Now showing items 461-480 of 1276

    • Newly-formed sea ice distinction near the oil platform Prirazlomnaya in the Pechora Sea using polarimetric Radarsat-2 SAR observations 

      Ivonin, Dmitry; Ivanov, Andrey; Johansson, Malin; Brekke, Camilla (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-04-01)
      A polarimetric approach developed to discriminate oil slicks and look-alikes was used to study the polarimetric properties of newly-formed ice (NFI) observed near the Prirazlomnaya oil platform. This approach is based on the multipolarization parameter called Resonant to Non-resonant signal Damping (RND), which is related to the ratio between the ice damping and the short wind waves and wave breakings. ...
    • Multi-mission remote sensing of low concentration produced water slicks 

      Johansson, Malin; Skrunes, Stine; Brekke, Camilla; Isaksen, Hugo (Journal article; Tidsskriftartikkel, 2021-04)
      Produced water is legally released from oil platforms and often detected by oil spill detection services despite their low oil concentrations. Using fully-polarimetric RADARSAT-2 and dual-polarimetric Sentinel-1 data we investigate their synthetic aperture radar (SAR) characteristics. Detectability ranges within the SAR and optical Sentinel-2 and PlanetScope images are assessed and compared to in-situ ...
    • Improving Chlorophyll-a Estimation from Sentinel-2 (MSI) in the Barents Sea using Machine Learning 

      Asim, Muhammad; Brekke, Camilla; Mahmood, Arif; Eltoft, Torbjørn; Reigstad, Marit (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-04-22)
      This article addresses methodologies for remote sensing of ocean Chlorophyll-a (Chl-a), with emphasis on the Barents Sea. We aim at improving the monitoring capacity by integrating in situ Chl-a observations and optical remote sensing to locally train machine learning (ML) models. For this purpose, in situ measurements of Chl-a ranging from 0.014–10.81 mg/m <sup>3</sup> , collected for the years ...
    • Towards Unsupervised Domain Adaptation for Diabetic Retinopathy Detection in the Tromsø Eye Study 

      Størdal, Magnus (Mastergradsoppgave; Master thesis, 2021-05-29)
      Diabetic retinopathy (DR) is an eye disease which affects a third of the diabetic population. It is a preventable disease, but requires early detection for efficient treatment. While there has been increasing interest in applying deep learning techniques for DR detection in order to aid practitioners make more accurate diagnosis, these efforts are mainly focused on datasets that have been collected ...
    • Detecting Unhealthy Comments in Norwegian using BERT 

      Warholm, Joakim (Mastergradsoppgave; Master thesis, 2021-05-28)
      In this work we present a new Norwegian labeled dataset of 7078 comments for unhealthy comment detection. The dataset is used to fine-tune a BERT model, and demonstrates that BERT has the ability to detect subtle forms of toxicity, also in Norwegian. We compare how the different newly released Norwegian BERT models perform when fine-tuned on our dataset, and we also experiment with how English data ...
    • Spectral shaping of ring resonator transmission response 

      Yadav, Mukesh; Noh, Jong Wook; Hjelme, Dag Roar; Aksnes, Astrid (Journal article; Tidsskriftartikkel; Peer reviewed, 2021)
      We present a Mach-Zehnder interferometer assisted ring resonator configuration (MARC) to realize resonator transmission spectra with unique spectral signatures and significantly large effective free spectral ranges. Transmission spectra with unique spectral signatures are generated by changing the angular separation between the through port and the drop port waveguides of the ring resonator (RR). ...
    • Radar imaging with EISCAT 3D 

      Stamm, Johann; Vierinen, Juha; Urco, Juan M.; Gustavsson, Björn; Chau, Jorge L. (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-04)
      A new incoherent scatter radar called EISCAT 3D is being constructed in northern Scandinavia. It will have the capability to produce volumetric images of ionospheric plasma parameters using aperture synthesis radar imaging. This study uses the current design of EISCAT 3D to explore the theoretical radar imaging performance when imaging electron density in the E region and compares numerical techniques ...
    • Predicting Energy Demand in Semi-Remote Arctic Locations 

