroid-Earth impact probabilities for objects on the Minor Planet Center’s (MPC) Near-Earth-Object Confirmation Page (NEOCP) and sends out alerts of imminent impactors to registered users. In addition to potential Earth-impacting objects, NEORANGER also monitors for other types of interesting objects such as Earth’s natural temporarily-captured satellites.

Methods. The system monitors the NEOCP for objects with new data and solves, for each object, the orbital inverse problem, which results in a sample of orbits that describes the, typically highly-nonlinear, orbital-element probability density function (PDF). The PDF is propagated forward in time for seven days and the impact probability is computed as the weighted fraction of the sample orbits that impact the Earth.

Results. The system correctly predicts the then-imminent impacts of 2008 TC3 and 2014 AA based on the first data sets available. Using the same code and configuration we find that the impact probabilities for objects typically on the NEOCP, based on eight weeks of continuous operations, are always less than one in ten million, whereas simulated and real Earth-impacting asteroids always have an impact probability greater than 10% based on the first two tracklets available.

• 419.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Wind Retrieval Measurements for the Mars Surface Exploration2016Konferansepaper (Annet vitenskapelig)

We present a novel method to quantify the heat transfer coefficient h at the near environment of a spacecraft operating under Mars surface atmospheric conditions. As part of the scientific instruments of the ExoMars 2018 Surface Platform, the HABIT (HabitAbility: Brines, Irradiance and Temperature) instrument will be operating on Mars surface in order to establish the habitability of the landing site. By resolving the energy balance equation in temperatures over the three HABIT Air Temperature Sensor (ATS), we will retrieve the fluid temperature Tf and the known as m-parameter directly related with the heat transfer coefficient and sensitive to variations in wind density and velocity field

• 420.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Centro de Astrobiologiá (INTA-CSIC), Madrid. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Granada.
Microgravity validation for xenon propellant distributions2017Konferansepaper (Fagfellevurdert)

In the current Electric Propulsion era, one of the most relevant propellants is xenon, which is generally stored in supercritical stage. Because of the increase in time of spacecraft lifetime, the amount of propellant stored on-board has been quadrupled in the recent years, and the need of more accurate gauging methods for measuring propellant usage along the missions has become more critical too. Thermal gradients affect the densities distribution of the stored propellants and this turns out to be critical in orbit because of the absence of convection in low-gravity environments. Recently we have proposed a new gauging method (Soria-Salinas, et al., 2017) that relies on the analysis of measurements from existing and operating technology (in TRL 9), i.e., this method does not imply the development of any new technology. This new method, the improved PVT method, improves by a factor 8 the accuracy of the standard PVT retrievals (Soria-Salinas, et al., 2017). A laboratory experimental validation has shown that, for CO2 at a pressure of about 70 bar, just below the critical pressure, the error of the mass retrieval using this new gauging method is only 0.1% of the initial mass at launch. However, for its complete validation, a microgravity study should be performed in order to quantify the effect of thermal gradients under the absence of convection in a low-g environment. The present work describes: 1) the design of a proposed in-flight microgravity validation experiment for a parabolic flight campaign such as those provided by the Airbus A-310 zero-G platform for microgravity research; and 2) comparative studies of the expected xenon density distribution of real size tanks under operation in orbit, through computational fluid dynamics (CFD) and heat transfer calculations.

• 421.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Convective Heat Transfer at the Martian Boundary Layer, Measurement and Model2016Konferansepaper (Annet vitenskapelig)
• 422.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Thermal and Heat Transfer Studies Using the HABIT Instrument on the ExoMars 2018 Surface Platform2016Konferansepaper (Annet vitenskapelig)
• 423.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Department of Water Resources Engineering., Lund University.
Convective Heat Transfer Measurements at the Martian Surface2015Konferansepaper (Annet vitenskapelig)
• 424.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Department of Signal and Telecommunication Theory, Universidad Autónoma de Madrid. Department of Signal and Telecommunication Theory, Universidad Autónoma de Madrid. Luleå tekniska universitet.
A Xenon Mass Gauging through Heat Transfer Modeling for Electric Propulsion Thrusters2017Inngår i: World Academy of Science, Engineering and Technology: An International Journal of Science, Engineering and Technology, ISSN 2010-376X, E-ISSN 2070-3740, Vol. 11, nr 1, s. 94-105Artikkel i tidsskrift (Fagfellevurdert)

The current state-of-the-art methods of mass gauging of Electric Propulsion (EP) propellants in microgravity conditions rely on external measurements that are taken at the surface of the tank. The tanks are operated under a constant thermal duty cycle to store the propellant within a pre-defined temperature and pressure range. We demonstrate using computational fluid dynamics (CFD) simulations that the heat-transfer within the pressurized propellant generates temperature and density anisotropies. This challenges the standard mass gauging methods that rely on the use of time changing skin-temperatures and pressures. We observe that the domes of the tanks are prone to be overheated, and that a long time after the heaters of the thermal cycle are switched off, the system reaches a quasi-equilibrium state with a more uniform density. We propose a new gauging method, which we call the Improved PVT method, based on universal physics and thermodynamics principles, existing TRL-9 technology and telemetry data. This method only uses as inputs the temperature and pressure readings of sensors externally attached to the tank. These sensors can operate during the nominal thermal duty cycle. The improved PVT method shows little sensitivity to the pressure sensor drifts which are critical towards the end-of-life of the missions, as well as little sensitivity to systematic temperature errors. The retrieval method has been validated experimentally with CO2 in gas and fluid state in a chamber that operates up to 82 bar within a nominal thermal cycle of 38 °C to 42 °C. The mass gauging error is shown to be lower than 1% the mass at the beginning of life, assuming an initial tank load at 100 bar. In particular, for a pressure of about 70 bar, just below the critical pressure of CO2, the error of the mass gauging in gas phase goes down to 0.1% and for 77 bar, just above the critical point, the error of the mass gauging of the liquid phase is 0.6% of initial tank load. This gauging method improves by a factor of 8 the accuracy of the standard PVT retrievals using look-up tables with tabulated data from the National Institute of Standards and Technology.

