Now showing items 1-20 of 481

    • 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)
    • 2018 Beam-park observations of space debris with the EISCAT radars 

      Vierinen, Juha; Kastinen, D; Markkanen, Jussi; Grydeland, Tom; Kero, Johan; Horstmann, A.; Hesselbach, S.; Kebschull, C.; Røynestad, Elisabeth; Krag, Holger (Journal article; Tidsskriftartikkel, 2019)
      Monitoring the evolution of the space debris environment requires regular radar observations of the space debris population. This study presents the results from 24 hours of beam-park observations of space objects conducted simultaneously with the EISCAT Svalbard and Tromsø radars on and between January 4th and 5th, 2018. The measurements are processed with a new matched filter bank analysis program, ...
    • The 3‐D Distribution of Artificial Aurora Induced by HF Radio Waves in the Ionosphere 

      Kvammen, Andreas; Gustavsson, Björn Johan; Sergienko, Tima; Brändström, Urban; Rietveld, Michael T; Rexer, Theresa; Vierinen, Juha (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-03-21)
      We present 3‐D excitation rate estimates of artificial aurora in the ionospheric F layer, induced by high‐frequency radio waves from the European Incoherent Scatter heating facility. Simultaneous imaging of the artificial aurora was done with four separate Auroral Large Imaging System stations, permitting tomography‐like 3‐D auroral reconstruction of the enhanced atomic oxygen emissions at 6,300, ...
    • 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 ...
    • Adaptive fluctuation imaging captures rapid subcellular dynamics 

      Opstad, Ida Sundvor; Ströhl, Florian; Birgisdottir, Åsa birna; Acuña Maldonado, Sebastian Andres; Kalstad, Trine; Myrmel, Truls; Agarwal, Krishna; Ahluwalia, Balpreet Singh (Journal article; Tidsskriftartikkel, 2019-07-22)
      In this work we have explored the live-cell friendly nanoscopy method Multiple Signal Classification Algorithm (MUSICAL) for multi-colour imaging of various organelles and sub-cellular structures in the cardiomyoblast cell line H2c9. We have tested MUSICAL for fast (up to 230Hz), multi-colour time-lapse sequences of various sub-cellular structures (mitochondria, endoplasmic reticulum, microtubules, ...
    • Adaptive fluctuation imaging captures rapid subcellular dynamics 

      Opstad, Ida Sundvor; Ströhl, Florian; Birgisdottir, Åsa birna; Maldonado, Sebastián Andrés Acuña; Kalstad, Trine; Myrmel, Truls; Agarwal, Krishna; Ahluwalia, Balpreet Singh (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-07-22)
      In this work we have explored the live-cell friendly nanoscopy method Multiple Signal Classification Algorithm (MUSICAL) for multi-colour imaging of various organelles and sub-cellular structures in the cardiomyoblast cell line H2c9. We have tested MUSICAL for fast (up to 230Hz), multi-colour time-lapse sequences of various sub-cellular structures (mitochondria, endoplasmic reticulum, microtubules, ...
    • Added value of multitemporal polarimetric UAVSAR data for permanent scatterers detection 

      Nikaein, Tina; Akbari, Vahid; Arefi, Hossein (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-11-05)
      In the last decades, differential synthetic aperture radar (SAR) interferometric (InSAR) (DInSAR) techniques have been used to estimate the Earth's surface deformation with high resolution. In this paper, we present an approach for increasing the quantity of permanent scattered pixels. These pixels are selected for DInSAR processing based on polarimetric information prepared by new sensors. The ...
    • 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 ...
    • The airglow layer emission altitude cannot be determined unambiguously from temperature comparison with lidars 

      Dunker, Tim (Journal article; Peer reviewed; Tidsskriftartikkel, 2018)
      I investigate the nightly mean emission height and width of the OH*(3–1) layer by comparing nightly mean temperatures measured by the ground-based spectrometer GRIPS 9 and the Na lidar at ALOMAR. The data set contains 42 coincident measurements taken between November 2010 and February 2014, when GRIPS 9 was in operation at the ALOMAR observatory (69.3° N, 16.0° E) in northern Norway. To closely ...
    • 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 ...
    • Arctic Field Summer Schools: training and awareness in the Arctic 

      Doulgeris, Anthony Paul; Alexeev, Vladimir A.; Murray, Maribeth S. (Conference object; Konferansebidrag, 2020-01)
      A series of three summer schools engaged nearly fifty graduate students in exploring science questions related to current Arctic challenges, and brought together leading Arctic researchers from the partner institutions. Each partner organised a Field School and each had their own unique styles and emphasis. This collaboration aimed to deepen the Arctic knowledge of the young generation, and to create ...
    • Arctic Sea Ice Characterization using Spaceborne Fully Polarimetric L-, C- and X-Band SAR with Validation by Airborne Measurements 

      Singha, Suman; Johansson, Malin; Hughes, Nick; Hvidegaard, Sine; Skourup, Henriette (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-04-26)
      In recent years, spaceborne synthetic aperture radar (SAR) polarimetry has become a valuable tool for sea ice analysis. Here, we employ an automatic sea ice classification algorithm on two sets of spatially and temporally near coincident fully polarimetric acquisitions from the ALOS-2, Radarsat-2, and TerraSAR-X/TanDEM-X satellites. Overlapping coincident sea ice freeboard measurements from airborne ...
    • 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 ...
    • Assessing polarimetric SAR sea-ice classifications using consecutive day images 

      Moen, Mari-Ann; Anfinsen, Stian Normann; Doulgeris, Anthony Paul; Renner, Angelika; Gerland, Sebastian (Journal article; Tidsskriftartikkel; Peer reviewed, 2015)
      This paper investigates automatic segmentation and classification of C-band, polarimetric synthetic aperture radar (SAR) satellite images of Arctic sea ice under freezing conditions prior to melt. The objective is to investigate the robustness of the results obtained under slightly varying environmental conditions and different viewing geometries. Initially, three geographically overlapping SAR ...
    • Assessment of land subsidence using interferometric synthetic aperture radar time series analysis and artificial neural network in a geospatial information system: Case study of Rafsanjan Plain 

      Bagheri, Mohsen; Dehghani, Maryam; Esmaeily, Ali; Akbari, Vahid (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-12-31)
      Land subsidence resulting from groundwater extraction is a widely recurring phenomenon worldwide. To assess land subsidence, traditional methods such as numerical and finite element methods have limitations due to the complex interactions between the different constructor factors of aquifer in each area. We produced a groundwater-induced subsidence map by applying the geological and hydrogeological ...
    • Assessment of Polarimetric Variability by Distance Geometry for Enhanced Classification of Oil Slicks Using SAR 

      Marinoni, Andrea; Espeseth, Martine; Gamba, Paolo; Brekke, Camilla; Eltoft, Torbjørn (Peer reviewed; Chapter; Bokkapittel, 2019-11-14)
      In this paper, we introduce a new approach for investigation of polarimetric Synthetic Aperture Radar (PolSAR) images for oil slick analysis. Our method aims at enhancing discrimination of oil types by exploring the polarimetric features that can be produced by processing PolSAR scenes without dimensionality reduction. Taking advantage of a mixture description of the interactions among classes within ...
    • 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 ...