• 20 years of research on the Alcator C-Mod tokamak 

      Greenwald, Martin; Bader, A; Baek, S; Bakhtiari, M; Barnard, H; Beck, W; Bergerson, W; Bespamyatnov, I; Bonoli, P; Brower, D; Brunner, D; Burke, W; Candy, J; Churchill, M; Cziegler, I; Diallo, A; Dominguez, A; Duval, B; Edlund, E; Ennever, P; Ernst, D; Faust, I; Fiore, C; Fredian, T; Garcia, Odd Erik; Gao, C; Goetz, J; Golfinopoulos, T; Granetz, R; Grulke, O; Hartwig, Z; Horne, S; Howard, N; Hubbard, A; Hughes, J; Hutchinson, I; Irby, J; Izzo, V; Kessel, C; Labombard, B; Lau, C; Li, C; Lin, Y; Lipschultz, B; Loarte, A; Marmar, E; Mazurenko, A; McCracken, G; McDermott, R; Meneghini, O; Mikkelsen, D; Mossessian, D; Mumgaard, R; Myra, J; Nelson-Melby, E; Ochoukov, R; Olynyk, G; Parker, R; Pitcher, S; Podpaly, Y; Porkolab, M; Reinke, M; Rice, J; Rowan, W; Schmidt, A; Scott, S; Shiraiwa, S; Sierchio, J; Smick, N; Snipes, JA; Snyder, P; Sorbom, B; Stillerman, J; Sung, C; Takase, Y; Tang, V; Terry, J; Terry, D; Theiler, C; Tronchin-James, A; Tsujii, N; Vieira, R; Walk, J; Wallace, G; White, A; Whyte, D; Wilson, J; Wolfe, S; Wright, G; Wright, J; Wukitch, S; Zweben, S (Journal article; Tidsskriftartikkel; Peer reviewed, 2014)
    • Accurate estimation of the illumination pattern’s orientation and wavelength in sinusoidal structured illumination microscopy 

      Lahrberg, Marcel; Singh, Mandeep; Khare, Kedar; Ahluwalia, Balpreet Singh (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-01-05)
      Structured illumination microscopy is able to improve the spatial resolution of wide-field fluorescence imaging by applying sinusoidal stripe pattern illumination to the sample. The corresponding computational image reconstruction requires precise knowledge of the pattern’s parameters, which are its phase (φ) and wave vector (<b>p</b>). Here, a computationally inexpensive method for estimation of ...
    • 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 ...
    • Agreement and Complementarity of Sea Ice Drift Products 

      Johansson, Malin; Berg, Anders (Journal article; Tidsskriftartikkel; Peer reviewed, 2016-01-08)
      Changes in Arctic sea ice have raised questions about changes in sea ice drift patterns. Reduced sea ice coverage may open up the Arctic to further exploration of maritime activities, particularly during the summer months. Given such changes, it is important to investigate differences between available sea ice drift products. Products based on synthetic aperture radar (SAR), radar scatterometer, and ...
    • Algal hot spots in a changing Arctic Ocean: Sea-ice ridges and the snow-ice interface 

      Fernández-Méndez, Mar; Olsen, Lasse Mork; Kauko, Hanna M.; Meyer, Amelie; Rösel, Anja; Merkouriadi, Ioanna; Mundy, Christopher John; Ehn, Jens K.; Johansson, Malin; Wagner, Penelope Mae; Ervik, Åse; Sorrell, BK; Duarte, Pedro; Wold, Anette; Hop, Haakon; Assmy, Phillipp (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-03-12)
      During the N-ICE2015 drift expedition north-west of Svalbard, we observed the establishment and development of algal communities in first-year ice (FYI) ridges and at the snow-ice interface. Despite some indications of being hot spots for biological activity, ridges are under-studied largely because they are complex structures that are difficult to sample. Snow infiltration communities can grow at ...
    • Amplitude and size scaling for interchange motions of plasma filaments 