• 425.
Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Department of Physics, University of Helsinki. University of Ljubljana, Faculty of Mathematics & Physics.
Gaia Data Release 2: Observations of solar system objects2018Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 16, nr A13Artikkel i tidsskrift (Fagfellevurdert)

Context. The Gaia spacecraft of the European Space Agency (ESA) has been securing observations of solar system objects (SSOs) since the beginning of its operations. Data Release 2 (DR2) contains the observations of a selected sample of 14,099 SSOs. These asteroids have been already identified and have been numbered by the Minor Planet Center repository. Positions are provided for each Gaia observation at CCD level. As additional information, complementary to astrometry, the apparent brightness of SSOs in the unfiltered G band is also provided for selected observations. Aims. We explain the processing of SSO data, and describe the criteria we used to select the sample published in Gaia DR2. We then explore the data set to assess its quality. Methods. To exploit the main data product for the solar system in Gaia DR2, which is the epoch astrometry of asteroids, it is necessary to take into account the unusual properties of the uncertainty, as the position information is nearly one-dimensional. When this aspect is handled appropriately, an orbit fit can be obtained with post-fit residuals that are overall consistent with the a-priori error model that was used to define individual values of the astrometric uncertainty. The role of both random and systematic errors is described. The distribution of residuals allowed us to identify possible contaminants in the data set (such as stars). Photometry in the G band was compared to computed values from reference asteroid shapes and to the flux registered at the corresponding epochs by the red and blue photometers (RP and BP). Results. The overall astrometric performance is close to the expectations, with an optimal range of brightness G similar to 12 - 17. In this range, the typical transit-level accuracy is well below 1 mas. For fainter asteroids, the growing photon noise deteriorates the performance. Asteroids brighter than G similar to 12 are affected by a lower performance of the processing of their signals. The dramatic improvement brought by Gaia DR2 astrometry of SSOs is demonstrated by comparisons to the archive data and by preliminary tests on the detection of subtle non-gravitational effects.

• 426.
Universität Bremen.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Development of an RT model for frequencies between 200 and 1000 GHz2007Rapport (Annet vitenskapelig)
• 427.
UK Met Office, Exeter.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. UK Met Office, Exeter. UK Met Office, Exeter. German Aerospace Center, DLR, Oberpfaffenhofen. RSMAS, University of Miami.
A strong ice cloud event as seen by a microwave satellite sensor: simulations and observations2008Inngår i: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 109, nr 9, s. 1705-1718Artikkel i tidsskrift (Fagfellevurdert)

In this article, brightness temperatures observed by channels of the Advanced Microwave Sounding Unit-B (AMSU-B) instrument are compared to those simulated by a radiative transfer model, which can take into account the multiple scattering due to ice particles by using a discrete ordinate iterative solution method. The input fields, namely, the pressure, temperature, humidity, and cloud water content are taken from the short range forecast from the Met Office mesoscale model (UKMES). The comparison was made for a case study on the 25 January 2002 when a frontal system associated with significant cloud was present over the UK. It is demonstrated that liquid clouds have maximum impact on channel 16 of AMSU whereas ice clouds have maximum impact on channel 20. The main uncertainty for simulating microwave radiances is the assumptions about microphysical properties, such as size distribution, shape and orientation of the cloud particles, which are not known in the mesoscale model. The article examines the impact of these parameters on the cloud signal. The polarisation signal due to oriented ice particles at these frequencies is also discussed.

• 428.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Simulation and Visualisation Software for an Elastic Aircraft for High Altitudes based on Game Engine Technology2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
• 429.
NASA Goddard Space Flight Center.
Jacobs Technology, NASA Johnson Space Center. NASA Ames Research Center, Moffett Field. Universidad Nacional Autónoma de México. NASA Goddard Space Flight Center. NASA Goddard Space Flight Center. NASA Goddard Space Flight Center. Jacobs Technology, NASA Johnson Space Center. NASA Johnson Space Center, Houston. NASA Johnson Space Center, Houston. Centro de Astrobiologia, INTA-CSIC, Madrid. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Instituto Andaluz de Cienccias de la Tierra (CSIC-UGR), Grenada.
The nitrate/perchlorate ratio on Mars as an indicator for habitability2015Konferansepaper (Fagfellevurdert)
• 430.
Solar System Exploration Division, Goddard Space Flight Center, National Aeronautics and Space Administration, Greenbelt, Maryland.
Evidence for indigenous nitrogen in sedimentary and aeolian deposits from the Curiosity rover investigations at Gale crater, Mars2015Inngår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 112, nr 14, s. 4245-4250, artikkel-id 6Artikkel i tidsskrift (Fagfellevurdert)

The Sample Analysis at Mars (SAM) investigation on the Mars Science Laboratory (MSL) Curiosity rover has detected oxidized nitrogen-bearing compounds during pyrolysis of scooped aeolian sediments and drilled sedimentary deposits within Gale crater. Total N concentrations ranged from 20 to 250 nmol N per sample. After subtraction of known N sources in SAM, our results support the equivalent of 110–300 ppm of nitrate in the Rocknest (RN) aeolian samples, and 70–260 and 330–1,100 ppm nitrate in John Klein (JK) and Cumberland (CB) mudstone deposits, respectively. Discovery of indigenous martian nitrogen in Mars surface materials has important implications for habitability and, specifically, for the potential evolution of a nitrogen cycle at some point in martian history. The detection of nitrate in both wind-drifted fines (RN) and in mudstone (JK, CB) is likely a result of N2 fixation to nitrate generated by thermal shock from impact or volcanic plume lightning on ancient Mars. Fixed nitrogen could have facilitated the development of a primitive nitrogen cycle on the surface of ancient Mars, potentially providing a biochemically accessible source of nitrogen.

