Viser treff 941-960 av 1057

    • Modeling iron abundance anhancements in the slow solar wind. 

      Byhring, Hanne Sigrun; Cranmer, S.R.; Lie-Svendsen, Øystein; Habbal, S. Rifai; Esser, Ruth (Journal article; Tidsskriftartikkel; Peer reviewed, 2011)
      We have studied the behavior of Fe ions in the slow solar wind, using a fluid model extending from the chromosphere to 1 AU. Emphasis is on elemental "pileup" in the corona, i.e., a region where the Fe density increases and has a local maximum. We study the behavior of individual Fe ions relative to each other in the pileup region, where Fe(+10) and Fe(+12) have been used as examples. We find that ...
    • A Simple and Extendable Segmentation Method for Multi-Polarisation SAR Images 

      Doulgeris, Anthony Paul (Conference object; Konferansebidrag, 2013)
      This work presents a simple feature-based multi-channel SAR segmentation method that produces good, smooth, fast and robust results for image segmentation and interpretation. A basic set of six features produce good class distinction for general applications, and the method is easily extendable with new features and for multi-source data fusion. Optional steps of sub-sampling and Markov Random ...
    • Elemental Abundances in the Fast Solar Wind Emanating from Chromospheric Funnels 

      Pucci, Stefano; Lie-Svendsen, Øystein; Esser, Ruth (Journal article; Tidsskriftartikkel; Peer reviewed, 2010)
      We carry out a model study to determine whether a funnel-type flow geometry in the solar wind source region leads to sufficiently fast hydrogen flow to offset heavy element gravitational settling and can thus explain why solar wind abundances are not much smaller than photospheric abundances. We find that high first ionization potential (FIP) elements are more susceptible to gravitational settling ...
    • Simultaneous observations of a Mesospheric Inversion Layer and turbulence during the ECOMA-2010 rocket campaign 

      Szewczyk, Artur; Strelnikov, Boris; Rapp, Markus; Strelnikova, Irina; Baumgarten, Gerd; Kaifler, Natalie; Dunker, Tim; Hoppe, Ulf-Peter (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      From 19 November to 19 December 2010 the fourth and final ECOMA rocket campaign was conducted at Andøya Rocket Range (69 N, 16 E) in northern Norway. We present and discuss measurement results obtained during the last rocket launch labelled ECOMA09 when simultaneous and true common volume in situ measurements of temperature and turbulence supported by ground-based lidar observations reveal ...
    • Ultrasonic properties of all-printed piezoelectric polymer transducers 

      Wagle, Sanat; Decharat, Adit; Melandsø, Frank (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      The ability of producing ultrasonic transducers from screen-printing has been explored experimentally, through printing and characterization of a large number of transducers. In an allprinted test design, 124 transducers with four different electrode sizes ranging from 1 to 4.9 mm2, were printed layer-by-layer on a high performance polyethyleneimine polymer. Inks from ferroelectric and conductive ...
    • Enhanced EISCAT UHF backscatter during high-energy auroral electron precipitation 

      Schlatter, Nicola M.; Ivchenko, Nickolay; Sergienko, T; Gustavsson, Björn Johan; Brändström, B. U. E. (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      Natural enhancements in the backscattered power of incoherent scatter radars up to 5 orders of magnitudes above the thermal backscatter are sometimes observed at high latitudes. Recently observations of enhancements in the backscattered power including a feature at zero Doppler shift have been reported. These enhancements are limited in altitude to tens of kilometers. The zero Doppler shift ...
    • Observations of HF-induced instability in the auroral E region 

      Schlatter, Nicola M.; Ivchenko, Nickolay; Gustavsson, Björn Johan; Leyser, Thomas; Rietveld, Michael T (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      Enhancements were observed in backscattered radar power during an ionospheric heating experiment from two distinct altitude regions in the auroral E region above Tromsø. For the experiment the EISCAT Tromsø heater was operated with O mode and X mode alternated at 4.04 MHz, close to the 3rd electron gyroharmonic. Ion-line data recorded with the EISCAT UHF radar reveal different temporal ...
    • Models for electrostatic drift waves with density variations along magnetic field lines 

      Garcia, Odd Erik; Pecseli, Hans (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      Drift waves with vertical magnetic fields in gravitational ionospheres are considered where the unperturbed plasma density is enhanced in a magnetic flux tube. The gravitational field gives rise to an overall decrease of plasma density for increasing altitude. Simple models predict that drift waves with finite vertical wave vector components can increase in amplitude merely due to a conservation of ...
    • Intermittent fluctuations in the Alcator C-Mod scrape-off layer 

      Garcia, Odd Erik; Fritzner, Sindre Markus; Kube, Ralph; Cziegler, Istvan; LaBombard, Brian; Terry, Jim L. (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      Fluctuations in the boundary region of the Alcator C-Mod tokamak have been analyzed using gas puff imaging data. It is found that the fluctuation amplitudes in the near scrape-off layer follow a normal distribution while the far scrape-off layer fluctuations are dominated by large amplitude bursts due to radial motion of blob-like structures and have a positively skewed and flattened amplitude ...
    • "Structure, composition, and dynamics of the middle atmosphere and lower ionosphere during a major meteor shower" 

      Hoppe, Ulf-Peter; Rapp, Markus (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
    • Development of the mesospheric Na layer at 69 degrees N during the Geminids meteor shower 2010 