      Kube, Ralph; Wiesenberger, Matthias; Garcia, Odd Erik (Journal article; Tidsskriftartikkel; Peer reviewed, 2016-12-07)
      The interchange dynamics and velocity scaling of blob-like plasma filaments are investigated using a two-field reduced fluid model. For incompressible flows due to buoyancy, the maximum velocity is proportional to the square root of the relative amplitude and the square root of its cross-field size. For compressible flows in a non-uniform magnetic field, this square root scaling only holds ...
    • Analysis of evolving oil spills in full-polarimetric and hybrid-polarity SAR 

      Espeseth, Martine Mostervik; Skrunes, Stine; Jones, Cathleen Elaine; Brekke, Camilla; Holt, Benjamin; Doulgeris, Anthony Paul (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-04-25)
      Oil spill detection using a time series of images acquired off Norway in June 2015 with the uninhabited aerial vehicle synthetic aperture radar is examined. The relative performance of a set of features derived from quad-polarization versus hybrid-polarity (HP) modes in detection of various types of slicks as they evolve on a high wind driven sea surface is evaluated. It is shown that the HP mode ...
    • Aspects of model-based decompositions in radar polarimetry 

      Doulgeris, Anthony Paul; Eltoft, Torbjørn (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-11-12)
      In this paper, we further analyse the problem that polarimetric target decomposition methods in general have more physical parameters than equations, making the decomposition under-determined and hence have no unique solution. The common approach to get around this problem is to make certain assumptions, thus fixing one or more parameters, allowing the other free parameters to be solved from the set ...
    • Assessment of RISAT-1 and Radarsat-2 for Sea Ice Observation from Hybrid-Polarity Perspective 

      Espeseth, Martine; Brekke, Camilla; Johansson, Malin (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-10-25)
      Utilizing several Synthetic Aperture Radar (SAR) missions will provide a data set with higher temporal resolution. It is of great importance to understand the difference between various available sensors and polarization modes and to consider how to homogenize the data sets for a following combined analysis. In this study, a uniform and consistent analysis across different SAR missions is carried ...
    • Auroral ion acoustic wave enhancement observed with a radar interferometer system 

      Schlatter, Nicola M.; Belyey, Vasyl; Gustavsson, Björn Johan; Ivchenko, Nickolay; Whiter, Daniel; Dahlgren, Hanna; Tuttle, Sam; Grydeland, Tom (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-07-20)
      Measurements of naturally enhanced ion acoustic line (NEIAL) echoes obtained with a five-antenna interferometric imaging radar system are presented. The observations were conducted with the European Incoherent SCATter (EISCAT) radar on Svalbard and the EISCAT Aperture Synthesis Imaging receivers (EASI) installed at the radar site. Four baselines of the interferometer are used in the analysis. Based ...
    • The auroral red line polarisation: modelling and measurements 

      Lilensten, J.; Bommier, V.; Barthelemy, M; Lamy, Herve; Bernard, D; Moen, Jøran Idar; Johnsen, Magnar Gullikstad; Løvhaug, Unni Pia; Pitout, Frederic (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-08-12)
      In this work, we model the polarisation of the auroral red line using the electron impact theory developed by Bommier et al. (2011). This theory enables the computation of the distribution of the Degree of Linear Polarisation (DoLP) as a function of height if the flux of precipitated electrons is provided as input. An electron transport code is used to infer the stationary electron flux at each ...
    • Auto-correlation function and frequency spectrum due to a super-position of uncorrelated exponential pulses 

      Garcia, Odd Erik; Theodorsen, Audun (Peer reviewed, 2017-03)
      The auto-correlation function and the frequency power spectral density due to a super-position of uncorrelated exponential pulses are considered. These are shown to be independent of the degree of pulse overlap and thereby the intermittency of the stochastic process. For constant pulse duration and a one-sided exponential pulse shape, the power spectral density has a Lorentzian shape which is flat ...
    • An Automatic U-distribution and Markov Random Field Segmentation Algorithm for PolSAR Images 

      Doulgeris, Anthony Paul (Journal article; Tidsskriftartikkel; Peer reviewed, 2015)
    • The behavior of electron density and temperature during ionospheric heating near the fifth electron gyrofrequency 