• 431.
Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe.
Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe. Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe. Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe. Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe. Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe. Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe. Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe. Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe. Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe. Instituto de Astrofísica de Andalucía CSIC, Granada. Instituto de Astrofísica de Andalucía CSIC, Granada. Institut für Atmosphäre und Umwelt, J. W. Goethe Universität Frankfurt am Main, Frankfurt.
Global distribution of mean age of stratospheric air from MIPAS SF6 measurements2008Inngår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 8, nr 3, s. 677-695Artikkel i tidsskrift (Fagfellevurdert)

Global distributions of profiles of sulphur hexafluoride (SF6) have been retrieved from limb emission spectra recorded by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on Envisat covering the period September 2002 to March 2004. Individual SF6 profiles have a precision of 0.5 pptv below 25 km altitude and a vertical resolution of 4–6 km up to 35 km altitude. These data have been validated versus in situ observations obtained during balloon flights of a cryogenic whole-air sampler. For the tropical troposphere a trend of 0.230±0.008 pptv/yr has been derived from the MIPAS data, which is in excellent agreement with the trend from ground-based flask and in situ measurements from the National Oceanic and Atmospheric Administration Earth System Research Laboratory, Global Monitoring Division. For the data set currently available, based on at least three days of data per month, monthly 5° latitude mean values have a 1σ standard error of 1%. From the global SF6 distributions, global daily and monthly distributions of the apparent mean age of air are inferred by application of the tropical tropospheric trend derived from MIPAS data. The inferred mean ages are provided for the full globe up to 90° N/S, and have a 1σ standard error of 0.25 yr. They range between 0 (near the tropical tropopause) and 7 years (except for situations of mesospheric intrusions) and agree well with earlier observations. The seasonal variation of the mean age of stratospheric air indicates episodes of severe intrusion of mesospheric air during each Northern and Southern polar winter observed, long-lasting remnants of old, subsided polar winter air over the spring and summer poles, and a rather short period of mixing with midlatitude air and/or upward transport during fall in October/November (NH) and April/May (SH), respectively, with small latitudinal gradients, immediately before the new polar vortex starts to form. The mean age distributions further confirm that SF6 is destroyed in the mesosphere to a considerable degree. Model calculations with the Karlsruhe simulation model of the middle atmosphere (KASIMA) chemical transport model agree well with observed global distributions of the mean age only if the SF6 sink reactions in the mesosphere are included in the model.

• 432.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Crowdsourcing GNSS Jamming Detection and Localization2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave

Global Navigation Satellite Systems (GNSS) have found wide adoption in various applications, be they military, civilian or commercial. The susceptibility of GNSS to radio-frequency interference can, thus, be very disruptive, even for emergency services, therefore threatening people's lives. An early prototype of a system providing relatively cheap widescale GNSS jamming detection, called J911, is explored in this thesis.

J911 is smartphone-based crowdsourcing of GNSS observations, most interesting of which are carrier-to-noise-density ratio ($\frac{C}{N_0}$) and Automatic Gain Control (AGC) voltage. To implement the prototype, an Android application to provide the measurements, a backend to parse and store the measurements, and a frontend to visualize the measurements were developed. In real-world use, the thesis argues, the J911 system would best be implemented over existing Enhanced 9-1-1 (E911) infrastructure, becoming a standardized part of the Public Switched Telephone Network (PSTN).

The Android application, running on a smartphone, would periodically construct messages to be sent to the backend over an Internet connection. The messages would include: current location from all location providers available in Android OS, observed satellites from all supported constellations, the satellites' $\frac{C}{N_0}$, and a timestamp. Once a message is received on the backend, the data would be extracted and stored in a database. The frontend would query the database and produce a map with the collected datapoints overlaid on top of it, whose color indicates received signal strength at that point. When a jammer gets close enough to a few smartphones, they will all be jammed, which is easily observed on the map. On top of that, if enough samples are gathered, a Power Difference of Arrival localization algorithm can be used to localize the jammer.

The smartphones that the system was planned to be tested with did not support AGC level readings, therefore in order to obtain AGC levels over time, a few SiGe GN3S Samplers, which are radio-frequency frontends, were used. In eastern Idaho, United States, over three nights in July 2017, an exercise, named 2017 DHS JamX, was performed with the help of the US Department of Homeland Security. Sadly, the approval for the publication of the test results did not come in time to be included in this thesis.

• 433.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Aalto University.
Generating Explanations of Robot Policies in Continuous State Spaces2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave

Transparency in HRI describes the method of making the current state of a robotor intelligent agent understandable to a human user. Applying transparencymechanisms to robots improves the quality of interaction as well as the userexperience. Explanations are an effective way to make a robot’s decision making transparent. We introduce a framework that uses natural language labels attached to a region inthe continuous state space of the robot to automatically generate local explanationsof a robot’s policy. We conducted a pilot study and investigated how the generated explanations helpedusers to understand and reproduce a robot policy in a debugging scenario.

• 434.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Electron heating in collisionless shocks observed by the MMS spacecraft2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave

Shock waves are ubiquitous in space and astrophysics. Shocks transform directed particle flow energy into thermal energy. As the major part of space is a collisionless medium, shocks in space physics arises through wave-particle interactions with the magnetic field as the main contributor.The heating processes are scale dependent. The large scale processes governs the ion heating and is well described by magnetohydrodynamics. The small scale processes governs the electron heating lies within the field of kinetic plasma theory and is still today remained disputed. A step towards the answer for the small scale heating would be to measure the scale, in order to relate it to a known instability or other small scale processes.The multi-spacecraft NASA MMS spacecraft carries several high resolute particle and field instruments enabling almost instantaneous 3D particle measurements and accurate measurements of the magnetic field. Also the separation between the four MMS spacecraft is as small as < 8km for a certain mission phase. This allows for new approaches when determining the scale which for shocks has not been possible before when using data from previous multi-spacecraft missions with spacecraft separation much larger. The velocity of the shock is large compared to the spacecraft,thus the shock width cannot be directly measured by each spacecraft. Either a constant velocity has to be estimated or we could use gradients of a certain parameter between the spacecraft as the shock flows over them. The usage of gradients is only possible with MMS as all the spacecraft could for MMS be within the shock simultaneously. The change for a parameter within the shockis assumed to be linear between the spacecraft and measurements. It is also assumed that the gradient of the parameter maximizes in the shock normal direction. Using these assumptions two methods have been developed. They have the same working principles but are using two or four spacecraft for linear estimation at each measurement point. From the gradient and parametric data the shock ramp width could then be found. The parameter used in this thesis is the electron temperature. The methods using one, two and four spacecraft were tested using electron temperature data from different shock crossings. Two problems with the gradient methods were found from the results, giving false data for certain time spans. To avoid these problems, the scale of the electron temperature gradient was determined for roughly half the shock ramp. It was found using the two and four spacecraft methods that an assumption of constant velocity for the shock speed is an uncertain assumption. The shock speed varies over short time scales and in the shock crossings analysed the constant velocity estimations were generally overestimated. From the two and four spacecraft methods roughly half of the temperature rise in the shock ramp occurred over 10.8km or 12.4 lpe. This is almost a factor of two greater than previous scale estimates using Cluster data and a multi-spacecraft timing method for shock speed estimation.From the results it is concluded that the methods when using gradients between spacecraft has some restrictions. They can only be used for MMS data, requires quasi-perpendicular high Mach number and will give false results if the temperature is disturbed by interacting hot plasma clouds. However, even though we have these limitations for the tested gradient methods, they were found better and more reliable compared to previous methods for shock scaling.

