Now showing items 1-20 of 929

    • A 10-year record of Arctic summer sea ice freeboard from CryoSat-2 

      Dawson, Geoffrey; Landy, Jack Christopher; Tsamados, Michel; Komarov, Alexander S.; Howell, Stephen; Heorten, Harold; Krumpen, Thomas (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-10-29)
      Satellite observations of pan-Arctic sea ice thickness have so far been constrained to winter months. For radar altimeters, conventional methods cannot differentiate leads from meltwater ponds that accumulate at the ice surface in summer months, which is a critical step in the ice thickness calculation. Here, we use over 350 optical and synthetic aperture radar (SAR) images from the summer months ...
    • 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, ...
    • 2022 Tonga Volcanic Eruption Induced Global Propagation of Ionospheric Disturbances via Lamb Waves 

      Zhang, Shun-Rong; Vierinen, Juha; Aa, Ercha; Goncharenko, Larisa P.; Erickson, Philip J.; Rideout, William; Coster, Anthea J.; Spicher, Andres (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-03-23)
      The Tonga volcano eruption at 04:14:45 UT on 2022-01-15 released enormous amounts of energy into the atmosphere, triggering very significant geophysical variations not only in the immediate proximity of the epicenter but also globally across the whole atmosphere. This study provides a global picture of ionospheric disturbances over an extended period for at least 4 days. We find traveling ionospheric ...
    • 21st Century Scenario Forcing Increases More for CMIP6 Than CMIP5 Models 

      Fredriksen, Hege-Beate; Smith, Christopher J.; Modak, Angshuman; Rugenstein, Maria (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-03-16)
      Although the Coupled Model Intercomparison Project 6 (CMIP6) protocol provides an experiment to estimate effective radiative forcing (ERF), it is only quantified for few models. We present new estimates of ERF for models participating in CMIP6 by applying the method developed in Fredriksen et al. (2021, https://doi.org/10.1029/2020JD034145), and validate our approach with available fixed-SST forcing ...
    • A 30-year probability map for oil spill trajectories in the barents sea to assess potential environmental and socio-economic threats 

      Pavlov, Victor; Martins de Aguiar, Victor Cesar; Hole, Lars Robert; Pongrácz, Eva (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-12-24)
      Increasing exploration and exploitation activity in the Arctic Ocean has intensified maritime traffic in the Barents Sea. Due to the sparse population and insufficient oil spill response infrastructure on the extensive Barents Sea shoreline, it is necessary to address the possibility of offshore accidents and study hazards to the local environment and its resources. Simulations of surface oil ...
    • 3D full-wave multi-scattering forward solver for coherent microscopes 

      Qin, Yingying; Butola, Ankit; Agarwal, Krishna (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-04-21)
      A rigorous forward model solver for conventional coherent microscope is presented. The forward model is derived from Maxwell’s equations and models the wave behaviour of light matter interaction. Vectorial waves and multiple-scattering effect are considered in this model. Scattered field can be calculated with given distribution of the refractive index of the biological sample. Bright field images ...
    • 3D refractive index reconstruction from phaseless coherent optical microscopy data using multiple scattering-based inverse solvers - a study 

      Qin, Yingying; Butola, Ankit; Agarwal, Krishna (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-11-27)
      Reconstructing 3D refractive index profile of scatterers using optical microscopy measurements presents several challenges over the conventional microwave and RF domain measurement scenario. These include phaseless and polarization-insensitive measurements, small numerical aperture, as well as a Green's function where spatial frequencies are integrated in a weighted manner such that far-field angular ...
    • 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 ...
    • Adhesive free PVDF copolymer focused transducers for high frequency acoustic imaging 

      Habib, Anowarul; Wagle, Sanat; Melandsø, Frank (Conference object; Konferansebidrag, 2019)
      The present study has demonstrated to produce a reliable PVDF copolymer focused transducers from a layer-by-layer deposition method by engraving milled spherical cavies in a PEI polymer substrate. The proposed method which process P(VDF-TrFE) from the fluid phase, is adhesive-free in the sense that it does not require any additional adhesive layers for material binding. The transducer was acoustically ...
    • ADNet++: A few-shot learning framework for multi-class medical image volume segmentation with uncertainty-guided feature refinement 

      Hansen, Stine; Gautam, Srishti; Salahuddin, Suaiba Amina; Kampffmeyer, Michael Christian; Jenssen, Robert (Journal article; Tidsskriftartikkel, 2023-08-02)
      A major barrier to applying deep segmentation models in the medical domain is their typical data-hungry nature, requiring experts to collect and label large amounts of data for training. As a reaction, prototypical few-shot segmentation (FSS) models have recently gained traction as data-efficient alternatives. Nevertheless, despite the recent progress of these models, they still have some essential ...
    • 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 ...
    • Airborne Investigation of Quasi-Specular Ku-Band Radar Scattering for Satellite Altimetry Over Snow-Covered Arctic Sea Ice 

      de Rijke Thomas, Claude; Landy, Jack Christopher; Mallett, Robbie; Willatt, Rosemary; Tsamados, Michel; King, Joshua (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-09-22)
      Surface-based Ku-band radar altimetry investigations indicate that the radar signal is typically backscattered from well above the snow–sea ice interface. However, this would induce a bias in satellite altimeter sea ice thickness retrievals not reflected by buoy validation. Our study presents a mechanism to potentially explain this paradox: probabilistic quasi-specular radar scattering from the ...
    • 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 ...