      Wu, Jun; Wu, Jian; Rietveld, Michael T.; Häggström, I.; Zhao, Haisheng; Xu, Zhengwen (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-01-27)
      The experimental phenomena involving the changes in electron temperature and electron density as a function of pump frequency during an ionospheric heating campaign at European Incoherent Scatter near Tromsø, Norway, are reported. When the pump frequency is slightly above the fifth electron gyrofrequency, the UHF radar observation shows some apparent enhancements over a wide altitude range in radar ...
    • Bistatic Observations of the Ocean Surface with HF Radar, Satellite and Airborne Receivers 

      Bernhardt, Paul A.; Siefring, Carl; Briczinski, Stanley; Vierinen, Juha; Miller, Ethan; Howarth, Andrew; James, H. Gordon; Blincoe, Eugene (Peer reviewed; Book; Chapter, 2017-12-25)
      A new concept has been developed which can view vast regions of the Earth's surface. Ground HF transmissions are reflected by the ionosphere to illuminate the ocean over a few thousand kilometers. HF receivers detect the radio waves scattered by the sea and land surface. Using the theory of radio wave scatter from ocean surfaces, the HF data is then processed to yield the directional wave-height ...
    • Blob Sizes and Velocities in the Alcator C-Mod Scrape-Off Layer 

      Kube, Ralph; Garcia, Odd Erik; LaBombard, Brian; Madsen, Jens; Terry, James L.; Zweben, Stewart (Conference object; Konferansebidrag, 2012)
      A new blob-tracking algorithm for the GPI diagnostic installed in the outboard-midplane of Alcator C-Mod is developed. I t tracks large-amplitude fluctuations propagating through the scrape-off layer and calculates blob sizes and velocities. We compare the results of this method to a blob velocity scaling from a simple blob-model for sheath-connected blobs. We further present initial results from a ...
    • Blob sizes and velocities in the Alcator C-Mod scrape-off layer 

      Kube, Ralph; Garcia, Odd Erik; LaBombard, Brian; Terry, J.L; Zweben, Stewart (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      Gas-puff imaging data is used to investigate the dynamics of blob-like structures in the scrape-off layer of Alcator C-Mod. A blob-tracking algorithm is developed and used to compute blob propagation velocities and cross-field sizes for a series of discharges where the line-averaged particle density View the MathML source is varied. We find that the mean radial blob velocity increases from View the ...
    • Burst statistics of fluctuations in a simple magnetized torus configuration 

      Rypdal, Kristoffer; Živkovic, Tatjana; Østvand, Lene (Working paper; Arbeidsnotat, 2009-04-19)
      In a toroidal plasma confined by a purely toroidal magnetic field the plasma transport is governed by electrostatic turbulence driven by the flute interchange instability on the low-field side of the torus cross section. In this paper we revisit experimental data obtained from the Blaamann torus at the University of Tromso. On time-scales shorter than the poloidal rotation time, the time series of ...
    • Can we extend local sea-ice measurements to satellite scale? An example from the N-ICE2015 expedition 

      Rösel, Anja; King, Jennifer; Doulgeris, Anthony P.; Wagner, Penelope M.; Johansson, Malin; Gerland, Sebastian (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-12-17)
      Knowledge of Arctic sea-ice conditions is of great interest for Arctic residents, as well as for commercial usage, and to study the effects of climate change. Information gained from analysis of satellite data contributes to this understanding. In the course of using in situ data in combination with remotely sensed data, the question of how representative local scale measurements are of a wider ...
    • Capillary suction model as pipes of different sizes: flow conditions and comparison with experiments 

      Nguyen, Hung Thanh; Jacobsen, Stefan; Melandsø, Frank (Conference object; Konferansebidrag, 2012)
      ABSTRACT Absorption of water in concrete is often described by the simple linear water uptake vs. square-root-of-time law. However, a deviation from this behaviour is frequently seen depending on factors such as initial water content, water/binder ratio and specimen thickness. The deviation increases with thickness (typically from 25 to 100 mm) and is seen even for very dry specimens with ...