• 435.
Bigelow Laboratory for Ocean Sciences, Maine. Centro de Astrobiología (CSIC-INTA), Madrid. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Centro de Astrobiología (CSIC-INTA), Madrid. Department of Geological Sciences, Universidad Católica del Norte, Antofagasta. Centro de Astrobiología (CSIC-INTA), Madrid. Centro de Astrobiología (CSIC-INTA), Madrid.
Molecular biomarkers in the subsurface of the Salar Grande (Atacama, Chile) evaporitic deposits2018Inngår i: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 140, nr 1, s. 31-52Artikkel i tidsskrift (Fagfellevurdert)

The Late Miocene–Pliocene aged hyperarid evaporitic system of Salar Grande is a unique, halite-rich sedimentary basin in the Cordillera de la Costa of the Central Andes (Chile) whose bio-sedimentary record is poorly understood. The persistence of hyperacidity over millions of years, the hypersalinity, and the intense UV radiation make it a terrestrial analogue to assess the potential presence of organic matter in the halite deposits found on Mars. We investigated the occurrence and distribution of biomolecules along a 100-m depth drill down to the ~ 9 Ma old detrital deposits topped by La Soledad Formation (ESF). We have identified two well-defined mineralogical and geochemical units by X-ray diffractometry (XRD) and ion chromatography: a nearly pure halite down to 40 m, and a detrital one down to 100 m depth. One-dimensional GC–MS and two-dimensional GC × GC-TOF–MS gas chromatography–mass spectrometry techniques allowed us to detect a variety of lipidic compounds (n-alkanes, n-alkanols, isoprenoids, steroids, and hopanoids), and a relative abundance of functionalized hydrocarbons (n-fatty acids or n-aldehydes), mostly in the upper halite. We also detected biopolymers and microbial markers by fluorescence sandwich-microarray immunoassays. A dominant prokaryotic origin was associated with halophile bacteria and archaea, with minor contributions of lichens, macrophytes, or higher plants. The lipidic record was also imprinted by oxic (high pristane over phytane ratios) and saline (squalane, and mono-methyl n-alkanes) signatures. The vertical abundance and distribution of biomarkers in the Salar Grande was explained by a generalized effect of xeropreservation, combined with salt encapsulation in the upper halite deposits, or with protective organics-mineral interactions in the deeper detrital unit. The results contribute to the interpretation of terrestrial bio-sedimentary records of halite deposits and their association to environmental conditions. The high potential for preservation of biosignatures at Salar Grande suggests that similar evaporitic deposits in Mars should be priority targets for searching for signs of life.

• 436.
Department of Physics, Cosmic-Ray Group, Kyoto University.
Department of Physics, Cosmic-Ray Group, Kyoto University. Department of Physics, Cosmic-Ray Group, Kyoto University. Department of Physics, Cosmic-Ray Group, Kyoto University. Department of Physics, Cosmic-Ray Group, Kyoto University. Department of Physics, Cosmic-Ray Group, Kyoto University. Department of Physics, Cosmic-Ray Group, Kyoto University. Department of Physics, Cosmic-Ray Group, Kyoto University. Department of Physics, Cosmic-Ray Group, Kyoto University. Department of Physics, Cosmic-Ray Group, Kyoto University. Department of Physics, Cosmic-Ray Group, Kyoto University. Department of Physics, Cosmic-Ray Group, Kyoto University. Department of Physics, Cosmic-Ray Group, Kyoto University. Department of Physics, Cosmic-Ray Group, Kyoto University. Department of Physics, Cosmic-Ray Group, Kyoto University. Department of Physics, Cosmic-Ray Group, Kyoto University. Department of Physics, Cosmic-Ray Group, Kyoto University. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. EISCAT Scientific Association, Kiruna.
SMILE-II: Observation of celestial and atmosphereic MeV gamma rays using a balloon-borne wide fields of view Electron-Tracking Compton Camera2011Inngår i: Proceedings of the 20th ESA Symposium on European Rocket and Balloon Programmes and Related Research: 22-26 May 2011, Hyère, France, Noordwijk: European Space Agency, ESA , 2011, s. 567-571Konferansepaper (Fagfellevurdert)

We have developed an Electron Tracking Compton Camera (ETCC) as an MeV gamma-ray telescope in the next generation. The ETCC consists of a gaseous time projection chamber and a position sensitive scintillation camera. We had launched a small size ETCC loaded on a balloon in 2006, and it was successful to obtain the fluxes of diffuse cosmic and atmospheric gamma rays in the energy range between 125 keV and 1.25 MeV. As the next flight (SMILE-II), we planned a long duration flight using a circumpolar balloon launched from Kiruna, and it will observe the celestial bright sources and the atmospheric gamma-ray burst due to the relativistic electron from the radiation belt. In this paper, we report the concepts of our detector and the performance of the SMILE-Il prototype.

• 437.
University of Tokyo, Deptartment of Earth & Planetary Science.
Tokyo Gakugei University, Department of Astronomy & Earth Science. Max-Planck-Institut für Solar System Research. National Institute for Information & Communication Technology, Applied Electromagnet Research. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. National Institute for Information & Communication Technology, Applied Electromagnet Research. Tokyo Gakugei University, Department of Astronomy & Earth Science.
Influence of CO2 line profiles on radiative and radiative-convective equilibrium states of the Venus lower atmosphere2010Inngår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 115, nr E06Artikkel i tidsskrift (Fagfellevurdert)

Influence of CO2 line profiles on vertical temperature distributions in the radiative and radiative-convective equilibria is examined in the Venus atmosphere. The CO2 opacity obtained by the Voigt (Lorentz) profile without the line cutoff is shown to be excessive since this opacity gives surface temperatures of about 860-1020 K in the radiative-convective equilibrium. On the other hand, the opacity obtained by the extremely sub-Lorentzian profiles of Pollack et al. (1993) and Tonkov et al. (1996) are underestimated; the surface temperature obtained with this opacity remains 600 K even in the radiative equilibrium. In this case, convection does not take place below the cloud layer because of the cloud opacity. It is also shown that Fukabori et al.' s (1986) and Meadows and Crisp's (1996) profiles, both of which have intermediate absorption coefficients, give temperature distributions close to the observed one in the radiative-convective equilibrium. In these cases, the convection layer extends from the surface to 30-50 km altitudes. Then, the temperature distribution below the cloud layer is determined by a dry adiabatic lapse rate and the temperature near the cloud bottom. The surface temperature in the radiative-convective equilibrium is strongly affected by the temperature near the cloud bottom in this situation. The detailed structure of the H2SO4 cloud must be taken into account to construct a realistic radiative transfer model.