      Dunker, Tim; Hoppe, Ulf-Peter; Stober, Gunter; Rapp, Markus (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      The ECOMA sounding rocket campaign in 2010 was performed to investigate the charge state and number density of meteoric smoke particles during the Geminids meteor shower in December 2010. The ALOMAR Na lidar contributed to the campaign with measurements of sodium number density, temperature and line-of-sight wind between 80 and 110 km altitude over Andøya in northern Norway. This paper ...
    • Thermospheric atomic oxygen density estimates using the EISCAT Svalbard Radar 

      Vickers, Hannah; Kosch, M. J.; Sutton, E.; Ogawa, Y.; La Hoz, Cesar (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      Coupling between the ionized and neutral atmosphere through particle collisions allows an indirect study of the neutral atmosphere through measurements of ionospheric plasma parameters. We estimate the neutral density of the upper thermosphere above ~250 km with the European Incoherent Scatter Svalbard Radar (ESR) using the year-long operations of the International Polar Year from March 2007 to ...
    • Serial Raman spectroscopy of particles trapped on a waveguide 

      Løvhaugen, Pål; Ahluwalia, Balpreet Singh; Huser, Thomas Rolf; Hellesø, Olav Gaute (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      We demonstrate that Raman spectroscopy can be used to characterize and identify particles that are trapped and propelled along optical waveguides. To accomplish this, microscopic particles on a waveguide are moved along the waveguide and then individually addressed by a focused laser beam to obtain their characteristic Raman signature within 1 second acquisition time. The spectrum is used to distinguish ...
    • Effects of Ocean Acidification and Warming on Sperm Activity and Early Life Stages of the Mediterranean Mussel (Mytilus galloprovincialis) 

      Vihtakari, Mikko; Hendriks, Iris E.; Holding, Johnna; Renaud, Paul E.; Duarte, Carlos M.; Havenhand, Jon N. (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      Larval stages are among those most vulnerable to ocean acidification (OA). Projected atmospheric CO2 levels for the end of this century may lead to negative impacts on communities dominated by calcifying taxa with planktonic life stages. We exposed Mediterranean mussel (Mytilus galloprovincialis) sperm and early life stages to pHT levels of 8.0 (current pH) and 7.6 (2100 level) by manipulating pCO2 ...
    • Comparison of feature based segmentation of full polarimetric SAR satellite sea ice images with manually drawn ice charts 

      Moen, Mari-Ann; Doulgeris, Anthony Paul; Anfinsen, Stian Normann; Renner, Angelika H.H.; Hughes, Nick; Gerland, Sebastian; Eltoft, Torbjørn (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      In this paper we investigate the performance of an algorithm for automatic segmentation of full polarimetric, synthetic aperture radar (SAR) sea ice scenes. The algorithm uses statistical and polarimetric properties of the backscattered radar signals to segment the SAR image into a specified number of classes. This number was determined in advance from visual inspection of the SAR image and by ...
    • Correction and Characterization of Radio Frequency Interference Signatures in L-band Synthetic Aperture Radar Data 

      Meyer, Franz; Nicoll, Jeremy; Doulgeris, Anthony Paul (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      Radio frequency interference (RFI) is a known issue in low-frequency radar remote sensing. In synthetic aperture radar (SAR) image processing, RFI can cause severe degradation of image quality, distortion of polarimetric signatures, and an increase of the SAR phase noise level. To address this issue, a processing system was developed that is capable of reliably detecting, characterizing, and mitigating ...
    • Satellittovervåking av isdrift i Arktis 

      Kræmer, Thomas (Conference object; Konferansebidrag, 2013)
    • A Multitexture Model for Multilook Polarimetric Synthetic Aperture Radar Data 

      Eltoft, Torbjørn; Anfinsen, Stian Normann; Doulgeris, Anthony Paul (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      A statistical model for multilook polarimetric radar data is presented where the polarimetric channels are associated with individual texture variables having potentially different statistical properties. The feasibility of producing closed form probability density functions under certain restrictions is outlined. Mellin kind statistics are derived under various assumptions on the texture variables, ...
    • An Advanced Non-Gaussian Feature Space Method for POL-SAR Image Segmentation 

      Doulgeris, Anthony Paul; Eltoft, Torbjørn (Conference object; Konferansebidrag, 2013)
      This work extends upon our simple feature-based multichannel SAR segmentation method to incorporate highly desirable statistical properties into a computationally simple approach. The desirable properties include Markov random field contextual smoothing and goodness-of-fit testing to automatically obtain the significant number of classes. To achieve this we need to find an explicit class model to ...
    • A Textural–Contextual Model for Unsupervised Segmentation of Multipolarization Synthetic Aperture Radar Images 

      Akbari, Vahid; Doulgeris, Anthony Paul; Gabriele, Moser; Eltoft, Torbjørn; Sebastiano, B. Serpico; Anfinsen, Stian Normann (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      This paper proposes a novel unsupervised, non-Gaussian, and contextual segmentation method that combines an advanced statistical distribution with spatial contextual informa-tion for multilook polarimetric synthetic aperture radar (PolSAR)data. This extends on previous studies that have shown the added value of both non-Gaussian modeling and contextual smoothing individually or for intensity channels ...