      Foldvik Eikeland, Odin; Bianchi, Filippo Maria; Chiesa, Matteo; Apostoleris, Harry; Hansen, Morten; Chiou, Yu-Cheng (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-03)
      Forecasting energy demand within a distribution network is essential for developing strategies to manage and optimize available energy resources and the associated infrastructure. In this study, we consider remote communities in the Arctic located at the end of the radial distribution network without alternative energy supply. Therefore, it is crucial to develop an accurate forecasting model to ...
    • A new auroral phenomenon, the anti-black aurora 

      Nel, A.E.; Kosch, M.J.; Keith Whiter, Daniel; Gustavsson, Björn Johan; Aslaksen, Torun Helene (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-01-19)
      Black auroras are small-scale features embedded in the diffuse background aurora, typically occurring post-substorm after magnetic midnight and with an eastward drift imposed. Black auroras show a significant reduction in optical brightness compared to the surrounding diffuse aurora, and can appear as slow-moving arcs or rapidly-moving patches and arc segments. We report, for the first time, an even ...
    • Direct and indirect impacts of climate change on wheat yield in the Indo-Gangetic plain in India 

      Daloz, Anne Sophie; Rydsaa, Johanne Hope; Sillmann, Jana; Hodnebrog, Øivind; Oort, Bob Eric Helmuth van; Emberson, Lisa; Zhang, Tianyi; Agrawal, Madhoolika (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-28)
      The Indo-Gangetic Plain (IGP) is one of the main wheat-production regions in India and the world. With climate change, wheat yields in this region will be affected through changes in temperature and precipitation and decreased water availability for irrigation, raising major concerns for national and international food security. Here we use a regional climate model and a crop model to better understand ...
    • Sea Ice Classification of SAR Imagery Based on Convolution Neural Networks 

      Khaleghian, Salman; Ullah, Habib; Kræmer, Thomas; Hughes, Nick; Eltoft, Torbjørn; Marinoni, Andrea (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-04-29)
      We explore new and existing convolutional neural network (CNN) architectures for sea ice classification using Sentinel-1 (S1) synthetic aperture radar (SAR) data by investigating two key challenges: binary sea ice versus open-water classification, and a multi-class sea ice type classification. The analysis of sea ice in SAR images is challenging because of the thermal noise effects and ambiguities ...
    • The Framework for Ice Sheet-Ocean Coupling (FISOC) V1.1 

      Gladstone, Rupert; Galton-Fenzi, Benjamin K.; Gwyther, David; Zhou, Qin; Hattermann, Tore; Zhao, Chen; Jong, Lenneke; Xia, Yuwei; Guo, Xiaoran; Petrakopoulos, Konstantinos; Zwinger, Thomas; Shapero, Daniel; Moore, John C. (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-11)
      A number of important questions concern processes at the margins of ice sheets where multiple components of the Earth system, most crucially ice sheets and oceans, interact. Such processes include thermodynamic interaction at the ice–ocean interface, the impact of meltwater on ice shelf cavity circulation, the impact of basal melting of ice shelves on grounded ice dynamics and ocean controls on ...
    • Investigation of Polar Mesospheric Summer Echoes Using Linear Discriminant Analysis 

      Jozwicki, Dorota; Sharma, Puneet; Mann, Ingrid (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-02)
      Polar Mesospheric Summer Echoes (PMSE) are distinct radar echoes from the Earth’s upper atmosphere between 80 to 90 km altitude that form in layers typically extending only a few km in altitude and often with a wavy structure. The structure is linked to the formation process, which at present is not yet fully understood. Image analysis of PMSE data can help carry out systematic studies to characterize ...
    • Automatic question generation and answer assessment: a survey 

      Das, Bidyut; Majumder, Mukta; Phadikar, Santanu; Sekh, Arif Ahmed (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-03-18)
      Learning through the internet becomes popular that facilitates learners to learn anything, anytime, anywhere from the web resources. Assessment is most important in any learning system. An assessment system can find the self-learning gaps of learners and improve the progress of learning. The manual question generation takes much time and labor. Therefore, automatic question generation from learning ...
    • MIR-based in-situ measurement of Silicon crystal-melt interface 