• 438.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Robotic Grasping of Large Objects for Collaborative Manipulation2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave

In near future, robots are envisioned to work alongside humans in professional anddomestic environments without significant restructuring of workspace. Roboticsystems in such setups must be adept at observation, analysis and rational de-cision making. To coexist in an environment, humans and robots will need tointeract and cooperate for multiple tasks. A fundamental such task is the manip-ulation of large objects in work environments which requires cooperation betweenmultiple manipulating agents for load sharing. Collaborative manipulation hasbeen studied in the literature with the focus on multi-agent planning and controlstrategies. However, for a collaborative manipulation task, grasp planning alsoplays a pivotal role in cooperation and task completion.In this work, a novel approach is proposed for collaborative grasping and manipu-lation of large unknown objects. The manipulation task was defined as a sequenceof poses and expected external wrench acting on the target object. In a two-agentmanipulation task, the proposed approach selects a grasp for the second agentafter observing the grasp location of the first agent. The solution is computed ina way that it minimizes the grasp wrenches by load sharing between both agents.To verify the proposed methodology, an online system for human-robot manipu-lation of unknown objects was developed. The system utilized depth informationfrom a fixed Kinect sensor for perception and decision making for a human-robotcollaborative lift-up. Experiments with multiple objects substantiated that theproposed method results in an optimal load sharing despite limited informationand partial observability.

• 439.
Department of Physics & Astronomy, University of Tennessee, Knoxville.
Department of Physics & Astronomy, University of Tennessee, Knoxville, Department of Earth & Planetary Sciences, University of Tennessee, Knoxville. Jet Propulsion Laboratory, California Institute of Technology, Pasadena. Department of Earth & Planetary Sciences, University of Tennessee, Knoxville. Jet Propulsion Laboratory, California Institute of Technology, Pasadena. Space Research Institute, RAS, Moscow. Space Research Institute, RAS, Moscow. Space Research Institute, RAS, Moscow. University of Arizona. Jet Propulsion Laboratory, California Institute of Technology, Pasadena. TechSource, Inc, Los Alamos. Space Research Institute, RAS, Moscow. Space Research Institute, RAS, Moscow. University of Arizona. Space Research Institute, RAS, Moscow. Space Research Institute, RAS, Moscow. Space Research Institute, RAS, Moscow. Brown university. Space Research Institute, RAS, Moscow. Space Research Institute, RAS, Moscow. Space Research Institute, RAS, Moscow. NASA Goddard Space Flight Center. Space Research Institute, RAS, Moscow. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Instituto Andaluz de Cienccias de la Tierra (CSIC-UGR), Grenada. Centro de Astrobiologia, INTA-CSIC, Madrid.
Thermal conductivity of the near-surface Martian regolith derived from variations in MSL passive neutron counts and ground temperature measurements2015Konferansepaper (Fagfellevurdert)
• 440.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Dynamic modelling of a landing gear2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave

Companies in the aerospace industry would benefit from a faster, more flexible wayto investigate physical system issues in the vehicles/aircraft during their lifetime.Current software and hardware provides us with the option of making a systemmodel to simulate investigated problems, saving money and time.This work focuses on a nose landing gear of the Airbus’ fighter jet - EurofighterTyphoon. The landing gear itself is a very complex system designed for highperformance rather than robust usage; it requires a lot of maintenance and testingduring its lifetime. A practical investigation tool is much needed.The primary objective of this work is developing of a simulation model for thenose landing gear in Matlab, Simulink using Simscape library. The model spreadsmainly across two domains: the hydraulic and the multibody domain.The resulting model can simulate extension and retraction behaviour of the realEurofighter nose landing gear under different in-flight conditions. Friction in thehydraulic actuator was derived from the model.Connecting the known parameters of the landing gear subsystems and adjustingthe model to mimic real system behaviour, it can be used to extract the derived parameters,which were previously unknown. The model solves the time-consuminginvestigations and is much more flexible than physical test benches. Finally, it canbe used for future development and planning by simple parameter adjustment.

• 441.
Atmospheric and Oceanic Sciences Group, Space Applications Centre, Indian Space Research Organisation, Ahmedabad.
Atmospheric and Oceanic Sciences Group, Space Applications Centre, Indian Space Research Organisation, Ahmedabad. Atmospheric and Oceanic Sciences Group, Space Applications Centre, Indian Space Research Organisation, Ahmedabad. Atmospheric and Oceanic Sciences Group, Space Applications Centre, Indian Space Research Organisation, Ahmedabad. Atmospheric and Oceanic Sciences Group, Space Applications Centre, Indian Space Research Organisation, Ahmedabad. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
An algorithm for the estimation of upper tropospheric humidity from Kalpana observations: Methodology and validation2011Inngår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, nr 1Artikkel i tidsskrift (Fagfellevurdert)

This study presents a methodology for estimating the upper tropospheric humidity (UTH) for a layer between 500 and 200 hPa from observations in the water vapor channel (5.6–7.2 μm) of the Indian geostationary satellite, Kalpana. Radiative transfer simulations for different UTH conditions have been used to develop the relationship between water vapor channel radiances and UTH. A new technique has been described to include the normalized reference pressure in the algorithm, to account for latitudinal variation of temperature that is derived from a diverse radiosonde profiles data set and is a polynomial function of the latitude for different months. This has an advantage that the forecast or analysis profiles from the operational numerical weather prediction model are not required to compute the normalized reference pressure. The operationally retrieved UTH products have been extensively compared and validated for the period of 1 March to 1 May 2009, using Meteosat-7 UTH products over the Indian Ocean and the UTH computed from the radiosonde profiles. The results suggest that UTH estimates from Kalpana match very well with the Meteosat-7 UTH products having RMS difference of ∼6%. Validation with the UTH computed from the radiosonde observed relative humidity shows that the RMS error of Kalpana UTH is 9.6% and the mean bias is −3.0%. Similar validation of Meteosat-7 UTH with the same set of radiosonde derived UTH shows an RMS error of 13.3% and the bias of −6.5%, which is higher in comparison to the Kalpana UTH.

• 442.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Inter-Satellite Link Antennas: Review and The Near Future2017Independent thesis Advanced level (degree of Master (Two Years)), 80 poäng / 120 hpOppgave

The emerging trend in distributed spacecraft systems of using multiple spacecraft which share functions as opposed to independent spacecraft has given opportunities for missions previously infeasible. Inter-satellite link (ISL) communications provide a direct link within the space segment without need of an intermediate ground segment to relay the data. As the distributed spacecraft systems (DSS) have become less exotic and more complex, the need and demand for inter-satellite antenna systems has increased and the requirements for the antenna systems more diverse and become more demanding. This document is a research of the antennas currently used for ISL, already flown or will be launched in the near future. While the emphasis is strongly in the antennas, the other parts of the ISL communications sub-systems are observed. To limit the scope of the work, optical cross links are not observed in this document. ISL used only for very close proximity, such as several kilometres, are given only limited scope as the main challenges on those do not involve antennas. Furthermore, the major emphasis is given to systems which can be seen as commercially important. This document is divided in five main sections and the conclusions. In the first section the features and the challenges of ISLs are described. In the second section a parametrisation system for antennas is defined and this system is used in following sections to describe the ISL sub-systems and antenna used in them. The third part is a survey of recently flown space missions with ISLs. The fourth section is a survey on the missions which are scheduled to fly in near future and a brief survey of the solutions offered by satellite service providers and manufacturers. Due to the limited technical data available, the fourth section contains far more reverse engineering and assumptions than the survey on legacy missions. The fifth section describes the several families of ISL suitable antennas under development and discusses about several topics which relate to the ISL antenna development. In this part also are defined several example antenna specifications and the applications of those. The study concludes that antennas suitable for inter-satellite links are not inherently different from ground segment communication antennas of the S/C. The major difference is the need for greater coverage, which can be attained by multiple antenna elements, beam steering or antenna pointing. Specific considerations are needed to be taken into account and often the use of ISLs will increase the technical challenges, but it can provide solutions for problems which cannot be solved otherwise.

• 443.
Department of Physics & Astronomy, University College London.
Observatoire de Paris. STFC Rutherford Appleton Laboratory. Max-Planck-Institut für Sonnensystemforschung. European Space Agency-ESTEC. European Space Agency-ESTEC. Geneva Observatory. INAF: Osservatorio Astronomico di Palermo G.S. Vaiana. Observatoire de Paris, Institut d’Astrophysique Spatiale. European Space Agency-ESTEC. Institut d’Estudis Espacials de Catalunya (ICE-CSIC). Leiden University. Department of Physics & Astronomy, University College London, STFC Rutherford Appleton Laboratory. Ecole Normale Superieure de Lyon. Oxford University. Queen Mary University of London. Observatoire de Paris. Royal Observatory. Aveiro University. University of Leuven. SRON Netherlands Institute for Space Research. California Institute of Technology, Jet Propulsion Laboratory. Observatoire de Paris. Campus Jussieu. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Department of Physics & Astronomy, University College London.
The EChO science case2015Inngår i: Experimental astronomy (Print), ISSN 0922-6435, E-ISSN 1572-9508, Vol. 40, nr 2-3, s. 329-391Artikkel i tidsskrift (Fagfellevurdert)

The discovery of almost two thousand exoplanets has revealed an unexpectedly diverse planet population. We see gas giants in few-day orbits, whole multi-planet systems within the orbit of Mercury, and new populations of planets with masses between that of the Earth and Neptune—all unknown in the Solar System. Observations to date have shown that our Solar System is certainly not representative of the general population of planets in our Milky Way. The key science questions that urgently need addressing are therefore: What are exoplanets made of? Why are planets as they are? How do planetary systems work and what causes the exceptional diversity observed as compared to the Solar System? The EChO (Exoplanet Characterisation Observatory) space mission was conceived to take up the challenge to explain this diversity in terms of formation, evolution, internal structure and planet and atmospheric composition. This requires in-depth spectroscopic knowledge of the atmospheres of a large and well-defined planet sample for which precise physical, chemical and dynamical information can be obtained. In order to fulfil this ambitious scientific program, EChO was designed as a dedicated survey mission for transit and eclipse spectroscopy capable of observing a large, diverse and well-defined planet sample within its 4-year mission lifetime. The transit and eclipse spectroscopy method, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allows us to measure atmospheric signals from the planet at levels of at least 10−4 relative to the star. This can only be achieved in conjunction with a carefully designed stable payload and satellite platform. It is also necessary to provide broad instantaneous wavelength coverage to detect as many molecular species as possible, to probe the thermal structure of the planetary atmospheres and to correct for the contaminating effects of the stellar photosphere. This requires wavelength coverage of at least 0.55 to 11 μm with a goal of covering from 0.4 to 16 μm. Only modest spectral resolving power is needed, with R ~ 300 for wavelengths less than 5 μm and R ~ 30 for wavelengths greater than this. The transit spectroscopy technique means that no spatial resolution is required. A telescope collecting area of about 1 m2 is sufficiently large to achieve the necessary spectro-photometric precision: for the Phase A study a 1.13 m2 telescope, diffraction limited at 3 μm has been adopted. Placing the satellite at L2 provides a cold and stable thermal environment as well as a large field of regard to allow efficient time-critical observation of targets randomly distributed over the sky. EChO has been conceived to achieve a single goal: exoplanet spectroscopy. The spectral coverage and signal-to-noise to be achieved by EChO, thanks to its high stability and dedicated design, would be a game changer by allowing atmospheric composition to be measured with unparalleled exactness: at least a factor 10 more precise and a factor 10 to 1000 more accurate than current observations. This would enable the detection of molecular abundances three orders of magnitude lower than currently possible and a fourfold increase from the handful of molecules detected to date. Combining these data with estimates of planetary bulk compositions from accurate measurements of their radii and masses would allow degeneracies associated with planetary interior modelling to be broken, giving unique insight into the interior structure and elemental abundances of these alien worlds. EChO would allow scientists to study exoplanets both as a population and as individuals. The mission can target super-Earths, Neptune-like, and Jupiter-like planets, in the very hot to temperate zones (planet temperatures of 300–3000 K) of F to M-type host stars. The EChO core science would be delivered by a three-tier survey. The EChO Chemical Census: This is a broad survey of a few-hundred exoplanets, which allows us to explore the spectroscopic and chemical diversity of the exoplanet population as a whole. The EChO Origin: This is a deep survey of a subsample of tens of exoplanets for which significantly higher signal to noise and spectral resolution spectra can be obtained to explain the origin of the exoplanet diversity (such as formation mechanisms, chemical processes, atmospheric escape). The EChO Rosetta Stones: This is an ultra-high accuracy survey targeting a subsample of select exoplanets. These will be the bright “benchmark” cases for which a large number of measurements would be taken to explore temporal variations, and to obtain two and three dimensional spatial information on the atmospheric conditions through eclipse-mapping techniques. If EChO were launched today, the exoplanets currently observed are sufficient to provide a large and diverse sample. The Chemical Census survey would consist of > 160 exoplanets with a range of planetary sizes, temperatures, orbital parameters and stellar host properties. Additionally, over the next 10 years, several new ground- and space-based transit photometric surveys and missions will come on-line (e.g. NGTS, CHEOPS, TESS, PLATO), which will specifically focus on finding bright, nearby systems. The current rapid rate of discovery would allow the target list to be further optimised in the years prior to EChO’s launch and enable the atmospheric characterisation of hundreds of planets.