      Jensen, Mathias N. (Master thesis; Mastergradsoppgave, 2020-06-29)
      The project explores the a proposed MIR-based measurement system for measuring the deflection of the interface between the crystal and melt during production of mono-crystalline Silicon in the Czochralski process. The absorption spectrum is modeled and the specific absorption for a select set of wavelengths is estimated for temperatures approching 1687K. It was estimated that the intrinsic absorption ...
    • Direct and indirect impacts of climate change on wheat yield in the Indo-Gangetic plain in India 

      Daloz, Anne Sophie; Rydsaa, Johanne Hope; Hodnebrog, Øivind; Sillmann, Jana; Oort, Bob Eric Helmuth van; Mohr, Christian Wilhelm; Agrawal, M.; Emberson, L.; Stordal, Frode; Zhang, T. (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-28)
      The Indo-Gangetic Plain (IGP) is one of the main wheat-production regions in India and the world. With climate change, wheat yields in this region will be affected through changes in temperature and precipitation and decreased water availability for irrigation, raising major concerns for national and international food security. Here we use a regional climate model and a crop model to better understand ...
    • The Impact of Turbulence on the Ionosphere and Magnetosphere 

      Guio, Patrick; Pécseli, Hans L (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-01-25)
      An important property associated with turbulence in plasmas and fluids is anomalous transport. Plasma, being a good conductor, can in addition be affected by turbulence causing an anomalous resistivity that can significantly exceed its classical counterpart. While turbulent transport may be adequately described in configuration space, some aspects of the anomalous resistivity are best accounted for ...
    • Formation of an additional density peak in the bottom side of the sodium layer associated with the passage of multiple mesospheric frontal systems 

      Narayanan, Viswanathan Lakshmi; Nozawa, Satonori; Oyama, Shin-Ichiro; Mann, Ingrid; Shiokawa, Kazuo; Otsuka, Yuichi; Saito, Norihito; Wada, Satoshi; Kawahara, Takuya D.; Takahashi, Toru (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-18)
      We present a detailed investigation of the formation of an additional sodium density peak at altitudes of 79–85 km below the main peak of the sodium layer based on sodium lidar and airglow imager measurements made at Ramfjordmoen near Tromsø, Norway, on the night of 19 December 2014. The airglow imager observations of OH emissions revealed four passing frontal systems that resembled mesospheric ...
    • Deep Image Translation With an Affinity-Based Change Prior for Unsupervised Multimodal Change Detection 

      Luppino, Luigi Tommaso; Kampffmeyer, Michael; Bianchi, Filippo Maria; Moser, Gabriele; Serpico, Sebastiano Bruno; Jenssen, Robert; Anfinsen, Stian Normann (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-17)
      Image translation with convolutional neural networks has recently been used as an approach to multimodal change detection. Existing approaches train the networks by exploiting supervised information of the change areas, which, however, is not always available. A main challenge in the unsupervised problem setting is to avoid that change pixels affect the learning of the translation function. We propose ...
    • Two-dimensional TIRF-SIM–traction force microscopy (2D TIRF-SIM-TFM) 

      Barbieri, Liliana; Colin-York, Huw; Korobchevskaya, Kseniya; Li, Di; Wolfson, Deanna; Karedla, Narain; Schneider, Falk; Ahluwalia, Balpreet Singh; Seternes, Tore; Dalmo, Roy Ambli; Dustin, Michael L.; Li, Dong; Fritzsche, Marco (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-04-12)
      Quantifying small, rapidly evolving forces generated by cells is a major challenge for the understanding of biomechanics and mechanobiology in health and disease. Traction force microscopy remains one of the most broadly applied force probing technologies but typically restricts itself to slow events over seconds and micron-scale displacements. Here, we improve >2-fold spatially and >10-fold temporally ...