• 444. Tinetti, Giovanna
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
The EChO science case2017Inngår i: EChO - Exoplanet Characterisation Observatory / [ed] Tinetti, Giovanna, Drossart, Pierre, Dordrecht: Springer Netherlands, 2017Kapittel i bok, del av antologi (Fagfellevurdert)

The discovery of almost two thousand exoplanets has revealed an unexpectedly diverse planet population.We see gas giants in few-day orbits, whole multi-planet systems within the orbit of Mercury, and newpopulations of planets with masses between that of the Earth and Neptune – all unknown in the SolarSystem. Observations to date have shown that our Solar System is certainly not representative of the generalpopulation of planets in our Milky Way. The key science questions that urgently need addressing aretherefore: What are exoplanets made of? Why are planets as they are? How do planetary systems work andwhat causes the exceptional diversity observed as compared to the Solar System? The EChO (ExoplanetCharacterisation Observatory) space mission was conceived to take up the challenge to explain this diversityin terms of formation, evolution, internal structure and planet and atmospheric composition. This requires indepthspectroscopic knowledge of the atmospheres of a large and well-defined planet sample for whichprecise physical, chemical and dynamical information can be obtained.In order to fulfil this ambitious scientific program, EChO was designed as a dedicated survey mission fortransit and eclipse spectroscopy capable of observing a large, diverse and well-defined planet sample withinits four-year mission lifetime. The transit and eclipse spectroscopy method, whereby the signal from the starand planet are differentiated using knowledge of the planetary ephemerides, allows us to measureatmospheric signals from the planet at levels of at least 10-4 relative to the star. This can only be achieved inconjunction with a carefully designed stable payload and satellite platform. It is also necessary to providebroad instantaneous wavelength coverage to detect as many molecular species as possible, to probe thethermal structure of the planetary atmospheres and to correct for the contaminating effects of the stellarphotosphere. This requires wavelength coverage of at least 0.55 to 11 μm with a goal of covering from 0.4to 16 μm. Only modest spectral resolving power is needed, with R~300 for wavelengths less than 5 μm andR~30 for wavelengths greater than this.The transit spectroscopy technique means that no spatial resolution is required. A telescope collecting area ofabout 1 m2 is sufficiently large to achieve the necessary spectro-photometric precision: for the Phase A studya 1.13 m2 telescope, diffraction limited at 3 μm has been adopted. Placing the satellite at L2 provides a coldand stable thermal environment as well as a large field of regard to allow efficient time-critical observationof targets randomly distributed over the sky. EChO has been conceived to achieve a single goal: exoplanetspectroscopy. The spectral coverage and signal-to-noise to be achieved by EChO, thanks to its high stabilityand dedicated design, would be a game changer by allowing atmospheric composition to be measured withunparalleled exactness: at least a factor 10 more precise and a factor 10 to 1000 more accurate than currentobservations. This would enable the detection of molecular abundances three orders of magnitude lower thancurrently possible and a fourfold increase from the handful of molecules detected to date. Combining thesedata with estimates of planetary bulk compositions from accurate measurements of their radii and masseswould allow degeneracies associated with planetary interior modelling to be broken, giving unique insightinto the interior structure and elemental abundances of these alien worlds.EChO would allow scientists to study exoplanets both as a population and as individuals. The mission cantarget super-Earths, Neptune-like, and Jupiter-like planets, in the very hot to temperate zones (planettemperatures of 300 K - 3000 K) of F to M-type host stars. The EChO core science would be delivered by athree-tier survey. The EChO Chemical Census: This is a broad survey of a few-hundred exoplanets, whichallows us to explore the spectroscopic and chemical diversity of the exoplanet population as a whole. TheEChO Origin: This is a deep survey of a subsample of tens of exoplanets for which significantly highersignal to noise and spectral resolution spectra can be obtained to explain the origin of the exoplanet diversity(such as formation mechanisms, chemical processes, atmospheric escape). The EChO Rosetta Stones: Thisis an ultra-high accuracy survey targeting a subsample of select exoplanets. These will be the bright"benchmark" cases for which a large number of measurements would be taken to explore temporalvariations, and to obtain two and three dimensional spatial information on the atmospheric conditionsthrough eclipse-mapping techniques.If EChO were launched today, the exoplanets currently observed are sufficient to provide a large and diversesample. The Chemical Census survey would consist of > 160 exoplanets with a range of planetary sizes,temperatures, orbital parameters and stellar host properties. Additionally, over the next ten years, severalnew ground- and space-based transit photometric surveys and missions will come on-line (e.g. NGTS,CHEOPS, TESS, PLATO), which will specifically focus on finding bright, nearby systems. The current5rapid rate of discovery would allow the target list to be further optimised in the years prior to EChO’s launch and enable the atmospheric characterisation of hundreds of planets.

• 445.
Space Systems Finland.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Department of Physics, University of Helsinki. Department of Physics, University of Helsinki. Space Systems Finland. Space Systems Finland. Space Systems Finland. Department of Physics, University of Helsinki. European Space Astronomy Center. European Space Astronomy Center. European Space Astronomy Center.
Added-value interfaces to asteroid photometric and spectroscopic data in the Gaia database2018Inngår i: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 62, nr 2, s. 464-476Artikkel i tidsskrift (Fagfellevurdert)

We present two added-value interfaces (AVIs) for analyzing photometric and spectroscopic data observed by the Gaia satellite. The Gaia Added-Value Interface for Temporal Analysis (GAVITEA) is used to calculate an estimate for the spin state and shape of an asteroid from its photometric data, and the Gaia Added-Value Interface for Spectral Classification (GAVISC) provides tools to define the taxonomic type and surface absorption coefficient based on spectroscopic asteroid data. Computations are mainly carried out using well-known methods of asteroid data analysis but the AVIs also offer the possibility to test novel methods that are specifically developed for analyzing temporally sparse photometric data, typical for Gaia.

• 446.
Departamento de Teoría de la Señal y Comunicaciones, Escuela Politécnica Superior , Universidad de Alcalá, Madrid.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. nstituto Andaluz de Ciencias de la Tierra (CSIC - UGR), Granada. Finnish Meteorological Institute, Helsinki. Finnish Meteorological Institute, Helsinki. Centro de Astrobiologí a (CSIC-INTA), Torrejón de Ardoz, Madrid. Centro de Astrobiología (CSIC - INTA), Torrejón de Ardoz, Madrid.
Analysis of wind-induced dynamic pressure fluctuations during one and a half Martian years at Gale Crater2017Inngår i: Icarus (New York, N.Y. 1962), ISSN 0019-1035, E-ISSN 1090-2643, Vol. 288, s. 78-87Artikkel i tidsskrift (Fagfellevurdert)

The Rover Environmental Monitoring Station (REMS) instrument on-board the Mars Science Laboratory (MSL) has acquired unprecedented measurements of key environmental variables at the base of Gale Crater. The pressure measured by REMS shows modulations with a very structured pattern of short-time scale (of the order of seconds to several minutes) mild fluctuations (typically up to 0.2 Pa at daytime and 1 Pa at night-time). These dynamic pressure oscillations are consistent with wind, air and ground temperature modulations measured simultaneously by REMS. We detect the signals of a repetitive pattern of upslope/downslope winds, with maximal speeds of about 21 m/s, associated with thermal changes in the air and surface temperatures, that are initiated after sunset and finish with sunrise proving that Gale, a 4.5 km deep impact crater, is an active Aeolian environment. At nighttime topographic slope winds are intense with maximal activity from 17:00 through 23:00 Local Mean Solar Time, and simultaneous changes of surface temperature are detected. During the day, the wind modulations are related to convection of the planetary boundary layer, winds are softer with maximum wind speed of about 14 m/s. The ground temperature is modulated by the forced convection of winds, with amplitudes between 0.2 K and 0.5 K, and the air temperatures fluctuate with amplitudes of about 2 K. The analysis of more than one and a half Martian years indicates the year-to-year repeatability of these environmental phenomena. The wind pattern minimizes at the beginning of the south hemisphere winter (Ls 90) season and maximizes during late spring and early summer (Ls 270). The procedure that we present here is a useful tool to investigate in a semi-quantitative way the winds by: i) filling both seasonal and diurnal gaps where wind measurements do not exist, ii) providing an alternative way for comparisons through different measuring principia and, iii) filling the gap of observation of short time-wind variability, where the REMS wind-sensor is blind

• 447.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Design and Testing of Thermal Chambers for Space Qualification and Planetary Protection2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
• 448.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Calibration and Validation of Satellite Altimetry Data over the Pertuis Charentais Region in France: An Analysis of Tidal Correction Impact: Master Thesis Report2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
• 449.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Wheel-terrain contact angle estimation for planetary exploration rovers2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave

During space missions, real time tele-operation of a rover is not practical because of significant signal latencies associated with inter planetary distances, making some degree of autonomy in rover control desirable. One of the challenges to achieving autonomy is the determination of terrain traversability. As part of this field, the determination of motion state of a rover on rough terrain via the estimation of wheel-terrain contact angles is proposed.

This thesis investigates the feasibility of estimating the contact angles from the kinematics of the rover system and measurements from the onboard inertial measurement unit (IMU), joint angle sensors and wheel encoders. This approach does not rely on any knowledge of the terrain geometry or terrain mechanical properties.

An existing framework of rover velocity and wheel slip estimation for flat terrain has been extended to additionally estimate the wheel-terrain contact angle along with a side slip angle for each individual wheel, for rough terrain drive. A random walk and a damped model are used to describe the evolution of the contact angle and side slip angle over an unknown terrain. A standard strapdown algorithm for the estimation of attitude and velocity from IMU measurements, is modified to incorporate the 3D kinematics of the rover in the implementation of a nonlinear Kalman filter to estimate the motion states. The estimation results from the filter are verified using tests performed on the ExoMars BB2. The obtained contact angle estimates are found to be consistent with the reference values.

• 450.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Cranfield University.
Vibro-acoustic monitoring for in-flight spacecraft2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave

The concept of using the vibration transmitted through the structure of space systems whilst they are in flight for monitoring purposes is proposed and analysed.The performed patent review seems to indicate that this technique is not currently used despite being, in principle, a good way to obtain valuable knowledge about the spacecraft’s condition. Potential sources of vibration were listed and some of them were down-selected via a trade-off analysis for implementation in a numerical model of a CubeSat structure. Models were proposed for the sources chosen and implemented in the Ansys Workbench software, along with a simplified structure designed to be representative of a generic picosatellite mission.The results confirmed very different amplitude and frequency ranges for the sources of interest, which would make it difficult to monitor them with one type of sensor.Basic system requirements for accelerometer operating under space conditions were derived and commercial sources were identified as already having the technologies needed.The conclusion was a positive evaluation of the overall concept, although revising negatively the initial expectations for its performance due to the diversity encountered in the sources.

678910 401 - 450 of 476
Referera
Referensformat
• apa
• ieee
• modern-language-association-8th-edition
• vancouver
• Annet format
Fler format
Språk
• de-DE
• en-GB
• en-US
• fi-FI
• nn-NO
• nn-NB
• sv-SE
• Annet språk
Fler språk
Utmatningsformat
• html
• text
• asciidoc
• rtf